CN116670839A - Mixed strain multi-quantum well super-radiation light-emitting diode - Google Patents

Abstract

Superluminescent Light Emitting Diodes (SLEDs) include an active layer that includes a set of hybrid strained quantum wells. The set of hybrid strained quantum wells includes a set of compressively strained quantum wells and a set of tensile strained quantum wells. The potential difference applied across the SLED causes electron carriers and hole carriers to move toward the active layer. The radiative recombination of electron and hole pairs in the set of compressively strained quantum wells may emit laterally polarized light and the radiative recombination of electron and hole pairs in the set of compressively strained quantum wells may emit vertically polarized light. The combination of transversely polarized light and longitudinally polarized light causes the SLED to emit incoherent light.

Description

Mixed strain multi-quantum well super-radiation light-emitting diode

Technical Field

Various embodiments of the present disclosure generally relate to Superluminescent Light Emitting Diodes (SLEDs). More particularly, various embodiments of the present disclosure relate to hybrid strain SLEDs.

Background

The optoelectronic characteristics of conventional Superluminescent Light Emitting Diodes (SLEDs) are related to an increase in optical power and are lower in low current conditions. This is a limitation for applications requiring SLEDs with high power in low current states. In view of the above, a technical solution is needed to overcome the above problems.

Limitations and disadvantages of conventional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present application as set forth in the remainder of the present application with reference to the drawings.

Disclosure of Invention

In one embodiment of the present disclosure, a Superluminescent Light Emitting Diode (SLED) is provided. The SLED includes an n-type region, a p-type region, and an intrinsic region. The intrinsic region includes an active layer sandwiched between two separate confinement heterostructure layers. The active layer has a set of hybrid strained quantum wells (MQWs) comprising a set of tensile strained quantum wells and a set of compressive strained quantum wells. The SLED is configured to emit incoherent light. Applying a potential difference across the n-type and p-type regions of the SLED causes electron carriers and hole carriers to move toward the active layer, wherein radiative recombination of electron and hole pairs in each compressively strained quantum well results in emission of laterally polarized light, and radiative recombination of electron and hole pairs in each compressively strained quantum well results in emission of longitudinally polarized light.

In some embodiments, the number of tensile strained quantum wells in the set of tensile strained quantum wells matches the number of compressive strained quantum wells in the set of compressive strained quantum wells.

In some embodiments, the compressive strain of the set of compressively strained quantum wells and the tensile strain of the set of tensile strained quantum wells range from 0.7 to 1% of the total strain of the set of compressively strained quantum wells and the set of tensile strained quantum wells.

In some embodiments, the percentage difference between the compressive strain of the set of compressively strained quantum wells and the tensile strain of the set of tensile strained quantum wells is less than 0.1%.

In some embodiments, the number of tensile strained quantum wells in the set of tensile strained quantum wells and the number of compressive strained quantum wells in the set of compressive strained quantum wells is between 6 and 10.

In some embodiments, each barrier layer of the plurality of barrier layers is between 5 nanometers and 5.5 nanometers thick.

In some embodiments, each of the set of tensile strained quantum wells and each of the set of compressive strained quantum wells has a thickness of 7.5 nanometers.

In some embodiments, the polarization extinction coefficient of the SLED is less than 1 db.

In some embodiments, the SLED further comprises a first Separation Constraint Heterostructure (SCH) layer and a second SCH layer. The active layer is sandwiched between the first SCH layer and the second SCH layer.

In some embodiments, the SLED further comprises a substrate, a buffer layer, an n-contact waveguide grating layer, and a graded index layer. A first multilayer is formed on top of the substrate. The first multilayer includes a buffer layer formed on the substrate, an n-contact waveguide grating layer formed on the buffer layer, and a graded index layer formed on the n-contact waveguide grating layer. The first SCH layer is formed on the graded index layer.

In some embodiments, the SLED further comprises an n-type metal layer formed under the substrate. The n-type metal layer includes a light absorbing layer.

In some embodiments, the SLED further comprises a second multilayer. A second plurality of layers is formed on the second SCH layer. The second plurality of layers includes a graded index layer, a p-contact waveguide grating layer, a p-contact layer, and a p-metal layer. A graded index layer is formed on the second SCH layer. A p-contact waveguide grating layer is formed on the graded index layer. A p-contact layer is formed on the p-contact waveguide grating layer. A p-type metal layer is formed on the p-type contact layer.

In some embodiments, radiative recombination in the active layer is based on applying a potential difference between the p-type metal layer and the n-type metal layer.

In some embodiments, the p-type metal layer and the p-contact layer form a p-cladding layer. Furthermore, the p-cladding layer has a ridge geometry.

In some embodiments, the first barrier layer and the second barrier layer have a thickness between 10 nanometers and 14 nanometers.

In some embodiments, the SLED has an operating current in the range of 100 milliamp-200 milliamp.

In some embodiments, the compressive strain and the tensile strain are 1.05% and 0.9% of the total strain of the set of compressively strained quantum wells and the set of tensile strained quantum wells.

In some embodiments, an increase in compressive strain of the set of compressively strained quantum wells increases the tensile strain of the set of tensile strained quantum wells.

In some embodiments, the first barrier layer has a thickness of 5 nanometers.

In some embodiments, the second barrier layer has a thickness of 14 nanometers.

