JP2009224467A - Electromagnetic wave radiation element - Google Patents
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本発明は、２つのコヒーレントな光波を入力、混合してその差周波数に対応したテラヘルツ電磁波を放射出力する電磁波放射素子に関する。 The present invention relates to an electromagnetic wave radiation element that inputs and mixes two coherent light waves and radiates and outputs a terahertz electromagnetic wave corresponding to the difference frequency.
電磁波を連続的に発生、放射させる技術として、トランジスタやダイオードによる発振回路を利用して電子を空間的に放射する電磁波放射素子（〜１００ＧＨｚ以下）があり、また、赤外から可視光以下の光領域では、半導体レーザや低温カスケードレーザを用いた光放射素子（〜１０ＴＨｚ以上）があるが、通信容量の拡大及び高速化の為、０．１ＴＨｚ〜１０ＴＨｚ領域で、常温で安定的に連続発振する固体放射素子の開発が望まれている。 As a technique for continuously generating and radiating electromagnetic waves, there is an electromagnetic radiation element (up to 100 GHz or less) that emits electrons spatially using an oscillation circuit such as a transistor or a diode. In the area, there are light emitting elements (~ 10 THz or more) using semiconductor lasers or low-temperature cascade lasers, but in order to expand communication speed and speed up, it continuously oscillates at room temperature in the range of 0.1 THz to 10 THz. Development of solid-state radiation elements is desired.
高電子移動度トランジスタ（HEMT）構造における２次元電子プラズモンのテラヘルツ帯への応用はM．DyakonovとM．Shurによって提案された（非特許文献１参照）。プラズモン共鳴周波数を決定する電子濃度は、ゲートバイアスで制御できるため、実用上重要な周波数可変特性を実現できる． The application of two-dimensional electron plasmons in the high electron mobility transistor (HEMT) structure to the terahertz band is Dyakonov and M.D. Proposed by Shur (see Non-Patent Document 1). Since the electron concentration that determines the plasmon resonance frequency can be controlled by gate bias, it is possible to realize a frequency variable characteristic that is practically important.
一般的なプラズモン共鳴型のフォトミキサ（プラズモン共振器）の構造及び動作原理を図６に示す。まず、２つの波長（ｆ１、ｆ２）のレーザの混合光をＨＥＭＴ構造のフォトミキサに入射する。フォトン２光波でバンド間励起された光伝導電子の持つ差周波（テラヘルツ成分）に同調して、テラヘルツ帯のプラズモン共鳴が誘起される（非特許文献２、非特許文献３参照）。この２次元電子プラズモン共鳴波は、非放射モードであって外部放射は果たせないが、２次元プラズモンの近傍に金属回折格子（グレーティング）を配したり、アンテナ構造を配することにより、非放射モードのテラヘルツ帯２次元電子プラズモン振動を放射モード電磁波へ変換することが可能となる（非特許文献３、４参照）。
FIG. 6 shows the structure and operation principle of a general plasmon resonance type photomixer (plasmon resonator). First, mixed light of lasers having two wavelengths (f1, f2) is incident on a photomixer having a HEMT structure. Terahertz band plasmon resonance is induced in synchronism with the difference frequency (terahertz component) of photoconductive electrons excited between bands by two photon light waves (see Non-Patent
トランジスタによる発振回路をはじめとする電子が空間を走行する通常の電磁波放射素子に比較して、電子集団の分極振動量子（プラズモン）の振動波を動作源とする本放射素子は、より高い周波数での動作が可能であり、テラヘルツ電磁波放射素子として期待されている。 Compared to ordinary electromagnetic radiation elements, in which electrons such as oscillation circuits using transistors travel in space, this radiation element, whose operating source is an oscillation wave of polarization oscillation quanta (plasmon) of an electron population, has a higher frequency. Therefore, it is expected as a terahertz electromagnetic wave radiation element.
発明者らは、特許文献１において、図７に示すようなテラヘルツ電磁波放射素子を提案し、２つのコヒーレントな光波をプラズモン共鳴型フォトミキサに入力し、２重回折格子電極ゲートを用いて、その差周波数に対応したテラヘルツ電磁波を効率的に放射出力することを示した。
しかしながら、ゲート電極格子が等間隔であった為、ドレインバイアス印加によって各ゲート電極格子下のプラズモン領域の電子濃度がソースからドレイン方向に単調に減少する分布となることから、次の問題を生じていた。すなわち、プラズマ周波数は、電子濃度の平方根に比例し、ゲート電極格子の寸法に反比例することから、各格子下のプラズマ周波数は一致せずにある周波数領域で分布することになる。
The inventors proposed a terahertz electromagnetic wave radiation element as shown in FIG. 7 in Patent Document 1, input two coherent light waves to a plasmon resonance type photomixer, and used a double diffraction grating electrode gate, It was shown that the terahertz electromagnetic wave corresponding to the difference frequency was radiated and output efficiently.
