KR20000021423A - Quantum resonant tunneling device having an emitter sub-mesa array structure - Google Patents

Abstract

PURPOSE: A quantum resonant tunneling device having an emitter sub-mesa array structure is provided to secure a stable operating characteristic by preventing an operating voltage and a power dissipation of a negative differential resistance from increasing. CONSTITUTION: A quantum resonant tunneling device having an emitter sub-mesa array structure comprises: a substrate; a first conductive layer formed on the substrate; an emitter sub-mesa array in which a plurality of multilayered layers of an emitter barrier layer and an emitter cap layer are disposed in a matrix form on the first conductive layer; an insulation layer surrounding the respective emitter sub-mesas; a first electrode formed on the first conductive layer; and an emitter electrode formed on the emitter cap layer.

Description

Quantum Resonant Tunneling Device with Emitter Sub-Mesa Array Structure

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor heterojunction quantum barrier resonant tunneling devices. In particular, an emitter mesa comprising an emitter barrier layer and a conductive emitter layer is formed in an array, and thus a low operating voltage. The present invention relates to a quantum resonant tunneling device having an emitter mesa array structure having high peak current and low power consumption, high current, and high speed operating characteristics.

In recent years, as semiconductor growth technologies such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) are developed, GaAs / AlAs, GaAs / GaAlAs, InAs / GaSb, InAs The development of semiconductor devices using heterojunction structures such as / ZnTe has been activated. Due to the band line-up of the heterojunction structure, the quantum resonant tunneling effect of the electron through the quantum-confined states of the electron appearing in the quantum well structure is an electronic device. Research on ultra-fast quantum resonant tunneling is being actively conducted because it can enable tera-class operation, fast switching time, and low power dissipation.

In particular, devices such as a resonant tunneling diode (RTD) having a negative differential resistance (NDR) characteristic of current caused by an electron resonant tunneling phenomenon are microwave devices such as a voltage controlled oscillator (VCO). It is of great technical importance as it is applied to microwave devices, ultra high speed switching devices and logic devices.

In order to improve a semiconductor device having such NDR characteristics at room temperature, it is necessary to obtain high peak current, high peak to valley current ratio (PVR), low capacitance, and low operating voltage. The quantum resonant tunneling electronic elements have low output in frequency oscillation.

In order to obtain a high pick current required for improving the characteristics of the quantum resonance tunneling device such as an increase in output, there is a method of increasing the size of the emitter mesa of the device. However, increasing the size of the emitter mesa results in an increase in power consumption as well as an increase in the operating voltage of the NDR region. That is, in the current-voltage characteristic curve of the vertical quantum resonance tunneling device, the NDR operating voltage is also adjusted according to the size of the emitter mesa. As the size of the emitter mesa increases, the current increases, but this causes the region where the NDR occurs to move towards higher voltages, which in turn tends to increase the operating voltage of the device, which leads to unstable circuitry and increased capacitance, resulting in higher device speed. In addition to the problem of inhibiting operation (high frequency oscillation), there is a problem that it is difficult to observe the NDR phenomenon caused by the quantum confinement level.

The present invention devised to solve the above problems can substantially increase the emitter mesa size of the device to obtain a high pick current required for improving the characteristics of the quantum resonant tunneling device and at the same time increases the emitter mesa size. Accordingly, an object of the present invention is to provide a quantum resonant tunneling device having an emitter sub-mesa array structure capable of securing stable operating characteristics of the device by preventing an increase in operating voltage and power consumption of the NDR region.

