SU1730218A1 - Method of producing single crystal films of semiconductor materials - Google Patents

Abstract

The invention relates to semiconductor technology and can be used when creating devices for optoelectronics and nonlinear optics, in particular for semiconductor lasers and frequency converters. Provides a predetermined linear density of packing defects in the film due to a change in the structure of material deposition from diamond or sphalerite to wurtzite. The method involves creating a supersaturation of components to a value of at least 60 kJ / mol and deposition of a film on a heated single-crystal substrate with a wurtzite structure oriented in the interval of planes from {0001} to {1120}. 1 tab. with C

Description

The invention relates to semiconductor technology and can be used to create devices for optoelectronics and nonlinear optics, in particular for semiconductor lasers and frequency converters, namely, to obtain semiconductor materials with previously unknown types of crystals. steel structure, for example, obtaining GaAs, which crystallizes under ordinary conditions in a cubic structure such as sphalerite, with a curvature modification with hexagonal symmetry.

Reducing the symmetry of the crystal lattice significantly changes the semiconductor band structure: the energy of interband transitions and the relative position of the energy minima at symmetric points of the Brillouin zone. In this case, the anisotropy of the electrophysical and optical properties of crystals is enhanced, which opens up additional possibilities for their use in nonlinear optics. At the same time, having acquired a new symmetry, the A3B5 materials remain phases with a narrow homogeneity region, which allows their conductivity type to be easily changed by introducing doping impurities. Methods for heteroepitaxial growth from supersaturated steam-h are known.

00

about

go

00

phase of the films of elements of group IV, compounds A3B5 and solid solutions based on them on an oriented single-crystal substrate of a different structural type than the material grown, for example, obtaining GaAs on and (Ca, Sr) F2, Si on CaFa using molecular beam epitaxy ( MPE) and gas-phase epitaxy using organometallic compounds - MOCVD.

In all these cases, the substrate was selected from considerations of the maximum crystalline similarity of the growth surface structure to the structure of flat grids of the growing crystal in the known thermodynamically equilibrium modification.

Thus, the crystal structure and orientation of the epitaxial layer were clearly defined.

Closest to the proposed method of producing single-crystal GaAs films on oriented substrates of ZnS and CdS crystals having a wurtzite structural type. The deposition of GaAs was carried out by the gas transport epitaxy method in a closed system at 700 ° C; chemical transport agent served as a pair of iodine. The supersaturation (A) in the deposition zone corresponded to a temperature differential relative to a source of 10 K, which is 2.1 kJ / mol in energy units. Epitaxial growth takes place on {0001}, {1010}, and {1120} planes having crystallographic similarity elements with (111), (110) and (112) GaAs (GaAs2B) cubic planes. The result of this method of growing was obtaining single-crystal GaAs films of a single structural type, sphalerite. In the epitaxial growth modes chosen in the prototype, a different result could not be obtained in principle.

The purpose of the invention is to provide in the film a predetermined linear density of packaging defects by changing the structure of the deposited material from diamond or sphalerite to wurtzite.

This goal is realized by creating supersaturation in the vapor phase and deposition of the growing substance on an oriented single crystal substrate with a wurtzite type structure (W). Moreover, in the vapor phase, a supersaturation with respect to the deposited substance with a diamond or sphalerite type structure of not less than 60 kJ / mol is created, and the growth is carried out on a substrate oriented in a given direction lying in the orientation interval {0001} - {1150}.

Heteroepitaxial growing of single-crystal films of Group IV elements, А3В5 compounds and solid solutions based on them is carried out on a substrate,

oriented in a given direction lying in the {0001} - {1120} orientation interval, which, together with the experimentally determined supersaturation value, leads to

structural type of layers from diamond or sphalerite to wurtzite, i.e., the possibility of obtaining a single-crystal film with a given density of packing defects. The proposed growth modes of single-crystal films were found experimentally, since the absence of thermodynamic data for previously unknown proto-modifications of compounds A3B and group IV elements

It does not allow to estimate the minimum value of supersaturation in the crystallization medium, which ensures the possibility of the formation of metastable phases.