However, since the gate electrode lattices are equally spaced, the distribution of the plasmon region under each gate electrode lattice monotonously decreases in the direction from the source to the drain due to the application of the drain bias, resulting in the following problems. It was. That is, since the plasma frequency is proportional to the square root of the electron concentration and inversely proportional to the size of the gate electrode lattice, the plasma frequency under each lattice is not matched and is distributed in a certain frequency region.
その結果、外部から入射されたレーザ２光波の差周波にプラズマ周波数が一致するごく限られたゲート電極格子領域のプラズモン共振器のみしかテラヘルツ電磁波放射に寄与できず、高効率な電磁波放射を得ることが困難であった。
本発明は、上記の従来技術が抱える問題点を解決し、非放射２次元電子プラズモン波から放射電磁波への変換効率を向上させ、狭帯域でかつ高出力なテラヘルツ波を放射する電磁波放射素子を得ることを目的とする。 The present invention solves the above-mentioned problems of the prior art, improves the conversion efficiency from a non-radiating two-dimensional electron plasmon wave to a radiated electromagnetic wave, and radiates a narrow band and high output terahertz wave. The purpose is to obtain.
課題を解決するための手段は、次のとおりである。
（１）半導体ヘテロ接合構造によって形成される２次元電子層と、該２次元電子層の両辺に電気的に接続され両者の間にバイアス電位が与えられたソース及びドレインと、該２次元電子層の上方に電子供給層を介して該２次元電子層と平行にかつ格子状に配置され、直流バイアス電位が与えられたゲート電極格子とを含み、該ゲート電極格子の配位に対応して２次元電子層の電子濃度を周期的に変調させるとともに、該２次元電子層に２つのコヒーレントな光波を入力、混合してその差周波数に対応したテラヘルツ電磁波を放射出力する電磁波放射素子において、
ドレイン及びソース間の直流バイアス電位に依存するゲート電極格子下の電子濃度の平方根とゲート電極格子の幅の比が一定値となるように、各ゲート電極格子の幅を定めることを特徴とする電磁波放射素子。
（２）半導体ヘテロ接合構造によって形成される２次元電子層と、該２次元電子層の両辺に電気的に接続され両者の間にバイアス電位が与えられたソース及びドレインと、該２次元電子層の上方に電子供給層を介して該２次元電子層と平行にかつ格子状に配置され、２つの異なる直流バイアス電位が交互に与えられる２重ゲート電極格子とを含み、該２重ゲート電極格子の配位に対応して２次元電子層の電子濃度を周期的に変調させるとともに、該２次元電子層に２つのコヒーレントな光波を入力、混合してその差周波数に対応したテラヘルツ電磁波を放射出力する電磁波放射素子において、
ドレイン及びソース間の直流バイアス電位に依存する一方のゲート電極格子下の電子濃度の平方根と該一方のゲート電極格子の幅の比が一定値となるように、該少なくとも一方のゲート電極格子の幅を定めることを特徴とする電磁波放射素子。
（３）上記ゲート電極格子の厚みは、上記ゲート電極格子と２次元電子層との間隔以下に設定されていることを特徴とする（１）又は（２）に記載の電磁波放射素子。
Means for solving the problems are as follows.
(1) A two-dimensional electronic layer formed by a semiconductor heterojunction structure, a source and a drain electrically connected to both sides of the two-dimensional electronic layer and applied with a bias potential therebetween, and the two-dimensional electronic layer And a gate electrode lattice disposed in parallel with the two-dimensional electron layer via the electron supply layer and provided with a DC bias potential, and corresponding to the configuration of the gate electrode lattice. In an electromagnetic wave emitting element that periodically modulates the electron concentration of a two-dimensional electron layer, inputs and mixes two coherent light waves into the two-dimensional electron layer, and radiates and outputs a terahertz electromagnetic wave corresponding to the difference frequency,
An electromagnetic wave characterized in that a width of each gate electrode lattice is determined so that a ratio of a square root of an electron concentration under the gate electrode lattice depending on a DC bias potential between a drain and a source and a width of the gate electrode lattice becomes a constant value. Radiating element.
