RU2474924C1 - Semiconductor nanoheterostructure inalas/ingaas with metac metamorphic buffer - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in a semiconductor metamorphic nanoheterostructure InAlAs/InGaAs, comprising a single-crystal semi-insulating substrate GaAs, a superlattice AlGaAs/GaAs, a buffer layer GaAs, a metamorphic buffer In_xAl_1-xAs with thickness of 1.0÷0.5 mcm with linear increase of InAs content x in thickness from x₁ to x₄, where X₁~0, x₄≥0.75, an inverse layer In_xAl_1-xAs with smooth reduction of InAs content x in thickness from x₄ to x_4', where x₄-x_4'=0.03÷0.08, a curing layer with a homogeneous composition In_x4'Al_1-x4'As, the active area InAlAs/InGaAs with high content of InAs (more than 70%), agreed along the lattice parameter with the curing layer, inside the metamorphic buffer at equal distances from each other and from the buffer borders there are two inverse layers introduced with smooth reduction of InAs content x in thickness by Δx=0.03÷0.06, every of which is followed by the curing layer having the composition matching the final composition of the inverse layer.

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

3 dwg

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

At present, on pseudomorphic HEMTs (pseudomorphic high electron mobility transistor, PHEMT) InAlAs / InGaAs nanoheterostructures with a high InAs content (from 50% to 70%, and in individual layers more than 70%) grown by molecular beam epitaxy on InP substrates, The fastest microwave transistors with record high values of f _T = 644 GHz and f _max = 681 GHz were obtained [1]. The increase in the speed of microwave transistors on such nanoheterostructures is due to a decrease in the effective electron mass with an increase in the InAs content in the active region of the PHEMT structures and a corresponding increase in the mobility μ _e and the drift velocity of electron saturation. But the relatively high cost of InP substrates compared with GaAs and their lower manufacturability, mainly due to brittleness, led to the search for alternative methods for producing nanoheterostructures with a high (more than 70%) InAs content in the active region based on the use of GaAs substrates.

The most successful and acceptable method was the use of the so-called metamorphic buffer In _x Al _1-x As. Nanoheterostructures grown using this method are called MNEMT (metamorphic high electron mobility transistor) structures. 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 content of InAs x in the ternary solid solution In _x Al _1-x As increases as the metamorphic buffer grows), and, consequently, by the lattice parameter. Thus, the metamorphic buffer matches 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 metamorphic buffer should be accompanied by a gradual relaxation of the mechanical stresses that inevitably arise due to the mismatch of the lattice parameters of the underlying and overlying layers. However, as practice has shown, the metamorphic buffer does not completely relax and mechanical stresses remain in its upper part, which affect the active layers growing higher. To avoid this, the metamorphic buffer is completed with the so-called inverse layer, when after reaching the maximum InAs content in the In _x Al _1-x As ternary solid solution at the top of the metamorphic buffer, the InAs content decreases either smoothly or stepwise. The described technological technique allows to eliminate mechanical stresses towards the end of the inverse layer and to obtain an unstressed “virtual” substrate for the subsequent growth of active layers. In this case, mechanical stresses remaining in the upper part of the metamorphic buffer cannot be transferred to the overlying layers and relax with the formation of a dislocation.

Heterostructures with a metamorphic buffer with a high InAs content in the active region are known, in particular, a nanoheterostructure on a GaAs substrate for FET transistors [2]. The nanoheterostructure consistently includes an ordinary GaAs buffer layer, a complex metamorphic buffer Al _x Ga _1-x As _1-y Sb _y, and an active region, which may consist of In _x Al _1-x As, In _x Ga _1-x As or InAs _x P _1-x . In this case, with the thickness of the metamorphic buffer, the value of y varies from 0 to 1, and x≈0.5. The disadvantage of this nanoheterostructure is the need to use an additional molecular source of Sb in addition to traditional sources of Al, Ga, In. In addition, no measures have been taken to reduce mechanical stress and dislocation density during the growth of the metamorphic buffer.

