JP2017135291A - Detection diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a HBD ensuring good detection characteristics, by performing zero bias operation in a THz frequency band, thereby suppressing deterioration of the I-V characteristics.SOLUTION: A detection diode includes a semiconductor multilayer structure where a high concentration n-type first semiconductor layer 11, a second semiconductor layer having a smaller electron affinity compared with the first semiconductor layer, and an n-type third semiconductor layer 13A are laminated in order, a heterobarrier is formed on the second semiconductor layer side of a boundary surface of the first semiconductor layer 11 and second semiconductor layer, the barrier height of the heterobarrier is adjusted by adjusting the doping level of the first semiconductor layer 11, an anode electrode 14 is formed on the first semiconductor layer 11, and a cathode electrode 15 is formed on the third semiconductor layer 13. The second semiconductor layer includes an undoped barrier layer 12A in contact with the first semiconductor layer 11, and an n-type barrier layer 12B in contact with the third semiconductor layer 13A.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a detection diode, and more particularly to a low-noise and high-speed semiconductor detection diode that receives an RF electrical signal in a THz frequency band (0.1 to 10 THz) and operates at zero bias.

Conventionally, nonlinear current-voltage characteristics (IV characteristics) of diodes are generally used as detection means in a radio system in the THz frequency band. Typically, Schottky Barrier Diode (SBD), Backward Diode, Planar Doped Barrier (PDB) Diode, etc. are used. For example, when detecting a weak signal in envelope detection using SBD, it is desirable to operate at zero bias in order to suppress the influence of power supply noise. To obtain good sensitivity, saturation current It is necessary to increase the value Is. When a receiver operating in the THz frequency band is configured, impedance matching is difficult to achieve because the impedance Z ₀ of the pure resistance antenna formed on the semiconductor substrate is as low as about 75Ω. At this time, in order to ensure the coupling efficiency, it is necessary to increase the saturation current value Is in order to bring the differential resistance value R _D of SBD closer to Z ₀ .

In order to increase the saturation current value Is, an SBD using InGaAsP lattice-matched to InP is known as a semiconductor material in which the barrier height φ _B decreases, that is, the saturation current density Jc (A / cm ² ) increases. Yes. However, when a high-frequency operation of several hundred GHz or more is performed, the necessary junction area is extremely small. Therefore, as long as an InGaAsP-based material lattice-matched to InP is used, a barrier can be obtained to a desired saturation current value Is. The height φ _B cannot be reduced. Accordingly, a hetero barrier diode (HBD) that can arbitrarily control the barrier height φ _B has been proposed (see, for example, Non-Patent Document 1).

FIG. 1 shows the structure of a conventional HBD. High concentration n ⁺ -InP cathode layer 3 (third semiconductor layer), undoped (= low concentration) InP barrier layer 2 (second semiconductor layer), high concentration n ⁺ -InGaAs anode layer 1 (first semiconductor layer) Of the semiconductor layer), the cathode layer 5 is formed on the cathode layer 3, and the anode electrode 4 is formed on the anode layer 1. The barrier layer 2 has a smaller electron affinity than the anode layer 1, and an energy barrier (heterobarrier) against electrons is formed on the barrier layer 2 side of the interface between them (InGaAs / InP interface). Since the barrier height φ _B is an amount measured from the Fermi level of the n ⁺ -InGaAs anode layer 1, it can be arbitrarily reduced to φ _B = 0 by adjusting the doping level of the anode layer 1.

Below, the relationship between each parameter and the differential resistance value R _D of the focus diode will be described. The non-linear IV characteristic of the HBD is obtained by using the saturation current value Is, the thermal voltage V _T , and the ideal coefficient n of the quasi-direction current.
I _D (V) = Is {exp [V × (nV _T ) ⁻¹ ] −exp [−V × (n−1) × (nV _T ) ⁻¹ ]} (1)
(For example, Non-Patent Document 2). Further, the saturation current value Is is defined by assuming that the junction area of the diode is S _j , the Richardson constant of the barrier material is A ^* , and the temperature is T (K).
Is (S _j , T) = S _j × A ^* × T ² × exp (−qφ _B / V _T ) (2)
Given in.

For example, if S _j = 1 μm ² , T = 300 K, A ^* = 9.2 A / cm ² / K, and qφ _B = 85 meV and n = 1.2, the differential resistance value R _D (= dV) of the diode is set. / DI) is calculated as 84Ω from the equation (1). This differential resistance value R _D is close to the impedance Z ₀ (75Ω) of the self-complementary antenna formed on the Si hemisphere lens. A sufficiently low differential resistance value R _D can be realized even with a small junction area necessary for operation in the THz frequency band, such as S _j = 1 μm ² . Therefore, this HBD can be applied as a low noise detection means that operates in the THz frequency band and operates at zero bias.