(2) a two-dimensional electronic layer formed by a semiconductor heterojunction structure, a source and a drain electrically connected to both sides of the two-dimensional electronic layer and applied with a bias potential therebetween, and the two-dimensional electronic layer A double gate electrode grid disposed in parallel with the two-dimensional electron layer via the electron supply layer and in a lattice shape, to which two different DC bias potentials are alternately applied. The electron concentration of the two-dimensional electron layer is periodically modulated corresponding to the coordination of the two, and two coherent light waves are input to the two-dimensional electron layer and mixed to emit terahertz electromagnetic waves corresponding to the difference frequency In an electromagnetic radiation element that
The width of the at least one gate electrode lattice so that the ratio of the square root of the electron concentration under one of the gate electrode lattices depending on the DC bias potential between the drain and the source and the width of the one gate electrode lattice becomes a constant value. An electromagnetic wave radiation element characterized by defining:
(3) The electromagnetic wave emission element according to (1) or (2), wherein the thickness of the gate electrode lattice is set to be equal to or less than a distance between the gate electrode lattice and the two-dimensional electron layer.
本発明によれば、非放射２次元電子プラズモン波から放射電磁波への変換効率が向上し、より狭帯域性でかつ高出力のテラヘルツ波を放射する電磁波放射素子を実現することができる。 ADVANTAGE OF THE INVENTION According to this invention, the conversion efficiency from a non-radiation two-dimensional electron plasmon wave to a radiation electromagnetic wave improves, and the electromagnetic wave radiation element which radiates | emits a terahertz wave with a narrow band property and high output is realizable.
以下、図面に基づき本発明を詳細に説明する。
図１は、本発明を具体化する電磁波放射素子の第一の実施例を示す構造断面図である。図中の半絶縁性バルク層を構成する基板の上に、半導体へテロ接合構造を形成する。半導体ヘテロ接合構造は、ワイドバンドギャップのバッファ層、ナローバンドギャップの真性半導体によるチヤネル層、ドナーを２次元的にドープしたワイドバンドギャップの電子供給層（キャリア供給層）から構成される。
その形成は、化合物トランジスタで量産・実用化されている分子線エピタキシー（MBE）や金属有機気相エピタキシー（MOWE）の技術によって、半絶縁性バルク層に半導体へテロ接合構造をナノメータ精度でエピタキシヤル成長させることによりなされる。
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a structural cross-sectional view showing a first embodiment of an electromagnetic wave radiation element embodying the present invention. A semiconductor heterojunction structure is formed on the substrate constituting the semi-insulating bulk layer in the drawing. The semiconductor heterojunction structure includes a wide band gap buffer layer, a narrow band gap intrinsic semiconductor channel layer, and a wide band gap electron supply layer (carrier supply layer) doped two-dimensionally with a donor.
Its formation is based on molecular beam epitaxy (MBE) and metal organic vapor phase epitaxy (MOWE), which are mass-produced and put into practical use for compound transistors, and a semiconductor heterojunction structure is epitaxially grown on a semi-insulating bulk layer with nanometer accuracy. Made by growing.
バッファ層、チャネル層、電子供給層が１組となって、チャネル層と電子供給層とのチャネル側界面に２次元的に電子が閉じ込められて２次元電子層が形成される。電子供給層の上部に更に強くｎ型にドープした半導体エピタキシヤル層をオーミック層として堆積して、チャネルの両端部分には、更に金属電極を成膜することで、金属電極とチャネル層がオーミック接続され、それぞれソース電極、ドレイン電極が形成される。一方チャネル上部の該オーミック層はリセスエッチングによって除去した後に、ゲート電極を形成する。 The buffer layer, the channel layer, and the electron supply layer form a pair, and the two-dimensional electron layer is formed by two-dimensionally confining electrons at the channel side interface between the channel layer and the electron supply layer. A semiconductor epitaxial layer that is more strongly n-doped on the electron supply layer is deposited as an ohmic layer, and a metal electrode is further formed on both ends of the channel so that the metal electrode and the channel layer are in ohmic contact. Then, a source electrode and a drain electrode are formed, respectively. On the other hand, the ohmic layer above the channel is removed by recess etching, and then a gate electrode is formed.