In various embodiments of the present disclosure, a Superluminescent Light Emitting Diode (SLED) is provided. The SLED includes a first multilayer and an active layer grown on the first multilayer. The active layer includes a plurality of barrier layers and a hybrid strained multiple quantum well structure. The plurality of barrier layers includes a first barrier layer and a second barrier layer. The hybrid strained multiple quantum well structure includes a set of tensile strained quantum wells and a set of compressive strained quantum wells. Each pair of quantum wells of the hybrid strained multi-quantum well structure includes a tensile strained quantum well of a set of tensile strained quantum wells and a compressive strained quantum well of a set of compressive strained quantum wells. A first barrier layer of the plurality of barrier layers is sandwiched between a pair of consecutive quantum wells of the hybrid strained multi-quantum well structure and a second barrier layer is sandwiched between a tensile strained quantum well and a compressive strained quantum well of each pair of quantum wells of the hybrid strained multi-quantum well structure. Based on the radiative recombination in the active layer, the set of compressively strained quantum wells is configured to emit light having a transverse polarization direction, the set of compressively strained quantum wells is configured to emit light having a perpendicular polarization direction, thereby configuring the SLED to emit incoherent light.

Compared to conventional SLEDs, the SLEDs of the present disclosure can be configured to operate at low currents, have a wider bandwidth, and emit incoherent light with a low degree of polarization.

Drawings

The figures illustrate various embodiments of the systems, methods, and other aspects of the present disclosure. It will be apparent to those skilled in the art that the element boundaries (e.g., blocks, groups of blocks, or other shapes) illustrated in the figures represent one example of boundaries. In some examples, one element may be designed as multiple elements, or multiple elements may be designed as one element. In some examples, an element shown as an internal component of one element may be implemented as an external component in another element, and vice versa.

Various embodiments of the present disclosure are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:

FIG. 1 is a schematic diagram illustrating a Superluminescent Light Emitting Diode (SLED) according to one embodiment of the present disclosure;

fig. 2 is a schematic diagram illustrating the structure of the active layer of the SLED of fig. 1 according to one embodiment of the present disclosure;

FIG. 3 is a schematic diagram illustrating one type of scanning electron micrograph of the SLED of FIG. 1 according to one embodiment of the present disclosure;

FIG. 4 is a scanning electron micrograph showing another type of SLED of FIG. 1 with improved topological properties according to one embodiment of the present disclosure;

FIG. 5 is a graph showing a comparison of light-current (LI) characteristics between a conventional SLED and another type of SLED of FIG. 1 according to one embodiment of the present disclosure;

FIG. 6 is a comparison graph showing light-current (LI) characteristics between different types of SLEDs of FIG. 1 according to one embodiment of the present disclosure;

FIG. 7 is a schematic diagram illustrating horizontal and vertical far field performance of one type of SLED of FIG. 1 according to one embodiment of the present disclosure; and

fig. 8 is a schematic diagram illustrating horizontal and vertical far field performance of one type of SLED having a light absorbing layer in the n-type metal layer of the SLED of fig. 1 according to one embodiment of the present disclosure.

Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of the exemplary embodiment is intended for purposes of illustration only and is not intended to limit the scope of the disclosure.

Detailed Description

The disclosure may be best understood by reference to the detailed drawings and description set forth herein. Various embodiments will be discussed below with reference to these figures. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to the figures is for explanatory purposes as the methods and systems may deviate from the embodiments described. In one example, the teachings presented and the needs of a particular application may result in a variety of alternative and suitable ways to implement the functions of any of the details described herein. Thus, any method may be extended beyond the specific implementation options described and shown in the embodiments below.

"semiconductor" in this document and throughout the disclosure refers to, but is not limited to, a material having a conductivity value between a conductor and an insulator. The material may be an elemental material or a compound material. Semiconductors may include, but are not limited to, elemental, binary, ternary, and quaternary alloys. Structures formed using a single semiconductor or multiple semiconductors may include a single semiconductor material, two or more semiconductor materials, a single component semiconductor alloy, two or more discrete component semiconductor alloys, and semiconductor alloys graded from a first semiconductor alloy to a second semiconductor alloy. The semiconductor may be one of undoped (intrinsic), p-type doped, n-type doped, graded doped from a first doping level of one type to a second doping level of the same type, and graded doped from a first doping level of one type to a second doping level of a different type. Semiconductors may include, but are not limited to, group III-V semiconductors such As aluminum (Al), gallium (Ga), indium (In), and semiconductors between arsenic (As) and tin (Sb), including, for example, gallium nitride (N), gaP, gallium arsenide (GaAs), indium phosphide (P), indium arsenide (InAs), aluminum nitride (AlN), and aluminum arsenide (AlAs).

As used herein and in this disclosure, a "substrate" refers to, but is not limited to, a surface upon which semiconductor structures, such as active layers, and embodiments of the present disclosure can be formed. This may include, but is not limited to, inP, gaAs, silicon, silica-on-silicon, silica-on-polymer, glass, metal, ceramic, polymer, or combinations thereof.

The term "metal" as disclosed herein and throughout refers to, but is not limited to, materials (elements, compounds and alloys) having good electrical and thermal conductivity properties due to the easy loss of shell electrons. This may include, but is not limited to, gold, chromium, aluminum, silver, platinum, nickel, copper, rhodium, palladium, tungsten, and combinations of these materials.