The cultivation of elements of group IV,

A3B5 and solid solutions based on them from the vapor phase can be carried out by several methods, differing in the choice of initial reagents and the mechanism of the processes leading to crystallization.

Comparison of such processes is advisable to carry out the most important thermodynamic characteristics, causing them to flow in a given direction, namely, temperature and

the amount of supersaturation, which characterizes in energy units the deviation of the system (vapor phase - a crystal of stable modification) from the state of heterogeneous equilibrium.

The creation of supersaturation in the crystallization medium not less than 60 kJ / mol is due to the following considerations.

For supersaturation values of 60 kJ / mol and more, the formation of a wurtzite modification takes place when the conditions for choosing the orientation of the substrate are met. If the supersaturation value is less than 60 kJ / mol on similarly oriented substrates crystallize

layers in which the linear density of stacking faults is less than unity, which is insufficient for the complete transformation (sphalerite-wurtzite) of the structural type of axially axial layers. In crystals with

The sphalerite structure may disrupt the alternation of atomic planes in the 111J direction with a minimum distance, where a is the period of ale, cells, i.e., the frequency of occurrence of packaging defects in this direction is a multiple of a / 3. Therefore, the maximum linear density of stacking faults in the 111 direction is the inverse value, i.e., 3 / a, which we subsequently adopted for 1, since for such a density, q. The sphalerite structure is completely transformed into a wurtzite structure. Then, we determine the degree of hexagonal excess (sphalerite-wurtzite) a a, where p is the observed packing defect density relative to the cubic phase, in inverse nm.

The second prerequisite for the implementation of the proposed method is the choice of the substrate, its orientation. This choice should provide on the surface of the crystal - substrate a high density of adsorption centers with the maximum potential depth for adatoms (admolecules) of the substance being crystallized, and, most importantly, the absence of a similar pattern of flat cubic crystal grids to it. This necessitates the use of hexagonal symmetry with a wurtzite structural type as a single crystal substrate, and the choice of orientation of the substrate according to the above criteria reduces the supersaturation required for reproduction in the epitaxial layer of the structural substrate type and reduces the likelihood of a parallel process. nucleation of a stable phase. To achieve this goal, compounds A3B5, elements of group IV according to the proposed method are grown on substrates with the structure of type W in the interval of orientation {0001} - {1120}. In this case, the use of substrates oriented in the interval {1122} - {1121} fully complies with the above criteria and makes it possible to obtain epitaxial layers with a structural type of wurtzite on them. Within the {0001} - {1122} and {1121} - {1120} intervals, a change in the angular position of the growth surface relative to the axis from the substrate leads to a monotonic change in the density of packing defects along the corresponding direction in the epitaxial layer.

The conditions for the implementation of the proposed method in different methods of epitaxy are given in the table.

Example 1. The growth of GaAs epitaxial layers was carried out by the combined pyrolysis of AzN3 and Ga (CHs) and H2 vapors at atmospheric pressure in the reactor. The partial pressures of Ca (CH3) and AzN3 were 30 and 120 Pa, respectively. The crystallization temperature of 650 ° C. The supersaturation in the vapor phase above the substrate, created by the products of pyrolysis

Ca (CH3) C, AzN3 (6a, As-i) and estimated relative to GaAszB, was 115 kJ / mol. The supersaturation was estimated using data on the vapor pressure of the components over GaAs.

along the line of three-phase equilibrium, the formula was used

15

 RS p 4 P8a P№

where Pi is the pressure of the components in the vapor phase at the substrate;

PI ° - equilibrium pressure.

The growth rate of the GaAs layers is 0.02 mmkm / s, 0.12 mm / min. GaAs epitaxial growth is carried out on plates cut from a Zno single crystal, 2Cdo, 8S (W). Plates are pre-polished

mechanically with diamond paste 0.5 µm and treated in a polishing etchant of composition: saturated solution teCraO B NaO - HzS04 - HF (15: 10: 4) at 110 - 120 ° С. Immediately before growing

GaAs substrates were cleaned by annealing in an atmosphere of H2 at 720 ° C for 5 min. Then the temperature dropped to 650 ° C and AsHa and Ca (CH3) 3 vapors were simultaneously introduced into the reactor. Growing time is 25 min.