ゲート電極回折格子は、電子濃度の平方根とゲート電極格子の幅の比が一定となるように、すなわち、電子濃度が高いソース電極近傍のゲート間隔の寸法を大きくし、ドレイン電極近傍のゲート電極の寸法を小さくするようにフオトリソグラフィー又は電子線リソグラフィー工程及びエッチング工程により加工する。 The gate electrode diffraction grating is designed so that the ratio of the square root of the electron concentration to the width of the gate electrode grating is constant, that is, the gate spacing in the vicinity of the source electrode having a high electron concentration is increased, and the gate electrode in the vicinity of the drain electrode is increased. Processing is performed by a photolithography or electron beam lithography process and an etching process so as to reduce the size.
さらに、ゲート電極を櫛状にエッチングし、奇数番の櫛同士をチャネルの外側で接続し、偶数番の櫛同士をチヤネルの外側で接続して、入れ子型２重回折格子状の複ゲート電極格子（便宜上、ゲート格子Ａ、Ｂと称する。図１においては、それぞれＧ１、Ｇ２に対応する。）を形成する。ゲート格子ＡとＢのバイアス電位を別にすることにより、ゲート格子直下の２次元電子層の電子濃度をゲート格子の周期で変調することができる。 Further, the gate electrode is etched into a comb shape, the odd-numbered combs are connected to each other outside the channel, and the even-numbered combs are connected to each other outside the channel to form a nested double diffraction grating-shaped double gate electrode Gratings (for convenience, referred to as gate gratings A and B, respectively, corresponding to G1 and G2 in FIG. 1) are formed. By separating the bias potentials of the gate lattices A and B, the electron concentration of the two-dimensional electron layer immediately below the gate lattice can be modulated by the period of the gate lattice.
例えば、ゲート格子Ａのバイアス電位を高く、ゲート格子Ｂのバイアス電位を低く設定して、チャネル層内のゲート格子Ａの直下にテラヘルツ帯プラズモン共鳴が可能な高い電子濃度のプラズモン共振器が形成される。この場合、ゲート格子Ａに定めた、「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件によって、ゲート格子Ａの櫛に対応して形成された全てのプラズモン共振器が同一のプラズマ周波数を有することとなり、従って、該全てのプラズモン共振器が単一周波数のテラヘルツ電磁波放射に寄与することができ、その結果、狭帯域かつ高出力高効率の電磁波放射が果たせる。 For example, by setting the bias potential of the gate lattice A high and the bias potential of the gate lattice B low, a high electron concentration plasmon resonator capable of terahertz band plasmon resonance is formed immediately below the gate lattice A in the channel layer. The In this case, all the plasmon resonators formed corresponding to the combs of the gate lattice A are identical under the condition that the ratio of the square root of the electron concentration and the width of the gate electrode lattice is constant, which is determined for the gate lattice A. Therefore, all the plasmon resonators can contribute to single-frequency terahertz electromagnetic wave radiation, and as a result, narrow-band, high-power and high-efficiency electromagnetic wave radiation can be achieved.
また、ゲート格子Ｂのバイアス電位を高く、ゲート格子Ａのバイアス電位を低く設定して、チャネル層内のゲート格子Ｂの直下にテラヘルツ帯プラズモン共鳴が可能な高い電子濃度のプラズモン共振器を形成することができる。この場合、ゲート格子Ｂに定めた、「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件によって、ゲート格子Ｂの櫛に対応して形成された全てのプラズモン共振器が同一のプラズマ周波数を有することとなり、従って、該全てのプラズモン共振器が単一周波数のテラヘルツ電磁波放射に寄与することができ、その結果、狭帯域かつ高出力高効率の電磁波放射が果たせる。 Further, the bias potential of the gate lattice B is set high and the bias potential of the gate lattice A is set low to form a high electron concentration plasmon resonator capable of terahertz band plasmon resonance immediately below the gate lattice B in the channel layer. be able to. In this case, all the plasmon resonators formed corresponding to the combs of the gate lattice B are the same under the condition that the ratio of the square root of the electron concentration to the width of the gate electrode lattice is constant. Therefore, all the plasmon resonators can contribute to single-frequency terahertz electromagnetic wave radiation, and as a result, narrow-band, high-power and high-efficiency electromagnetic wave radiation can be achieved.
