JP2011114120A - Resonance tunnel diode and terahertz oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfy a high peak current density and a low peak voltage at the same time and to lower a bias voltage. <P>SOLUTION: A resonance tunnel diode has an emitter layer 92 made of InGaAs doped with an impurity, a first barrier layer 94 made of AlAs, a well layer 95 made of electrically neutral InGaAs, a second barrier layer 96 made of AlAs, electron transit layers 97 to 99, and a collector layer 100 made of InGaAs doped with an impurity. The electron transient layers comprise a first electron transit layer 97 made of electrically neutral InGaAs, a spike dope layer (second electron transit layer) 98 made of InGaAs doped with an impurity, and a third electron transit layer 99 made of electrically neutral InGaAs. The spike dope layer 98 is doped with the impurity having the same conductivity type with the emitter layer 92 and collector layer 100. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

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.

  Resonant tunneling diodes (hereinafter referred to as RTDs) having negative differential resistance have oscillations in the terahertz frequency band due to the short tunneling time when electrons travel, the short charging time caused by high current density and small parasitic capacitance. Therefore, it is expected as a compact terahertz light source that operates 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 a negative differential resistance region in current-voltage characteristics (hereinafter referred to as IV characteristics). Parameters characterizing the RTD IV characteristics include a peak current density J _P and a peak voltage V _P , and a current density minimum value J _{V in} a negative differential resistance region called a valley current density. The product of the peak current density J _P and the peak voltage V _P can be regarded as an index of the power consumption of the oscillation element. Since the peak current density J _P can be charged in a short time higher RTD capacity, although it is possible to obtain a high oscillation frequency also increases power consumption of the oscillator accordingly.

Recently, the inventors have realized fundamental wave oscillation at 831 GHz by an oscillator using an RTD composed of an InGaAs layer and an AlAs layer stacked on an InP substrate (see Non-Patent Document 1). Such room-temperature oscillation at a high frequency near 1 THz is caused by a very high peak current density J _P exceeding 1 × 10 ⁶ A / cm ² of RTD and a clear negative differential resistance as described in Non-Patent Document 1. Can be realized. On the other hand, the bias voltage applied to the element for oscillating operation is relatively high as shown in Non-Patent Document 1, and exceeds 1V. In order to fabricate an oscillator that simultaneously satisfies oscillation in the terahertz frequency band and low power consumption, it is necessary to satisfy both high J _P and low V _P in the RTD IV characteristics.

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”, Appl. Phys. Express 2, 054501, 2009

Conventionally, when generally the RTD to try to high speed operation, for example, shortening the charging time of the device capacitance to obtain a high peak current density J _p by reducing the mesa area of the element, a method has been adopted that. However, although this method operates at high speed, there is a problem in that power consumption increases because the bias voltage applied to the RTD becomes relatively high. The reason why the bias voltage becomes high is that when a voltage is applied to the RTD to the vicinity of the operating voltage, the conduction band of the electron transit layer between the RTD double barrier structure and the collector layer is greatly bent, and is conducted between the emitter and the collector. This is because a large potential difference occurs in the belt.

The present invention has been made in order to solve the above-described problems, and in order to produce a terahertz oscillator that simultaneously satisfies oscillation in the terahertz frequency band and low power consumption, a high peak current density J _P and a low current-voltage characteristic are provided. An object of the present invention is to provide an RTD layer structure that can simultaneously satisfy the peak voltage V _P and reduce the bias voltage required for the oscillation operation.

  The resonant tunnel diode of the present invention includes an emitter layer made of a semiconductor doped with impurities, a first barrier layer that serves as a barrier against electrons in the emitter layer, a well layer made of an electrically neutral semiconductor, A second barrier layer serving as a barrier against electrons in the emitter layer; and a semiconductor, and electrons flow from the emitter layer through the first barrier layer, the well layer, and the second barrier layer. An electron transit layer and a collector layer made of a semiconductor doped with an impurity are sequentially stacked. The electron transit layer includes a first electron transit layer made of an electrically neutral semiconductor and a semiconductor doped with an impurity. And a third electron transit layer made of an electrically neutral semiconductor, and at least the emitter layer, the collector layer, and the second electron transit layer have the same conductivity. Indicates type And it is characterized in that it is doped with impurities.

