Method for the production of a nitride compound semiconductor layer

Abstract

Described is a method for producing a nitride compound semiconductor layer, involving the steps of:depositing a first seed layer (1) comprising a nitride compound semiconductor material on a substrate (10);desorbing at least some of the nitride compound semiconductor material in the first seed layer from the substrate (10);depositing a second seed layer (2) comprising a nitride compound semiconductor material; andgrowing the nitride compound semiconductor layer (3) containing a nitride compound semiconductor material onto the second seed layer (2).

Claims

1. A method for the production of a nitride compound semiconductor layer, comprising the steps: deposition of a first seed layer comprising a nitride compound semiconductor material onto a substrate by epitaxial deposition from the gas phase using epitaxy sources; at least partial desorption of the nitride compound semiconductor material of the first seed layer from the substrate by switching off the epitaxial sources or by heating the substrate to at least 900 C.; deposition of a second seed layer comprising a nitride compound semiconductor material at a temperature of between 450 C. and 850 C.; and growth of the nitride compound semiconductor layer comprising a nitride compound semiconductor material onto the second seed layer.

2. The method according to claim 1, wherein the substrate is a sapphire substrate.

3. The method according to claim 1, wherein the substrate is a prepatterned substrate.

4. The method according to claim 1, wherein the nitride compound semiconductor material of the first seed layer comprises Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1.

5. The method according to claim 1, wherein the nitride-compound semiconductor material of the second seed layer comprises Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1.

6. The method according to claim 1, wherein the nitride compound semiconductor material of the nitride compound semiconductor layer comprises Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1.

7. The method according to claim 1, wherein deposition of the first seed layer, the second seed layer and/or the nitride compound semiconductor layer proceeds by deposition from the gas phase.

8. The method according to claim 1, wherein the substrate is heated for desorption of the nitride compound semiconductor material of the first seed layer to a temperature of at least 950 C.

Description

(1) The invention is explained in greater detail below with reference to exemplary embodiments in conjunction with FIGS. 1 and 2, in which:

(2) FIGS. 1A to 1E show a schematic representation of an exemplary embodiment of the method on the basis of schematically illustrated intermediate steps, and

(3) FIG. 2 is a graph showing the full width at half maximum (FWHM) of an X-ray diffraction reflection of the nitride compound semiconductor layer produced as a function of a spatial coordinate x of the substrate for four different exemplary embodiments of the method.

(4) In the figures identical or identically acting components are in each case provided with the same reference numerals. The components illustrated and the size ratios of the components to one another should not be regarded as to scale.

(5) As shown in FIG. 1A, in the method a substrate 10 is provided which comprises a lattice structure suitable for growth of a nitride compound semiconductor material. The substrate 10 is preferably a sapphire substrate. Alternatively, it would be possible for the substrate for example to comprise SiC, GaN or silicon.

(6) The substrate 10 may be a substrate with a planar surface or alternatively a prepatterned substrate, which for example comprises periodically arranged three-dimensional patterns which are grown over on growth of the nitride compound semiconductor layer.

(7) In the intermediate step of the method shown in FIG. 1B, a first seed layer 1 has been applied to the substrate 10. The first seed layer 1 comprises a nitride compound semiconductor material, in particular Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1. The first seed layer 1 may for example comprise GaN or AlN.

(8) As may be seen in FIG. 1B, in the exemplary embodiment the first seed layer 1 has not yet grown together to yield a continuous layer, but rather comprises a plurality of islands 11, which are distributed over the surface of the substrate 10. Such island growth generally takes place in the initial stage of epitaxial growth, when the layer thickness is still very slight and uniform seeding is unfavorable from an energy standpoint. The first seed layer 1 may for example have a thickness of between 5 nm and 50 nm.

(9) In one configuration of the method, deposition of the first seed layer 1 takes place by epitaxial deposition from the gas phase in a coating installation 4. The nitride compound semiconductor material or the components of the nitride compound semiconductor material are in this case supplied by suitable epitaxy sources 41, 42 of the coating installation 4. Suitable epitaxy methods are for example MOVPE, CVD, MBE or HVPE. The epitaxy sources 41, 42 may in particular be gas inlets, through which gases, which contain components of the nitride compound semiconductor material, are admitted to the coating installation 4.

(10) In one alternative configuration of the method, the material for deposition of the first seed layer 1 is not supplied from epitaxy sources but rather is desorbed from at least one component 43 of the coating installation 4 in which the method is carried out. The at least one component 43 may for example be the walls of the coating installation 4.

(11) For example, the material of the first seed layer 1 may be desorbed from walls 43 of the coating installation 4. This may in particular be brought about in that the material to be desorbed is heated on the walls 43 to a temperature of at least 900 C. Alternatively or in addition, it is possible for desorption to be brought about by modification of another process parameter, in particular the pressure or flow conditions in the coating installation 4. For example, an increase in the pressure or a modification of the gas flow, by which for example eddies are generated, may bring about intensified desorption of nitride compound semiconductor material from the at least one component 43 of the coating installation 4.