H. Ito and T. Ishibashi, “Fermi-level managed barrier diode for broadband and low-noise terahertz-wave detection,” Electronics Letters, Vol. 51, Issue 18, pp. 1440-1442, 2015. M. S. Tyagi et al., “Metal-Semiconductor Schottky Barrier Junctions and Their Applications,” edited by B. L. Sharma _Plenum, New York, 1984, Chap.1, p.19. S. M. Sze, “Physics of Semiconductor Devices,” John Wiley and Sons, 1981, Chap.5, p.250.

However, the HBD using a low concentration InP barrier layer has the following problems by reducing the barrier height qφ _B.

FIG. 2 shows an example of a conduction band edge profile of a conventional HBD. This is a result of calculating a conduction band edge profile (band profile) of an HBD having a heterostructure at the InGaAs / InP interface in consideration of the non-parabolicity of the band and the energy distribution of the electronic charge. In the structure of the HBD, the thickness of the undoped InP barrier layer 2 is 1000 A, and the carrier concentration of the n ⁺ -InP cathode layer 3 is 1 × 10 ¹⁸ / cm ³ . The electron energy is the conduction band edge E _C1 = 0 of the n ⁺ -InGaAs anode layer 1, and the position of the Fermi level (Ef) of the anode layer 1 is indicated by a broken line.

The conduction band edge (E _C2 ) of the barrier layer 2 when the Fermi level (Ef) is changed is shown, and the barrier height qφ _B is used as a parameter.
(A) Ef−E _C1 = 140 meV, qφ _B = 100 meV
(B) Ef−E _C1 = 114 meV, qφ _B = 126 meV
(C) Ef−E _C1 = 88 meV, qφ _B = 152 meV
Shows the case.

When the barrier height qφ _B is high (C), the InP barrier near the InGaAs / InP hetero interface has a triangular potential shape, but the Fermi level is raised to increase the barrier height qφ _B. It can be seen that the band shape in the vicinity of the hetero interface is flattened as the size is reduced (B) to (A). This bending of the band is due to the negative charge of electrons spread and distributed in the undoped InP barrier layer 2, and as the barrier height qφ _B decreases, all of the electrons whose energy is distributed above the Fermi level. Since the amount of charge increases, the influence of planarization is strong.

As described above, by adjusting the doping level of the first semiconductor layer, the position of the Fermi level can be raised and lowered to adjust the barrier height of the heterobarrier. However, as is clear from the calculation results, as the Fermi level Ef increases, the band shape tends to be convex upward and become flat. Since the optimum barrier height qφ _B is about 100 meV or less, the conventional HBD has a problem that the band shape in the vicinity of the heterointerface is flattened.

The first problem that the InP barrier near the InGaAs / InP heterointerface becomes flat is the deterioration of the ideal coefficient n value (= n value increase). The peak position xm of the “effective” potential for electrons is not at the heterointerface. This is because the image power works on electrons near the InGaAs / InP interface.
xm 電 界 electric field strength near the interface ^-1/2
And away from the interface to the InP side. Since the electric field strength decreases as the barrier height qφ _B decreases, xm increases and the n value of the HBD increases. As a result, the non-linearity of the IV characteristic of the HBD becomes weak, and the detection performance deteriorates.

Second, when the barrier shape near the InGaAs / InP hetero interface becomes flat, the diode current itself is modulated and lowered. This is because, as the electric field strength of the barrier decreases, the parameter governing the electron heat emission current in the vicinity of the interface shown in Equation (2) changes from the state controlled by heat emission to the state controlled by diffusion. This is because there is a tendency (for example, Non-Patent Document 3). When the electron transport mechanism tends to be diffusion-controlled, the effective I _S (S _j , T) decreases, the HBD current itself decreases, and the differential resistance value R _D increases and the detection current decreases. When the diode area is increased to reduce the differential resistance value R _D , the junction capacitance increases, and therefore the frequency characteristics deteriorate.

  An object of the present invention is to ensure good detection characteristics by suppressing deterioration of IV characteristics in an HBD that performs zero bias operation in the THz frequency band.

