WO2005060010A1 - 受光素子およびそれを用いた光受信機 - Google Patents
受光素子およびそれを用いた光受信機 Download PDFInfo
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- WO2005060010A1 WO2005060010A1 PCT/JP2004/018916 JP2004018916W WO2005060010A1 WO 2005060010 A1 WO2005060010 A1 WO 2005060010A1 JP 2004018916 W JP2004018916 W JP 2004018916W WO 2005060010 A1 WO2005060010 A1 WO 2005060010A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
- H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
- H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
- H01L31/107—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier working in avalanche mode, e.g. avalanche photodiodes
Definitions
- the present invention relates to a light receiving element and an optical receiver using the same.
- a photodiode is a light receiving element having a signal amplification function.
- APDs have an integrated structure in which the functions of multiplication and light absorption are integrated, and a SAM (separated absorption and multiplication) structure in which the functions of light absorption and carrier multiplication are separated.
- SAM separated absorption and multiplication
- the use of a SAM type structure is effective when fabricating an APD using a compound semiconductor.
- the optimum material can be selected for each of the light absorption layer and the multiplication layer, and it is possible to design an APD with higher light receiving capacity and multiplication capacity compared to the integrated structure. This is because it is possible.
- An APD having a SAM structure has a layer structure including a light absorption layer and a multiplication layer.
- a SAM APD When a SAM APD is irradiated with light from a direction horizontal to the stacking direction, a carrier is generated in the light absorbing layer. The generated carriers travel in accordance with an electric field applied internally depending on the applied voltage, and a part thereof is introduced into the multiplication layer. Carriers introduced into the multiplication layer undergo collision ionization inside the multiplication layer, and the generated carriers undergo a chain reaction in which they are again impactionized. This causes the signal carrier to be avalanche multiplied and sent out to an external electrode (or electric wire).
- Patent Document 1 describes an APD having a SAM type structure including an avalanche multiplication layer.
- Paragraph 0024 of the document shows a layer structure in which an electric field relaxation layer and an avalanche multiplication layer are provided below the light absorption layer, and light guide layers having the same thickness are provided above and below the light absorption layer.
- Paragraph 0035 also describes a light receiving element having a similar layer structure.
- FIG. 14 is a diagram showing a layer structure of a semiconductor light receiving element described in the document.
- An n-type light guide layer 111, a multiplication layer 112, an electric field relaxation layer 113, an absorption layer 114, a p-type light guide layer 115, And the cladding layer 116 are laminated in this order. Incident light is introduced from the end face of the absorption layer 114 and is guided through the layer.
- the n-type light guide layer 111 and the p-type light guide layer 115 are set to have the same thickness.
- Patent Document 2 describes another example of a SAM APD.
- the light receiving element described in the document has an avalanche multiplication layer having a super lattice structure.
- FIG. 15 shows the APD described in FIG. 2 and paragraph 0018 of the same document.
- the illustrated APD describes a light receiving element having a layered structure including a light absorbing layer 26 and low refractive index layers provided above and below the light absorbing layer 26.
- the low-refractive-index layer located below the light-absorbing layer includes a lower cladding layer 22, a second core layer 23, a superlattice avalanche multiplication layer 24, and an electric field relaxation layer 25.
- the low-refractive-index layer located above the light-absorbing layer 26 is composed of an upper second core layer 27 and an upper clad layer 28. Accordingly, as described in paragraphs 0012 and 0014 of Patent Document 2 and FIG. 2, the refractive index is distributed in a symmetrical step shape with the light absorbing layer 26 as a center, and the spot size is increased by making the guided light multimode. (Fig. 2). Thereby, the optical coupling with an optical fiber having a large exit spot size is improved, and the tolerance is also improved.
- the lower cladding layer 22, the second core layer 23, the superlattice avalanche multiplication layer 24, and the electric field relaxation layer 25 have the same refractive index.
- Patent Document 1 Japanese Patent Application Laid-Open No. 2001-237454
- Patent document 2 JP-A-9-1181351
- the above-described conventional APD has the following improvements.
- the multiplication layer 112 needs to generate an avalanche breakdown, and therefore needs to be formed of a semiconductor material having a wider band gap than an adjacent light absorption layer. There is. Therefore, the multiplication layer 112 is made of a material having a lower refractive index than the absorption layer.
