RU113072U1 - SEMICONDUCTOR NANOGETEROSTRUCTURE WITH STAGED QUANTUM ALGaAs / GaAs / InGaAs / GaAs / AlGaAs QUANTUM ON A GaAs SUBSTRATE WITH COMBINED ALLOYING - Google Patents

Abstract

Semiconductor nanoheterostructure including a single-crystal semi-insulating GaAs substrate (1), a GaAs buffer layer (2), an AlxGa1-xAs layer (3), a stepped quantum well (4), an AlxGa1-xAs barrier layer (8), and a GaAs contact layer (9 ), characterized in that the stepped quantum well (4) consists of several layers: the upper transition GaAs layer (16, 20), which contains two Si δ-layers (17, 19) separated by a GaAs layer (18) 0.5 -3 nm, a volume-doped InyGa1-yAs layer (15) and a lower transition GaAs layer (10, 14), in which there are two Si δ-layers (11, 13) separated by a GaAs layer (12) 0.5-3 nm, while the ratio of donor concentrations in the delta-doped layers and in the bulk of the InyGa1-yAs layer is from 0.3 to 3.

Description

The proposed utility model relates to semiconductor nanoheterostructures used for the manufacture of microwave transistors and monolithic integrated circuits of C- and X-bands with high output power.

At present, Russia is facing an unfavorable situation in the development of high-power microwave transistors and monolithic integrated circuits of C- and X-bands, which are inferior to foreign analogues in all characteristics (output power, efficiency, etc.), which makes it impossible to create high-performance domestic radars, satellite television, multi-channel wireless communication systems. One of the problems of creating domestic devices of this type is the use of obsolete materials with body-alloyed gallium arsenide. In the search for new basic materials for solid-state microwave electronics, the fastest and most cost-effective way is to maximize the capabilities of materials and technologies developed abroad with well-developed processing. Such an established technology is now RNEMT (pseudomorphic high electron mobility transistor) heterostructure technology.

To create high-power high-frequency devices, RNEMT heterostructures with a quantum well (QW) In _y Ga _1-y As as an active layer are widely used [1]. An increase in the transistor power requires a simultaneous increase in the maximum drain current and maintaining a high breakdown voltage of the transistor. The drain current is provided by high values of the concentration and drift velocity of electron saturation. A significant increase in the concentration of two-dimensional electron gas can be obtained in RNEMT heterostructures with AlGaAs / InGaAs / AlGaAs QWs using double-sided delta doping with silicon through spacer layers. A typical concentration range in such structures is n _s = (2 ÷ 4) · 10 ¹² cm ^-2 . However, an excessive increase in doping leads to parallel conductivity along the donor layers and, as a result, a significant decrease in electron mobility. To reduce the negative effect of the parallel conduction channel, it is necessary to increase the band gap in the Al _x Ga _1-x As barrier. However, when the AlAs content is higher than 0.25, part of the Si donor impurity forms DX centers — electron traps, which negatively affects the operation of the device; therefore, this method is not always applicable.

The design of heterostructure layers for high-power transistors affects several aspects. Firstly, a sufficiently large voltage amplitude is applied to the gate of powerful transistors, and to reduce the gate-channel leakage current, a high energy barrier in the wide-gap gate layer is required. Secondly, in high-power transistors, it is necessary to provide a large breakdown voltage between the source and drain, especially when closing the channel. For this purpose, try to avoid areas with reduced potential, with the exception of the channel area. The use of delta-doping technology is automatically associated with the creation of a V-shaped potential well formed by ionized silicon donors. In this case, through the donor states in the barrier, a tunnel surge of the gate leakage current occurs, including at a positive bias applied to the gate. In addition, in the case of a doped barrier, the built-in field between the surface of the heterostructure and the QW increases, which leads to an increase in the tunnel transparency of the barrier layer and, as a consequence, to a decrease in the breakdown voltage.

The increase in the drain-source breakdown voltage largely depends on the layout of the transistor topology, the location of the gate relative to the drain, the thought-out recess of the upper layers of the heterostructure, and the use of an overhanging gate. A slight increase in breakdown voltage was observed in the so-called inverted heterostructures, where the donor layer was located below the channel. However, from the point of view of the fundamental properties associated with the design of the heterostructure, it is important to minimize the effect of impact ionization, for which it is necessary to increase the energy of the forbidden band in the most narrow-gap region of the heterostructure — the channel. So, in the InGaAs layer, the InAs content is usually reduced to 10-15% in comparison with PHEMT heterostructures. In this case, to preserve the QW capacity, it is necessary to increase the height of the barrier layer. It is also necessary to increase the purity and structural perfection of the AlGaAs barrier.