In one configuration example of the resonant tunneling diode of the present invention, the semiconductor is InGaAs, and the electron transit layer is n in the first and third electron transit layers made of electrically neutral InGaAs. It has the said 2nd electron transit layer to which type impurity doping was given.
Also, 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 and the first layer are formed on a substrate. The 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, 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 the collector layer, and a layer stacked so as to be in contact with the collector layer outside the collector layer, and having the same conductivity as the emitter layer and the collector layer And a sub-collector layer made of a semiconductor doped with impurities of a type and having a higher concentration of impurities than the emitter layer and 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 electron transit layer is composed of three layers of the first electron transit layer, the second electron transit layer, and the third electron transit layer, and the second electron transit layer is the emitter layer. By doping with an impurity having the same conductivity type as the collector layer, it is possible to obtain a low peak voltage V _P while maintaining a high peak current density J _P, and to reduce the bias voltage necessary for the oscillation operation Can do. As a result, in the present invention, it is possible to realize a terahertz oscillator that simultaneously satisfies the oscillation in the terahertz frequency band and the low power consumption.

1 is a perspective view showing a structure of a terahertz oscillator according to an embodiment of the present invention. 1 is an exploded perspective view of a terahertz oscillator according to an embodiment of the present invention. 1 is an equivalent circuit diagram of a terahertz oscillator according to an embodiment of the present invention. It is sectional drawing which shows the structure of the resonant tunnel diode which concerns on embodiment 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 embodiment of this invention. It is a figure which shows the current-voltage characteristic of the resonant tunnel diode which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing the structure of a terahertz oscillator according to an embodiment of the present invention.
In the terahertz oscillator shown in FIG. 1, a right electrode 2 made of gold (Au), panadium (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, panadium 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 protrusion 8 is formed at the tip of the protrusion 7, and the RTD 9 is arranged so as to be sandwiched between the right electrode 2 and the lower side of the protrusion 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 recesses 5 and 6 (D in FIG. 1) is preferably about 4 μm, and the width of the projection 7 (W in FIG. 1) is preferably about 6 μm. It is set as appropriate according to the design according to the frequency.

FIG. 2 is an exploded perspective view of the terahertz oscillator according to the present embodiment. As shown in FIG. 2, 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. 3 is an equivalent circuit diagram of the terahertz oscillator according to the present embodiment. In FIG. 3, 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 doubles as a resonator and an electromagnetic wave radiation antenna. As shown in FIGS. 1 and 3, 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 is 1 / [2π {L (C _RTD + C _ANT )} ^1/2 ].

Next, the structure of the RTD 9 used for the above terahertz oscillator will be described. FIG. 4 is a cross-sectional view showing the structure of the RTD 9 of this embodiment. The RTD 9 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), and n-type indium gallium arsenide. An emitter layer 92 made of (n-In _0.53 Ga _0.47 As), a spacer layer 93 made of undoped indium gallium arsenide (un-In _0.53 Ga _0.47 As), and a first barrier layer 94 made of aluminum arsenic (AlAs), A well layer 95 made of undoped indium gallium arsenide (un-In _0.8 Ga _0.2 As), a second barrier layer 96 made of aluminum arsenic (AlAs), and undoped indium gallium arsenide (un-In _0.53 Ga _0.47 As). A first electron transit layer 97 and n-type indium gallium arsenide A spike doped layer 98 which is a second electron transit layer made of (n-In _0.53 Ga _0.47 As), a third electron transit layer 99 made of undoped indium gallium arsenide (un-In _0.53 Ga _0.47 As), n -type indium gallium arsenide (n-In _0.7 Ga _0.3 as, or n-In _0.53 Ga _0.47 as) and the collector layer 100 made of, n-type indium gallium arsenide (n-In _0.7 Ga _0.3 as and n-In _0.53 Ga _0.47 as) And a sub-collector layer 101 composed of the layers. 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 sub-collector layer 101 reduce the ohmic contact resistance between the right electrode 2 and the left electrode 4, and the parasitic resistance component from the right electrode 2 to the emitter layer 92, respectively, By reducing the parasitic resistance component, the parasitic resistance component of the entire device is reduced.