- the refractive index of the multiplication layer 112 is designed to be high, such light leakage can be improved by using a force S.
- a narrow band gap layer semiconductor is used, and the high electric field in the multiplication layer 112 is high.
- the present invention is to solve a problem peculiar to a light receiving element having such a photomultiplier layer, and an object of the present invention is to provide a light receiving element that stably realizes high quantum efficiency. is there.
- a laminate including a first light guide layer, a multiplying layer having a larger band gap than the first light guide layer, and a light absorption layer sandwiched between these layers.
- a light-receiving element comprising a film and configured to receive a directional force light in a direction parallel to the lamination direction of the laminated film, wherein an optical axis of the light is located at an end face of the first light guide layer.
- a problem specific to the light receiving element including the multiplication layer that is, light leakage through the low-refraction multiplication layer, and a local height at the incident end face. Generation of a current density region can be suppressed.
- the light is suitably incident on the first guide layer, and the incident light is coupled to the light absorbing layer while being guided to the first guide layer. Therefore, light leakage to the multiplication layer can be effectively suppressed.
- it is possible to reduce the current concentration at the incident end face, which occurs when light is incident from the end face of the light absorbing layer as usual, and to improve the durability of the element. As a result, it is possible to realize a device structure having high quantum efficiency and high reliability.
- the “guide layer” in the present invention is a layer through which light leaked from the absorption layer is guided, and has a certain degree of effect of confining light to the absorption layer.
- a structure including a clad layer and a substrate When a structure including a clad layer and a substrate is provided, these are disposed outside the “guide layer” as viewed from the absorption layer.
- the light receiving element wherein the light incident position at which the output of the light receiving element is maximum is located at the end face of the first light guide layer.
- the light incident position where the output is maximum is located at the end face of the first light guide layer, so that the incident light is guided to the first guide layer and is connected to the light absorption layer by mounting. It is possible to suitably adopt a method of causing the above.
- the device further comprises a second light guide layer formed on the opposite side of the multiplication layer from the first light guide layer, wherein the thickness of the first light guide layer is Second light guide layer A light receiving element characterized by having a thickness larger than the thickness of the light receiving element.
- the first light guide layer is formed to be thicker than the second light guide layer.
- a method in which the light is guided by one guide layer and the light absorption layer is coupled to the light absorbing layer in a frame-wise manner can be suitably adopted.
- a highly reliable element structure having high quantum efficiency can be realized.
- the thickness of the first light guide layer is preferably at least 0.1, more preferably at least l ⁇ m. By doing so, the effect of suppressing light leakage through the multiplication layer and alleviating the current density at the incident end face can be obtained sufficiently sufficiently.
- the upper limit of the thickness is appropriately set according to the waveguide length of the light receiving element, the wavelength of the incident light, and the like. From the viewpoint of improving the efficiency of optical coupling between the first optical guide layer and the absorption layer, for example, ⁇ m or less.
- the thickness of the first light guide layer is preferably at least 1.2 times the wavelength of light guided in the light receiving element, more preferably at least twice.
- the upper limit of the thickness is appropriately set according to the waveguide length of the light receiving element, the wavelength of incident light, and the like. From the viewpoint of improving the efficiency of optical coupling between the first light guide layer and the absorption layer, for example, the light receiving It should be 10 times or less the wavelength of light guided in the device.
- the thickness of the absorption layer is preferably 0.6 ⁇ or less, more preferably 0.3 / im or less. By doing so, a light-receiving element with high speed and high sensitivity can be obtained.
- an optical waveguide for making light incident on the light receiving element, and light emitted from the optical waveguide is condensed on an end face of the first light guide layer and the first light is
- An optical receiver is provided that is configured to be incident into the guide layer.
- this optical receiver includes the light-receiving element having the above-described structure, it has both good quantum efficiency and high reliability.
- FIG. 1 is a cross-sectional view schematically showing a layer structure of a semiconductor APD according to an embodiment.
- FIG. 2 is a diagram showing how light is guided when light is incident on an APD having the layer structure of FIG. 1.
