RU111352U1 - SEMICONDUCTOR METAMORPHIC NANOGETEROSTRUCTURE InAlAs / InGaAs - Google Patents

Abstract

 Semiconductor metamorphic InAlAs / InGaAs nanoheterostructure, including a single-crystal semi-insulating GaAs substrate, InxAl1-xAs metamorphic buffer with a linear increase in InAs x content in thickness (x = x1 → x4, where x1 ~ 0), Inverse InxAl1-xAs layer with decrease thickness (x = x4 → x4 ', where x4'-x4 = 0.05 ÷ 0.10), a healing layer with a homogeneous composition Inx4'Al1-x4'As and an active InAlAs / InGaAs region with a high InAs content, matched by the parameter gratings with a healing layer, characterized in that on a single-crystal semi-insulating GaAs substrate, it is metamorphic below An Al0.4Ga0.6As / GaAs superlattice is formed about the 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) Al1- (x2 + Δx) superlattices are introduced into the metamorphic buffer As / In (x2-Δx) Ga1- (x2-Δx) As and! In (x3 + Δx) Al1- (x3 + Δx) As / In (x3-Δx) Ga1- (x3-Δx) As, symmetrically mismatched by Δx = 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 x1 to x2, from x2 to x3, and from x3 to x4, where 0.4 <x2 <0.6, and 0.6 <x3 <0.75, and the InAs x content in the active region is more than 70% (x4'≥0.7, x4≥0.75).

Description

Technical field

The proposed utility model 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 high InAs content in the active region, grown on InP substrates, they can produce the fastest microwave transistors [1] ([1] lain Thayne, Khaled Elgaid, David Moran, Xin Cao, Euan Boyd, Helen McLelland, Martin Holland, Stephen Thoms, Colin Stanley. "50 nm metamorphic GaAs and InP HEMTs." Thin Solid Films 515, 4373-4377 (2007).). 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 PHEMT 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 fabricated 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 chemical composition gradually varying in thickness (namely: the content of InAs x in the ternary solid solution In _x Al _1-x As increases as MMB grows), and, consequently, by 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 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 [2] ([2] S. Mendach, CM Hu, Ch. Heyn, S. Schnull, HP Oepen, R. Anton, W. Hansen. "Strain relaxation in high-mobility InAs inserted-channel heterostructures with metamorphic buffer" Physica E 13, 1204-1207 (2002).) 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 dislocation and other defects from entering the active region of the nanoheterostructure, which leads to a deterioration in such electrophysical parameters as mobility and carrier concentration. And 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 is the structure described in [3] ([3] S. Bollaert, Y. Cordier, M. Zaknoune, H. Happy, V. Hoel, S. Lepilliet, D. Teron, A.Cappy. "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 .) (Fig. 1), including a GaAs single crystal semi-insulating substrate (1), on which an In _x Al _1-x As metamorphic buffer (2) is formed with a linear increase in the InAs x content in thickness (x = x ₁ → x ₄ , where x ₁ = 0, and x ₄ = 0.60), the inverse layer In _x Al _1-x As (3) with an abrupt decrease in the InAs x content in thickness (x = x ₄ → x ₄ ', where x ₄ = 0.60, x ₄ '= 0.50), a healing layer with a homogeneous composition In _x4 ' Al _{1-x4 '} As (4) and an active InALAs / hiGaAs region with a high InAs content (50%) (5), matched by the lattice parameter with a 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.

Utility Model Disclosure

The problem solved by this useful model 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 a nanoheterostructure.

The 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, and a metamorphic In _x Al _1-x As buffer (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), an inverse layer In _x Al _1-x As (4) with a smooth or stepwise decrease in the InAs x content by thickness (x = x ₄ → x ₄ ', where x ₄ ' -x ₄ = 0.05 ÷ 0.1), the healing layer with a homogeneous composition In _{x4 '} Al _1-x4' As (5), the active region InAlAs / InGaAs (6 ) with a high InAs content (over 70%), matched by the lattice parameter with the healing layer, two mechanically strained superlattices In _{(x2 + Δx)} + Al _{1- (x2 + Δx)} + As / In _(x2-Δx) Ga _{1- (x2-Δx} are introduced into the metamorphic buffer (3) ₎ 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 in the data points that 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 claimed utility model. 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 claimed utility model.

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

Utility Model Implementation

The device according to the claimed utility model 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 → 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 at Δх = 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 ₃ → 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 the dislocations growing into the active region and also hinder the 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 of 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 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 claimed utility model, we obtained the following sample of the semiconductor metamorphic InAlAs / InGaAs nanoheterostructure (Fig. 3).

The single-crystal semi-insulating substrate (1) is made of GaAs with a crystallographic orientation of (100). 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 InAl _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 terminates in 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 / (V · s) and 35000 cm ² / (V · s), respectively.

Claims (1)

InAlAs / InGaAs semiconductor metamorphic nanoheterostructure, including a single-crystal semi-insulating GaAs substrate, In _x Al _1-x As metamorphic buffer with a 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 decreasing thickness of InAs x (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 GaAs substrate the same metamorphic buffer forms an Al _0.4 Ga _0.6 As / GaAs superlattice; 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 superlattices are introduced into the metamorphic buffer _{- (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, symmetrically mismatched by Δx = 0.05 ÷ 0.10 relative to the current composition of the metamorphic buffer in data points that 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, and the InAs x content in the active region is more than 70% (x _{4 '} ≥0.7, x ₄ ≥0.75).