One of the promising directions for creating high-power microwave transistors is the use of structures like DC HFET (Doped Channel Heterostructure Field Effect Transistor) with volume doped QWs [2, 3]. The uniformly doped channel of the DC HFET transistor allows you to create a high electron concentration and, as a result, a larger drain current and a higher output power. This type of transistor has a high linearity (I – V characteristic, drain-gate characteristic), since there are no spurious conductivities in the AlGaAs layer compared to the RNEMT structure on the same QW. DC HFET structures are a good compromise between P-HEMT and PTSh technology when creating transistors with large channel conductivity (and of course output power) and high breakdown voltage. However, there are a number of disadvantages associated with the use of DC HFET. First, in these structures, the electron mobility is significantly reduced compared to the RHEMT structures due to the strong Coulomb interaction, since ionized donors are in the same spatial region as the electrons of the 2D gas. Thus, in this type of structure strong electron scattering is manifested, and hence a reduced efficiency due to ohmic heating of the channel. Another negative effect is an increase in the probability of interband electron scattering between the first and second size quantization subbands for wide QWs (above 15 nm). In addition, with an increase in the QW width, the probability of impact ionization increases due to the size quantization effect, which reduces the breakdown voltage of the transistor.

Thus, a promising direction in the development of heterostructures for high-power microwave transistors is the search for new designs of heterostructures with well-designed QW structure, doping principles, and upper layer construction above the QW.

Closest to the proposed structure and adopted as a prototype of the present invention is the structure described in [4] (FIG. 1) having a single-crystal semi-insulating GaAs substrate (1) on which a GaAs buffer layer (2), an Al _x Ga ₁ layer are formed _-x As (3), quantum well (4), consisting of layers - In _y Ga _1-y As (5), delta-silicon layer (δ-Si) (6), In _y Ga _1-y As (7 ), the Al _x Ga _1-x As (8) barrier layer and the GaAs contact layer (9). A significant drawback of this structure is the maximally heterogeneous arrangement of the impurity in a sufficiently wide QW, which leads to the appearance of an additional bend in the bottom of the well and reduces the benefit from the asymmetric distribution of donors. Such a QW is more sensitive to changes in the bottom profile during its depletion, which leads to a bipolar dependence of the slope on the drain current. Moreover, in such a structure it is impossible to obtain an electron concentration in the QW of more than 5 · 10 ¹² cm ^-2 due to the self-compensation effect and amphoteric behavior of donor silicon atoms at a high doping concentration.

The technical result to which the claimed utility model is directed is to increase the concentration of two-dimensional electron gas, as well as to minimize unwanted electron scattering by donors due to the combined doping of the step quantum well AlGaAs / GaAs / InGaAs / GaAs / AlGaAs.

Said technical result is achieved in that the semiconductor nanogeterostruktur comprising a monocrystalline semi-insulating substrate is GaAs (1), a buffer layer of GaAs (2), a layer of Al _x Ga _1-x As (3), the barrier layer is Al _x Ga _1-x As (8), GaAs contact layer (9), step quantum well (4) consists of the upper GaAs transition layer (16, 20), in which there are two δ (Si, 17, 19) Si layers separated by a 0.5 GaAs layer (18) -3 nm, of a body-doped In _y Ga _1-y As layer (15) and a lower GaAs transition layer (10, 14), in which there are two δ (Si, 11, 13) Si layers separated by a GaAs layer (12) thick 0.5 0.5-3 nm, while the ratio of donor concentrations in the delta-doped layers and in the bulk of the In _y Ga _1-y As layer is from 0.3 to 3.

The utility model is illustrated by the following drawings:

Figure 1 presents a diagram of a semiconductor nanoheterostructure selected as a prototype of this utility model. The following successive layers are indicated.

Figure 2 presents a diagram of a semiconductor nanoheterostructure, demonstrating the essence of this utility model.