- FIG. 3 is a diagram showing a layer structure of an APD according to an embodiment.
- FIG. 4 is a diagram showing a cross-sectional structure of a passive element according to the embodiment.
- FIG. 5 is a view showing a modification of the element structure of FIG. 4.
- FIG. 6 is a diagram showing a structure of an optical receiver according to an embodiment.
- FIG. 7 is a side view of the optical receiver in FIG. 6.
- FIG. 8 is a side view showing another structure of the optical receiver according to the embodiment.
- FIG. 9 is a diagram showing a cross-sectional structure of the optical integrated device according to the embodiment.
- FIG. 10 is a schematic diagram showing a basic configuration example of a WDM system using an APD according to the embodiment.
- FIG. 11 is a schematic diagram showing a transmission / reception module.
- FIG. 12 is a diagram showing a structure of an APD according to an example.
- FIG. 13 is a diagram showing a light intensity distribution in a waveguide direction calculated by the BPM method for the APD according to the embodiment.
- FIG. 14 is a diagram showing a layer structure of a conventional semiconductor light receiving element.
- FIG. 15 is a cross-sectional view showing a conventional light receiving element.
- FIG. 16 is a diagram showing a layer structure of an APD according to an example.
- FIG. 17 is a diagram showing a layer structure of an APD according to the embodiment.
- FIG. 18 is a diagram showing a layer structure of an APD according to the embodiment.
- FIG. 19 is a diagram showing a layer structure of an APD according to the embodiment.
- FIG. 20 is a diagram for explaining the significance of a light confinement coefficient.
- the semiconductor APD according to the present embodiment relates to a SAM APD.
- a SAM APD In order to obtain sufficient quantum efficiency with a thin light-absorbing layer, it has a horizontal incidence structure in which light is incident horizontally on the junction surface.
- FIG. 1 is a diagram showing a layer structure of the semiconductor APD according to the present embodiment.
- an n-side light guide layer 111, a multiplication layer 112, an electric field relaxation layer 113, an absorption layer 114, a p-side light guide layer 115, and a p-side cladding layer 116 are laminated in this order.
- the material and thickness of each layer are as shown in FIG.
- the wavelength composition of the illustrated semiconductor layer is 1.
- the thickness is an example, and the design can be changed as appropriate. The same applies to the constituent materials.
- the p-side light guide layer 115 corresponds to the first light guide layer in the present invention
- the n-side light guide layer 111 corresponds to the second light guide layer in the present invention.
- the light receiving element includes a first light guide layer (P-side light guide layer 115), a multiplication layer 112 having a larger band gap than the first light guide layer, and a A laminated film including a light absorbing layer (absorbing layer 114) sandwiched therebetween, and configured to receive light from a direction horizontal to the laminating direction of the laminated film (a direction horizontal to the substrate).
- the optical axis of the incident light is configured to be located at the end face of the first light guide layer (P-side light guide layer 115), and the light incident position at which the output of the light receiving element becomes the maximum is the first light incident position. It is located on the end face of the guide layer (p-side light guide layer 115).
- FIG. 2 is a diagram showing how light is guided when light enters the APD having the layer structure of FIG.
- the left side of the figure shows the refractive index of each layer.
- An n-side light guide layer 111 and a p-side light guide layer 115 are arranged above and below the high refractive index absorption layer 114.
- a multiplication layer 112 having a low refractive index is provided between the n-side light guide layer 111 and the absorption layer 114.
- Light is incident on the end surface of the p-type light guide layer 115 on the left side in the figure such that the optical axis of the incident light is positioned. The incident light is coupled to the absorption layer while being guided in the p-side light guide layer 115.
- the light introduced into the absorption layer 114 becomes electrons and holes that are photoelectrically converted in the layer, and the electrons are introduced into the multiplication layer 112 via the electric field relaxation layer 113.
- the carriers are turned into collision ions inside the multiplication layer 112, and the generated carriers again cause a chain reaction that causes collision ions. This allows signal key Carriers are avalanche multiplied and sent to external electrodes or wires
- the P-side light guide layer 115 and the n-side light guide layer 111 are layers that suppress guided light from entering a radiation mode (a mode in which the guided light is not combined with the absorption layer and is emitted to the substrate side or the upper part of the element).
