JP5648915B2 - Resonant tunnel diode and terahertz oscillator - Google Patents

Description

  The present invention relates to a layer structure of a resonant tunnel diode that constitutes an oscillation element that serves as a light source in a terahertz frequency band, and a terahertz oscillator using the resonant tunnel diode.

  The terahertz frequency band from 100 GHz to 10 THz is close to the upper limit of the operating frequency of electronic devices, and there is no small light source that can be used easily. So far, it has been limited to special measurement / analysis and radio astronomy. It was. A small terahertz frequency band light source that operates at room temperature is expected to be applied to a wide range of fields such as security technology by imaging and short-distance and large-capacity wireless communication technology.

  A resonant tunneling diode (RTD) having a negative differential resistance has a short tunnel time when electrons travel, a short depletion layer (electron travel layer) travel time, a high current density, and a small parasitic capacitance. Due to the short charging time provided, it is possible to oscillate in the terahertz frequency band, and it is expected as a compact terahertz light source operating at room temperature. Among them, RTDs composed of InGaAs layers and AlAs layers stacked on InP substrates can obtain a relatively large negative differential resistance at room temperature due to the large discontinuity of the conduction band between InGaAs and AlAs, resulting in excellent oscillation. Bring properties.

The RTD oscillates in the negative differential resistance region in the current-voltage characteristic. Parameters that characterize the RTD current-voltage characteristics include a peak current density J _P and a peak voltage V _P.
The inventors of the present invention used an oscillator using an RTD composed of an InGaAs layer and an AlAs layer stacked on an InP substrate, particularly an RTD having a high peak current density J _P exceeding 1 × 10 ⁶ A / cm ² , 831 GHz. Room temperature fundamental wave oscillation was realized (see Non-Patent Document 1).

  The inventors have found in Non-Patent Document 1 that the oscillation frequency obtained experimentally is lower than the theoretically expected oscillation frequency. And it was considered that the reason for limiting the increase in the oscillation frequency in the experiment was a decrease in the traveling speed of electrons due to scattering between Γ-L valleys when traveling in the electron traveling layer.

Recently, in an oscillator using an RTD composed of an InGaAs layer and an AlAs layer that are also stacked on an InP substrate, in order to suppress a decrease in electron velocity due to the Γ-L valley scattering, a step-like consisting emitter and the spacer has a potential shape, by applying a graded emitter structure, low V _P of, i.e. to achieve low voltage operation of the oscillator, by shortening the electron transit time associated with the low voltage operation, at room temperature The fundamental wave oscillation was successfully improved to 1.04 THz (see Non-Patent Document 2).
As described above, an oscillation frequency exceeding 1 THz is realized by a conventional RTD. However, for use as a light source in a terahertz frequency band, further increase in the oscillation frequency is desired.

Safumi Suzuki, Atsushi Teranishi, Kensuke Hinata, Masahiro Asada, Hiroki Sugiyama, and Haruki Yokoyama, “Fundamental Oscillation of up to 831 GHz in GaInAs / AlAs Resonant Tunneling Diode”, Applied Physics Express 2, Japan Society of Applied Physics, 054501, 2009 April 17, Safumi Suzuki, Atsushi Teranishi, Masahiro Asada, Hiroki Sugiyama, and Haruki Yokoyama, “Increase of Fundamental Oscillation Frequency in Resonant Tunneling Diode with Thin Barrier and Graded Emitter Structures”, 2010 35th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz 2010), IEEE, Tu-C1.2, Rome, September 5, 2010

  As described above, in order to improve the oscillation frequency of the oscillator using the RTD, it is necessary to suppress scattering between Γ-L valleys when electrons travel through the electron travel layer by lowering the operating voltage. However, lowering the operating voltage means that the difference between the potential of the collector layer and the potential of the double barrier layer during device operation is reduced.

  In RTD, electrons that have passed through the double barrier layer travel from the high potential double barrier layer toward the low potential collector layer. There, the double barrier layer acts as an electron launcher, and the larger the potential difference between the double barrier layer and the collector layer, the easier the electrons travel ballistically.

  In the RTD operating at a low voltage, the effect of the double barrier layer as a launcher is reduced. For this reason, the number of electrons traveling ballistically at high speed after passing through the double barrier layer is reduced, and the traveling time of the electrons in the electron traveling layer is increased. This decrease in the electronic traveling speed is considered to limit the increase in the oscillation frequency. Therefore, in order to further increase the operating frequency of the low operating voltage RTD oscillator as described in Non-Patent Document 2, it is necessary to promote the launcher effect of the double barrier layer and suppress the decrease in the electron velocity.