The semiconductor nanoheterostructure (Fig. 2) includes a single-crystal semi-insulating GaAs substrate (1) on which a GaAs buffer layer (2), an Al _x Ga _1-x As layer (3), a step quantum well (4), and an Al _x Ga barrier layer are formed _1-x As (8) and GaAs contact layer (9). In the proposed nanoheterostructure, combined doping with silicon is used: in the upper transition layer (PS 2) (16, 20) there are two δ-layers of Si (17, 19) separated by a GaAs (18) layer 0.5-3 nm thick, in the lower PS 1 (10 14) there are two δ-layers of Si (11, 13) separated by a GaAs (12) layer 0.5–3 nm thick; bulk doping is used in the central region of the In _y Ga _1-y As (15) QW. The ratio of the concentrations of delta doping to volume doping is from 0.3 to 3. The stepwise QW thickness is 18 nm. The molar fractions of the components in the ternary compounds Al _x Ga _1-x As and In _y Ga _1-y As are x = 0.38 and y = 0.15. All layers were grown by molecular beam epitaxy.

Thus, the proposed nanoheterostructure with a combined doped channel combines the principles of DC HFET with uniformly doped QW and RNEMT with two-sided delta doping. Placement of donors not in one but in two delta layers in each PS is associated with a decrease in the risk of amphoteric behavior of silicon with a high degree of doping. GaAs substations perform several functions. First, they prevent the formation of DX centers due to diffusion of impurity atoms into the wide-gap AlGaAs barrier (8). Secondly, they form an intermediate barrier in the QW, increasing the electron energy in the region of the delta layer. When using combined doping in the proposed nanoheterostructure, there are no regions with a reduced potential, with the exception of the QW region, which increases the breakdown voltage of the transistor made on the basis of this nanoheterostructure. The GaAs transition layers are well doped and have a large threshold electron concentration, which allows one to create a high electron concentration in the QW. Volume doping of the central region of the QW allows one to compensate for the bending of the bottom of the QW. In addition, in this case, the unwanted electron scattering by donors is minimized by reducing the spatial overlap of donors in the delta layers and the electron density in the structure.

The applicant has not identified any technical solutions identical to the claimed, which allows us to conclude that the invention meets the criterion of "novelty." In particular, the authors are not aware of the use of AlGaAs / GaAs / InGaAs / GaAs / AlGaAs step quantum wells with combined doping.

BIBLIOGRAPHY

[1] A.Yu Egorov., A.G. Gladyshev, E.V. Nikitina, D.V. Denisov, N.K. Polyakov, E.V. Pirogov, A.A. Gorbazevich. "Double pulse doped InGaAs / AlGaAs / GaAs pseudomorphic high-electron-mobility transistor heterostructures." Semiconductors. 44 (7), 2010, p. 919-923

[2] WC Liu, KH Yu, RC Liu, KW Lin, KP Lin, CH Yen, CC Cheng and KB Thei. "Investigation of temperature-dependent characteristics of an n ⁺ - InGaAs / n-GaAs composite doped channel HFET." IEEE Trans. Electron Devices, 48 (12), 2001, p. 2677-2682

[3] US005701020A "Pseudomorphic step-doped-channel field-effect transistor"

[4] M. Nawaz, J. M. Miranda, P. Sakalas, S. M. Wang, Q. X. Zhao, M. Willander and H. Zirath. "Design, processing and characterization of delta-doped channel AlGaAs / InGaAs / GaAs HFETs" Semicond. Sci. Technol, 15, 2000, p. 728-735.

Claims (1)

A semiconductor nanoheterostructure including a single-crystal semi-insulating GaAs substrate (1), a GaAs buffer layer (2), an Al _x Ga _1-x As layer (3), a step quantum well (4), and an Al _x Ga _1-x As ( 8) and a GaAs contact layer (9), characterized in that the stepwise quantum well (4) consists of several layers: the upper GaAs transition layer (16, 20), in which there are two δ-layers of Si (17, 19) separated by a layer GaAs (18) with a thickness of 0.5-3 nm, a body-doped In _y Ga _1-y As layer (15) and a lower GaAs transition layer (10, 14), in which there are two δ-layers of Si (11, 13) separated layer m GaAs (12) with a thickness of 0.5-3 nm, while the ratio of donor concentrations in the delta-doped layers and in the volume of the In _y Ga _1-y As layer is from 0.3 to 3.