1A is a cross-sectional view of a quantum resonant tunneling element having an emitter sub-mesa array structure according to a first embodiment of the present invention;

1B and 1C are cross-sectional and longitudinal cross-sectional views of the emitter portion in the quantum resonant tunneling element shown in FIG. 1A, respectively;

2A is a cross-sectional view of a quantum resonant tunneling element having an emitter sub-mesa array structure according to a second embodiment of the present invention;

2B and 2C are cross-sectional and longitudinal cross-sectional views of the emitter portion in the quantum resonant tunneling element shown in FIG. 2A, respectively;

3A is a cross-sectional view of a quantum resonant tunneling element having an emitter sub-mesa array structure according to a third embodiment of the present invention;

3B and 3C are cross-sectional views of the emitter portion in the quantum resonance tunneling element shown in FIG. 3A, respectively;

4A, 4B, and 4C are thermal equilibrium states and electron resonance tunneling voltages of a quantum resonant tunneling device having an AlAs / GaAs triple barrier emitter sub-mesa array structure formed according to a fourth embodiment of the present invention, respectively. An energy diagram showing an applied state and a non-resonant tunneling voltage applied state,

5A, 5B and 5C show a thermal equilibrium state of a quantum resonant tunneling element having a five-barrier structure formed according to a fifth embodiment of the present invention, a state in which an electron resonant tunneling voltage is applied, and an off-resonant tunneling voltage, respectively. Energy band chart showing status,

6A is a graph showing I-V characteristics according to changes in emitter mesa area of a quantum resonant tunneling device having an emitter sub-mesa array structure;

6B is a graph showing I-V characteristics according to the change in the number of emitter mesas of a quantum resonant tunneling device having an emitter sub-mesa array structure.

* Explanation of reference numerals for the main parts of the drawings

10: substrate 11A, 11B: undoped spacer layer

12A, 12B, 12C: quantum barrier layer 13A, 13B: quantum well layer

14: insulating layer 15: collector electrode

16: emitter electrode EB: emitter barrier layer

EC: emitter cap layer C: collector

The present invention for achieving the above object is a substrate; A first conductive layer formed on the substrate; Emitter sub-measuring a plurality of emitter sub-mesa consisting of an emitter barrier layer and an emitter cap layer stacked on the first conductive layer in a matrix Mesa arrays; An insulating film surrounding each emitter sub-mesa forming the emitter sub-mesa array; A first electrode formed on the first conductive layer; And it provides a quantum resonant tunneling device comprising an emitter electrode formed on the emitter cap layer.

The former quantum well bond energy levels are determined by the width of the quantum wells or the epistructure of the quantum barrier of the double junction material used, and by these quantum well bond levels the NDR (Negative differential resistance) The operating voltage of the device is determined. According to the present invention, a plurality of small emitter sub-mesas are arranged to form an emitter mesa in an array structure, thereby maintaining a high PVR by increasing an amount of current while maintaining a low operating voltage. It is a feature of the present invention to provide a quantum resonant tunneling element having an emitter sub-mesa array structure capable of adjusting the magnitude of current by the number of sub-mesas.

In addition, in the quantum resonant tunneling device having an emitter sub-mesa array structure, the width of each of the quantum barrier layer and the quantum well layer is formed as an asymmetrical combination structure, and thus the effect of the relatively thin outer barrier layer is obtained. This reduces the capacitance and increases the resonance tunneling effect of electrons at low voltages by aligning by stark shift of low energy quantum bond levels, resulting in high power consumption and high power at room temperature. It is another feature to provide a possible improved quantum resonant tunneling element.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

FIG. 1A is a cross-sectional view of a quantum resonant tunneling device having an emitter sub-mesa array structure according to a first embodiment of the present invention, and has a quantum resonant tunneling device having a triple quantum barrier layer having a two-terminal structure. It is showing.

As shown in FIG. 1A, a quantum resonant tunneling device according to a first embodiment of the present invention includes a substrate 10, a first collector stacked on a collector C, and a conductive spacer C formed on the substrate. Layer 11A, first quantum barrier layer 12A, first quantum well layer 13A, second quantum barrier layer 12B, second quantum well layer 13B, third quantum barrier layer 12C, and The emitter barrier layer EB made of the second spacer layer 11B and the plurality of emitter E sub-mesas made of a conductive emitter cap layer EC formed on the emitter barrier layer EB are formed. Achieve. Each emitter (E) sub-mesa consisting of an emitter barrier layer (EB) and a conductive emitter cap layer (EC) is separated by an insulating layer 14, and the collector electrode 15 is disposed on the conductive collector (C) layer. ) Is formed, and the emitter electrode 16 is formed on the emitter cap layer EC.

