Method for producing a nitride compound semiconductor device

Abstract

A method is provided for producing a nitride compound semiconductor device. A growth substrate has a silicon surface. A buffer layer, which comprises Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1, is grown onto the silicon surface of the substrate. A semiconductor layer sequence is grown onto the buffer layer. The buffer layer includes a material composition that varies in such a way that a lateral lattice constant of the buffer layer increases stepwise or continuously in a first region and decreases stepwise or continuously in a second region, which follows the first region in the growth direction. At an interface with the semiconductor layer sequence, the buffer layer includes a smaller lateral lattice constant than a semiconductor layer of the semiconductor layer sequence adjoining the buffer layer.

Claims

1. A method for producing an optoelectronic device, the method comprising: providing a growth substrate with a silicon surface; growing a buffer layer onto the silicon surface in a growth direction, the buffer layer comprising Al.sub.xIn.sub.yGa.sub.1-x-yN with 01, 0y1 and x+y1, wherein the buffer layer comprises a material composition that varies in such a way that a lateral lattice constant of the buffer layer increases stepwise or continuously in a first region and decreases stepwise or continuously in a second region that follows the first region in the growth direction; and growing a semiconductor layer sequence that includes an active layer onto the buffer layer, wherein, at an interface with the semiconductor layer sequence, the buffer layer has a smaller lateral lattice constant than a semiconductor layer of the semiconductor layer sequence that adjoins the buffer layer, wherein semiconductor layer sequence is a light emitting diode layer sequence.

2. The method according to claim 1, wherein the buffer layer comprises Al.sub.xGa.sub.1-xN with 0x1.

3. The method according to claim 1, wherein, starting from the growth substrate, an aluminum content of the buffer layer decreases in the first region and increases in the second region, and where x represents the aluminum content.

4. The method according to claim 1, wherein, at the interface with the growth substrate, the buffer layer has an aluminum content of x0.8.

5. The method according to claim 1, wherein, at the interface with the growth substrate, the buffer layer has an aluminum content of x0.9.

6. The method according to claim 1, wherein the buffer layer has a minimum aluminum content of x0.6.

7. The method according to claim 1, wherein the buffer layer has a minimum aluminum content of x0.2.

8. The method according to claim 1, wherein the buffer layer has an aluminum content of x0.6 at the interface with the semiconductor layer sequence.

9. The method according to claim 1, wherein the buffer layer has an aluminum content of x0.8 at the interface with the semiconductor layer sequence.

10. The method according to claim 1, wherein the semiconductor layer that adjoins the buffer layer comprises Al.sub.mIn.sub.nGa.sub.1-m-nN, and wherein m0.5.

11. The method according to claim 1, wherein the semiconductor layer that adjoins the buffer layer comprises Al.sub.mIn.sub.nGa.sub.1-m-nN, and wherein m0.2.

12. The method according to claim 1, wherein the silicon surface is a plane.

13. The method according to claim 1, further comprising detaching the growth substrate after growing the semiconductor layer sequence.

14. The method according to claim 13, wherein the buffer layer is at least partly removed after the growth substrate has been detached.

15. The method according to claim 1, further comprising joining the semiconductor layer sequence to a carrier substrate on an opposite side from the growth substrate.

16. A method for producing an optoelectronic device, the method comprising: providing a growth substrate with a silicon surface; growing a buffer layer onto the silicon surface in a growth direction, the buffer layer comprising Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1, wherein the buffer layer comprises a material composition that varies in such a way that a lateral lattice constant of the buffer layer increases stepwise or continuously in a first region and decreases stepwise or continuously in a second region that follows the first region in the growth direction; growing a semiconductor layer sequence that includes an active layer onto the buffer layer, wherein, at an interface with the semiconductor layer sequence, the buffer layer has a smaller lateral lattice constant than a semiconductor layer of the semiconductor layer sequence that adjoins the buffer layer; detaching the growth substrate after growing the semiconductor layer sequence; and at least partially, removing the buffer layer after the growth substrate has been detached, wherein semiconductor layer sequence is a light emitting diode layer sequence.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in greater detail below with reference to exemplary embodiments in conjunction with FIGS. 1 to 4, in which:

(2) FIG. 1 shows a layer sequence applied to a silicon substrate in one exemplary embodiment of the method for producing a nitride compound semiconductor device;

(3) FIG. 2 shows a layer sequence applied to a silicon substrate in a further exemplary embodiment of the method for producing a nitride compound semiconductor device;

(4) FIG. 3 shows a layer sequence applied to a silicon substrate in a comparative example not according to the invention; and

(5) FIG. 4 is a graph of measured half-value widths of X-ray diffraction reflections of the layer sequence according to the exemplary embodiment of FIG. 1 compared with the layer sequence in the comparative example of FIG. 3.

(6) 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.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(7) In the method, as shown in FIG. 1, a growth substrate 1 is provided which comprises a silicon surface. The growth substrate 1 may, for example, be a silicon wafer. It is however alternatively also possible for the growth substrate 1 to be an SOI substrate. The silicon surface of the growth substrate 1 is preferably a (111) crystal plane, which is particularly well suited to the growth of nitride compound semiconductors due to its hexagonal symmetry. Compared with substrates of sapphire, GaN or SiC used generally to grow nitride compound semiconductor materials, the growth substrate 1 with the silicon surface has the advantage of being comparatively inexpensive.

(8) In the method, firstly a buffer layer 2 of Al.sub.xIn.sub.yGa.sub.1-x-yN with 0x1, 0y1 and x+y1 is grown onto the silicon surface of the growth substrate 1. In the exemplary embodiment the indium content y=0, i.e., the buffer layer comprises Al.sub.xGa.sub.1-xN with 0x1. In the exemplary embodiment shown, the material composition of the buffer layer 2 has been varied during growth such that the lateral lattice constant of the buffer layer 2 increases continuously in a first region 2a and decreases continuously in a second region 2b following in the growth direction.

(9) This is achieved in that the aluminum content x of the nitride compound semiconductor material of the buffer layer 2 is varied during growth. The profile of the aluminum content x in the buffer layer 2 and an adjacent semiconductor layer 4 of the semiconductor layer sequence 3 grown onto the buffer layer 2, the sequence being a light-emitting diode layer sequence in the exemplary embodiment, is shown schematically in FIG. 1.

(10) The aluminum content x of the buffer layer 2 amounts at the interface between the growth substrate 1 and the buffer layer 2 advantageously to x0.8, preferably x0.9, in particular x=1, as in the exemplary embodiment shown.

(11) Starting from the growth substrate 1, the aluminum content x firstly decreases continuously in the first region 2a. As a consequence, the lateral lattice constant of the nitride compound semiconductor material increases continuously. Between the first region 2a and the second region 2b the aluminum content x reaches a minimum, and accordingly the lattice constant of the nitride compound semiconductor material reaches a maximum. Between the first region 2a and the second region 2b the aluminum content x is advantageously at a minimum, at which x0.6, preferably x0.2 or even x0.1.

(12) In the second region 2b of the buffer layer 2, which follows the first region 2a in the growth direction, the aluminum content x of the buffer layer 2 again increases continuously. At the interface between the buffer layer 2 and the adjacent semiconductor layer 4 of the light-emitting diode layer sequence 3, the aluminum content x reaches a value of advantageously x0.6, preferably x0.8 or even x=1, as in the exemplary embodiment shown.

(13) In a next method step a semiconductor layer sequence 3 is grown onto the previously grown buffer layer 2. In the exemplary embodiment, the semiconductor layer sequence 3 is the light-emitting diode layer sequence of an optoelectronic device. The light-emitting diode layer sequence 3 is based on a nitride compound semiconductor.

(14) The light-emitting diode layer sequence 3 in particular contains an active layer 5, which is suitable for emitting radiation. The active layer 5 may, for example, take the form of a pn-junction, of a double heterostructure, of a single quantum well structure or of a multiple quantum well structure. The term quantum well structure here includes any structure in which charge carriers undergo quantization of their energy states by inclusion (confinement). In particular, the term quantum well structure does not provide any indication of the dimensionality of the quantization. It thus encompasses inter alia quantum troughs, quantum wires and quantum dots and any combination of these structures.