  The present invention has been made in order to solve the above-described problems. In an RTD with a low operating voltage, the speed of electrons passing through the double barrier layer is suppressed from decreasing when the electron travels through the electron transit layer. The purpose is to improve the frequency.

The resonant tunnel diode of the present invention serves as a barrier against electrons in the emitter layer made of an impurity-doped semiconductor, a spacer layer made of an electrically neutral semiconductor, and electrons in each of the emitter layer and the spacer layer. A first barrier layer, a well layer made of an electrically neutral semiconductor, a second barrier layer serving as a barrier against electrons in each of the emitter layer and the spacer layer, and an electrically neutral layer An electron transit layer made of a semiconductor, through which electrons flow from the emitter layer through the spacer layer, the first barrier layer, the well layer, and the second barrier layer, and a collector layer made of a semiconductor doped with impurities bets are sequentially stacked, the electron transit layer, the second conduction band energy at the bonding surface between the barrier layer is rather higher than the conduction band energy of the collector layer, the near distance between the collector layer Conduction band energy approaches the conduction band energy of the collector layer according to Ku, wherein Ri is the conduction band energy at the bonding surface between the collector layer same as name and conduction band energy of said collector layer, said emitter layer and said spacer layer by varying the composition of the emitter layer in the layer, said first conduction band energy as the distance approaches the barrier layer is characterized in Rukoto a low.
The resonant tunnel diode of the present invention includes an emitter layer made of a semiconductor doped with impurities, a spacer layer made of an electrically neutral semiconductor, and a barrier against electrons in each layer of the emitter layer and the spacer layer. A first barrier layer, a well layer made of an electrically neutral semiconductor, a second barrier layer serving as a barrier against electrons in each of the emitter layer and the spacer layer, and an electrically neutral layer An electron transit layer through which electrons flow from the emitter layer through the spacer layer, the first barrier layer, the well layer, and the second barrier layer, and a semiconductor doped with impurities. A collector layer is sequentially stacked, and the electron transit layer has a conduction band energy at a junction surface with the second barrier layer higher than a conduction band energy of the collector layer, and is separated from the collector layer. As the conduction band energy approaches the conduction band energy of the collector layer, the conduction band energy at the interface with the collector layer becomes the same as the conduction band energy of the collector layer, the semiconductor is InGaAs, The InGaAs constituting the electron transit layer has an In composition on the second barrier layer side higher than the In composition of InGaAs constituting the collector layer, and the In composition increases as the distance from the collector layer decreases. And the In composition of the InGaAs that constitutes the collector layer is the same as the In composition of the InGaAs that constitutes the collector layer.

Further , in one configuration example of the resonant tunneling diode of the present invention, the semiconductor is InGaAs, and the InGaAs constituting the emitter layer and the spacer layer has an In composition as the distance from the first barrier layer decreases. It is characterized by being lowered.
In one configuration example of the resonant tunneling diode of the present invention, the electron transit layer, the emitter layer, and the spacer layer are characterized in that conduction band energy changes stepwise.
In one configuration example of the resonant tunneling diode of the present invention, each of the electron transit layer and the emitter layer includes a plurality of layers.

Further, in one configuration example of the resonant tunneling diode of the present invention, when a negative voltage is applied to the emitter layer and a positive voltage is applied to the collector layer, the emitter layer, the spacer layer, The first barrier layer, the well layer, the second barrier layer, the electron transit layer, and the collector layer are stacked in this order.
Also, in one configuration example of the resonant tunneling diode of the present invention, when a positive voltage is applied to the emitter layer and a negative voltage is applied to the collector layer, the collector layer and the electron transit layer are formed on a substrate. The second barrier layer, the well layer, the first barrier layer, the spacer layer, and the emitter layer are stacked in this order.
Further, one configuration example of the resonant tunneling diode of the present invention is further laminated so as to be in contact with the emitter layer outside the emitter layer, and is an impurity having the same conductivity type as the emitter layer and the collector layer, and A sub-emitter layer made of a semiconductor doped with an impurity having a higher concentration than the emitter layer, and an impurity having the same conductivity type as that of the emitter layer and the collector layer, stacked outside the collector layer so as to be in contact with the collector layer And a sub-collector layer made of a semiconductor doped with an impurity having a higher concentration than that of the collector layer.