(12) In the intermediate step shown in FIG. 1C, the nitride compound material of the first seed layer 1 is desorbed at least in part from the substrate 10. After desorption of the nitride compound semiconductor material, only residues 12 of the nitride compound semiconductor material or constituents thereof, such as for example residual GaN or Ga islands, remain on the substrate 10. It is furthermore also possible for constituents of the substrate material to be dissolved out of the surface of the substrate 10 during desorption of the nitride compound semiconductor material. This may be caused by the nitride compound semiconductor material having previously reacted chemically with the substrate material, for example in a reaction of GaN with Al.sub.2O.sub.3 of the sapphire substrate. This may bring about roughening or the formation of defects 13 on the surface of the substrate 10.

(13) Desorption of the nitride compound semiconductor material of the first seed layer 1 from the substrate 10 may be brought about, in one embodiment, in that epitaxy sources 41, 42 used to produce the first seed layer are switched off. In this case, as a result of the lack of supply of the components for forming the nitride compound semiconductor material, under the given process conditions part of the nitride compound semiconductor material already present on the surface is desorbed from the surface once again. Alternatively or in addition, it is also possible for the substrate 10 to be heated for at least partial desorption of the nitride compound semiconductor material of the first seed layer 1, preferably to a temperature of at least 950 C.

(14) In a subsequent intermediate step of the method shown in FIG. 1D, a second seed layer 2 is deposited. The second seed layer 2 may, in the case of complete desorption of the previously deposited first seed layer, be deposited onto the surface of the substrate 10 or, in the case of incomplete desorption of the first seed layer, be deposited onto the residues of the first seed layer and the surface of the substrate 10. Deposition of the second seed layer 2 proceeds by epitaxial deposition, in particular by means of MOVPE, CVD, MBE or HVPE. Deposition of the second seed layer preferably proceeds at a temperature of between 450 C. and 850 C., i.e. low temperature seeding takes place. The second seed layer 2 is preferably deposited with a thickness of between 2 nm and 100 nm. Like the previously applied first seed layer 1, the second seed layer 2 may also, after deposition, be an island-type layer, which comprises islands 22 which have not yet grown together to yield a continuous layer. The second seed layer 2 preferably comprises a nitride compound semiconductor material of the composition Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1 and may optionally be doped with a p-dopant or an n-dopant.

(15) In a subsequent method step shown in FIG. 1E, a nitride compound semiconductor layer 3 is grown onto the second seed layer 2. The nitride compound semiconductor layer 3 is preferably grown at a substrate temperature of at least 1050 C. Like the first seed layer 1 and the second seed layer 2, the nitride compound semiconductor layer 3 comprises a nitride compound semiconductor material with the composition Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1, wherein the nitride compound semiconductor materials of the first seed layer, second seed layer and nitride compound semiconductor layer need not necessarily be identical. The nitride compound semiconductor layer 3 may be doped with a p-dopant such as for example magnesium or an n-dopant such as for example silicon.

(16) The nitride compound semiconductor layer 3 may advantageously be used as buffer layer for growth of an epitaxial layer sequence for a semiconductor device, in particular an optoelectronic device such as for example an LED or a semiconductor laser. Because, with the method described herein, a particularly low dislocation density is achieved for the nitride compound semiconductor layer 3, better quality may be achieved for semiconductor layers grown subsequently, in particular the semiconductor layers for an optoelectronic device. The efficiency and long-term stability of the optoelectronic device may advantageously be improved in this way.

(17) FIG. 2 plots the full width at half maximum FWHM of the (102) X-ray reflection of a nitride compound semiconductor layer as a function of a spatial coordinate x on the substrate, the nitride compound semiconductor layer being produced according to different exemplary embodiments of the method.

(18) For curve 5, the first seed layer was produced by very slight desorption of the nitride compound semiconductor material from the walls of the coating installation, for curve 6 it was produced with greater desorption, for curve 7 it was produced with even greater desorption and for curve 8 with targeted deposition of the nitride compound semiconductor material from epitaxy sources.

(19) The different levels of desorption of the nitride compound semiconductor material in production of the first seed layer is caused in the exemplary embodiments of curves 6, 7 and 8 by the different number of coating operations performed previously in the coating installation. Since in each coating operation nitride compound semiconductor material also becomes attached to the walls of the coating installation, desorption from the walls increases as the number of coating operations increases, until the coating installation is cleaned.

(20) A comparison of curves 5, 6 and 7 shows that the full width at half maximum of the (102) X-ray reflection decreases with an increasing rate of desorption from the walls of the coating installation during production of the first seed layer and thus the layer quality improves. The full width at half maximum FWHM of the (102) X-ray reflection is approximately proportional to the square root of the dislocation density. Through targeted deposition of the first seed layer from epitaxy sources (curve 8), it is possible to achieve similarly low dislocation densities of the nitride compound semiconductor layers deposited thereon as by major desorption from the walls of the coating installation (curve 7).

(21) The invention is not restricted by the description given with reference to the exemplary embodiments. Rather, the invention encompasses any novel feature and any combination of features, including in particular any combination of features in the claims, even if this feature or this combination is not itself explicitly indicated in the claims or exemplary embodiments.