As used herein and throughout the disclosure, "electrode," "contact," "track," or "termination" refers to, but is not limited to, a material that has good electrical conductivity and optical opacity. This includes structures formed from thin films, thick films, and plated films of materials including, but not limited to, metals such as gold, chromium, aluminum, silver, platinum, nickel, copper, rhodium, palladium, tungsten, and combinations of these materials. Other electrode configurations may employ a combination of metals, such as a chromium adhesion layer and a gold electrode layer.

As used herein and in this disclosure, a tensile strained quantum well refers to, but is not limited to, a quantum well having a lattice constant that is smaller than the lattice constant of the underlying layer, resulting in a quantum well having a stretched lattice constant.

As used herein and in this disclosure, compressively strained quantum wells refer to, but are not limited to, quantum wells having a lattice constant that is greater than the lattice constant of the underlying layer, resulting in a quantum well having a lattice constant that is compressed.

As used herein and in this disclosure, a polarization extinction coefficient or polarization extinction ratio refers to, but is not limited to, a coefficient or ratio of measured degrees of polarization in decibels.

Optical gain, as used herein and in this disclosure, refers to, but is not limited to, the energy or power transmitted by an optical medium (e.g., an active layer in this disclosure) to light rays that are traversing the optical medium.

As used herein and in this disclosure, amplified spontaneous emission gain refers to, but is not limited to, the gain produced by the process of amplifying spontaneous emitted light by stimulated emission in an optical medium.

Light having a transverse polarization direction as used herein and in the present disclosure refers to, but is not limited to, light vibrating in a transverse electric field (TE) direction.

Light having a perpendicular polarization direction as used herein and in the present disclosure refers to, but is not limited to, light vibrating in the Transverse Magnetic (TM) direction.

Incoherent light, as used herein and throughout the present disclosure, refers to, but is not limited to, light in which photons have different frequencies and phases relative to each other.

Radiative recombination as disclosed herein and throughout refers to, but is not limited to, the process by which recombination of electrons and holes results in photon emission.

The Separation Confinement Heterostructure (SCH) layer as used herein and in the present disclosure refers to, but is not limited to, a pair of quantum well layers sandwiching an active layer. The SCH layer has a lower refractive index than the quantum well layer and provides vertical optical confinement for the SLED device. The material of the SCH layer may include, but is not limited to, undoped gallium indium phosphide (InGaAsP), undoped aluminum indium arsenide (inagaas), and undoped InGaAs.

References to "one embodiment," "another embodiment," "one example," "another example," "for example," etc., indicate that the embodiment or example so described may include a particular feature, structure, characteristic, attribute, element, or limitation, but every embodiment or example does not necessarily include the particular feature, structure, characteristic, attribute, element, or limitation. Furthermore, repeated use of the phrase "in one embodiment" does not necessarily refer to the same embodiment.

Referring now to fig. 1, a Superluminescent Light Emitting Diode (SLED) 100 according to one embodiment of the present disclosure is shown. SLED 100 is a semiconductor light source that emits light that is incoherent. SLED 100 can be used in a variety of optical systems for fiber optic gyroscopes, navigation systems, and gas sensors. The SLED 100 includes a substrate 102 and a first multilayer formed sequentially over the substrate 102. The formation of the first multilayer herein may refer to depositing and/or growing the first multilayer. The first metal layer 104 is formed under the substrate 102 and is configured as a cathode terminal. In one embodiment, the first metal layer 104 is an n-type metal layer 104. The n-type metal layer 104, i.e., the first metal layer 104, includes a light absorbing layer.

The first multilayer includes a buffer layer 106, an n-contact waveguide grating layer 108, and a first graded index layer 110. The SLED 100 further includes a first Separation Constraint Heterostructure (SCH) layer 112, an active layer 114, a second SCH layer 116, and a second multilayer. A second plurality of layers is formed on the second SCH layer 116. The second multilayer includes a second graded index layer 118, a p-contact waveguide grating layer 120, a p-contact layer 122, and a second metal layer 124. In one embodiment, the second metal layer 124 is a p-type metal layer 124. The structure of the active layer 114 includes a set of mixed compressed and stretched individual quantum wells, as explained in detail in fig. 2. The set of mixed compressively and tensile strained individual quantum wells emit oppositely polarized light that is balanced by the compressively and tensile strained quantum wells, resulting in the emission of incoherent light by SLED 100. Thus, the SLED 100 is a hybrid strain SLED 100.

Buffer layer 106 is formed over substrate 102 using suitable thin film deposition techniques including, but not limited to, physical Vapor Deposition (PVD) such as thermal evaporation, electron beam evaporation, and sputter deposition, and Chemical Vapor Deposition (CVD) such as metal organic CVD, laser CVD, and plasma enhanced CVD. The buffer layer 106 is fabricated using a suitable metal oxide, such as zinc (Zn), titanium (Ti), tungsten (W), niobium (Ni), or a suitable combination thereof.

As described with reference to buffer layer 106, n-contact waveguide grating layer 108 is formed on buffer layer 106 using a suitable thin film deposition technique. The n-contact waveguide grating layer 108 may include a waveguide layer and/or a grating layer. The n-contact waveguide grating layer 108 is formed of a suitably doped n-type material, such as phosphorus, arsenic, or any combination thereof. The n-contact waveguide grating layer 108 passes light of the corresponding wavelength and blocks light of other wavelengths.

A first graded index layer 110 is formed on the n-contact waveguide grating layer 108. The first graded index layer 110 may be formed of a transparent dielectric such as silicon oxide or a mixture of dielectric materials having a higher refractive index than silicon oxide such as niobium oxide, tantalum oxide, titanium oxide, other metal oxides, oxynitrides, silicon nitride, or suitable combinations thereof. The first graded index layer 110 prevents scattering of light emitted by the SLED 100. The first graded index layer 110 has a lower refractive index than the n-contact waveguide grating layer 108.