The first and second spacer layers 11A and 11B are undoped semiconductor layers. Further, the width of the second quantum barrier layer 12B is relatively wider than that of the first quantum barrier layer 12A and the third quantum barrier layer 12C. In addition, the width of the first quantum well layer 13A and the width of the second quantum well layer 13B are not the same. That is, the width of the quantum well layers 13A and 13B in the direction of the emitter electrode 16 in the substrate 10 increases or decreases. In FIG. 1A, the case of increase is shown as an example.

FIG. 1B is a horizontal cross-sectional view showing that the emitter sub-mesas of small size are arranged in a 3 × 3 array in the quantum resonant tunneling device shown in FIG. 1A, and FIG. 1C is an emitter mesa in the quantum resonant tunneling device shown in FIG. Vertical cross-sectional view showing the structural characteristics of.

In the two-terminal resonance tunneling device according to the first embodiment of the present invention described above, an emitter sub-mesa including an emitter barrier layer EB and a conductive emitter cap layer EC is an array structure. In this way, current characteristics and output can be improved while obtaining a low operating voltage. In addition, in the design of the epi structure, the quantum-barrier width of the quantum barrier layers 12A, 12B, and 12C is gradually increased and decreased again in three or more quantum barrier layers (two or more quantum well layers). The quantum-well widths of the quantum well layers 13A and 13B, which provide a quantum-confined state of electrons, are gradually increased or decreased to form an asymmetric junction structure.

Therefore, when the resonant voltage is applied, the energy of each quantum well can be aligned with the low quantum bond levels, thereby increasing the resonance tunneling effect through these matched states and obtaining a low pick voltage. And increase the pick current. In addition, the width of the first and third quantum barrier layers 12A and 12C is relatively smaller than the width of the second quantum barrier layer 12B, thereby reducing the capacitance of the device. When the off resonant voltage is applied, the width of the intermediate barrier layer (second quantum barrier layer) is relatively large to compensate for the reduction in the effective barrier width of the device due to the voltage drop, and the valley current (valley). current can be reduced, resulting in high PVR.

FIG. 2A is a cross-sectional view of a quantum resonance tunneling device having an emitter sub-mesa array structure according to a second embodiment of the present invention, and has a emitter structure of a double quantum barrier layer having a three-terminal structure. FIG. The resonant tunneling device is shown.

As shown in FIG. 2A, the quantum resonance tunneling device according to the second embodiment of the present invention includes a substrate 20, a collector-type collector C formed on the substrate 20, and a collector formed sequentially on the collector C. A potential spacer layer 28, a potential change absorbing layer (spacer layer) 29, a conductive base layer (B), a first spacer layer (21A), and a first quantum barrier layer ( 22A), the emitter barrier layer EB consisting of the quantum well layer 23, the second quantum barrier layer 22B, and the second spacer layer 11B, and the conductive emitter formed on the emitter barrier layer EB. A plurality of emitter E sub-mesas consisting of the cap layer EC constitute the array. Each emitter sub-mesa consisting of an emitter barrier layer EB and a conductive emitter cap layer EC is separated by an insulating layer 24, a collector electrode 25 is formed on the collector C layer, and a base The base electrode 26 is formed on the layer B, and the emitter electrode 27 is formed on the conductive emitter cap layer EC. The potential change absorbing layer 29 and the first and second spacer layers 21A and 21B are undoped semiconductor layers, and the layers block the diffusion of the doped impurities and change the potential by voltage in the resonance tunneling structure. It serves to reduce.

