Preparation method of a coating of gallium nitride
The invention concerns a monocrystalline coating crack-free coating of gallium nitride or mixed gallium nitride and another metal, on a substrate likely to cause extensive stresses in the coating, said substrate being coated with a buffer layer, wherein: at least a monocrystalline layer of a material having a thickness ranging between 100 and 300 nm, preferably between 200 and 250 nm, and whereof crystal lattice parameter is less than the crystal lattice parameter of the gallium nitride or of the mixed gallium nitride with another metal, is inserted in the coating of gallium nitride or mixed gallium nitride with another metal. The invention also concerns the method for preparing said coating. The invention further concerns electronic and optoelectronic devices comprising said coating.
1. A crack free monocrystalline layer of gallium nitride or of a mixed nitride of gallium and another metal, on a substrate that could cause tension stresses in the layer, said substrate being covered by a buffer layer; and in which at least one monocrystalline intermediate layer, which is monocrystalline upon deposition, of a material with a thickness of between 200 and 300 nm, and for which the lattice parameter is smaller than the lattice parameter of the gallium nitride or of the mixed nitride of gallium and another metal, is inserted in the layer of gallium nitride or of the mixed nitride of gallium and another metal.
2. The crack free monocrystalline layer according to claim 1 , which has a thickness of 2 μm or more.
3. The crack free monocrystalline layer according to claim 1 , which has a thickness of between 2 and 5 μm.
4. The crack free monocrystalline layer according to claim 1 , in which the mixed nitride of gallium and another metal is selected from the group consisting of mixed nitrides of gallium and aluminium or indium.
5. The crack free monocrystalline layer according to claim 1 , in which the substrate is selected from the group consisting of silicon and silicon carbide substrates.
6. The crack free monocrystalline layer according to claim 1 , in which the buffer layer is an AlN layer.
7. The crack free monocrystalline layer according to claim 1 , in which the intermediate layer is a layer of AlN or AlGaN.
8. The crack free monocrystalline layer according to claim 1 , comprising 1 to 5 intermediate layers.
9. The crack free monocrystalline layer according to claim 1 , wherein the at least one monocrystalline layer has a thickness of between 200 and 250 nm.
10. The crack free monocrystalline layer according to claim 1 , in which the intermediate layer is a layer of AlN.
11. A method for preparation of a crack free monocrystalline layer of gallium nitride or of a mixed nitride of gallium and another metal on a substrate that could create tension stresses in the layer, said process comprising the following steps in sequence:
a) possible exposure of the heated substrate surface to ammonia;
b) deposition of a single atomic layer of aluminium;
c) deposition of a buffer layer;
d) growth of a deposit of gallium nitride or of a mixed nitride of gallium and another metal;
e) interruption of the growth of the deposit of gallium nitride or of the mixed nitride of gallium and another metal;
f) growth of an intermediate monocrystalline layer of a material for which the lattice parameter is smaller than the lattice parameter of gallium nitride or of the mixed nitride of gallium and another metal, and the thickness of which is between 200 and 300 nm;
g) repetition of steps d) to f) if necessary;
h) continuation of the growth of the deposit of gallium nitride or of a mixed nitride of gallium and another metal, until the final required thickness of the layer of gallium nitride or of the mixed nitride of gallium and another metal;
i) cooling of the substrate and the layer of gallium nitride or of the mixed nitride of gallium and another metal; and
j) producing the crack free monocrystalline layer of claim 1 .
12. The method according to claim 11 , in which the conditions under which the intermediate layer (step f)) is grown are such that this layer is monocrystalline.
13. The method according to claim 12 , in which the growth temperature of the monocrystalline intermediate layer is between 800 and 1000° C.
14. The method according to claim 11 , in which the final thickness of the layer of gallium nitride or of the mixed nitride of gallium and another metal is greater than or equal to 2 μm.
15. The method according to claim 14 , in which the final thickness of the layer of gallium nitride or of the mixed nitride of gallium and another metal is between 2 and 5 μm.
16. The method according to claim 11 , in which the mixed gallium nitride is chosen to be a mixed nitride of gallium with aluminium or indium.
17. The method according to claim 11 , in which the substrate is chosen from among silicon and silicon carbide substrates.
18. The method according to claim 11 , in which the buffer layer is an AlN layer.
19. The method according to claim 11 , in which the intermediate layer is a layer of AlN or AlGaN.
20. The method according to claim 11 , in which steps d) to f) are repeated between 1 and 5 times.
21. The method according to claim 11 , in which the deposition of the buffer layer, the growth or deposition of gallium nitride or of the mixed nitride of gallium and another metal, and the growth of the intermediate monocrystalline layer are done by Molecular Beam Epitaxy (MBE), or Metalorganic Chemical Vapour Deposition (MOCVD), or Hydride Vapour Phase Epitaxy (HVPE).
22. The method according to claim 21 , in which the intermediate monocrystalline layer is grown by Molecular Beam Epitaxy at a temperature of between 800 and 1000° C., at a growth rate of between 0.1 and 0.5 μm/h.
23. A method of using a crack free monocrystalline layer of gallium nitride or of a mixed nitride of gallium and another metal, the method comprising
covering a buffer layer on a substrate with the crack free monocrystalline layer of claim 1 to form a laminate; and
producing from the laminate an electronic or opto-electronic device.