RU2474923C1 - SEMICONDUCTOR METAMORPHIC NANOHETEROSTRUCTURE InAlAs/InGaAs - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in a semiconductor metamorphic nanoheterostructure, comprising a single-crystal semi-insulating substrate GaAs, a superlattice Al_0.4Ga_0.6As/GaAs, a metamorphic buffer In_xAl_1-xAs with linear increase of InAs content x in thickness (x=x₁→x₄, where x₁~0, x₄≥0.75), an inverse layer In_xAl_1-xAs with smooth or uneven reduction of InAs content x in thickness (x=x₄→x_4', where x₄ ^,-x₄=^:0.05÷0.1, x_4'≥0.7), a curing layer with homogeneous composition In_xAl_1-xAs, an active area InAl As/InGaAs with high InAs content, agreed along the lattice perimeter with the curing layer, inside the metamorphic buffer there are two mechanically stressed superlattices In_(x2+Δx)Al_1-(x2-Δx)As/In_(x2-Δx)Ga_1-(x2-Δx)As and In_(x3+Δx)Al_1-(x3+Δx)As/In_(x3-Δx)Ga_1-(x3-Δx)As introduced, symmetrically mismatched at Δx=0.05÷0.10 relative to the current composition of the metamorphic buffer in these points, which divide the metamorphic buffer into three parts, in every of which the content of InAs x in thickness increases accordingly from x₁ to x₂, from x₂ to x₃ and from x₃ to x₄, where 0.4<x₂<0.6, and 0.6<x₃<0.75.

EFFECT: reduced density of dislocations penetrating an active area of a nanoheterostructure.

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Description

Technical field

The present invention relates to semiconductor MNEMT (metamorphic high electron mobility transistor) nanoheterostructures used for the manufacture of microwave transistors and monolithic integrated circuits with a high operating frequency and high breakdown voltages.

State of the art

Currently, PHEMT (pseudomorphic high electron mobility transistor) nanoheterostructures of the type In _0.52 Al _0.48 As / In _0.53 Ga _0.47 As, i.e. with a high InAs content in the active region grown on InP substrates, it is possible to fabricate the fastest microwave transistors [1]. This is possible due to a decrease in the effective mass of electrons with an increase in the InAs content in the active region of MNEMT or RNEMT structures, which entails a corresponding increase in the mobility and drift velocity of electron saturation.

But due to the high cost of InP substrates and their lower manufacturability, caused mainly by their fragility, as well as low breakdown voltage in microwave transistors made on InP structures, the search and development of new nanoheterostructures with a high InAs content in the active region grown on GaAs substrates is an urgent task.

The most successful and acceptable method was the use of the so-called metamorphic buffer (IMB) In _x Al _1-x As. Nanoheterostructures grown using this method are called MNEMT (metamorphioc high electron mobility transistor). The essence of the method is to grow between the substrate and the active region a relatively thick (usually 1 ÷ 2 μm) transition layer (metamorphic buffer) with a gradually varying chemical composition (namely: the InAs content in the In _x Al _1-x As ternary solid solution increases as the IMB grows), and, consequently, the lattice parameter. Thus, the IMB agrees the lattice parameter of the substrate with the lattice parameter of the active region. Metamorphic technology allows you to get a “virtual” substrate with the required lattice parameter, directly on which active layers of the required composition are already grown.

The growth of an ideal IMB should be accompanied by a gradual relaxation of mechanical stresses that inevitably arise due to the mismatch of the lattice parameters of the underlying and overlying layers. However, as practice has shown, it is usually not possible to completely get rid of mechanical stresses and dislocations. Therefore, a number of methods are proposed for reducing the defectiveness of MMB.

In article [2], a nanoheterostructure adopted as an analogue is described, where the active region is grown on a metamorphic buffer with a stepwise change in the molar fraction of InAs (10% for every 100 nm). MMB itself grows on a single-crystal semi-insulating GaAs substrate. In this case, as in most NEMT and RNEMT nanoheterostructures, a short-period AlAs / GaAs (or Al _x Ga _1-x As / GaAs) superlattice is formed directly on the substrate before the MMB growth, which plays a double role. First, as can be seen from [2], it improves the electrophysical parameters of the heterostructure, and secondly, it prevents the segregation of unintentional background impurities from the substrate into the active regions of the nanoheterostructure during its epitaxial growth.