A first SCH layer 112 is formed on the first graded index layer 110. An active layer 114 is grown on the first multilayer. In other words, the active layer 114 is formed on the first SCH layer 112. A second SCH layer 116 is formed on the active layer 114. Thus, the active layer 114 is sandwiched between the first SCH layer 112 and the second SCH layer 116. The refractive index of the first and second SCH layers 112, 116 is lower than that of the active layer 114 and provides a vertical optical confinement for the light emitted from the SLED 100.

A second plurality of layers is formed on the second SCH layer 116. The second multilayer includes a second graded index layer 118, a p-contact waveguide grating layer 120, a p-contact layer 122, and a second metal layer 124. In one embodiment, the second metal layer 124 is a p-type metal layer 124. The second metal layer 124 and the p-type contact layer 122 form a p-cladding layer, giving the p-cladding layer a ridge geometry. The ridge geometry shapes the current spreading curve flowing in the SLED 100 into a funnel shape, thereby limiting current leakage in the SLED 100.

A second graded index layer 118 is formed on the second SCH layer 116. The materials and methods of forming the second graded index layer 118 are similar to those of the first graded index layer 110. The second graded index layer 118 reduces scattering of light emitted in the active layer 114. The second graded index layer 118 has a lower refractive index relative to the second SCH layer 116.

The p-contact waveguide grating layer 120 is formed on the second SCH layer 116 using a suitable thin film deposition technique, as described above. The p-contact waveguide grating layer 120 may include a waveguide layer and/or a grating layer. The p-contact waveguide grating layer 120 is formed of a suitably doped p-type material, such as aluminum, boron, or any combination thereof. The p-contact waveguide grating layer 120 passes light of the corresponding wavelength and blocks light of other wavelengths.

A p-contact layer 122 is formed on the p-contact waveguide grating layer 120. The p-contact layer 122 provides hole carriers that move toward the active layer 114 and recombine with electron carriers. A second metal layer 124 is formed on the p-contact layer 122. The second metal layer 124, the P-contact layer 122, the P-contact waveguide grating layer 120, and the second graded index layer 118 form the P-type region of the SLED 100 (shown as "P" in fig. 1). The second metal layer 124 is configured as an anode terminal to apply a potential difference across the SLED 100.

The first graded index layer 110, N-contact waveguide grating layer 108, buffer layer 106, substrate 102, and first metal layer 104 form an N-type region of the SLED 100 (shown as "N" in fig. 1). The second SCH layer 116, active layer 114, and first SCH layer 112 form the intrinsic region of the SLED 100 (shown as "I" in fig. 1). The intrinsic region of SLED 100 has a lower conductivity relative to the p-type and n-type regions of SLED 100. The intrinsic region of SLED 100 is the undoped region of SLED 100.

In operation, when a potential difference is applied across first metal layer 104 and second metal layer 124, hole carriers flow from the p-type region of SLED 100 and electron carriers flow from the n-type region of SLED 100 to the intrinsic region of SLED 100. The generation of incoherent light is based on electron-hole recombination in the active layer 114, that is, radiative recombination is induced in the active layer 114 due to injected electron and hole carriers. The first SCH layer 112 and the second SCH layer 116 act as dopant back-off layers and modifiers for incoherent light in the vertical emission direction of the SLED 100. Thus, the undoped first SCH layer 112 and second SCH layer 116 provide a vertical optical confinement for incoherent light emitted by the radiative recombination process in the active layer 114 of the SLED 100.

Referring now to fig. 2, a structure of an active layer 114 is shown, according to one embodiment of the present disclosure. The active layer 114 includes a hybrid strained multiple quantum well structure 202, 204, 206, 208, 210 and 212, and a plurality of barrier layers 214, 216, 218, 220 and 222. The hybrid strained multiple quantum well structure 202, 204, 206, 208, 210 and 212 includes a set of tensile strained quantum wells 202, 206 and 210 and a set of compressive strained quantum wells 204, 208 and 212. A set of tensile strained quantum wells 202, 206, and 210 includes a first tensile strained quantum well 202, a second tensile strained quantum well 206, and a third tensile strained quantum well 210. The set of compressively strained quantum wells 204, 208, and 212 includes a first compressively strained quantum well 204, a second compressively strained quantum well 208, and a third compressively strained quantum well 212. The number of tensile strained quantum wells in the set of tensile strained quantum wells 202, 206, and 210 matches the number of compressive strained quantum wells in the set of compressive strained quantum wells 204, 208, and 212. Further, the number of tensile strained quantum wells in the set of tensile strained quantum wells 202, 206, and 210 and the number of compressive strained quantum wells in the set of compressive strained quantum wells 204, 208, and 212 is between 6 and 10.

The first tensile strained quantum well 202 and the first compressive strained quantum well 204 form a first pair of quantum wells 202 and 204 of the hybrid strained multiple quantum well structure 202, 204, 206, 208, 210 and 212. The second tensile strained quantum well 206 and the second compressive strained quantum well 208 form a second pair of quantum wells 206 and 208 of the hybrid strained multiple quantum well structure 202, 204, 206, 208, 210 and 212. Likewise, a third tensile strained quantum well 210 and a third compressive strained quantum well 212 form a third pair of quantum wells 210 and 212 of the hybrid strained multiple quantum well structure 202, 204, 206, 208, 210 and 212. Thus, the first pair of quantum wells 202 and 204, the second pair of quantum wells 206 and 208, and the third pair of quantum wells 210 and 212 are consecutive pairs of quantum wells.