- the multiplication layer 112 is a layer that causes avalanche multiplication by application of a high electric field and generates a large amount of carriers.
- the multiplication layer 112 is a narrower gap than the absorption layer 114 described later, and can reduce the ⁇ current even when a high electric field is applied, thereby causing avalanche multiplication.
- the refractive index is low, the presence of this layer at the center of the waveguide structure is disadvantageous when light confinement is considered. Since it is preferable that an electric field is applied uniformly to the multiplication layer 112, the impurity concentration should be set as low as possible.
- the impurity concentration of the multiplication layer 112 is, for example, 1 ⁇ 10 17 l ⁇ 10 18 cm ⁇ 3 .
- the thickness of the multiplication layer 112 is preferably 1 / m or less from the viewpoint of improving the GB product. In addition, from the viewpoint of suppressing the multiplication and the current, it is preferably at least 0.02 ⁇ , and more preferably at least 0.0 ⁇ .
- the electric field relaxation layer 113 is a layer provided to reduce a difference between a high electric field applied to the multiplication layer 112 and a relatively low electric field applied to the absorption layer 114. By providing this layer, a high electric field can be stably applied to the multiplication layer 112.
- the electric field relaxation layer 113 contains a ⁇ -type impurity, and the same constituent material as the absorption layer 114 and the multiplication layer 112 can be used.
- the thickness of the electric field relaxation layer 113 can be, for example, 0.02-0.4 ⁇ , and the ⁇ -type impurity concentration can be 0.5 ⁇ 10 18 ⁇ 2 ⁇ 10 18 cm — 3 .
- the absorption layer 114 is a layer that plays a role of converting incident light into electricity, and has a band gap capable of absorbing light to be received.
- the constituent material of the absorption layer 114 is appropriately selected according to the wavelength of the incident light.
- the thickness of the absorbing layer 114 is preferably l xm or less, more preferably 0.5 zm or less.
- the lower limit is not particularly limited, but it is preferable to set the lower limit to, for example, 0.01 zm or more. If the thickness of the absorption layer 114 is too large, the traveling time of the carrier becomes longer, and it becomes difficult to obtain high-speed and high-sensitivity characteristics.
- the thickness of the absorption layer 114 is preferable to reduce the thickness of the absorption layer 114 as much as possible, but in this case, it is not possible to secure a sufficient amount of generated carriers. Problem arises.
- the carrier generation region in the absorption layer 114 can be widened. Even if the layer thickness is small, a sufficiently high carrier generation amount can be obtained. As a result, according to the present embodiment, it is possible to reduce the layer thickness of the absorption layer 114 and to achieve high quantum efficiency while improving high-speed and high-sensitivity characteristics.
- the p-side light guide layer 115 is a layer that serves to suppress the light guided through the absorption layer 114 from leaking to the p-type semiconductor side. In the present embodiment, this layer further functions as a layer that guides incident light.
- the p-side light guide layer 115 is made of p-type InAlGaAs, and has a thickness about five times that of the n-type light guide layer 111. In the present embodiment, it is set to 1.5 z m.
- the cladding layer 116 is formed of a layer having a lower refractive index than the p-side light guide layer 115, and functions to confine light.
- An electrode (not shown) is formed on the cladding layer 116.
- the incident light whose optical axis center is located enters the p-side light guide layer 115 instead of the absorption layer 114. Further, the p-side light guide layer 115 is formed thicker than the n-type light guide layer 111. Therefore, the APD according to the present embodiment has the following effects.
- the thickness of the p-type light guide layer 115 is increased, and the incident position of light is at the end face of the p-type light guide layer 115. A high property and element structure can be obtained.
- the structure of the p-type guide layer has a gradient composition.
- the schematic structure is the same as that of the first embodiment, except that the composition of the P-type guide layer is an inclined structure that changes gradually in the laminating direction.
- FIG. 3 is a diagram showing a layer structure of an APD according to the present embodiment.
- a p-type guide layer 118 having an inclined structure is provided instead of the p-type light guide layer 115.
- the composition of the p-type guide layer 118 is composed of InAlGaAs or InGaAsP, and the composition ratio changes in a graded manner, whereby the refractive index modulation shown on the left side of FIG. 3 is performed.