A significant drawback of this device is that it is not possible to prevent the dislocations and other defects from entering the active region of the nanoheterostructure, which leads to a deterioration of such electrophysical parameters as mobility and carrier concentration. This, in turn, limits the working frequency band, breakdown voltage, and other characteristics of microwave transistors and large integrated circuits created on this nanoheterostructure.

Closest to the proposed structure and adopted as a prototype of the present invention is the structure described in [3] (Fig. 1), including a single-crystal semi-insulating GaAs substrate (1), on which a metamorphic buffer (2) In _x Al _1-x As is formed with a linear increase in the InAs x content over the thickness (x = x ₁ → x ₄ , where x ₁ = 0 and x ₄ = 0.60), an Inverse Al _x Al _1-x As layer (3) with an abrupt decrease in the InAs x content over the thickness (x = x ₄ → x ₄ ', where x ₄ = 0.60, x ₄ ' = 0.50), the healing layer with a homogeneous composition In _{x4 '} Al _1-x4' As (4) and the active region InAlAs / InGaAs with a high content m InAs (50%) (5), matched by the lattice parameter with the healing layer.

The active region is an InGaAs quantum well bounded by InAlAs barriers, in which a two-dimensional electron gas is formed. In one of the barriers is a delta layer of Si atoms, which are donors. A significant drawback of this structure is that the accumulated stresses and the resulting dislocations emerge on the surface of the metamorphic buffer, on which the active region of the nanoheterostructure is formed, which is responsible for the microwave characteristics and microwave parameters of devices fabricated on this nanoheterostructure. This entails a relatively low electron mobility in the channel, which as a result limits the working frequency band of the microwave transistor created on this structure.

Disclosure of invention

The objective of the present invention is to increase the operating frequency of microwave transistors made on the basis of nanoheterostructures with a high InAs content in the active region grown on GaAs substrates. The technical result that allows us to complete the task is to reduce the density of dislocations that have penetrated into the active region of the nanoheterostructure.

According to the invention, this technical result is achieved due to the fact that in a semiconductor metamorphic nanoheterostructure (Fig. 2), which includes a single-crystal semi-insulating GaAs substrate (1), an Al _0.4 Ga _0.6 As / GaAs superlattice (2), and an In _x Al _1-x metamorphic buffer As (3) with a linear increase in the InAs x content over the thickness (x = x ₁ → x ₄ , where x ₁ ~ 0, x ₄ ≥0.75), the inverse layer In _x Al _1-x As (4) with a smooth or spasmodic decrease thickness of InAs x (x = x ₄ → x ₄ ', where x ₄ ' -x ₄ = 0.05 ÷ 0.1, x _{4 '} ≥0.7), a healing layer with a homogeneous composition In _x4' Al _{1-x4 '} As (5 ), the active region of InAlAs / InGaA s (6) with a high InAs content (more than 70%), matched by the lattice parameter with the healing layer, two mechanically stressed superlattices In _{(x2 + Δx)} Al _{1- (x2 + Δx)} As / In are introduced into the metamorphic buffer (3) _(x2-Δx) Ga _{1- (x2-Δx)} As and In _{(x3 + Δx)} Al _{1- (x3 + Δx)} As / In _(x3-Δx) Ga _{1- (x3-Δx)} As, symmetrically mismatched on Δх = 0.05 ÷ 0.10 relative to the current composition of the metamorphic buffer at these points, which divide the metamorphic buffer into three parts, in each of which the InAs x content in thickness increases, respectively, from x ₁ to x ₂ , from x ₂ to x ₃ and from x ₃ to x ₄ , where 0.4 <x ₂ <0.6, and 0.6 <x ₃ <0.75.

Brief Description of the Drawings

Figure 1 presents a diagram of a semiconductor metamorphic nanoheterostructure in cross section (side view), selected as a prototype of the present invention. The following successive layers and their composition are indicated.

Figure 2 presents a diagram of a semiconductor metamorphic nanoheterostructure in cross section (side view), demonstrating the essence of the present invention.

Figure 3 presents a diagram of a semiconductor metamorphic nanoheterostructure in cross section (side view) grown according to the present invention.