Closest to the proposed nanoheterostructure and adopted as a prototype of the present invention is a nanoheterostructure described in [3], (Fig.1). This nanoheterostructure includes a GaAs single crystal semi-insulating substrate (1), an AlGaAs / GaAs superlattice (2), a GaAs buffer layer (3), and a step-graded metamorphic buffer (4) In _x Al _1-x As with an increase in InAs x content over thickness (x = x ₁ → x ₄ , where x ₁ = 0.15, and x ₄ = 0.80) with two different gradients of variation of the InAs content, ending with inverse layer (5) with a sharp decrease in the InAs x content by Δx = 0.08, the healing layer with homogeneous composition In _{x4 '} Al _1-x4' As (6), and the active region (7) with a high InAs content (72%), matched by the lattice parameter with the healing layer.

The active region (7) is an InGaAs quantum well, bounded by InAlAs barriers, in which a two-dimensional electron gas is formed. The superlattice (2) is traditional and widely used in heterostructures; its role is to prevent the segregation of background impurities from the substrate into subsequent epitaxial layers.

A disadvantage of the described structure is the occurrence of dislocations formed upon relaxation of the compression regions in a metamorphic buffer. Misfit dislocations always occur, which propagate parallel to the growth plane and extend to the lateral faces of the nanoheterostructure. But threading dislocations also arise, which are formed as a result of the bending of misfit dislocations if any defect blocks their sliding parallel to the growth plane, and propagate perpendicular to the growth plane to the overlying layers, reaching the active region of the nanoheterostructure. For this reason, the occurrence of germinating dislocations greatly increases the scattering of electrons in the channel and, therefore, worsens the instrumental parameters. Dislocation gliding can be blocked by regions of phase separation, which occurs especially actively in the metamorphic In _x Al _1-x As buffer with a large composition difference and a large final x value [4]. In this regard, it becomes necessary to develop a special technology for the growth of a metamorphic buffer for InAlAs / InGaAs nanoheterostructures on a GaAs substrate with a high InAs content in the active region (more than 70%).

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 penetrating into the active region of the nanoheterostructure.

According to the invention, this technical result is achieved due to the fact that in the semiconductor metamorphic nanoheterostructure InAlAs / InGaAs (Fig. 2), which includes a single-crystal semi-insulating GaAs substrate (1), an AlGaAs / GaAs superlattice (2), a GaAs buffer layer (3), metamorphic 1.0 x 1.5 μm In _x Al _1-x As (4) buffer with a linear increase in the InAs x content in thickness from x ₁ to x ₄ , where x ₁ ~ 0, x ₄ ≥0.75, In _x Al _1-x inverse layer As (5) with a smooth decrease in the InAs x content over the thickness from x ₄ to x _{4 '} , where x ₄ -x _4' = 0.03 ÷ 0.08, a healing layer with a homogeneous composition In _{x4 '} Al _1-x4' As (6), active about InAlAs / InGaAs (7) with a high InAs content (more than 70%), matched by the lattice parameter with the healing layer, two inverse layers are introduced into the metamorphic buffer (4) at equal distances from each other and from the buffer boundaries (9 and 12) with a smooth decrease in the InAs x content over thickness by Δх = 0.03 ÷ 0.06, each of which is followed by a healing layer (10 and 13) with a composition that coincides with the final composition of the inverse layer.

Brief Description of the Drawings

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

Figure 2 presents a diagram of a cross section of a semiconductor metamorphic nanoheterostructure, demonstrating the essence of the present invention. The following successive layers and their composition are indicated.

Figure 3 explains the principle of changing the composition of the metamorphic buffer proposed in the present invention.

The implementation of the invention

Semiconductor nanoheterostructures with metamorphic buffer consists of a monocrystalline semi-insulating substrate GaAs (1), the superlattice AlGaAs / GaAs (2) serving to prevent segregation background impurities from the substrate in subsequent epitaxial layers, a buffer layer GaAs (3), a metamorphic buffer (4) In _x Al _1-x As with a linear increase in the InAs x content over the thickness from x ₁ to x ₄ , where x ₁ ~ 0, x ₄ ≥0.75, of the inverse layer (5) with a smooth decrease in the InAs x content over the thickness from x ₄ to x _{4 '} , where x ₄ -x _4' = 0.03 ÷ 0.08, which serves to eliminate the accumulated towards the end of the metamorphic buffer mechanical stresses, the healing layer (6) with a homogeneous composition In _{x4 '} Al _1-x4' As, which serves to reduce residual mechanical stresses and to smooth the surface relief, and the active region (7) with a high InAs content (more than 70%), consistent 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.