The plurality of barrier layers 214, 216, 218, 220, and 222 includes a first barrier layer 214, a second barrier layer 216, a third barrier layer 218, a fourth barrier layer 220, and a fifth barrier layer 222. One of the plurality of barrier layers 214, 216, 218, 220, and 222 is sandwiched between successive pairs of quantum wells of the hybrid strained multi-quantum well structure 202, 204, 206, 208, 210, and 212. Thus, the second barrier layer 216 is sandwiched between the first pair of quantum wells 202 and 204 and the second pair of quantum wells 206 and 208. Further, a fourth barrier layer 220 is sandwiched between the second pair of quantum wells 206 and 208 and the third pair of quantum wells 210 and 212.

Another barrier layer is sandwiched between the tensile strained quantum well and the compressive strained quantum well of each pair of quantum wells of the hybrid strained multiple quantum well structure 202, 204, 206, 208, 210 and 212. Thus, the first barrier layer 214 is sandwiched between the first tensile strained quantum well 202 and the first compressive strained quantum well 204. The third barrier layer 218 is sandwiched between the second tensile strained quantum well 206 and the second compressive strained quantum well 208. Further, a fifth barrier layer 222 is sandwiched between the third tensile strained quantum well 210 and the third compressive strained quantum well 212.

Based on the radiative recombination in the active layer 114, a set of compressively strained quantum wells 204, 208, and 212 are configured to emit light with a lateral polarization direction, while a set of tensile strained quantum wells 202, 206, and 210 are configured to emit light with a perpendicular polarization direction. Thus, the SLED 100 is configured to emit incoherent light resulting from the combination of transversely polarized light and longitudinally polarized light.

The set of compressively strained quantum wells 204, 208, and 212 and the set of tensile strained quantum wells 202, 206, and 210 are grown by a Metal Organic Chemical Vapor Deposition (MOCVD) technique, wherein adjustment of the InxGa 1-xaryp 1-y stoichiometry results in the growth of the set of compressively strained quantum wells 204, 208, and 212 and the set of tensile strained quantum wells 202, 206, and 210. Precursor gases of suitable materials, set at predetermined power levels, are used to grow compressively strained quantum wells and tensile strained quantum wells using MOCVD, as will be appreciated by those skilled in the art. During epitaxial growth of SLED 100, "x" and "y" can vary depending on the ratio of gases used during growth, which results in different compositions of compressively and tensilely strained quantum wells. During formation of a compressively strained quantum well, the strain applied to the quantum well causes the lattice constant of the quantum well to be different from the underlying barrier layer. Compressive strain is used in compositions where the epitaxial cells of the quantum wells are larger than the lattice matched cells. In one example, the lattice constant of the first compressively strained quantum well 204 is higher than the first barrier layer 214. Likewise, the remaining compressively strained quantum wells are grown in a manner similar to that of the first compressively strained quantum well 204.

During the formation of a tensile strained quantum well, the strain imposed on the quantum well causes the lattice constant of the quantum well to differ from that of the underlying layer. Tensile strain is used in compositions in which the unit cells of the tensile strained quantum well are smaller than the lattice matched unit cells of the underlying layer. In one example, the lattice constant of the second tensile strained quantum well 206 is smaller than the second barrier layer 216. Similarly, the remaining tensile strained quantum wells are grown in a manner similar to the formation of the second tensile strained quantum well 206. In other embodiments, the set of compressively strained quantum wells 204, 208, and 212 and the set of tensile strained quantum wells 202, 206, and 210 may be formed using other CVD processes, PVD processes, atomic Layer Deposition (ALD) processes, other suitable thin film deposition processes, or suitable combinations thereof.

The barrier layer separates each of the compressively and tensile strained quantum wells. The thin barrier layer facilitates valence band intermixing between the compressively strained quantum well and the tensile strained quantum well, while the thick barrier layer between the compressively strained quantum well and the tensile strained quantum well may improve the epitaxial quality of the active layer 114. The barrier layers have different material compositions than the quantum wells for promoting the growth of strained quantum wells of the hybrid strained multi-quantum well structures 202, 204, 206, 208, 210 and 212.

In one embodiment of the first type of SLED 100, the compressive strain of the set of compressively strained quantum wells 204, 208, and 212 and the tensile strain of the set of tensile strained quantum wells 202, 206, and 210 are in the range of 0.7 to 1% of the total strain of the set of compressively strained quantum wells 204, 208, and 212 and the set of tensile strained quantum wells 202, 206, and 210. Furthermore, the percentage difference between the compressive strain of the set of compressively strained quantum wells 204, 208, and 212, referred to as the net strain, and the tensile strain of the set of tensile strained quantum wells 202, 206, and 210 is less than 0.1%, i.e., in the range of 0-0.1%. Experimental results show that a net strain value greater than 0.1% results in a degradation of the epitaxial quality of the active layer 114. In one example, the compressive strain is 0.7% of the total strain and the tensile strain is 0.7% -0.8% of the total strain. Each of the set of tensile strained quantum wells 202, 206, and 210 and the set of compressive strained quantum wells 204, 208, and 212 have a thickness of 7.5 nanometers. Further, the thickness of each of the plurality of barrier layers, i.e., the first through fifth barrier layers 214, 216, 218, 220, and 222, is between 5 nanometers and 5.5 nanometers. The number of quantum wells of the set of tensile strained quantum wells 202, 206 and 210 and the set of compressive strained quantum wells 204, 208 and 212 is in the range of 6-10.