  In order to achieve the above object, according to one embodiment of the present invention, a high-concentration n-type first semiconductor layer and a second electron affinity smaller than that of the first semiconductor layer are provided. And the n-type third semiconductor layer 1 are sequentially stacked, and a heterobarrier is formed on the second semiconductor layer side of the interface between the first semiconductor layer and the second semiconductor layer, By adjusting the doping level of the first semiconductor layer, the barrier height of the heterobarrier is adjusted, an anode electrode is formed on the first semiconductor layer, and on the third semiconductor layer A semiconductor stacked structure in which a cathode electrode is formed, wherein the second semiconductor layer includes an undoped barrier layer in contact with the first semiconductor layer and an n-type barrier layer in contact with the third semiconductor layer. It is characterized by that.

  In order to solve the problem of “bending of the barrier layer band due to the negative charge of electrons” in the conventional typical HBD, the present invention provides means for realizing an appropriate barrier shape. That is, by providing a part of the second semiconductor layer, a region where n-type doping (introduction of donor) is performed on the cathode (third semiconductor layer) side, the band profile of the heterobarrier can be improved. It is possible to solve the problem of deterioration of the IV characteristics of the HBD that is operated with zero bias in the THz frequency band, and to ensure good detection characteristics.

It is a figure which shows the structure of the conventional HBD. It is a figure which shows an example of the profile of the conduction band edge of the conventional HBD. It is a figure which shows the structure of HBD concerning one Embodiment of this invention. It is a figure which shows the 1st example of the profile of the conduction band edge of HBD concerning one Embodiment of this invention. It is a figure which shows the 2nd example of the profile of the conduction band edge of HBD concerning one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows the structure of an HBD according to an embodiment of the present invention. High concentration n + -InGaAs sub-cathode layer 13B, high concentration n ⁺ -InP cathode layer 13A (third semiconductor layer), n-InP barrier layer 12B, undoped (= low concentration) InP barrier layer 12A (second concentration) Semiconductor layer), a high-concentration n ⁺ -InGaAs anode layer 11 (first semiconductor layer) are sequentially stacked, a cathode electrode 15 is formed on the sub-cathode layer 13B, and an anode electrode 14 is formed on the anode layer 11. Yes.

  In order to manufacture this HBD, the sub-cathode layer 13B to the anode layer 11 are sequentially epitaxially grown on the semi-insulating InP substrate by MO-VPE method or MBE method, and the substrate is subjected to mesa etching. Thereafter, the anode electrode 14 and the cathode electrode 15 are patterned to form ohmic contact. In the conventional HBT, the InP barrier layer is undoped (= low concentration). In the present embodiment, a part of the InP barrier layer, a region where n-type doping (introduction of donor) is performed on the cathode side. Is provided. The donor distribution in the n-type doping region may be uniform or may increase toward the cathode side.

In the present embodiment, as described above, in order to suppress the flattening of the band shape due to the “negative electron charge” in which energy is distributed above the Fermi level, the band bending due to the “positive donor charge” is suppressed. To compensate. More specifically, since the band profile (potential change) is uniquely determined by the balance between the energy-dependent electron charge distribution n (x) and the donor charge amount Nd (x), the n ⁺ -InP cathode of the InP barrier layer A band profile is adjusted by providing a doped n-InP barrier layer 12B on the layer 13A side. With such a design, the conduction band on the cathode side is lowered so that the band profile linearly descends on the cathode side, and the InP barrier near the InGaAs / InP heterointerface is triangular. Since the peak position xm of the potential with respect to the electrons approaches the n ⁺ -InGaAs anode layer as the electric field near the interface increases, deterioration of the n value can be suppressed.

  In this way, according to the present embodiment, by compensating for the “band bending due to electronic charges” in the conventional HBD and improving the problem of “flattening the band near the heterointerface”, a good I− The V characteristic can be ensured and the reception sensitivity in the THz frequency band can be improved.

FIG. 4 shows a first example of a conduction band edge profile of an HBD according to an embodiment of the present invention. The barrier height qφ _B measured from the Fermi level is set to qφ _B = 100 meV, and the doped n-InP barrier layer 12B is provided on the n ⁺ -InP cathode layer 13A side. For the n-InP barrier layer 12B, doping with a constant concentration (N _D ) similar to the carrier concentration in the barrier layer near the interface between the n ⁺ -InGaAs anode layer 11 and the InP barrier layer 12A is used. It is the calculation result of the band profile when arrange | positioning in the optimal position. The position of the n-InP barrier layer 12B is adjusted by the barrier height qφB and the width of the barrier layers (12A, 12B), but is arranged with a width of about 1/2 to 2/3 on the cathode side of the InP barrier layer. By doing so, a good band profile can be obtained. In the example of the structure of the HBD of this embodiment, the carrier concentration of the n ⁺ -InGaAs anode layer 11 is 5 × 10 ¹⁸ / cm ^3, and the width of 700 A and N _D = N is present on the cathode side of the n-InP barrier layer 12B. An n-type impurity is introduced at 1 × 10 ¹⁷ / cm ³ . Considering the barrier height qφ _B = 100 meV, the carrier concentration in the barrier layer near the interface can be estimated to be approximately 1/50 of the carrier concentration of the n ⁺ -InGaAs anode layer 11, which is the n-InP barrier layer. It is about the same as the doping concentration of 12B.