The implementation of the invention

The device according to the present invention operates as follows.

As shown in Fig. 2, an Al _0.4 Ga _0.6 As / GaAs (2) superlattice is formed directly on a single-crystal semi-insulating GaAs substrate (1), which prevents the segregation of unintentional background impurities from the substrate into the active regions of the nanoheterostructure during its epitaxial growth. Above, a metamorphic buffer (3) is formed with a linear increase in the InAs x content over the thickness (x = x ₁ → x ₄ , where x ₁ ~ 0, and x ₄ ≥0.75). A linear change in x from 0 to 0.75 changes the lattice parameter and matches it with the lattice parameter of the active region. Two mechanically strained superlattices In _{(x2 + Δx)} Al _{1- (x2 + Δx)} As / In _(x2-Δx) Ga _{1- (x2-Δx)} As (8) and In _{(x3 + Δx )} Al _{1- (x3 + Δx)} As / In _(x3-Δx) Ga _{1- (x3-Δx)} As (10), symmetrically mismatched by Δx = 0.05 ÷ 0.10 relative to the current composition of the metamorphic buffer at these points. In this case, the metamorphic buffer is divided into three parts (7, 9, 11), each of which is an In _x Al _1-x As layer with an InAs x content linearly increasing in thickness, where x = x ₁ → x ₂ (7) , x = x ₂ → x ₃ (9), x = x ₁ → x ₄ (11). The superlattices introduced into the IMB differ both in composition and purpose from the Al _0.4 Ga _0.6 As / GaAs superlattice located directly on the substrate. The layers of these superlattices are symmetrically mismatched with respect to the IMB composition at a given thickness, which leads to the formation of short-period fields of elastic deformation and the absence of a longer-range field of elastic deformation. Short-period deformation fields lead to bending of dislocations growing into the active region, and also prevent phase separation of the ternary In _x Al _1-x As solid solution at large x values.

In each superlattice, InGaAs layers have a reduced InAs content relative to the current composition of the metamorphic buffer, and InAlAs layers have a high InAs content. This is done in order not to create additional quantum wells for electrons in the superlattices and not to obtain parallel conductivity along the superlattices.

An inverse layer (4) is formed above MMB (3), in which the InAs x content smoothly changes from x ₄ to x ₄ ', and the difference in InAs content is 0.05–0.10. Inverse layer (4) allows you to eliminate the mechanical stresses remaining in the IMB (3), and to obtain an unstressed "virtual" substrate for the subsequent growth of the healing layer (5) and the active region (6).

The inverse layer (4) is followed by a healing layer with a homogeneous composition In _{x4 '} Al _1-x4' As (5), above which there is an active region (6), matched by the lattice parameter with the healing layer. The content of InAs in the layers of the active region is more than 70%.

All the described layers, with the exception of the δ-layer of silicon, are undoped.

The introduction into the metamorphic buffer of symmetrically mismatched superlattices allows us to achieve a technical result - to reduce the density of germinating dislocations.

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 introducing stressed superlattices inside the IMB to suppress dislocations and phase separation.

The creation of nanoheterostructures in accordance with the declared features and design of the IMB provides the possibility of growing structures with a high InAs content in the active region and with high mobility values.

According to the present invention, we obtained the following sample of a semiconductor metamorphic nanoheterostructure InAlAs / InGaAs (Fig. 3).