  The terahertz oscillator according to the present invention includes a resonant tunnel diode, a slot antenna that is a resonator connected to the resonant tunnel diode, and a power source that applies a bias voltage between an emitter layer and a collector layer of the resonant tunnel diode. It is characterized by the following.

  According to the present invention, the potential of the electron transit layer at the junction surface with the second barrier layer is lower than the potential of the collector layer, and the potential approaches the potential of the collector layer as the distance from the collector layer decreases. By adopting a structure in which the potential at the junction surface with the layer is the same as the potential of the collector layer, a double barrier layer (first barrier layer, well layer, second barrier layer), an electron transit layer, And the electron launcher effect at the interface between the double barrier layer and the electron transit layer can be promoted, so that the speed of electrons in the electron transit layer can be increased. As a result, in the present invention, even when the bias voltage is lowered, the traveling speed of electrons from the double barrier layer to the collector layer is not lowered, so that the operating speed of the resonant tunneling diode can be improved. Therefore, if the resonant tunnel diode of the present invention is used for an oscillator, the oscillation frequency of the oscillator can be increased.

  In the present invention, the bias voltage can be easily lowered by making the emitter layer and the spacer layer have a structure in which the potential increases as the distance from the first barrier layer decreases. As a result, in the present invention, the power consumption of the resonant tunneling diode and the oscillator can be reduced by lowering the bias voltage.

  Further, in the present invention, the InGaAs constituting the electron transit layer has a higher In composition on the second barrier layer side than the In composition of InGaAs constituting the collector layer, and the In composition becomes smaller as the distance from the collector layer becomes closer. By approaching the In composition of the InGaAs constituting the collector layer and the In composition at the junction surface with the collector layer being the same as the In composition of the InGaAs constituting the collector layer, The effective mass of electrons can be reduced, the speed of electrons can be further increased, and the operating speed of the resonant tunneling diode can be further improved. As a result, in the present invention, the oscillation frequency of the oscillator can be further increased.

It is sectional drawing which shows the structure of the resonant tunnel diode which concerns on the reference example of this invention. It is a figure which shows the result of having calculated the conduction band profile in the oscillator operating point bias voltage of the resonant tunnel diode which concerns on the reference example of this invention. It is a figure which shows the result of having calculated the conduction band profile in the oscillator operating point bias voltage of the resonant tunnel diode which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the resonant tunnel diode which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the structure of the terahertz oscillator based on the 2nd Embodiment of this invention. It is a disassembled perspective view of the terahertz oscillator which concerns on the 2nd Embodiment of this invention. It is an equivalent circuit diagram of the terahertz oscillator according to the second embodiment of the present invention. It is a figure which shows the result of having calculated the conduction band profile in the oscillator operating point bias voltage of the resonant tunnel diode which concerns on the 2nd Embodiment of this invention.

[ Reference example ]
Hereinafter, reference examples of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the structure of an RTD according to a reference example of the present invention. The RTD 20 of this reference example includes a buffer layer 22 made of an electrically neutral semiconductor, a sub-emitter layer 23 made of an impurity-doped semiconductor, an emitter layer 24 made of an impurity-doped semiconductor, A spacer layer 25 made of a neutral semiconductor, a first barrier layer 26 serving as a barrier against electrons in each of the sub-emitter layer 23, the emitter layer 24 and the spacer layer 25, and an electrically neutral semiconductor. A well layer 27, a second barrier layer 28 that serves as a barrier against electrons in each of the sub-emitter layer 23, the emitter layer 24, and the spacer layer 25, and an electrically neutral semiconductor. From the emitter layer 24, the spacer layer 25, the first barrier layer 26, the well layer 27, and the second barrier layer 28, and an impurity-doped half layer. A collector layer 30 made of the body is made of a sequentially laminated structure on the substrate 21.

  The RTD 20 has a structure in which the RTD 20 is ohmically connected to the lower right electrode 31 and the upper left electrode 32. The sub-emitter layer 23 and the collector layer 30 reduce the ohmic contact resistance between the right electrode 31 and the left electrode 32, and the parasitic resistance component from the right electrode 31 to the emitter layer 24 and the parasitic resistance from the left electrode 32 to the collector layer 30, respectively. By reducing the resistance component, the parasitic resistance component of the entire element is reduced.