- the wavelength composition is changed to 1.0111, 1.2 ⁇ m.
- the p-type guide layer 118 has an inclined structure in which the refractive index increases in the direction of the absorption layer.
- the light receiving element includes a first light guide layer (p-side light guide layer 118), a multiplication layer 112 having a larger band gap (average value) than the first light guide layer, A laminated film including a light absorbing layer (absorbing layer 114) sandwiched between the layers, and light is incident from a direction horizontal to the laminating direction of the laminated film (public publication horizontal to the substrate 110). It is configured to The light incident position where the output of the light receiving element becomes maximum is located at the end face of the first light guide layer (P-side light guide layer 118).
- the first light guide layer (p-side light guide layer 118) has a configuration in which the refractive index decreases as the distance from the absorption layer increases.
- the p-type guide layer 118 has an inclined structure (graded structure), light can be efficiently introduced into the absorption layer 114, and the quantum efficiency can be further improved. Become.
- FIG. 4 is a diagram showing a cross-sectional structure of the passive element according to the present embodiment.
- An n-side light guide layer 111, a multiplication layer 112, an electric field relaxation layer 113, an absorption layer 114, and a p-side light guide A layer 115 and a p-side cladding layer 117 are stacked in this order, and an electrode 120 is provided on the p-side cladding layer 117.
- the upper portion from the absorption layer 114 is processed into a mesa shape.
- the side surface of the mesa is covered with a protective film 22 made of SiN.
- the light receiving element includes a first light guide layer (p-side light guide layer 115), a multiplication layer 112 having a band gap larger than that of the first light guide layer, and is sandwiched between these layers. And a light absorbing layer (absorbing layer 114).
- the light absorbing layer (absorbing layer 114) is provided with a light absorbing layer (absorbing layer 114). ing.
- the light incident position where the output of the light receiving element becomes maximum is located at the end face of the first light guide layer (P-side light guide layer 115).
- the illustrated structure can be formed by stacking the above semiconductor layers, providing a mask on the p-type cladding layer 117, and performing etching.
- the etching is preferably wet etching.
- the spread of current can be prevented by adopting the ridge structure, and the speed of the device can be increased.
- the side surfaces of the multiplication layer 112 and the electric field relaxation layer 113 to which a high electric field is applied are not exposed, the reliability and durability of the element are improved.
- FIG. 5 shows a modification of the element structure of FIG.
- the upper part of the absorption layer 114 is processed into a mesa shape, and the mesa side surface is covered with a protective film 22 made of SiN.
- the altered portion 24 is formed on the side surface of the multiplication layer 112 and the electric field relaxation layer 113.
- the altered portion 24 is a region whose resistance has been increased by oxidation or ion implantation.
- the multiplication layer and the electric field relaxation layer are composed of a semiconductor containing A1
- the oxidation can be performed.
- a method of contacting with water vapor can be adopted.
- the reliability of the side surfaces of the multiplication layer 112 and the electric field relaxation layer 113 is further improved, and the reliability and durability of the element can be stably improved.
- FIG. 6 shows the structure of the optical receiver according to the present embodiment.
- the signal introduced from the optical fiber 211 is input to the APD 220 through the lens 214.
- APD 220 for example, one having the configuration of the above-described embodiment can be used.
- APD220 is connected to preamplifier 230 and A
- the signal input to the PD 220 is output to the high frequency connector 234 through the microstrip line (MSL) 232.
- MSL microstrip line
- FIG. 7 is a side view of the optical receiver.
- An optical fiber 211 and a ceramic carrier 204 are provided on a substrate 202.
- An optical fiber is mounted on the ceramic carrier 204.
- Each part is arranged and fixed so that the light emitted from the optical fiber 211 is incident on the p-type light guide layer 222 of the APD 220.
- the thickness of the p-type light guide layer 222 is adjusted so that the light confinement coefficient of the incident light on the end face of the p-type light guide layer 222 is 60% or more.
- the light confinement coefficient refers to the ratio of the amount of light guided to the p-type light guide layer 222 to the total amount of incident light.
- FIG. 20 is a diagram for explaining the meaning of the optical confinement coefficient.
