Growth of A-B crystals without crystal lattice curvature
The present invention relates to a process for the production of III-V-, IV-IV- or II-VI-compound semiconductor crystals. The process starts with providing of a substrate with optionally one crystal layer (buffer layer). Subsequently, a gas phase is provided, which comprises at least two reactants of the elements of the compound semiconductor (II, III, IV, V, VI) which are gaseous at a reaction temperature in the crystal growth reactor and can react with each other at the selected reactor conditions. The ratio of the concentrations of two of the reactants is adjusted such that the compound semiconductor crystal can crystallize from the gas phase, wherein the concentration is selected that high, that crystal formation is possible, wherein by an adding or adjusting of reducing agent and of co-reactant, the activity of the III-, IV- or II-compound in the gas phase is decreased, so that the growth rate of the crystals is lower compared to a state without co-reactant. Therein, the compound semiconductor crystal is deposited at a surface of the substrate, while a liquid phase can form on the growing crystal. Further, auxiliary substances may be added, which can also be contained in the liquid phase, but is only incorporated in low amounts into the compound semiconductor crystal. Herein, 3D- and 2D-growth modes can be controlled in a targeted manner. The addition of auxiliary substances and the presence of a liquid phase favour these means. The product is a single crystal of the respective III-V-, IV-IV- or II-VI-compound semiconductor crystal, which, compared to respectively conventional compound semiconductor crystals has a lower concentration of inclusions or precipitates and nevertheless has no or only a very low curvature.
1. A Process for the production of an A-B compound semiconductor crystal, wherein A is at least one element of the third (III), fourth (IV), or second (II) main/sub group of the periodic table, selected from Cd, Zn, Hg, Al, Ga, In, Si, C or Ge, wherein B is at least one element of the V-, IV- or VI-main/sub group of the periodic table of elements, selected from C, Ge, N, P, As, Sb, S, Se, or Te, the process comprising:
i) providing in a reactor a substrate, having surfaces which are not perpendicular to a desired growth direction of the A-B compound semiconductor crystal;
ii) growing an A-B layer in an epitaxial “3D” growth mode on the substrate, the A-B layer having a structured surface with elevations and subjacent gaps between elevations;
iii) filling of the gaps between the elevations by growing or depositing on the layer an additional filling layer of A-B material to obtain a smooth surface; and
iv) growing an A-B layer on the smooth surface in an epitaxial “2D”-growth mode,
wherein at least step ii), optionally also steps iii) and/or iv):
comprises the at least one III-, IV-, or II-element forming a liquid metal film on a surface of a crystal growth zone of the A-B compound semiconductor crystal; and
is performed in the presence of at least one auxiliary substance that is different from but isoelectric to the at least one III-, IV- or II-element or the A-B compound semiconductor crystal, the at least one auxiliary substance contributing to the formation of the liquid metal film but not being substantially incorporated into the A-B compound semiconductor crystal.
2. The process according to claim 1 , wherein the additional filling layer does not comprise pores.
3. The process according to claim 1 and comprising an hydride vapor phase epitaxy HVPE process.
4. The process according to claim 1 wherein concentration of III-, IV- or II-precipitates and/or unstoichiometrical III-V-, IV-VI-, or II-VI-inclusions in the A-B compound semiconductor crystal is less than 1×10 4 cm −3 .
5. The process according to claim 4 wherein the A-B compound semiconductor crystal comprises at least analytically detectable traces of an auxiliary substance.
6. The process according to claim 5 , wherein the auxiliary substance is present in a maximal concentration of 1×10 17 cm −3 .
7. The process according to claim 1 wherein the A-B compound semiconductor crystal is characterized by a crystal lattice curvature radius of at least 25 m.
8. The process according to claim 1 wherein the auxiliary substance comprises indium.
9. A process for producing a compound semiconductor crystal comprising a first element chosen from elements in group II, group III, or group IV, and a second element chosen from elements in group IV, group V, or group VI, the method comprising:
providing a substrate and a gas phase above the substrate in a crystal growth reactor, the gas phase comprising a first reactant of the first element, a second reactant of the second element, and having a temperature at which the first and second reactants react to crystalize on a crystal growth zone supported by the substrate and form the compound semiconductor crystal, wherein the gas phase contains during at least one deposition phase an amount of at least one of the first reactant and the second reactant sufficient to enable growth of the compound semiconductor crystal;
adding an amount of a reducing agent that reduces the first reactant; and
adding an amount of at least one co-reactant capable of reacting with the first element;
wherein the addition of the reducing agent and co-reactant decrease activity of the first reactant in the gas phase and moderate growth rate of the compound semiconductor crystal so that growth of the compound semiconductor crystal is not stopped but proceeds at a growth rate lower than a growth rate at which growth would proceed absent the co-reactant.
10. The process according to claim 9 , wherein adding the reducing agent comprises adding the reducing agent in an amount that generates formation of an elementary metal of the first element, on a surface of the crystal growth zone.
11. The process according to claim 9 , wherein the compound semiconductor is selected from GaN, AlN, Ga 1-x Al x N (0<x<1), GaAs, GaP, InP, GaSb, SiC, CdTe, ZnTe or HgTe.
12. The process according to claim 9 , wherein the reducing agent comprises hydrogen.
13. The process according to claim 9 and comprising, adding to the gas phase at least one gaseous auxiliary substance which is isoelectronic with regard to the semiconductor crystal and which is incorporated into the compound semiconductor at a concentration less than 1×10 17 cm −3 .
14. The process according to claim 10 , wherein the elementary metal has a form of a liquid metal film.
15. The process according to claim 9 wherein the first reactant is a precursor selected from GaCl, GaCl 3 , AlCl, AlCl 3 , InCl, InCl 3 , GaI, GaI 3 , InI, InI 3 , SiCl y H 4-y (where y is an integer 0<y<4), CH 4 , CCl 4 , CH z Cl (4-z) (z =1, 2 or 3 ), simple or higher silanes, simple or higher germanes and simple or higher hydrocarbons.
16. The process according to claim 9 wherein the second reactant is a precursor of a group V element selected from NH 3 , AsH 3 , or PH 3 .
17. The process according to claim 13 wherein the auxiliary substance is an In compound.
18. The process according to claim 17 wherein the In compound is InCl or InCl 3 .
19. The process according to claim 9 wherein the substrate comprises a buffer layer of the compound semiconductor crystal.