したがって、例えば、ゲート格子Ａのバイアス電位をゲート格子Ｂのそれに比して常に高く設定し、常に、プラズモン共振器をゲート格子Ａの直下のチャネル層内に形成する場合には、少なくともゲート格子Ａのみが、「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件を満たせばよく、ゲート格子Ｂが、「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件を満たす必要はない。例えば、ゲート格子Ａのみが「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件を満たし、ゲート格子Ｂは等間隔であってもよい。その逆もまたしかりである。要は、プラズモン共鳴に寄与する少なくとも１組のゲート格子が「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件を満たせばよいのである。 Therefore, for example, when the bias potential of the gate grating A is always set higher than that of the gate grating B and the plasmon resonator is always formed in the channel layer immediately below the gate grating A, at least the gate grating A However, it is only necessary to satisfy the condition that “the ratio of the square root of the electron concentration to the width of the gate electrode lattice is constant”, and the gate lattice B satisfies the condition of “the ratio of the square root of the electron concentration to the width of the gate electrode lattice is constant”. There is no need to satisfy. For example, only the gate lattice A may satisfy the condition that “the ratio of the square root of the electron concentration to the width of the gate electrode lattice is constant”, and the gate lattice B may be equally spaced. The reverse is also true. In short, it is sufficient that at least one set of gate lattices that contribute to plasmon resonance satisfy the condition that the ratio of the square root of the electron concentration to the width of the gate electrode lattice is constant.
２重回折格子ゲートは、モリブデン等の導電率の低い準金属材料で形成するのがよい。２重回折格子ゲートのプラズマ周波数を２次元電子層のそれに接近できるからであり、これにより、テラヘルツ電磁波放射効率の増大が可能となる。また、ゲート電極の厚みはできる限り薄く（ゲート電極と２次元電子層との間隔以下に）形成することが放射率の向上には重要である。 The double diffraction grating gate is preferably formed of a quasi-metallic material having low conductivity such as molybdenum. This is because the plasma frequency of the double diffraction grating gate can be approximated to that of the two-dimensional electron layer, thereby increasing the terahertz electromagnetic wave radiation efficiency. In addition, it is important for improving the emissivity to form the gate electrode as thin as possible (less than the distance between the gate electrode and the two-dimensional electron layer).
２重回折格子型ゲート電極を、例えば、半導体ヘテロ接合構造内に該２次元電子層の上部に積層してなる第２の２次元電子層をエッチング加工することによって形成すれば、電極の厚みは極限的に薄くでき、かつ、電極の導電率も２次元電子層のそれと同程度に低減できるので、２重回折格子型ゲートのプラズマ周波数を２次元電子層のプラズマ周波数に接近でき、放射効率の向上が果たせる。更には、該第２の２次元電子層の導電率がゲートバイアス電位によって制御できることから、２重回折格子型ゲートのプラズマ周波数を可変制御することも可能である。従って、放射したい電磁波周波数に応じて放射効率をより向上させることが可能である。 If the double diffraction grating gate electrode is formed by etching a second two-dimensional electron layer formed by laminating the two-dimensional electron layer in the semiconductor heterojunction structure, for example, the thickness of the electrode Can be made extremely thin, and the electrical conductivity of the electrode can be reduced to the same level as that of the two-dimensional electron layer, so that the plasma frequency of the double grating gate can be close to the plasma frequency of the two-dimensional electron layer, and radiation Efficiency can be improved. Furthermore, since the conductivity of the second two-dimensional electron layer can be controlled by the gate bias potential, the plasma frequency of the double diffraction grating gate can be variably controlled. Therefore, it is possible to further improve the radiation efficiency according to the electromagnetic wave frequency to be radiated.
以上が、本発明の代表的な実施例であるが、さらに放射効率を向上するために、例えば、以下のように、素子の縦方向に共振器構造を形成することができる。すなわち、上記のようにして、素子本体が作成された後に、半絶縁性バルク層を裏面から選択的にエッチングもしくは研磨し、低誘電材料のクラッド材を充填する。このクラッド材は、半絶縁性バルク層の周囲を被覆するように、図１に図示した左右両側だけでなく、図１中の手前側と奥側も被覆する。このように、半絶縁性バルク層の側面をそれよりも誘電率の低いクラッド層で覆うと、縦型共振器内への電磁波の閉じ込めが強まり、放射損を低減でき、より変換効率の向上が図れる。 The above is a typical embodiment of the present invention. In order to further improve the radiation efficiency, for example, a resonator structure can be formed in the longitudinal direction of the element as follows. That is, after the element body is formed as described above, the semi-insulating bulk layer is selectively etched or polished from the back surface and filled with a low dielectric material clad material. This clad material covers not only the left and right sides shown in FIG. 1 but also the front side and the back side in FIG. 1 so as to cover the periphery of the semi-insulating bulk layer. In this way, when the side surface of the semi-insulating bulk layer is covered with a cladding layer having a lower dielectric constant, the confinement of electromagnetic waves in the vertical resonator becomes stronger, radiation loss can be reduced, and conversion efficiency can be further improved. I can plan.