  FIG. 2 is a diagram showing a calculation result of a conduction band profile in the vicinity of an operating voltage as the oscillator of the RTD 20 shown in FIG. The horizontal axis represents the thickness of the layer structure with the substrate surface as the origin, and the vertical axis represents energy. Here, a state in which a negative voltage is applied to the sub-emitter layer 23 on the substrate side and a positive voltage is applied to the collector layer 30 is shown. The energy difference between the flat region on the emitter layer 24 side and the flat region on the collector layer 30 side corresponds to the applied bias voltage.

In this reference example , as shown in FIG. 2, in the electron transit layer 29 of the RTD 20, the potential seen from the electrons in the conduction band of the electron transit layer 29 heterojunction with the second barrier layer 28 is changed, and the second The potential of the electron transit layer 29 at the junction surface with the barrier layer 28 is lower than the potential of the collector layer 30, and the potential of the electron transit layer 29 approaches the potential of the collector layer 30 as the distance from the collector layer 30 decreases. The potential of the electron transit layer 29 at the junction surface with the collector layer 30 is the same as the potential of the collector layer 30.

With this structure, in this reference example , the potential difference between the double barrier layer (the first barrier layer 26, the well layer 27, the second barrier layer 28) and the electron transit layer 29 can be increased. Since the electron launcher effect at the interface between the double barrier layer and the electron transit layer 29 can be promoted, the speed of electrons in the electron transit layer 29 can be increased. As a result, in this reference example , the traveling speed of electrons from the double barrier layer to the collector layer 30 does not decrease even when the bias voltage is decreased, so that the operating speed of the RTD can be improved. Therefore, if the RTD of this reference example is used for an oscillator, the oscillation frequency of the oscillator can be increased.

[ First Embodiment ]
Next, a first embodiment of the present invention will be described. Also in the present embodiment, the structure of the RTD is the same as that of the reference example , so that description will be made using the RTD code shown in FIG. FIG. 3 is a diagram showing a result of calculating a conduction band profile in the vicinity of the operating voltage as the RTD oscillator according to the present embodiment. As in the case of FIG. 2, FIG. 3 shows a state in which a negative voltage is applied to the sub-emitter layer 23 on the substrate side and a positive voltage is applied to the collector layer 30.

  In the present embodiment, by changing the composition of the emitter layer 24 in the layer, the potential seen from the electrons in the conduction band of the emitter layer 24 is changed, and as the distance from the first barrier layer 26 becomes closer, the emitter layer 24 and the spacer layer 25 have a high potential. With this structure, the bias voltage can be easily reduced in this embodiment. As a result, in this embodiment, the power consumption of the RTD can be reduced by lowering the bias voltage.

[ Second Embodiment ]
Next, a second embodiment of the present invention will be described. The present embodiment shows a specific example of the RTD described in the reference example and the first embodiment . FIG. 4 is a cross-sectional view showing the structure of the RTD according to the present embodiment. The RTD 9 of the present embodiment includes a buffer layer 90 made of undoped indium gallium arsenide (un-In _0.53 Ga _0.47 As), a sub-emitter layer 91 made of n-type indium gallium arsenide (n-In _0.53 Ga _0.47 As), An emitter layer 92 made of n-type indium gallium arsenide (n-In _0.53 Ga _0.47 As) and a graded emitter layer 93 made of n-type indium gallium arsenide (n-In _0.51 Ga _0.49 As and n-In _0.49 Ga _0.51 As) A spacer layer 94 made of undoped indium gallium arsenide (un-In _0.47 Ga _0.53 As), a first barrier layer 95 made of aluminum arsenic (AlAs), and undoped indium gallium arsenide (un-In _0.8 Ga _0.2 As). A well layer 96 made of aluminum, and a second layer made of aluminum arsenic (AlAs). Barrier layer 97, a first electron transit layer 98 made of undoped indium gallium arsenide (un-In _0.7 Ga _0.3 As), and a second electron transit made of undoped indium gallium arsenide (un-In _0.6 Ga _0.4 As). A layer 99, a third electron transit layer 100 made of undoped indium gallium arsenide (un-In _0.53 Ga _0.47 As), and n-type indium gallium arsenide (n-In _0.7 Ga _0.3 As and n-In _0.53 Ga _0.47 As). The collector layer 101 is made of a structure in which the collector layer 101 is sequentially laminated on the substrate 1.

  The RTD 9 has a structure in which the RTD 9 is ohmically connected to the lower right electrode 2 and the upper left electrode 4. The sub-emitter layer 91 and the collector layer 101 reduce the ohmic contact resistance between the right electrode 2 and the left electrode 4, the parasitic resistance component from the right electrode 2 to the emitter layer 92, and the parasitic resistance from the left electrode 4 to the collector layer 101, respectively. By reducing the resistance component, the parasitic resistance component of the entire element is reduced.