- the incident light has an intensity distribution close to a Gaussian distribution in the layer thickness direction.
- the integrated value of the distribution function in the p-type light guide layer 222 with respect to the total integrated value of this distribution function (corresponding to the area of the hatched portion in the figure) is defined as the light confinement coefficient.
- the light confinement coefficient is usually less than 40% in a conventional light receiving element that aligns the optical axis of incident light with the light absorbing layer.
- the thickness of the p-type light guide layer 222 is 1.0 / im or more
- the optical mode diameter of the emitted light near the tip of the optical fiber is 3.0 / im
- the light confinement coefficient is 60 / im. % Or more.
- the alignment between the optical fiber 211 and the APD 220 is performed according to a conventional method of adjusting the position while monitoring the output of the APD.
- the light incident position where the output of the APD 220 is maximum is located at the end face of the P-type light guide layer 222, and as shown in FIG. It is aligned to penetrate inside.
- the layer thickness of the p-type light guide layer 222 can be increased to, for example, the above, so that the alignment is easy and the tolerance is improved. Further, light leakage through the multiplication layer included in the APD 220 can be effectively suppressed.
- the optical receiver according to the present embodiment has high quantum efficiency because the thickness of the p-type light guide layer 222 is increased and the incident position of light is set to the end face of the p-type light guide layer 222. A highly reliable element structure can be obtained.
- a force that employs a method of condensing light using a lens is used.
- a method of directly entering light into the p-type light guide layer 115 of the APD 150 from the tip of the optical fiber 211 is preferred.
- the optical receiver according to the present embodiment includes an optical integrated device including a passive device.
- the optical integrated device according to the present embodiment includes a waveguide section and an image receiving element section formed on a substrate 110, and has a structure in which these are butt-joined.
- the waveguide section has a structure in which a lower guide layer 120, a waveguide layer 122, and an upper guide layer 124 are stacked in this order.
- the lower guide layer 120 and the upper guide layer 124 are made of InGaAsP, InAlGaAs or InP
- the waveguide layer 122 is made of InGaAsP or InAlGaAs having a higher refractive index than the above-mentioned guide layer.
- the passive element section has a structure in which a multiplication layer 112, an electric field relaxation layer 113, an absorption layer 114, a p-type light guide layer 115, and a cladding layer 116 are stacked in this order.
- the materials and thicknesses of these layers are the same as those described in the first embodiment. That is, the light receiving element according to the present embodiment includes a first light guide layer (P-side light guide layer 115), a multiplication layer 112 having a larger band gap than the first light guide layer, and a And a light absorbing layer (absorbing layer 114) sandwiched between the layers, so that light is incident from a direction horizontal to the laminating direction of the layered film (public announcement horizontal to the substrate). Have been.
- the light incident position where the output of the light receiving element becomes maximum is located at the end face of the first light guide layer (P-side light guide layer 115).
- the waveguide layer 122 is in contact with the p-side light guide layer 115 and is knot jointed.
- the light guided through the waveguide layer 122 is arranged so as to enter the end face of the p-side light guide layer.
- the optical receiver according to the present embodiment has a high quantum efficiency and a high reliability because the thickness of the p-type light guide layer 115 is increased and the light incident position is on the end face of the p-type light guide layer 115.
- An element structure having high performance can be obtained.
- the process tolerance is high and the structure is excellent in practicality.
- FIG. 10A is a schematic diagram illustrating an example of a basic configuration of the WDM system.
- a plurality of DF BLDs (lasers) 10 oscillating at wavelengths of ⁇ 1- ⁇ ⁇ ⁇ ⁇ with a certain wavelength interval are arranged.
- These DFBs 10 are directly modulated, and their optical outputs are multiplexed by a multiplexer 100 and transmitted via one optical fiber 200 and an optical amplifier 300.
- the transmitted optical signal is separated into the original wavelengths by the demultiplexer 400.
- the separated light is converted by the APD 20 into an electric signal.
- FIG. 10B is a schematic diagram illustrating another example of the WDM system.
- each DFB laser 10 is not directly modulated, but is driven by a DC signal, and its optical output is modulated by the external modulator 30. Therefore, there is an advantage that modulation can be performed at a higher speed than the system shown in FIG. 10 (a).