The single-crystal semi-insulating substrate (1) is made of GaAs with a crystallographic orientation (10 0). It contains a five-period Al _0.4 Ga _0.6 As / GaAs superlattice (2), Al _0.4 Ga _0.6 As and GaAs layer thicknesses are 24 Å and 14 Å, respectively. The metamorphic In _x Al _1-x As buffer (3) was formed above, the value of x changes from 0.06 at the beginning of the metamorphic buffer to 0.75 at its end, and the thickness of the metamorphic buffer in this example is 1.2 μm. Two mechanically stressed superlattices In _0.39 Ga _0.61 As / In _0.53 Al _0.47 As (8) and In _0.62 Ga _0.38 As / In are inserted inside the metamorphic buffer at 0.54 and 0.90 of its thickness for the current compositions of In _0.49 Al _0.51 As and In _0.73 Al _0.27 As _0.77 Al _0.23 As (10), each with 5 periods, in the first superlattice, the InGaAs and InAlAs layers were 32 Å and 36 Å thick, and in the second, 34 Å and 56 Å thick, respectively. In this case, the metamorphic buffer is divided into three parts (7, 9, 11), each of which is an In _x Al _1-x As layer with an InAs x content linearly increasing in thickness. Behind the metamorphic buffer (3) is the inverse layer (4) In _x Al _1-x As, the value of x varies from 0.75 at the beginning of the inverse layer to 0.70 at its end at a thickness of 40 nm. The inverse layer is followed by a healing layer of In _0.70 Al _0.30 As (5) 0.16 μm thick. The semiconductor nanoheterostructure is completed by the active region (6), which consists of an In _0.76 Ga _0.24 As channel 164 Å thick, an In _0.70 Al _0.30 As spacer 64 Å thick, a δ-layer silicon with a concentration of 1.7 · 10 ¹² cm ^-2 , an In _0.70 Al _0.30 barrier As 219 Å thick and the In _0.76 Ga _0.24 As protective layer 73 Å thick. All semiconductor layers are grown by molecular beam epitaxy.

The electron mobility values of 12000 cm ² / (V · s) at room temperature and 41000 cm ² / (V · s) at T = 77 K were obtained; the relative error is 10%. These values are higher than the best demonstrated in the article [3]: 9570 cm ² / (B · c) and 35000 cm ² / (B · c), respectively.

Information sources

1. Iain Thayne, Khaled Elgaid, David Moran, Xin Cao, Euan Boyd, Helen McLelland, Martin Holland, Stephen Thorns, Colin Stanley. "50 nm metamorphic GaAs and InP HEMTs." Thin Solid Films 515, 4373-4377 (2007).

2. S. Mendach, C. M. Hu, Ch. Heyn, S. Schnull, H. P. Oepen, R. Anton, W. Hansen. "Strain relaxation in high-mobility InAs inserted-channel heterostructures with metamorphic buffer." Physica E 13, 1204-1207 (2002).

3. S. Bollaert, Y. Cordier, M. Zaknoune, H. Happy, V. Hoel, S. Lepilliet, D. Teron, A. Happy. "The indium content in metamorphic In _x Al _1-x As / In _x Ga _1-x As HEMT on GaAs substrate: a new structure parameter." Solid-State Electronics 44 (2000), p.1021-1027.

Claims (1)

InAlAs / InGaAs semiconductor metamorphic nanoheterostructure including a single-crystal semi-insulating GaAs substrate, In _x Al _1-x As metamorphic buffer with linear increase in InAs x content in thickness (x = x ₁ → x ₄ , where x ₁ ~ 0), In _x inverse layer Al _1-x As with a decrease in the InAs x content in thickness (x = x ₄ → x ₄ ', where x ₄ ' -x ₄ = 0.05 ÷ 0.10), a healing layer with a homogeneous composition In _{x4 '} -Al _{1 -x4 '} As and the active region InAlAs / InGaAs with a high InAs content, matched by the lattice parameter with a healing layer, characterized in that on a single-crystal semi-insulating substrate G aAs, an Al _0.4 Ga _0.6 As / GaAs superlattice is formed below the metamorphic buffer, a decrease in the InAs x content over the thickness in the inverse layer can be either spasmodic or smooth, two mechanically strained In _{(x2 + Δx)} Al _{1- (x2} superlattices are introduced into the metamorphic buffer _{+ Δx)} As / In _(x2-Δx) Ga _{1- (x2-Δx)} As and In _{(x3 + Δx)} Al _{1- (x3 + Δx)} As / In _(x3-Δx) Ga _{1- (x3-Δx )} As symmetrically mismatched at Δх = 0.05 ÷ 0.10 relative to the current composition of the metamorphic buffer at these points, which divide the metamorphic buffer into three parts, in each of which the InAs x content increases in thickness, respectively from x ₁ to x ₂ , from x ₂ to x ₃ and from x ₃ to x ₄ , where 0.4 <x ₂ <0.6, and 0.6 <x ₃ <0.75, and the content of InAs x in active region more than 70% (x _{4 '} ≥0.7, x ₄ ≥0.75).

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