FIG. 2B is a horizontal cross-sectional view showing that the emitter sub-mesas of small size are arranged in a 2 × 2 array in the quantum resonant tunneling device shown in FIG. 2A, and FIG. 2C is a view showing each emitter in the quantum resonant tunneling device shown in FIG. Vertical cross section showing the structural characteristics of the mesa.

The two-terminal double barrier resonant tunneling element of the second embodiment of the present invention described above comprises a plurality of emitter mesas composed of an emitter barrier layer EB and a conductive emitter cap layer EC, and an quantum well layer. The width of 23 is relatively large, so that the current characteristics and output can be improved while obtaining a low operating voltage.

3A is a cross-sectional view of a quantum resonant tunneling device having an emitter sub-mesa array structure according to a third embodiment of the present invention, and has a quantum resonant tunneling device having an emitter barrier structure of a triple quantum barrier layer having a three-terminal structure. It is showing.

As shown in FIG. 3A, the quantum resonance tunneling device according to the third exemplary embodiment of the present invention is formed on the substrate 30, the conductive collector C formed on the substrate 30, and the conductive collector C formed on the substrate 30. The first spacer layer 31A and the first quantum barrier layer 32A sequentially stacked on the collector potential barrier layer 38, the potential change absorbing layer 39, the conductive base layer B, and the conductive base layer B. ), The first quantum well layer 33A, the second quantum barrier layer 32B, the second quantum well layer 33B, the third quantum barrier layer 32C and the second spacer layer 31B. A plurality of emitter (E) sub-mesas consisting of a layer (EB) and a conductive emitter cap layer (EC) formed on each emitter barrier layer (EB) constitute an array. Each emitter (E) sub-mesa consisting of an emitter barrier layer (EB) and a conductive emitter cap layer (EC) is separated by an insulating layer 34, and a collector electrode 35 is formed on the conductive collector (C) layer. The base electrode 36 is formed on the conductive base layer B, and the emitter electrode 37 is formed on the conductive emitter cap layer EC. The potential change absorbing layer 39 and the first and second spacer layers 31A and 31B are undoped semiconductor layers.

FIG. 3B is a horizontal cross-sectional view showing that the emitter sub-mesas of small size are arranged in a 1 × 2 array in the quantum resonant tunneling device shown in FIG. 3A, and FIG. 3C is a view showing each emitter in the quantum resonant tunneling device shown in FIG. 3A. Vertical cross-sectional view showing the structural characteristics of.

The two-terminal triple barrier resonant tunneling element of the third embodiment of the present invention described above comprises a plurality of emitter sub-mesa comprising an emitter barrier layer EB and a conductive emitter cap layer EC. Can be formed into an array to improve current characteristics and output while achieving low operating voltages.

On the other hand, in the above-described three-terminal resonant tunneling elements of the second and third embodiments, tunneling of electrons occurs in the emitter E mesa array and an electron projection occurs in the base region when an external voltage is applied. The electrons projected to the base layer pass through the collector potential barrier layers 28 and 38 to reach the collector layer C. In such a structure, the energy change of the quantum bond levels by the stark shift can be controlled by the widths of the potential change absorbing layers (buffer layers) 29 and 39.

4A, 4B, and 4C are thermal equilibrium states and electron resonance tunneling voltages of a quantum resonant tunneling device having an AlAs / GaAs triple barrier emitter sub-mesa array structure formed according to a fourth embodiment of the present invention, respectively. An energy band diagram showing an applied state and a non-resonant tunneling voltage applied state.