(15) Furthermore, the light-emitting diode layer sequence 3 contains at least one semiconductor layer 4 of a first conduction type and at least one semiconductor layer 6 of a second conduction type, wherein the at least one semiconductor layer 4 is, for example, n-doped and the at least one semiconductor layer 6 is, for example, p-doped.

(16) The aluminum content of the buffer layer 2 is preferably increased continuously in the second region 2b such that the aluminum content at the interface with the light-emitting diode layer sequence 3 is greater than the aluminum content of the semiconductor layer 4 of the light-emitting diode layer sequence 3 which adjoins the buffer layer 2. The semiconductor layer 4 adjoining the light-emitting diode layer sequence 3 advantageously comprises Al.sub.mIn.sub.nGa.sub.1-m-nN, wherein m0.5. In particular, m may be 0.2 or even 0.1. Because the aluminum content of the semiconductor layer 4 adjoining the buffer layer 2 is smaller than the aluminum content of the buffer layer 2 at the interface with the light-emitting diode layer sequence 3, the semiconductor layer 4 adjoining the buffer layer 2 is grown with compressive strain. This has the advantage of counteracting any tensile strain which may arise on cooling of the layer system from growth temperature to room temperature.

(17) FIG. 2 shows a layer sequence in a further exemplary embodiment of the method for producing a nitride compound semiconductor device. The layer sequence differs from the exemplary embodiment of FIG. 1 in that the aluminum content x in the buffer layer 2 does not vary continuously but rather stepwise. In a first region 2a facing the growth substrate 1 the aluminum content x in the buffer layer 2 decreases stepwise, and in a second region 2b facing the light-emitting diode layer sequence 3 it increases again stepwise. In other words, the buffer layer 2 comprises a plurality of sublayers in the first region 2a, wherein the aluminum content x decreases stepwise from sublayer to sublayer. Furthermore, the buffer layer comprises a plurality of sublayers in the second region 2b, wherein the aluminum content x increases stepwise from sublayer to sublayer.

(18) With regard to advantages and further advantageous configurations, the second exemplary embodiment corresponds to the above-described first exemplary embodiment.

(19) For the purposes of comparison, FIG. 3 shows a layer sequence on a growth substrate 1 of silicon in a comparative example not according to the invention for producing an optoelectronic nitride compound semiconductor device. In this comparative example the aluminum content x of the buffer layer 2 reduces continuously in conventional manner from the growth substrate 1 in the growth direction, in order to adapt the aluminum content to the aluminum content of the semiconductor layer 4, adjoining the buffer layer 2, of the light-emitting diode layer sequence 3. In this procedure the buffer layer 2 has substantially the same lattice constant at the interface with the light-emitting diode layer sequence 3 as the semiconductor layer 4, adjoining the buffer layer 2, of the light-emitting diode layer sequence 3. In contrast to the above-described exemplary embodiments of FIG. 1 and FIG. 2, there is therefore no abrupt change in the lattice constant of the nitride compound semiconductor material at the interface between the buffer layer 2 and the light-emitting diode layer sequence 3.

(20) FIG. 4 shows the full half-value width (FWHMFull Width at Half Maximum) of the X-ray diffraction reflections of the crystal planes (002), (102) and (201) for the layer sequence of the exemplary embodiment of FIG. 1 (S1) and the layer sequence of the comparative example of FIG. 3 (S3). The comparison shows that the full half-value width of the measured X-ray diffraction reflections for the layer sequence S1 produced according to the method described herein is less than for the layer sequence S3, which has been produced in accordance with the comparative example not according to the invention. The smaller half-value widths of the reflections in the case of examination using X-ray diffraction point to a reduced defect density of the layer sequence in the exemplary embodiment according to the invention.

(21) Transmission electron micrographs (not shown) of the layer sequence produced using the method according to the invention revealed that dislocations in particular bend due to the jump in the lateral lattice constant at the interface between the buffer layer and the semiconductor layer sequence. There is furthermore a reduction in dislocations at the interface between the buffer layer and the semiconductor layer sequence applied thereto due to annihilation.

(22) 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.