Buffer layer 90, sub-emitter layer 91, emitter layer 92, graded emitter layer 93, spacer layer 94, first barrier layer 95, well layer 96, second barrier layer 97, first electron transit layer 98, first The thicknesses of the second electron transit layer 99, the third electron transit layer 100, and the collector layer 101 are 200 nm, 400 nm, 20 nm, 5 nm, 2 nm, 1.2 nm, 4.5 nm, 1.2 nm, 10 nm, 10 nm, respectively. 5 nm and 23 nm. The graded emitter layer 93 is composed of two layers of n-In _0.51 Ga _0.49 As with a thickness of 2.5 nm and n-In _0.49 Ga _0.51 As with a thickness of 2.5 nm in order from the side closer to the substrate 1. The collector layer 101 is composed of two layers of n-In _0.53 Ga _0.47 As having a thickness of 15 nm and n-In _0.7 Ga _0.3 As having a thickness of 8 nm in order from the side closer to the substrate 1.

The dopant of the sub-emitter layer 91 is Si, the doping concentration is 2 × 10 ¹⁹ cm ⁻³ , the dopant of the emitter layer 92 and the graded emitter layer 93 is Si, the doping concentration is 3 × 10 ¹⁸ cm ⁻³ , and the collector layer 101. The dopant is Si, and the doping concentration is 2 × 10 ¹⁹ cm ⁻³ .

  Next, a terahertz oscillator using the RTD 9 of this embodiment will be described. FIG. 5 is a perspective view showing the structure of the terahertz oscillator according to the present embodiment. In the terahertz oscillator shown in FIG. 5, a right electrode 2 made of gold (Au), palladium (Pd), titanium (Ti) or the like is laminated on a substrate 1 made of indium phosphide (InP). Similarly, the left electrode 4 made of gold, palladium or titanium is laminated so as to face the right electrode 2 with an insulator 3 made of silicon oxide interposed therebetween.

  The left electrode 4 has two concave portions 5 and 6 formed in the central portion of the portion overlapping the right electrode 2 and the insulator 3, and the portion sandwiched between the two concave portions 5 and 6 is formed. A convex portion 7 is formed. Further, a projection 8 is formed at the tip of the projection 7, and the RTD 9 shown in FIG. 4 is arranged so as to be sandwiched between the right electrode 2 below the projection 8. A DC power supply 11 is connected to the right electrode 2 and the left electrode 4, and a resistor 10 for preventing parasitic oscillation is connected.

  A slot antenna is formed from the right electrode 2 and the left electrode 4. The right electrode 2 and the left electrode 4 are formed so as to be short-circuited in a high frequency by the insulator 3 and to be cut off in a direct current manner. The depth of the concave portions 5 and 6 (D in FIG. 5) is preferably about 4 μm, and the width of the convex portion 7 (W in FIG. 5) is preferably about 6 μm, but this size is not limited to this, and the high frequency that oscillates It is set as appropriate according to the design according to the frequency.

FIG. 6 is an exploded perspective view of the terahertz oscillator of this embodiment. As shown in FIG. 6, the right electrode 2, the insulator 3, the left electrode 4, and the RTD 9 are stacked on the substrate 1 to constitute a terahertz oscillator.
FIG. 7 is an equivalent circuit diagram of the terahertz oscillator according to the present embodiment. In FIG. 7, G _RTD is the resistance component of _RTD 9, G _ANT is the resistance component of the slot antenna, C _RTD is the capacitance component of _RTD 9, C _ANT is the capacitance component of the slot antenna, and L is the inductance component of the slot antenna.

The slot antenna composed of the right electrode 2 and the left electrode 4 serves as both a resonator and an electromagnetic wave radiation antenna. As shown in FIGS. 5 and 7, when a bias voltage is supplied from the DC power supply 11 to the terahertz oscillator, electromagnetic waves are radiated in two directions, upward and downward, with respect to the substrate 1. At this time, the oscillation frequency f of the terahertz oscillator is 1 / [2π {L (C _RTD + C _ANT )} ^1/2 ].

  Next, the characteristics of the RTD 9 and the terahertz oscillator of this embodiment will be described. Table 1 shows the parameter values of the RTD 9 sample A having the structure shown in FIG. In addition, as a sample for comparison, the parameters of Sample B in which the composition of the electron transit layer is the same as that of the collector layer and there is no stepwise distribution of composition are also shown.