Two additional inverse layers (9 and 12) are introduced inside the metamorphic buffer (4). They are located at equal distances from each other and from the boundaries of the metamorphic buffer. Inverse layers consist of In _x Al _1-x As, in which x gradually decreases in thickness from x ₂ to x _{2 '} , where x ₂ -x _2' = 0.03 ÷ 0.06 (9) and from x ₃ to x _{3 '} , where x ₃ -x _{3 '} = 0.03 ÷ 0.06 (12). After each inverse layer, a healing layer is grown with a constant composition that coincides with the final composition of the inverse layer: the healing layer In _{x2 '} Al _1-x2' As (10) after the inverse layer (9) and the healing layer In _{x3 '} Al _1-x3' As (13) after the inverse layer (12), respectively. Thus, the composition and lattice parameter of the In _x Al _1-x As ternary solution in the metamorphic buffer everywhere change continuously, without jumps (Fig. 3). In this case, the metamorphic buffer is divided into three parts (8, 11, 14), each of which is an In _x Al _1-x As layer with an InAs x content linearly increasing in thickness.

The technical result is achieved due to the fact that each inverse layer prevents the relaxation of a part of the metamorphic buffer lying below it, and the entire system of inverse layers prevents the relaxation of the entire metamorphic buffer and, therefore, prevents the formation of dislocations. In addition, inverse layers, creating local fields of mechanical deformation, prevent the growth of dislocations in the overlying layers, causing them to bend sideways. A decrease in the density of dislocations leads to higher carrier mobility and, as a result, expands the operating frequency band of the microwave transistor.

All described layers, with the exception of the δ-layer of silicon, are undoped. All layers were grown by molecular beam epitaxy.

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 inverse layers inside the IMB to suppress dislocations.

[1] Dae-Hyun Kim and Jesus A. del Alamo. 30-nm InAs PHEMTs with f _T = 644 GHz and f _max = 681 GHz. IEEE Electron Device Letters, vol. 31, No. 8, August 2010, p.806-808.

[2] EP 0 840 942 B1 "GaAs substrate with compositionally graded AlGaAsSb buffer for fabrication of high-indium FETs".

[3] F. Capotondi, G. Biasiol, D. Ercolani, V. Grillo, E. Carlino, F. Romanato, L. Sorba. "Strain induced effects on the transport properties of metamorphic InAlAs / InGaAs quantum wells." Thin Solid Films 484, 400-407 (2005).

[4] Nathaniel J. Quitoriano and Eugene A. Fitzgerald. "Relaxed, high-quality InP on GaAs by using InGaAs and InGaP graded buffers to avoid phase separation." J. Appl. Physics, vol. 102, p. 033511.

Claims (1)

Semiconductor nanoheterostructure InAlAs / InGaAs with a metamorphic buffer, including a single-crystal semi-insulating GaAs substrate, an AlGaAs / GaAs superlattice, a GaAs buffer layer, an In _x Al _1-x As metamorphic buffer, an inverse layer of In _x Al _1-x As, which heals with a healing layer composition In _{x4 '} Al _1-x4' As and the active region InAlAs / InGaAs with a high InAs content (more than 70%), matched by the lattice parameter with a healing layer, characterized in that the InAs x content in thickness in the inverse In _x Al ₁ layer _-x As continuously decreases from x up to ₄ x ₄ where x ₄ -x _{4 '=} 0,03 ÷ 0,08, InAs x content of the schine in metamorphic buffer increases linearly from x ₁ to x _4, where x ₁ = 0, x ₄ ≥0,75, metamorphic buffer inward at equal distances from each other and the boundaries of the buffer layer introduces two inverse In _x Al _1-x As with a smooth decrease in the InAs x content in thickness by Δх = 0.03 ÷ 0.06, each of which is followed by a healing layer with a composition that coincides with the final composition of the inverse layer, the thickness of the metamorphic buffer is 1.0 ÷ 1.5 μm.

Images