最後の工程として、半絶縁性バルク層の下面に、ITO（酸化インジウム・スズ）などの可視から近赤外光に対しては透明で金属並みの導電率を有し、テラヘルツ電磁波には反射特性を示す透明金属を成膜する。これによって、光波入力は透過し、テラヘルツ電磁波にはミラーとして機能する透明金属ミラーを形成できる。 As the final step, the bottom surface of the semi-insulating bulk layer is transparent to visible to near infrared light such as ITO (indium tin oxide) and has a conductivity similar to that of metal. A transparent metal showing is formed. As a result, a transparent metal mirror that transmits light wave input and functions as a mirror can be formed for terahertz electromagnetic waves.
次にゲート回折格子を１組しか有しない構造においても、該ゲート格子が「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件を満たす場合には、従来の等間隔格子の場合に比して、第一の実施例と同様の効果が得られる。
図２は、ゲート回折格子を１組しか有しない本発明の第二の実施例を示す模式図である。
図２から分かるように、第二の実施例の構造断面図は図１と基本的に同じで、違いはゲート格子が１組しかないことのみである。
Next, even in a structure having only one set of gate diffraction gratings, when the gate grating satisfies the condition that the ratio of the square root of the electron concentration and the width of the gate electrode grating is constant, As compared with the above, the same effect as the first embodiment can be obtained.
FIG. 2 is a schematic diagram showing a second embodiment of the present invention having only one set of gate diffraction gratings.
As can be seen from FIG. 2, the structural sectional view of the second embodiment is basically the same as FIG. 1, except that there is only one set of gate grids.
この場合、該チヤネル層とその上部の該電子供給層の厚みや不純物濃度分布さらにはゲート金属種を適切に設計選択して、ゲートバイアスが０Ｖのときに、チャネル層の２次元電子濃度がプラズモン共振器が動作する電子濃度と大きく異なる濃度に予め設計しておくことになる。そして、ゲート格子にバイアスを適当に印加し、ゲート格子直下の電子濃度を変調することによって、ゲート格子直下のチャネル層にプラズモン共振器が形成される。ゲート格子の寸法を「電子濃度の平方根とゲート電極格子の幅の比が一定」の条件を満たすように設定することによって、全てのプラズモン共振器が同一のプラズマ周波数を有することとなり、従って、該全てのプラズモン共振器が単一周波数のテラヘルツ電磁波放射に寄与することができ、その結果、狭帯域かつ高出力高効率の電磁波放射が果たせる。 In this case, when the thickness and impurity concentration distribution of the channel layer and the electron supply layer on the channel layer and the gate metal species are appropriately designed and selected, the two-dimensional electron concentration of the channel layer becomes plasmon when the gate bias is 0V. The concentration is designed in advance so as to be significantly different from the electron concentration at which the resonator operates. A plasmon resonator is formed in the channel layer immediately below the gate lattice by appropriately applying a bias to the gate lattice and modulating the electron concentration directly below the gate lattice. By setting the dimensions of the gate grating to satisfy the condition that the ratio of the square root of the electron concentration to the width of the gate electrode grating is constant, all the plasmon resonators have the same plasma frequency. All plasmon resonators can contribute to single-frequency terahertz electromagnetic radiation, and as a result, narrow-band, high-power, high-efficiency electromagnetic radiation can be achieved.
図３は、従来技術と本発明の比較説明図である。図３の上図は、ゲート電極格子の幅が等しい従来構造の電磁波放射素子を示し、図３の下図は、上述した本発明の原理である、プラズマ共鳴周波数のスペクトルの幅が狭まると同時に強度が増大していることを説明するものである。 FIG. 3 is a comparative illustration of the prior art and the present invention. The upper diagram of FIG. 3 shows a conventional electromagnetic wave emitting element having the same gate electrode grid width, and the lower diagram of FIG. 3 shows the principle of the present invention described above, and the intensity of the spectrum of the plasma resonance frequency is reduced at the same time. This is an explanation of the increase.