- the power provided with the optical amplifier 300 may be omitted.
- FIG. 11 shows such a transmission / reception module.
- an optical transmission / reception module 4 has a function including both an optical transmission module and an optical reception module.
- the optical transmission unit is composed of an optical fiber 5, an optical waveguide 9, an LD 6, a transmission circuit, a circuit board 8, and the like.
- the transmission circuit includes an LD driver that drives the laser, a laser output control unit, a flip-flop circuit, and the like.
- the optical receiving unit includes an optical fiber 5, an optical waveguide 9, a PD 15, a receiving circuit, a circuit board 8, and the like.
- the PD 15 may be the APD light receiving device of the present invention, and it is possible to obtain higher light receiving sensitivity by applying the device of the present invention.
- the receiving circuit is composed of a PRE IC with pre-amplification function, a CDR LSI composed of a clock extraction unit and an equivalent amplification unit, an APD bias control circuit, and the like.
- the WDM filter wavelength demultiplexer
- the WDM filter is disposed near the branch point of the optical waveguide, and has a function of transmitting transmission light as it is and reflecting reception light. Actually, lead frames and wires are attached, but these are not shown. By using such a transmission / reception module, two-way communication becomes possible.
- the above-mentioned APD may be an electron multiplication type (that is, one using an InAlAs multiplication layer), and a hole multiplication type APD in which a force InP is used as a multiplication layer.
- the configuration of such an APD includes an n-InP cladding layer on the substrate side, a quaternary n-side optical guide layer (In GaAsP or InAlGaAsP) having a wavelength composition of 1.2 / im force, an InGaAs absorption layer, and an electric field relaxation layer (n-InP).
- Examples include a multiplication layer composed of InP) and InP, a quaternary p-side optical guide layer (InGaAsP or InAlGa AsP) having a wavelength composition of 1.2 ⁇ m, and a p_InP cladding layer.
- the n-side light guide layer may be made thick.
- the device is configured using the InGaAsP-based semiconductor layer, but other III-V compound semiconductors may be used.
- a Group III-V compound semiconductor in which a Group III atom contains any of B, Al, Ga, In, and Tl and a Group V atom contains any of N, P, As, Sb, and Bi You can also.
- Specific examples include InGaAsP, AlGaInAs, AlGaInAsP, AlGalnP, InGaAsSb, InGaPSb, InGaAsN, AlGaInN, TlGaInAs, TlGaInAsN, and Tl GalnPN.
- FIG. 12 is a diagram illustrating the structure of the APD according to the present embodiment.
- a SAM structure was formed on the SI-InP substrate.
- a tapered structure with a wider waveguide width at the input end was applied to increase the coupling efficiency with the fiber and the tolerance.
- the area other than the n-electrode contact was etched down to the SI-InP substrate to reduce the parasitic capacitance on the P-side pad.
- the waveguide width at the incident surface is 7 / m
- the width at the end of the waveguide is 5 / m
- the waveguide length is 50 ⁇ .
- the layer structure consists of an n-InGaAsP guide layer with a composition power shorter than the signal light wavelength of 0.2 ⁇ m, an InAlAs multiplication layer of 0.2 zm, and a p_InAlAs electric field relaxation layer of 0.2 zm on the InP substrate. It has a structure in which an InGaAs absorption layer is 0.4 xm, and a p_InGaAsP guide layer, whose composition is shorter than the signal light wavelength, is 1. O xm laminated. The structure is such that the maximum output is obtained when light enters the p-InGaAsP guide layer. The incident light is guided as shown in FIG. 2 and is coupled to the absorption layer. In other words, the light enters the p-side light guide layer at the end face, and is coupled to the absorption layer while guiding, so that the concentration of the photocurrent at the end face is reduced.
- Example 2 Example 2
- the light intensity distribution in the waveguide direction of the APD described in the first embodiment was calculated by the BPM method.
- the layer structure used for the calculation is the same as that shown in the first embodiment (FIG. 16).
- the thickness of the absorbing layer was set to 0.
- a symmetrical guide structure in which the p-side light guide layer and the n-side light guide layer are the same was also evaluated. .