Note that the spike doped layer is a layer formed by performing spiked n-type impurity doping in a very narrow region in an electrically neutral InGaAs layer (an ultrathin film layer doped with n-type impurity is electrically charged). In particular, a doping profile formed by being sandwiched between neutral layers). Although ideally δ-doped, it has a thickness of 1 atomic layer or more and 15% or less of the total thickness of the first, second, and third electron transit layers 97 to 99 from the viewpoint of ease of production. The collector layer 100 may have a doping concentration of 50% or more of the n-type impurity doping concentration. Note that the thickness of the spike doped layer 98 is one of the factors that influence the device capacity. In particular, the thickness of the spike doped layer 98 exceeds 15% with respect to the total thickness of the first, second, and third electron transit layers 97-99. As a result, the element capacitance increases until the high-frequency characteristics of the RTD are significantly degraded. Further, the impurity doping concentration of the spike doped layer 98 affects the conduction band profile of the third electron transit layer 99 and the collector layer 100 as described later, but is less than 50% of the n-type impurity doping concentration of the collector layer 100. Then, the potential of the conduction band is not sufficiently increased, and the effect of the present invention cannot be sufficiently obtained. Basically, the higher the concentration, the better, but there is an upper limit to the concentration at which the crystal quality such as defect density is not deteriorated depending on the semiconductor constituting the spike doped layer 98 and the type of the n-type impurity. The upper limit of the concentration is also determined thereby. For example, when n-type indium gallium arsenide (n-In _0.53 Ga _0.47 As) used in this embodiment is doped with Si as an n-type impurity, special conditions such as crystal growth are used at a low temperature. But crystal defects and no impurity doping concentration less than 1 × 10 ²⁰ cm ^-3 is significantly increased, thereby significantly deteriorating the device characteristics.

The thicknesses of the buffer layer 90, the sub-emitter layer 91, the emitter layer 92, the spacer layer 93, the first barrier layer 94, the well layer 95, the second barrier layer 96, the collector layer 100, and the sub-collector layer 101 are each 200 nm. , 400 nm, 25 nm, 2 nm, 1.4 nm, 4.5 nm, 1.4 nm, 25 nm, and 23 nm. The subcollector 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 thicknesses of the first electron transit layer 97, the spike doped layer 98, and the third electron transit layer 99 are d _S1 , d _SD , and d _S2 , respectively. These thicknesses d _S1 , d _SD and d _S2 will be described later.

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 is Si, the doping concentration is 3 × 10 ¹⁸ cm ⁻³ , and the dopant of the collector layer 100 is Si, The doping concentration is 3 × 10 ¹⁸ cm ⁻³ , the dopant of the subcollector layer 101 is Si, and the doping concentration is 2 × 10 ¹⁹ cm ⁻³ . The dopant of the spike doped layer 98 is also Si, and the doping concentration is N _D. This doping concentration N _D will be described later.

Table 1 shows the values of parameters d _S1 , d _S2 , d _SD , and N _D of the samples A, B, and C of the RTD 9 having the structure of FIG. Sample A is a comparative reference sample that does not include the spike dope layer.

  FIG. 5 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, B, and C having the RTD structure illustrated 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 91 on the substrate side and a positive voltage is applied to the sub-collector layer 101 is shown. 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 double barrier structure portion composed of the first and second barrier layers 94 and 96 and the well layer 95, the inclination of the conduction band is equal between the samples A to C. However, as is clear from the fact that the energy on the collector layer 100 side increases in the order of the samples A, B, and C, the spike dope layer 98 is inserted into the first and third electron transit layers 97 and 99, It can be seen that the operating voltage can be lowered with increasing the doping concentration of the spike doped layer 98.

  FIG. 6 is a diagram showing IV characteristics of samples A, B, and C measured experimentally. Here, the negative bias voltage is a polarity for applying a negative voltage to the sub-emitter layer 91 on the substrate side, and corresponds to the band profile of FIG. That is, under a negative bias voltage, electrons flow from the sub-emitter layer 91 on the substrate side to the sub-collector layer 101.

The peak current density J _P , the peak voltage V _P , the product of the peak current density J _P and the peak voltage V _{P in} the IV characteristics under the negative bias voltage of each sample A, B, and C, and the negative differential resistance characteristic index become, Table 2 shows the difference ΔJ peak current density J _P and the current density minima J _V.