The resonant tunneling device having the AlAs / GaAs triple-barrier emitter mesa array structure is grown on a GaAs (001) semi-insulated substrate by molecular beam epitaxy (MBE) and has an n ⁺ type GaAs collector layer having a thickness of 0.5 μm from the substrate, 4.5 nm thick undoped GaAs spacer layer, 1.6 nm wide undoped AlAs third quantum barrier layer (B ₃ ), 4.5 nm wide undoped GaAs second quantum well layer (QW ₂ ), 2.9 nm wide undoped AlAs second quantum barrier layer (B ₂ ), undoped GaAs first quantum well layer (QW ₁ ) of 5.8 nm width, undoped AlAs first quantum barrier layer (B ₁ ) of 1.6 nm width, ratio of 4.5 nm wide A doped GaAs spacer layer, consisting of an n ⁺ type emitter cap layer having a thickness of 0.5 μm. The n ⁺ -type GaAs collector layer, and the silicon is injected in the concentration ^-3 1 × 10 ¹⁸ ㎝, n ⁺ type emitter cap layer is 1 × 10 ¹⁸ ㎝ ^-3 concentration of the silicon is injected in.

That is, FIG. 4A shows an energy band diagram of thermal equilibrium when no voltage is applied to the quantum resonant tunneling element having the AlAs / GaAs triple barrier emitter sub-mesa array structure formed as described above, and FIG. 4B. Shows that when the electron resonant voltage ( _Ver ) is applied, the quantum confinement ground states (E ⁰ _Q1 , E ⁰ _Q2 ) having the low energy of each quantum well are aligned. 4C is an energy band diagram showing the operating state of the device when an electron non-resonant voltage, i.e., an electron off-resonant voltage (V _eor ) is applied.

5A, 5B, and 5C show a state of thermal equilibrium, a state in which an electron resonant tunneling voltage is applied, and a state in which a non-resonant tunneling voltage is applied, respectively, of a quantum resonant tunneling element having a triple barrier emitter sub-mesa array structure As the energy band diagram shown, the width of the quantum barrier layer is gradually increased in order of the fifth, fourth, third, second, and first quantum barrier layers B ₅ , B ₄ , B ₃ , B ₂ , and B ₁ . The quantum well layer increases and decreases again, and the quantum well layer has an asymmetric structure in which the width gradually decreases in the order of the fourth, third, second, and first quantum well layers (QW ₄ , QW ₃ , QW ₂ , QW ₁ ,). An example of a quantum resonant tunneling device having a quantum barrier layer and a quantum well layer is shown.

Figure 6a is the emitter sub-consists of a graph showing the IV characteristics of the emitter mesa area change in the quantum resonant tunneling device having a mesa array structure, AlAs / GaAs 3 heavy-wall structure according to the prior art ² × 4 ㎛ 2 In the case of one emitter sub-mesa having a size (1 × 1 array structure) (a), according to the fourth embodiment of the present invention described above, an AlAs / GaAs triple barrier emitter sub-mesa array structure is provided. If the resonant tunneling element consists of five emitter sub-mesas (1 × 5 array structure) (b), and the emitter sub-mesas (9 × 3 × 3 array structure) (c) It is a characteristic curve graph between voltage (IV).

In the case of five emitter sub-mesas (b), the size of the entire mesa is 40 μm.²(C) the total mesa size is 72 μm²2 × 4 μm²Size The size of the emitter mesa is substantially increased compared to the case of (a) consisting of one basic emitter sub-mesa. FIG. 6A shows that even when the size of the emitter mesa is substantially increased (b, c), the emitter sub-mesa is composed of one emitter sub-mesa. While maintaining, the first quantum well layer (QW)_OneGround state and second quantum well layer (QW)₂It has been shown that the pick current of the resonant tunneling through the line-up state of) increases to 5 times and 9 times of (a). That is, the results of FIG. 6A show that the quantum resonant tunneling device of the conventional single emitter mesa structure has a problem of increasing the operating voltage that occurs when the area of the emitter mesa is increased to increase the pick current. It has been shown that this can be solved by manufacturing a resonant tunneling device.