In another embodiment of the second type of SLED 100, the compressive and tensile strains are 1.05% and 0.9% of the total strain of the set of compressively strained quantum wells 204, 208, and 212 and the set of tensile strained quantum wells 202, 206, and 210, respectively. The thickness of each quantum well of the set of tensile strained quantum wells 202, 206, and 210 and the set of compressive strained quantum wells 204, 208, and 212 is 7.5 nanometers. Each of the plurality of barrier layers, i.e., the first through fifth barrier layers 214, 216, 218, 220, and 222, has a thickness between 10 nanometers and 14 nanometers. The number of quantum wells of the set of tensile strained quantum wells 202, 206 and 210 and the set of compressive strained quantum wells 204, 208 and 212 is 6 such that 3 tensile strained quantum wells and 3 compressive strained quantum wells are included in the hybrid strained multi-quantum well structure 202, 204, 206, 208, 210 and 212.

In yet another embodiment of the third type of SLED 100, the compressive and tensile strains are 0.95% and 0.9% of the total strain of the set of compressively strained quantum wells 204, 208, and 212 and the set of tensile strained quantum wells 202, 206, and 210, respectively. Each of the set of tensile strained quantum wells 202, 206, and 210 and each of the set of compressive strained quantum wells 204, 208, and 212 have a thickness of 8 nanometers. Each of the plurality of barrier layers, i.e., the first through fifth barrier layers 214, 216, 218, 220, and 222, has a thickness of 14 nanometers. In addition, the compressive strain of a set of compressively strained quantum wells 204, 208, and 212 increases from 0.95% to 1%. The number of quantum wells for the set of tensile strained quantum wells 202, 206, and 210 and the set of compressive strained quantum wells 204, 208, and 212 is 6, such that 3 tensile strained quantum wells and 3 compressive strained quantum wells are included in the hybrid strained multi-quantum well structure 202, 204, 206, 208, 210, and 212.

In another embodiment of the dual barrier SLED 100, the fourth type of SLED 100, each barrier layer, i.e., the first barrier layer 214, the third barrier layer 218, and the fifth barrier layer 222, sandwiched between the tensile strained quantum well and the compressive strained quantum well of each pair of quantum wells has a thickness in the range of 5 nanometers to 5.5 nanometers. In addition, the barrier layers sandwiched between a continuous pair of quantum wells, such as the second barrier layer 216 and the fourth barrier layer 220, among the plurality of barrier layers 214, 216, 218, 220, and 222 have thicknesses in the range of 10 nm to 14 nm. The number of quantum wells of the set of tensile strained quantum wells 202, 206, and 210 and the set of compressive strained quantum wells 204, 208, and 212 is 6, thereby including 3 tensile strained quantum wells and 3 compressive strained quantum wells in the hybrid strained multi-quantum well structure 202, 204, 206, 208, 210, and 212. The fourth type of SLED 100 provides a thick barrier layer (10 nm to 14 nm) that helps to reduce defects at the interface (interface defects) due to lattice constant mismatch between the barrier layer and the quantum well, while a thin barrier layer (5 nm to 5.5 nm) helps to mix the valence band between the compressively strained quantum well and the tensile strained quantum well.

Fig. 3 is a schematic diagram 300 showing a scanning electron micrograph of a first type of SLED 100 (also referred to as a single barrier hybrid strained Multiple Quantum Well (MQW) SLED 100) according to one embodiment of the present disclosure. The uppermost barrier layer is very thin (between 5 nm and 5.5 nm thick). As shown in fig. 3, the uppermost barrier layer may take on a wavy surface morphology.

Fig. 4 is a schematic diagram 400 showing a scanning electron micrograph of a fourth type of SLED 100 (also referred to as a dual barrier hybrid strained MQW SLED 100) with improved topological properties according to one embodiment of the present disclosure. Each of the first, third and fifth barrier layers 214, 218, 222 is 5 nanometers thick to promote valence band intermixing between the tensile and compressive strained quantum wells of the same pair of quantum wells, which results in a low degree of polarization of the emitted light. In addition, each of the second barrier layer 216 and the fourth barrier layer 220 has a thickness of 14 nanometers, which results in improved topological properties of the active layer 114 compared to the first type of SLED 100.

Fig. 5 is a graph 500 illustrating a comparison of photo-electrical (LI) characteristics between a second SLED 100 and a conventional SLED according to one embodiment of the present disclosure. The Y-axis represents the power of the light emitted by the conventional SLED and the second SLED 100 in milliwatts (0-16 milliwatts) and the X-axis represents the operating current of the conventional SLED and the second SLED 100 in milliamps (1 milliamp-193 milliamps). In fig. 5, curve 500a represents the LI characteristics of a conventional SLED, while curve 500b represents the LI characteristics of a second SLED 100. In conventional SLEDs, the active layer includes only one set of compressively strained quantum wells separated by barrier layers. In conventional SLEDs, the number of quantum wells is 7 and the compressive strain is 1.05% of the total strain. The second type of SLED 100 of the present disclosure includes 6 quantum wells, further including three 0.9% tensile strained quantum wells in addition to the other three compressive strained quantum wells. Due to the hybrid strained multiple quantum well structures 202, 204, 206, 208, 210 and 212, in low current systems, the second SLED 100 achieved higher optical power than the conventional SLEDs, as seen in the comparison of the LI characteristics of curve 500b with the LI characteristics of curve 500a, respectively.