  FIG. 8 is a diagram illustrating a result of calculating a conduction band profile in the vicinity of an operating voltage as an oscillator of the samples A and B having the RTD structure illustrated in FIG. 2 and 3, FIG. 8 shows a state in which a negative voltage is applied to the sub-emitter layer 91 on the substrate side and a positive voltage is applied to the collector layer 101. The energy difference between the region where the band on the emitter layer 92 side is flat and the region where the band on the collector layer 100 side is flat corresponds to the applied bias voltage.

In the present embodiment, the electron transit layer is composed of three InGaAs layers of the first electron transit layer 98, the second electron transit layer 99, and the third electron transit layer 100, of which the first electron transit layer is formed. Since the layer 98 and the second electron transit layer 99 are composed of InGaAs having a high In composition, the electron transit layer is viewed from the electrons in the conduction band of the electron transit layer heterojunction with the second barrier layer 97. The potential of the electron transit layer at the interface with the second barrier layer 97 is lower than the potential of the collector layer 101 by changing the potential, and the potential of the electron transit layer becomes lower as the distance from the collector layer 101 becomes closer. The potential of the electron transit layer at the junction surface with the collector layer 101 is the same as the potential of the collector layer 101. There. With such a structure, the effect described in the reference example can be obtained.

  The potential difference in the region where the band on the emitter layer 92 side is flat and the energy difference at the junction interface between the second barrier layer 97 and the electron transit layer are the double barrier layers (first barrier layer 95, well layer 96, first layer This is an index of the launcher effect when electrons tunnel through the second barrier layer 97). In other words, the greater this energy difference, the greater the launcher effect when electrons tunnel through the double barrier layer.

  According to FIG. 8, the energy difference DA of the sample A is about 280 meV, and the energy difference DB of the sample B is 160 meV. Since the electron transit layer has a three-layer structure and InGaAs having an In composition higher than that of the third electron transit layer 100 is used for the first and second electron transit layers 98 and 99, the sample is more sampled than the sample B. It can be seen that A gives a larger energy difference. That is, it can be seen that the launcher effect of the double barrier layer is larger in the sample A of the present embodiment.

  In addition, the effective mass of electrons in InGaAs having a high In composition is smaller than the effective mass of electrons in lattice-matched InGaAs. Therefore, since the effective mass of the electrons in the electron transit layer is smaller in the sample A of the present embodiment than in the sample B, the speed of the electrons in the electron transit layer is increased.

  The inventors produced a terahertz oscillator as shown in FIG. 5 using the above samples A and B as RTDs 9 respectively. When sample A was used, 1.08 THz was obtained as the maximum oscillation frequency of the oscillator, and when sample B was used, 1.04 THz was obtained as the maximum oscillation frequency.

  When the transit time of the electron transit layer was calculated from the obtained maximum oscillation frequency, the electron transit layer transit time of Sample A was 140 fs, and the electron transit layer transit time of Sample B was 170 fs. That is, it can be seen that the sample A of the present embodiment can shorten the electron travel time by 30 fs. This reduction in travel time is achieved by using an electron transit layer made of InGaAs having a high In composition, thereby promoting the electron launcher effect at the interface between the double barrier layer and the electron transit layer, and in the electron transit layer. This suggests that the effective mass of electrons has been reduced and the speed of electrons has been increased.

In the present embodiment, the emitter layer is composed of two InGaAs layers, ie, the emitter layer 92 and the graded emitter layer 93, and the graded emitter layer 93 is composed of InGaAs whose In composition gradually decreases. The potential of the emitter layer as viewed from the electrons in the conduction band is changed so that the potentials of the emitter layer and the spacer layer increase as the distance from the first barrier layer 95 decreases. With such a structure, the effect described in the first embodiment can be obtained.

  As described above, in the present embodiment, the launcher effect of the double barrier layer can be promoted and the effective mass of electrons can be reduced, and the transit time of electrons in the electron transit layer can be shortened. Higher frequency can be realized. In this embodiment, the bias voltage can be reduced, and the power consumption of the RTD and the terahertz oscillator can be reduced.