Figure 6b is a graph showing the IV characteristics according to the change in the number of emitter sub-mesa of the quantum resonant tunneling device having an emitter mesa array structure, formed of InGaAs / InAlAs triple barrier heterojunction and the overall size of the emitter mesa 6 This is a comparison of the case of the same μm ² but different numbers of sub-mesas. In Fig. 6B, (d) shows a characteristic curve graph of current-voltage (IV) of a quantum resonant tunneling element composed of a single emitter mesa having a size of 2 × 3 μm ² (6 μm ² ). This is a graph of the current-voltage characteristic curve of mesa diodes when two emitter mesas having a size of 1 × 3 μm ² form a 1 × 2 array structure. The results in FIG. 6B show that although the same emitter mesa area has the same emitter mesa area, in the case of a device composed of a plurality of emitter sub-mesas (arrays) than in a device composed of one emitter sub-mesa (e) NDR It shows that the region moves towards lower voltages and the NDR region is better defined. That is, it can be seen that the current in the case of the single emitter mesa structure (d) increases more than in the case of the multiple emitter sub-mesa structure (e), but the operating voltage becomes high and the circuit tends to be unstable.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made in the art without departing from the technical spirit of the present invention. It will be apparent to those of ordinary knowledge.

According to the present invention, the emitter mesa of heterojunction quantum resonant tunneling devices is formed in the form of an array of emitter sub-mesas of small size, thereby reducing the capacitance of the device and resonating electrons. By increasing the tunneling effect, a high pick current and a low pick voltage can be realized at a low operating voltage at room temperature, thereby increasing the PVR. Accordingly, the present invention can improve the speed index of the device can be applied to ultra-high speed logic device, switching device and the like. In other words, various types of semiconductors may be used according to variables of the resonant tunneling structure, that is, a change in position, a change in the quantum well quantum level according to the selection of heterojunction materials, a multi level in the number of quantum well levels, and a change in the number of quantum wells. The device can be tailored (Tailoring) can be applied as a high-speed logic functional device that can reduce the number of logic devices.

In addition, the present invention by reducing the capacitance at room temperature (resonant tunneling) by forming an asymmetrical width of the quantum barrier layer and the width of the quantum well layer constituting the emitter barrier layer of each emitter sub-mesa, respectively, resonant tunneling (resonant tunneling) high pick current due to enhancement effect, PVR increase of current due to increase of effective energy barrier, low operating voltage characteristics of the device to achieve ultra-low power consumption, high power, broadband oscillator, etc. It can be applied to improved high speed switching device and logic device.

Claims (7)

In quantum resonant tunneling device, Board; A first conductive layer formed on the substrate; Emitter sub-measuring a plurality of emitter sub-mesa consisting of an emitter barrier layer and an emitter cap layer stacked on the first conductive layer in a matrix Mesa arrays; An insulating film surrounding each emitter sub-mesa forming the emitter sub-mesa array; A first electrode formed on the first conductive layer; And An emitter electrode formed on the emitter cap layer Quantum resonant tunneling device comprising a. The method of claim 1, A second conductive layer formed between the substrate and the first conductive layer; And And a second electrode formed on the second conductive layer. The method of claim 2, And between the second conductive layer and the first conductive layer, a collector potential barrier layer and a potential change absorbing layer. The method according to claim 1 or 2, The emitter barrier layer, n pieces alternately stacked on the collector ( And a quantum barrier layer of n) and n-1 quantum well layers to form a heterojunction structure. The method of claim 4, wherein An undoped first spacer layer formed between the first conductive layer and the emitter barrier layer; And And a undoped second spacer layer formed between the emitter barrier layer and the emitter cap layer. The method of claim 4, wherein The quantum barrier layer is at least three layers, And a width of the quantum barrier layer increases in a direction from the substrate toward the emitter electrode, and then decreases in sequence. The method of claim 6, The quantum well layer is composed of at least two, A quantum well tunneling device, characterized in that the width of the quantum well layer increases in sequence or decreases in sequence.