Fig. 6 is a graph 600 illustrating a comparison of light-current (LI) characteristics between a first type of SLED 100 and a third type of SLED 100 according to one embodiment of the present disclosure. The Y-axis represents the power of the light emitted by the first type of SLED 100 and the third type of SLED 100 (at 0-20 mW), while the X-axis represents the operating current of the first type of SLED 100 and the third type of SLED 100 (at 1-193 mA). The third type of SLED 100 includes 6 alternating quantum wells. The third type of SLED 100 is a strain modulated SLED 100. The 6 alternating quantum wells include 3 compressively strained quantum wells and 3 tensile strained quantum wells. Each quantum well has a thickness of 8 nanometers, each of the first through fifth barrier layers 214, 216, 218, 220, and 222 has a thickness of 14 nanometers, the tensile strained quantum well has a strain of 0.9%, and the compressive strained quantum well has a strain of 0.95%.

As will be appreciated by those skilled in the art, to obtain increased Amplified Spontaneous Emission (ASE) gain from a tensile strained quantum well, it is necessary to increase the tensile strain of the quantum well. However, this may lead to epitaxial defects which in turn reduce ASE gain. The third type of SLED 100 provides an alternative method to increase the tensile ASE gain of the SLED 100. As the strain on the compressively strained quantum well increases, additional strain on the tensile strained quantum well is imposed on the same pair of quantum wells. In one example, the strain on the first tensile strained quantum well 202 is increased by increasing the strain on the first compressive strained quantum well 204. Likewise, the strain on the remaining tensile strained quantum wells is increased by increasing the corresponding strain on the compressively strained quantum wells of the corresponding pair of quantum wells. As shown in graph 600, when the strain on the compressively strained quantum well increases from 0.95% (power represented by curve 600 a) to 1.0% (power represented by curve 600 b), the power increases significantly.

The Polarization Extinction Ratio (PER) depends on the Transverse Electric (TE) and Transverse Magnetic (TM) fields of the non-strain modulated hybrid strain SLED 100 (e.g., the first type of SLED 100). Since the number of tensile and compressive strained quantum wells is equal and the optical gain of each tensile strained quantum well is high, the PER value of the first type of SLED 100 is 8 decibels (dB) and has a dominant TM mode. Traditionally, the PER value decreases with increasing TE mode intensity, which is caused by the higher strain of the compressively strained quantum well. However, in the third type of SLED 100, PER increases from 8dB to 10-12dB as the dominant TM mode increases.

As will be appreciated by those skilled in the art, the TM mode intensity gain increases with increasing tensile strain optical gain. An increase in the compressive strain of the compressively strained quantum well results in an increase in the tensile strain of the corresponding tensile strained quantum well in the same pair of quantum wells, further resulting in an increase in the tensile strain optical gain and TM mode intensity gain. Furthermore, the addition of compressively strained quantum wells increases the superlinear characteristics of the third type of SLED 100 relative to the first type of SLED 100.

Fig. 7 is a graph 700 illustrating horizontal far field performance 702 and vertical far field performance 704 of a first type of SLED 100 according to one embodiment of the present disclosure. The X-axis represents the far field angle θ (-90 degrees to 90 degrees) and the Y-axis represents the normalized intensity (0.2 to 1 arbitrary unit (au)). Horizontal far field performance refers to the full width half maximum of the optical output power intensity of the SLED 100 as measured along the X-axis. Vertical far field performance refers to the full width half maximum of the optical output power intensity of the SLED 100 as measured along the Y-axis. Incorporating a first type of SLED 100 that emits incoherent light of low polarization into an optical system requires that the optical output of the first type of SLED 100 be coupled into an optical fiber (not shown). By coupling the SLED 100 with a single mode fiber, a coupling efficiency of up to 45% of the total light output can be achieved.

Fig. 8 is a graph illustrating horizontal far field performance 802 and vertical far field performance 804 of a first type of SLED 100 having a light absorbing layer in an n-type metal layer 104 according to one embodiment of the present disclosure. In one embodiment, the light absorbing layer is an indium gallium arsenide (InGaAsP) layer. The X-axis represents the far field angle θ (-90 degrees to 90 degrees) and the Y-axis represents the normalized intensity (0.2 to 1 au). Horizontal far field performance refers to the full width half maximum of the optical output power intensity of the SLED 100 as measured along the X-axis. Vertical far field performance refers to the full width half maximum of the optical output power intensity of the SLED 100, as measured along the Y-axis. To achieve more rounded far field performance, the thickness of the first SCH layer 112 is reduced in the first type of SLED 100 to allow for optical mode expansion of incoherent light. As a result, the shape of the optical mode changes from elliptical to circular. The circular optical mode improves the coupling efficiency of the optical mode to the optical fiber.

Thus, a SLED 100 with the hybrid strained multiple quantum well structures 202, 204, 206, 208, 210 and 212 fabricated by the above-described method produces emission of incoherent light with reduced epitaxial defects of the active layer 114 of the SLED 100 and improves the coupling efficiency of coupling the SLED 100 to the optical fiber and, furthermore, the polarization of incoherent light emitted by the first type of SLED 100 and the fourth type of SLED 100 is very low (e.g., PER is less than 1dB, i.e., in the range of 0-1 dB). The second type of SLED 100 and the third type of SLED 100 emit light at high power and operate at low operating currents (e.g., 100-200 mA). Furthermore, the incoherent light emitted is within a wide bandwidth.