  In the present embodiment, assuming a bias polarity in which electrons flow from the substrate side to the surface side, the graded emitter layer 93 is disposed on the substrate side with respect to the double barrier portion, and the first, second, and third The electron transit layers 98, 99, and 100 were installed on the surface side of the double barrier portion. When assuming a bias polarity in which electrons flow from the surface side to the substrate side, that is, a polarity in which a positive voltage is applied to the sub-emitter layer 91 and a negative voltage is applied to the collector layer 101, two graded emitter layers 93 are provided. The first, second, and third electron transit layers 98, 99, and 100 may be provided on the substrate side with respect to the double barrier portion. That is, in FIG. 4, the same effect as in the present embodiment can be obtained even if a structure in which the structure from the emitter layer 92 to the third electron transit layer 100 is inverted is used.

  In the present embodiment, an example is shown in which the electron transit layer is formed of InGaAs having three different In compositions. However, the composition distribution in the electron transit layer for obtaining the effect of the present embodiment is as follows. Not as long. The structure of the electron transit layer is such that the In composition changes stepwise from the second barrier layer side to the collector layer side, and is made of InGaAs with a high In composition on the second barrier layer side, and as the distance from the collector layer decreases. The In composition of InGaAs constituting the collector layer may be approached. The In composition and thickness of each InGaAs layer may be configured in a range where lattice relaxation due to lattice mismatch does not occur.

  As the In composition increases, the compressive strain applied to the electron transit layer increases and the critical film thickness decreases. The upper limit value of the In composition of InGaAs constituting the electron transit layer is a value of the In composition that matches the critical thickness determined by the In composition.

  In this embodiment, for ease of manufacturing, the electron transit layer is divided into three layers, and the potential is changed stepwise by changing the mixed crystal composition in each layer. Since the same effect as that of the stepped potential structure can be obtained even in a structure in which the potential of the electron transits continuously changes, the electron transit layer may be configured by a gradient composition layer in which the composition changes continuously.

  In the present embodiment, an example in which the graded emitter layer 93 and the spacer layer 94 are composed of InGaAs having three different In compositions has been described. However, the composition of each layer for obtaining the effect of the present embodiment is shown. The configuration is not limited to this, and it is sufficient that the In composition is gradually decreased from the composition of InGaAs constituting the emitter from the emitter layer to the barrier layer. For example, the same effect can be obtained even if the graded emitter layer 93 and the spacer layer 94 are made of InGaAs having four or five different In compositions.

  As the In composition decreases, tensile strain applied to the spacer layer 94 and the graded emitter layer 93 increases, and the critical film thickness decreases. The lower limit of the In composition of InGaAs constituting the spacer layer 94 and the graded emitter layer 93 is a value of the In composition that matches the critical film thickness determined by the In composition of the spacer layer 94 and the graded emitter layer 93. .

  In the present embodiment, the emitter layer is composed of two layers of the emitter layer 92 and the graded emitter layer 93, and the potential is changed stepwise by changing the mixed crystal composition in each layer. As in the case of the layer, even if the potential is changed continuously, the same effect as that of the stepped potential structure can be obtained. Therefore, even if the emitter layer is constituted by the gradient composition layer whose composition changes continuously, I do not care.

In the reference example and the first and second embodiments , the sub-emitter layers 23 and 91 are provided outside the emitter layers 24 and 92. Similarly, outside the collector layers 30 and 101 (collector layers 30, 101 and the left electrodes 4 and 32) may be provided with a subcollector layer. The subcollector layer may be made of a semiconductor doped with impurities having the same conductivity type as that of the emitter layers 24 and 92 and the collector layers 30 and 101 and having a higher concentration of impurities than the collector layers 30 and 101.

In the third embodiment , an example in which the RTD structure described in the reference example and the first embodiment is realized by an InGaAs / InP-based semiconductor material has been described. As long as the potential band structure (band lineup) described in the embodiment can be realized, an RTD can be manufactured using a semiconductor material other than an InGaAs / InP system.

  The present invention can be applied to a resonant tunnel diode and a terahertz oscillator using the resonant tunnel diode.

  DESCRIPTION OF SYMBOLS 1,21 ... Board | substrate, 2,31 ... Right electrode, 3 ... Insulator, 4, 32 ... Left electrode, 5, 6 ... Concave part, 7 ... Convex part, 8 ... Protrusion part, 9, 20 ... Resonant tunnel diode, 10 ... Resistance 11 ... DC power source 22,90 ... Buffer layer 23,91 ... Sub-emitter layer 24,92 ... Emitter layer 25,94 ... Spacer layer 26,27,95,97 ... Barrier layer 27 96 ... well layer, 29, 98, 99, 100 ... electron transit layer, 30, 101 ... collector layer, 93 ... graded emitter layer.