また図４は、従来の電磁波放射素子と本発明の電磁波放射素子との数値解析結果を示す図である。横軸は周波数（ＴＨｚ）、縦軸は電界強度である。そして従来の電磁波放射素子の結果を縦軸の右スケールで、また本発明の電磁波放射素子の結果を左スケールでそれぞれ示す。縦軸の右スケールは表示の便宜上、左スケールの１０倍に拡大して表示されている。
図４から分かるように、従来の電磁波放射素子では周波数の幅が広く電界強度も小さいのに対し、本発明の電磁波放射素子では周波数の幅が狭くかつ強度が大きくなっている。
FIG. 4 is a diagram showing the numerical analysis results of the conventional electromagnetic radiation element and the electromagnetic radiation element of the present invention. The horizontal axis represents frequency (THz) and the vertical axis represents electric field strength. The result of the conventional electromagnetic wave emission element is shown on the right scale of the vertical axis, and the result of the electromagnetic wave emission element of the present invention is shown on the left scale. The right scale of the vertical axis is displayed in an enlarged manner 10 times the left scale for convenience of display.
As can be seen from FIG. 4, the conventional electromagnetic wave radiation element has a wide frequency width and a small electric field strength, whereas the electromagnetic wave radiation element of the present invention has a narrow frequency width and a high strength.
図５は、従来の電磁波放射素子と本発明の電磁波放射素子の性能比較表である。非特許文献１、３〜６及び特許文献１に開示の素子と本発明の電磁波放射素子との性能を比較したものである。図中、◎〇△×はそれぞれ特性の評価に関し、優、良、可、不可を示す。
さらに特許文献１の電磁波放射素子との比較では詳細は次のようになる。
FIG. 5 is a performance comparison table between the conventional electromagnetic radiation element and the electromagnetic radiation element of the present invention. The performance of the element disclosed in
Further, details of the comparison with the electromagnetic wave radiation element of Patent Document 1 are as follows.
（１） 放射電界強度について
放射電界強度は、出力パワーであり、図３ならびに図４から分かるように、特許文献１の電磁波放射素子では、回折格子のアンテナ効果はあるものの、電子濃度の分布広がりによりスペクトルはブロードになり、所望の周波数に放射エネルギーを集中させることができない。従って△とした。一方、本発明の電磁波放射素子では所望の単一周波数に放射電力が集中できるため、◎印となる。
(1) Radiation electric field strength Radiation electric field strength is output power. As can be seen from FIGS. 3 and 4, the electromagnetic wave radiation element of Patent Document 1 has an antenna effect of a diffraction grating, but spreads the distribution of electron concentration. This broadens the spectrum and cannot concentrate the radiant energy at the desired frequency. Therefore, it was set as △. On the other hand, in the electromagnetic wave radiating element of the present invention, the radiated power can be concentrated on a desired single frequency, so that it is marked with ◎.
（２） 非放射−放射モード変換効率について
非放射−放射モード変換効率は、単位出力を得るのにどれだけ少ないエネルギーで済むか、という効率であるが、特許文献１の電磁波放射素子では、単一素子内部に、プラズモン共振器を回折格子の本数分だけ複数存在するために入射レーザー光を大面積で効率よく吸収できること、さらに、回折格子のアンテナ効果によって非放射プラズモン分極波を放射モード電磁波に効率よく変換できることから○印となる。一方、本発明の電磁波放射素子では放射電力を所望の周波数に集中させることができることから、◎印となる。
(2) Non-radiation-radiation mode conversion efficiency The non-radiation-radiation mode conversion efficiency is the efficiency of how much energy is required to obtain a unit output. Since there are multiple plasmon resonators for the number of diffraction gratings in one element, incident laser light can be efficiently absorbed in a large area, and non-radiative plasmon polarization waves can be converted into radiation mode electromagnetic waves by the antenna effect of the diffraction grating. The circle is marked because it can be converted efficiently. On the other hand, in the electromagnetic wave radiation element of the present invention, the radiated power can be concentrated at a desired frequency, so that it is marked with ◎.