Example 2. Layers are oriented in the {1121JA and {1122} A planes. The formed epitaxial layers repeat the structural type and orientation of the substrate, which is established by X-ray diffraction

analysis of the obtained heterostructure and electron diffraction patterns in the grown layers. In the spectra of optical absorption and photoluminescence of GaAs (W), a shift of the edge band in

the short-wavelength region of 70 meV relative to its position in GaAs (Zb).

Example 3. The substrate is oriented in the plane {0001} A. The epitaxial layer has a sphalerite structure and orientation

that installed by the same methods. Optical absorption and PL spectra are common for compensated GaAs (Zb).

EXAMPLE 4 Substrate Orientation {1120}, 5 K {1121} A. The layers are characterized by the presence of stacking faults along one of the directions 111, which is parallel to the direction 0001 in the substrate crystal, the thickness of the double boundaries observed in the transmission microscope corresponds to the degree of hexagonal transformation of the crystal, 39.

Example 5. Substrate orientation {0001} A, 5 ° to {1122} A. Packing defects are observed in the epitaxial layer with a linear density corresponding to "0.08.

EXAMPLE 6. Substrate orientation {1121} A,. The linear density of stacking faults in the direction of the 0001 epitaxial layer corresponds to a 0.93.

„Example 7. Substrate orientation {1122} A, 5 to {0001}. In the epitaxial layer in the direction of 1000, there are packaging defects with a linear density corresponding to 86.

Example 8, Substrate Zno, 8Mgo, 2S (W) is oriented in the {1121} A plane. The initial composition of the gas phase: AzNz (120 Pa); RNZ (40 Pa); Ca (CH3) s (30 Pa). An epitaxial layer of the GaPo, 2sAso, 72 solid solution, which repeats the substrate structure (W), was obtained.

Example 9. The cultivation of epitaxial GaAs layers by the method of molecular beam beam epitaxy (MBE) was carried out at an Riber plant in standard operating modes of evaporators: TAS 310 ° C, Tea 980 ° C. Substrate orientation Zno, 2Mgo, 8S - {1121} A.

Example 10. The temperature of the substrate 600 ° C. The corresponding supersaturation, estimated from the deviation of the crystallization temperature from the zero growth rate of GaAs on the GaAs substrate (100) under the same initial conditions for the Ga and As flow, is 60 kJ / mol. The epitaxial growth rate is 0.58 µm / h. The resulting layers have a wurtzite structure and repeat the orientation of the substrate.

Example 11. The temperature of the substrate 620 ° C. The estimated supersaturation is 54 kJ / mol, the growth rate of the layer is 0.50 μm / h.

The grown layers have a polycrystalline structure and contain grains of hexagonal and cubic symmetry.

Example 12. Ge epitaxial layers were grown during the process of pyrolysis of the NES in an atmosphere of H2 at 680 ° C, the partial pressure of GeH4 was 40 Pa. Under these conditions, the change in the free energy of the system during the precipitation of Ge with the diamond structure by the reaction: GeH4 - Ge + 2Ha - (supersaturation) is 102 kJ / mol. The growth rate of the films is 0.03 μm / min.

Example 13. Substrate Zno, sMgo, 2S is oriented in the {1122} plane. The grown layers according to XRD and TEM data have a wurtzite structure regardless of the polarity of the substrate.

Example 14. The substrate is oriented in the {0001} plane. Layers have microtwins structure. The density of packaging defects is 0.28.

Thus, as can be seen from the above examples, the proposed method provides for obtaining epitaxial layers of monocrystalline films of group IV elements, compounds А В and solid solutions based on them with a given linear density of packaging defects due to the transformation of their structural type from diamond or sphalerite to wurtzite.

Claims (1)

Invention Formula A method of producing single crystal films of semiconductor materials, including creating a supersaturation of components in the vapor phase and deposition of a film on a heated oriented single crystal substrate with a wurtzite structure, characterized in that, in order to provide a specified linear density of packing defects in the film by changing the structure of the deposited material from diamond or sphalerite to wurtzite, deposition is carried out on a substrate oriented in the interval of planes from {0001} to {1120} with a supersaturation value of at least 60 k g / mol,