Compared with the profile (A) in FIG. 2 (qφ _B = 100 meV), which is a calculation result in the conventional example, in FIG. 4, the InP barrier portion near the InGaAs / InP heterointerface is restored to a triangular shape. I understand. Assuming that the electric field strength at the interface is 7.1 kV / cm and the mobility of InP is 4,000 cm ² / Vs, the effective diffusion rate can be estimated as v _D = 2.8 × 10 ⁷ cm / s. it can. On the other hand, the heat release rate is about v _th = 1 × 10 ⁷ cm / s and v _th <v _D , indicating that the electron transport mechanism of HBD is limited by heat release. Therefore, according to the present embodiment, by compensating for “band bending due to electronic charge” in the conventional HBD and improving the problem of “band flattening in the vicinity of the hetero interface”, good IV characteristics can be obtained. And the reception sensitivity in the THz frequency band can be improved.

FIG. 5 shows a second example of the conduction band edge profile of the HBD according to one embodiment of the present invention. It is a calculation result of the band profile when the doping of the n-InP barrier layer 12B is more appropriately adjusted and arranged. On the cathode side of the undoped InP barrier layer 12A, as an n-InP barrier layer 12B, a width 800A and N _D (x) = 4 × 10 ¹⁶ / cm ³ to 4 × 10 from the barrier layer 12A to the cathode layer 13A. ^An n-type impurity is introduced so that the concentration increases exponentially up to ¹⁷ / cm ³ .

  Compared with the band profile shown in FIG. 4, it can be seen that the InP barrier portion near the InGaAs / InP heterointerface has a better triangular shape. Since the energy distribution of electrons in the n-InP barrier layer 12B changes exponentially, a better band profile can be obtained than the barrier layer 12 having a constant concentration described above. In this way, according to the present embodiment, by compensating for the “band bending due to electronic charges” in the conventional HBD and improving the problem of “flattening the band near the heterointerface”, a good I− The V characteristic can be ensured and the reception sensitivity in the THz frequency band can be improved.

1,11 High concentration n ⁺ -InGaAs anode layer 2,12A Undoped (= low concentration) InP barrier layer 3,13A High concentration n ⁺ -InP cathode layer 4,14 Anode electrode 5,15 Cathode electrode 12B n- InP barrier layer 13B High concentration n ⁺ -InGaAs sub-cathode layer

Claims (5)

A high concentration n-type first semiconductor layer;
A second semiconductor layer having a smaller electron affinity compared to the first semiconductor layer;
The n-type third semiconductor layer 1 is sequentially stacked,
A hetero barrier is formed on the second semiconductor layer side of the interface between the first semiconductor layer and the second semiconductor layer, and the barrier of the hetero barrier is adjusted by adjusting the doping level of the first semiconductor layer. The height has been adjusted,
A semiconductor stacked structure in which an anode electrode is formed on the first semiconductor layer and a cathode electrode is formed on the third semiconductor layer;
The detection diode, wherein the second semiconductor layer includes an undoped barrier layer in contact with the first semiconductor layer and an n-type barrier layer in contact with the third semiconductor layer.   2. The detection diode according to claim 1, wherein the n-type barrier layer is doped with an n-type impurity having a constant concentration.   2. The n-type barrier layer is introduced so that an n-type impurity concentration increases exponentially from the undoped barrier layer toward the third semiconductor layer. The detection diode according to 1.   4. The detection diode according to claim 1, wherein the first semiconductor layer is made of InGaAs, and the second semiconductor layer is made of InP. 5. A high concentration n-type InGaAs anode layer;
An InP barrier layer having a lower electron affinity compared to the anode layer;
An n-type InP cathode layer is sequentially laminated,
A heterobarrier is formed on the barrier layer side of the interface between the anode layer and the barrier layer,
An anode electrode is formed on the anode layer, and a semiconductor laminated structure in which a cathode electrode is formed on the cathode layer,
The detection diode, wherein the barrier layer includes an undoped InP barrier layer in contact with the anode layer and an n-type InP barrier layer in contact with the cathode layer.