- the device having the asymmetric structure guide layer has a structure in which the maximum output is obtained when light is incident on the p-type light guide layer.
- FIG. 13 shows the calculation results.
- Fig. 13 (a) shows a calculation example of the symmetric structure guide layer
- Fig. 13 (b) shows a calculation example of the asymmetric structure guide layer.
- the ⁇ -side guide layer is made thicker than in the structure of FIG. 13 (a).
- the light incident position was set at the center of the light absorbing layer.
- the light incident position was aligned with the center of the p-type light guide layer.
- the symmetrical structure guide layer of FIG. 13 (a) since the input light is coupled around the absorption layer, the photocurrent density is concentrated on the light absorption layer near the end face.
- the emission mode toward the substrate becomes dominant, and it is difficult to increase the external quantum efficiency even when the waveguide length is increased. That is, the radiation mode exists and the quantum efficiency decreases.
- the light incident on the p-side light guide layer is coupled to the absorption layer while being guided, so that the photocurrent can be dispersed, and the radiation mode to the substrate side is also suppressed. External quantum efficiency can be improved.
- the photocurrent density can be further dispersed.
- the end face current was reduced and the light-proof input characteristics could be improved by about 24 times. Therefore, a receiver with a dynamic range improved by 36 dB can be configured.
- the APD described in the first embodiment was manufactured, and the characteristics of the device were evaluated.
- the layer structure is as shown in FIG.
- the wavelength composition of the illustrated semiconductor layer is 1.
- the light incident position was aligned with the center of the p-type light guide layer. Equipped with an asymmetric structure guide layer This device has a structure that can obtain the maximum output when light is incident on the P-type light guide layer.
- the breakdown voltage of the obtained APD was 20V, and the multiplication current was 0.6 ⁇ m.
- the quantum efficiency was 80%.
- the maximum response frequency was 10 GHz with a 50 ⁇ load, and the GB product was 150 GHz.
- the frequency characteristics were evaluated by connecting the APD according to the present example to a preamplifier having a transimpedance of 1 ⁇ or more. As a result, a band of 15 GHz was obtained.
- the average receiving sensitivity of the receiver was _29dBm, and at the lowest level, -26dBm could be secured. This is a very sensitive APD optical receiver for 10Gb / s.
- a layer structure shown in FIG. 19 can be adopted.
- the effective refractive index of the p guide layer 115 increases from the cladding layer side toward the absorption layer. Therefore, similar to the second embodiment, excellent device characteristics can be obtained.
- the layered structure of the present embodiment does not require graded growth and can be manufactured by a simple process.
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- Condensed Matter Physics & Semiconductors (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Hardware Design (AREA)
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- Power Engineering (AREA)
- Light Receiving Elements (AREA)
Abstract
Description
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Cited By (3)
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JP2007311455A (ja) * | 2006-05-17 | 2007-11-29 | Nec Corp | 半導体受光素子 |
US20230108564A1 (en) * | 2019-07-15 | 2023-04-06 | Slt Technologies, Inc. | Power photodiode structures and devices |
JP7307287B1 (ja) * | 2022-07-19 | 2023-07-11 | 三菱電機株式会社 | 半導体受光素子 |
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JP3708758B2 (ja) * | 1999-07-12 | 2005-10-19 | 日本電信電話株式会社 | 半導体受光素子 |
JP3544352B2 (ja) * | 2000-10-30 | 2004-07-21 | 日本電気株式会社 | 半導体受光素子 |
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Cited By (5)
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JP2007311455A (ja) * | 2006-05-17 | 2007-11-29 | Nec Corp | 半導体受光素子 |
US20230108564A1 (en) * | 2019-07-15 | 2023-04-06 | Slt Technologies, Inc. | Power photodiode structures and devices |
US12040417B2 (en) * | 2019-07-15 | 2024-07-16 | Slt Technologies, Inc. | Power photodiode structures and devices |
JP7307287B1 (ja) * | 2022-07-19 | 2023-07-11 | 三菱電機株式会社 | 半導体受光素子 |
WO2024018500A1 (ja) * | 2022-07-19 | 2024-01-25 | 三菱電機株式会社 | 半導体受光素子 |
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JPWO2005060010A1 (ja) | 2007-07-12 |
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