（３） 周波数可変性について
周波数可変性は、基本的に電界効果型トランジスタ（HEMT）構造が基礎となる場合には、ゲートバイアス制御により電子濃度変調が果たせるため、プラズマ共鳴周波数を可変制御できる。特許文献１の電磁波放射素子では、単純なHEMT構造ではなく、縦型共振器と２重回折格子ゲートの相乗効果によって可動周波数帯域の拡大が図れることから◎印となる。本発明もその点に変わりはなく、特許文献１の電磁波放射素子と同じで◎印となる。
以上のとおり、本発明の電磁波放射素子は、放射電界強度、非放射−放射モード変換効率及び周波数可変性ともに、従来の電磁波放射素子よりも優れていることが分かる。
(3) Frequency variability When the frequency variability is basically based on a field effect transistor (HEMT) structure, electron density modulation can be performed by gate bias control, so that the plasma resonance frequency can be variably controlled. In the electromagnetic wave radiation element of Patent Document 1, the movable frequency band can be expanded by the synergistic effect of the vertical resonator and the double diffraction grating gate, not the simple HEMT structure, so that the mark is marked. In the present invention, there is no change in that point, and it is the same as the electromagnetic wave radiation element of Patent Document 1 and marked with ◎.
As described above, it can be seen that the electromagnetic wave radiation element of the present invention is superior to the conventional electromagnetic wave radiation element in terms of radiation field strength, non-radiation-radiation mode conversion efficiency, and frequency variability.
本発明によれば、ドレイン・ソース間直流バイアス電位に依存する各格子下の電子濃度に応じて、電子濃度の平方根とゲート電極格子の幅の比が一定値となるように、ゲート電極回折格子の幅を定めることにより、高い利得と極めて狭帯域なスペクトルを持つテラヘルツの電磁波放射素子を実現できる為、従来よりも大容量で高速な通信システムへの適用が期待される。 According to the present invention, the gate electrode diffraction grating has a constant ratio of the square root of the electron concentration and the width of the gate electrode grating according to the electron concentration under each grating depending on the drain-source DC bias potential. The terahertz electromagnetic wave radiation element having a high gain and a very narrow band spectrum can be realized by determining the width of the antenna, and therefore, it is expected to be applied to a communication system with a larger capacity and higher speed than before.
Claims (3)
ドレイン及びソース間の直流バイアス電位に依存するゲート電極格子下の電子濃度の平方根とゲート電極格子の幅の比が一定値となるように、各ゲート電極格子の幅を定めることを特徴とする電磁波放射素子。 A two-dimensional electronic layer formed by a semiconductor heterojunction structure; a source and a drain electrically connected to both sides of the two-dimensional electronic layer to which a bias potential is applied; and above the two-dimensional electronic layer A two-dimensional electron layer corresponding to the configuration of the gate electrode lattice, including a gate electrode lattice arranged in parallel with the two-dimensional electron layer via the electron supply layer and in a lattice shape and provided with a DC bias potential In the electromagnetic wave emitting element that periodically modulates the electron concentration of the two, and inputs and mixes two coherent light waves into the two-dimensional electron layer to emit and output a terahertz electromagnetic wave corresponding to the difference frequency,
An electromagnetic wave characterized in that a width of each gate electrode lattice is determined so that a ratio of a square root of an electron concentration under the gate electrode lattice depending on a DC bias potential between a drain and a source and a width of the gate electrode lattice becomes a constant value. Radiating element.
ドレイン及びソース間の直流バイアス電位に依存する一方のゲート電極格子下の電子濃度の平方根と該一方のゲート電極格子の幅の比が一定値となるように、該少なくとも一方のゲート電極格子の幅を定めることを特徴とする電磁波放射素子。 A two-dimensional electronic layer formed by a semiconductor heterojunction structure; a source and a drain electrically connected to both sides of the two-dimensional electronic layer to which a bias potential is applied; and above the two-dimensional electronic layer A double gate electrode grid arranged parallel to the two-dimensional electron layer via the electron supply layer and in a lattice shape, to which two different DC bias potentials are alternately applied, and the configuration of the double gate electrode grid Electromagnetic wave radiation that periodically modulates the electron concentration of the two-dimensional electron layer in response to the two, and inputs and mixes two coherent light waves into the two-dimensional electron layer to radiate and output a terahertz electromagnetic wave corresponding to the difference frequency In the element
The width of the at least one gate electrode lattice so that the ratio of the square root of the electron concentration under one gate electrode lattice depending on the DC bias potential between the drain and the source and the width of the one gate electrode lattice becomes a constant value. An electromagnetic wave radiation element characterized by defining:
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| WO2012073298A1 (en) | 2010-12-03 | 2012-06-07 | 国立大学法人東北大学 | Terahertz electromagnetic wave conversion device |
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