According to Table 2, the peak current density J _P is 1.6 to 1.8 × 10 ⁶ A / cm ² , which is approximately the same between samples A to C. On the other hand, it can be seen that the peak voltage V _P can be lowered by inserting the spike doped layer 98 into the first and third electron transit layers 97 and 99 and increasing the doping concentration of the spike doped layer 98. As the peak voltage V _P decreases, the product of the peak current density J _P and the peak voltage V _P also decreases significantly. When the terahertz oscillator is realized using the RTD of the present embodiment, the oscillator This indicates that low power consumption can be achieved. It can also be seen that there is no decrease in ΔJ due to the insertion of the spike doped layer 98, and the negative differential resistance characteristic is not impaired.

  In addition, by the terahertz oscillator using the above samples B and C as the RTD 9, the inventors have confirmed that an oscillation frequency exceeding 800 GHz can be obtained in the same manner as when the sample A is used as the RTD 9. It has been confirmed that the high-frequency characteristics of the RTD are not impaired by the structure of the form.

As described above, in the present embodiment, in the RTD, the electron transit layer includes the first electron transit layer 97, the spike doped layer (second electron transit layer) 98, and the third electron transit layer 99. The spike doped layer 98 is doped with an impurity having the same conductivity type as the sub-emitter layer 91, the emitter layer 92, the collector layer 100, and the sub-collector layer 101. Band bending can be suppressed. As a result, in this embodiment, it is possible to obtain a low peak voltage V _P while maintaining a high peak current density J _P , and a bias voltage necessary for the oscillation operation can be reduced. The terahertz oscillator can be realized.

  In this embodiment, it is assumed that the bias polarity in which electrons flow from the substrate side to the surface side, and the spike dope layer 98 and the first and third electron transit layers 97 and 99 are arranged on the surface side of the double barrier portion. Installed. In the case of 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 sub-collector layer 101, the spike doped layer 98 and the second The first and third electron transit layers 97 and 99 may be provided closer to the substrate than the double barrier portion. That is, in FIG. 4, the same effect as in this embodiment can be obtained even if a structure in which the structure from the emitter layer 92 to the collector layer 100 is inverted is used.

  The present invention can be applied to a resonant tunneling diode.

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2 ... Right electrode, 3 ... Insulator, 4 ... Left electrode, 5, 6 ... Concave part, 7 ... Convex part, 8 ... Protrusion part, 9 ... Resonant tunnel diode, 10 ... Resistance, 11 ... DC power supply, DESCRIPTION OF SYMBOLS 90 ... Buffer layer, 91 ... Sub-emitter layer, 92 ... Emitter layer, 93 ... Spacer layer, 94, 96 ... Barrier layer, 95 ... Well layer, 97, 99 ... Electron transit layer, 98 ... Spike dope layer, 100 ... Collector Layer, 101... Subcollector layer.

Claims (6)

An emitter layer made of a semiconductor doped with impurities;
A first barrier layer that serves as a barrier against electrons in the emitter layer;
A well layer made of an electrically neutral semiconductor;
A second barrier layer serving as a barrier against electrons in the emitter layer;
An electron transit layer made of a semiconductor, in which electrons flow from the emitter layer through 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 includes a first electron transit layer made of an electrically neutral semiconductor, a second electron transit layer made of an impurity-doped semiconductor, and a third electrode made of an electrically neutral semiconductor. The electronic traveling layer of
A resonant tunnel diode, wherein at least the emitter layer, the collector layer, and the second electron transit layer are doped with impurities having the same conductivity type. The resonant tunneling diode of claim 1, wherein
The semiconductor is InGaAs;
The electron transit layer has the second electron transit layer in which the n-type impurity doping is performed in the first and third electron transit layers made of electrically neutral InGaAs. Tunnel diode. The resonant tunneling diode according to claim 1 or 2,
When a negative voltage is applied to the emitter layer and a positive voltage is applied to the collector layer, the emitter layer, the first barrier layer, the well layer, the second barrier layer on a substrate, The resonant tunneling diode, wherein the electron transit layer and the collector layer are stacked in this order. The resonant tunneling diode according to claim 1 or 2,
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 and an emitter layer stacked in this order. The resonant tunneling diode according to any one of claims 1 to 4,
Further, the impurity layer is laminated outside the emitter layer so as to be in contact with the emitter layer, and has 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 and the collector layer. A sub-emitter layer made of a doped semiconductor;
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 than the emitter layer and the collector layer A resonant tunneling diode comprising a subcollector layer made of a semiconductor. Resonant tunnel diode according to any one of claims 1 to 5,
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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