Claims (9)

An emitter layer made of a semiconductor doped with impurities;
A spacer layer made of an electrically neutral semiconductor;
A first barrier layer serving as a barrier against electrons in each layer of the emitter layer and the spacer layer;
A well layer made of an electrically neutral semiconductor;
A second barrier layer serving as a barrier against electrons in each layer of the emitter layer and the spacer layer;
An electron transit layer made of an electrically neutral semiconductor, in which electrons flow from the emitter layer through the spacer layer, the first barrier layer, the well layer, and the second barrier layer;
A collector layer made of a semiconductor doped with impurities is sequentially stacked,
The electron transit layer, the second conduction band energy at the bonding surface between the barrier layer is rather higher than the conduction band energy of the collector layer, the collector layer is a conduction band energy as the distance approaches between the collector layer the closer to the conduction band energy, Ri conduction band energy at the bonding surface between the collector layer are the same as name and conduction band energy of the collector layer,
RTD said emitter layer and said spacer layer, by varying the composition of the emitter layer in the layer, said first conduction band energy as the distance approaches the barrier layer is characterized by Rukoto a low . An emitter layer made of a semiconductor doped with impurities;
A spacer layer made of an electrically neutral semiconductor;
A first barrier layer serving as a barrier against electrons in each layer of the emitter layer and the spacer layer;
A well layer made of an electrically neutral semiconductor;
A second barrier layer serving as a barrier against electrons in each layer of the emitter layer and the spacer layer;
An electron transit layer made of an electrically neutral semiconductor, in which electrons flow from the emitter layer through the spacer layer, the first barrier layer, the well layer, and the second barrier layer;
A collector layer made of a semiconductor doped with impurities is sequentially stacked,
The electron transit layer has a conduction band energy at the interface with the second barrier layer that is higher than the conduction band energy of the collector layer, and the conduction band energy of the collector layer decreases as the distance from the collector layer decreases. Approaching the conduction band energy, the conduction band energy at the interface with the collector layer becomes the same as the conduction band energy of the collector layer,
The semiconductor is InGaAs;
The InGaAs constituting the electron transit layer has an In composition on the second barrier layer side higher than the In composition of InGaAs constituting the collector layer, and the In composition increases as the distance from the collector layer decreases. A resonant tunneling diode characterized by approaching the In composition of InGaAs constituting the layer and having the same In composition at the junction surface with the collector layer as the In composition of InGaAs constituting the collector layer. The resonant tunneling diode of claim 1 , wherein
The semiconductor is InGaAs;
The resonant tunnel diode, wherein the InGaAs constituting the emitter layer and the spacer layer has an In composition that decreases as the distance from the first barrier layer decreases. The resonant tunneling diode according to any one of claims 1 to 3 ,
The resonant tunneling diode according to claim 1, wherein a conduction band energy of the electron transit layer, the emitter layer, and the spacer layer changes stepwise. The resonant tunneling diode according to claim 4 ,
The electron tunneling layer and the emitter layer each include a plurality of layers. The resonant tunneling diode according to any one of claims 1 to 3 ,
When a negative voltage is applied to the emitter layer and a positive voltage is applied to the collector layer, the emitter layer, the spacer layer, the first barrier layer, the well layer, the second layer on the substrate. The resonant tunnel diode is characterized in that the barrier layer, the electron transit layer, and the collector layer are stacked in this order. The resonant tunneling diode according to any one of claims 1 to 3 ,
When a positive voltage is applied to the emitter layer and a negative voltage is applied to the collector layer, the collector layer, the electron transit layer, the second barrier layer, the well layer, the first layer on the substrate. A resonant tunneling diode comprising: a barrier layer, a spacer layer, and an emitter layer stacked in this order. The resonant tunneling diode according to any one of claims 1 to 7 ,
Further, the semiconductor layer is laminated outside the emitter layer so as to be in contact with the emitter layer, and has an impurity having the same conductivity type as the emitter layer and the collector layer, and is doped with an impurity having a higher concentration than the emitter layer. A sub-emitter layer,
A sub-layer made of a semiconductor that is stacked outside the collector layer so as to be in contact with the collector layer, doped with impurities having the same conductivity type as the emitter layer and the collector layer, and having a higher concentration of impurities than the collector layer. A resonant tunneling diode comprising a collector layer. Resonant tunnel diode according to any one of claims 1 to 8 ,
A slot antenna which is a resonator connected to the resonant tunneling diode;
A terahertz oscillator comprising a power supply for applying a bias voltage between an emitter layer and a collector layer of the resonant tunneling diode.

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