Among other features, consistent with the technology of the present disclosure, a hybrid strained multiple quantum well SLED 100 is provided. While various exemplary embodiments of the disclosed systems and methods have been described above, it should be understood that they have been presented by way of example only, and not limitation. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed.

In the claims, the terms "comprising," "including," and "having" do not exclude the presence of other elements or steps than those listed in a claim. The terms "a" or "an", as used herein, are defined as one or more. Unless otherwise indicated, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

While various embodiments of the present disclosure have been illustrated and described, it will be clear that the present disclosure is not limited to only these embodiments. Many modifications, variations, changes, substitutions and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the present disclosure as described in the claims.

Claims (20)

1. A super luminescent diode (SLED) comprises

A first multilayer; and

an active layer grown on the first multilayer, the active layer comprising:

a plurality of barrier layers including a first barrier layer and a second barrier layer; and

a hybrid strained multi-quantum well structure comprising a set of tensile strained quantum wells and a set of compressive strained quantum wells, wherein each pair of quantum wells of the hybrid strained multi-quantum well structure comprises one tensile strained quantum well of the set of tensile strained quantum wells and one compressive strained quantum well of the set of compressive strained quantum wells, wherein a first barrier layer of the plurality of barrier layers is sandwiched between a consecutive pair of quantum wells of the hybrid strained multi-quantum well structure, a second barrier layer is sandwiched between the tensile strained quantum wells and the compressive strained quantum wells of each pair of quantum wells of the hybrid strained multi-quantum well structure, wherein based on radiative recombination in the active layer, the set of compressive strained quantum wells is configured to emit light with a transverse polarization direction, the set of tensile strained quantum wells is configured to emit light with a perpendicular polarization direction, such that the SLED is configured to emit incoherent light.

2. The SLED of claim 1, wherein a number of tensile strained quantum wells in the set of tensile strained quantum wells matches a number of compressive strained quantum wells in the set of compressive strained quantum wells.

3. The SLED of claim 1, wherein the compressive strain of the set of compressively strained quantum wells and the tensile strain of the set of tensile strained quantum wells are in the range of 0.7% to 1% of the total strain of the set of compressively strained quantum wells and the set of tensile strained quantum wells.

4. The SLED of claim 1, wherein a percentage difference between a compressive strain of the set of compressively strained quantum wells and a tensile strain of the set of tensile strained quantum wells is less than 0.1%.

5. The SLED of claim 1, wherein the number of tensile strained quantum wells in the set of tensile strained quantum wells and compressive strained quantum wells in the set of compressive strained quantum wells is between 6 and 10.

6. The SLED of claim 1, wherein a thickness of each barrier layer of the plurality of barrier layers is in a range of 5 nanometers to 5.5 nanometers.

7. The SLED of claim 1, wherein each tensile strained quantum well of the set of tensile strained quantum wells and each compressive strained quantum well of the set of compressive strained quantum wells are 7.5 nanometers thick.

8. The SLED of claim 1, wherein the polarization extinction coefficient of the SLED is less than 1 decibel.

9. The SLED of claim 1, further comprising a first Separation Constraint Heterostructure (SCH) layer and a second SCH layer, wherein the active layer is sandwiched between the first SCH layer and the second SCH layer.

10. The SLED of claim 9, further comprising:

a substrate, wherein the first multilayer is formed on top of the substrate, and wherein the first multilayer comprises:

a buffer layer formed on the substrate;

an n-contact waveguide grating layer formed on the buffer layer; and

and a graded index layer formed on the n-contact waveguide grating layer, wherein the first SCH layer is formed on the graded index layer.

11. The SLED of claim 10, further comprising:

an n-type metal layer formed under the substrate, wherein the n-type metal layer includes a light absorbing layer.

12. The SLED of claim 11, further comprising:

a second multi-layer formed on the second SCH layer, wherein the second multi-layer includes:

a graded index layer formed on the second SCH layer;

a p-contact waveguide grating layer formed on the graded index layer;

a p-contact layer formed on the p-contact waveguide grating layer; and

and a p-type metal layer formed on the p-contact layer.

13. The SLED of claim 12, wherein the radiative recombination in the active layer is based on applying a potential difference between the p-type metal layer and the n-type metal layer.

14. The SLED of claim 12, wherein the p-type metal layer and the p-type contact layer form a p-type cladding layer, and wherein the p-type cladding layer has a ridge geometry.

15. The SLED of claim 12, each of the first and second barrier layers having a thickness in the range of 10 nm to 14 nm.

16. The SLED of claim 1, wherein an operating current of the SLED is in the range of 100 milliamp-200 milliamp.

17. The SLED of claim 16, wherein compressive strain and tensile strain are 1.05% and 0.9% of the total strain of the set of compressively strained quantum wells and the set of tensile strained quantum wells, respectively.

18. The SLED of claim 1, wherein an increase in compressive strain of the set of compressively strained quantum wells increases the tensile strain of the set of tensile strained quantum wells.

19. The SLED of claim 18, wherein the first barrier layer has a thickness of 5 nanometers.

20. The SLED of claim 18, wherein the second barrier layer has a thickness of 14 nanometers.