JP3616020B2 - Gallium nitride semiconductor device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a gallium nitride-based semiconductor layer in which dislocation termination does not occur on the surface of a semiconductor layer.
[0002]
[Prior art]
In recent years, semiconductor devices using nitride crystals such as gallium nitride (GaN) have been developed and applied to light-emitting elements such as blue LEDs. A gallium nitride based semiconductor layer used in such a semiconductor device using a nitride crystal is usually formed by growing GaN or the like on a sapphire substrate using MOCVD. FIG. 4 shows an example of a conventional gallium nitride based semiconductor layer in which a GaN layer 12 is formed on a substrate 10 such as sapphire described above.
[0003]
[Problems to be solved by the invention]
However, in the conventional method for forming a gallium nitride based semiconductor layer, as shown in FIG. 4, when the GaN layer 12 is grown on the substrate 10 such as sapphire by the above-described MOCVD, the sapphire used for the substrate 10. 10 ⁸ to 10 ⁹ cm ⁻² dislocations 14 are generated due to lattice mismatch between GaN and GaN. This dislocation 14 is a defect that occurs along a certain line in the crystal structure, and as shown in FIG. 4, a termination 15 is generated on the flat surface 16 of the semiconductor layer. When the end 15 of the dislocation 14 is generated on the surface 16, there is a problem that the dislocation 14 propagates into the element even if various devices are formed on the surface 16, thereby reducing the performance of the element. That is, for example, the light emitting efficiency of a light emitting device using a gallium nitride based semiconductor layer is lowered, the lifetime of the nitride based laser is shortened, and the reverse leakage current of the pn junction is increased.
[0004]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a gallium nitride based semiconductor device in which dislocation termination does not occur on the surface and a method for manufacturing the same.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for manufacturing a gallium nitride semiconductor device having a gallium nitride semiconductor layer in which dislocation termination does not occur on the surface, and grows InGaN / GaN MQW at a growth temperature T1. The temperature is increased from T1 to the growth temperature T2 of the gallium nitride based semiconductor layer in a nitrogen atmosphere, and the gallium nitride based semiconductor layer is grown on the InGaN / GaN MQW at the temperature T2, and the InGaN / GaN MQW and nitridation are performed. A device structure is grown using a gallium semiconductor layer as a base layer .
[0006]
According to the above configuration, a V-groove defect is generated on the surface of the InGaN / GaN MQW, the dislocation direction is changed from the vertical direction of the semiconductor layer to the lateral direction by this V-groove defect, and a loop is formed by the adjacent dislocations. Dislocations do not propagate in the GaN layer formed on the InGaN / GaN MQW. Therefore, it is possible to form a gallium nitride based semiconductor layer in which dislocation termination does not occur on the surface.
[0007]
In the method of manufacturing a gallium nitride based semiconductor device, the growth step of InGaN / GaN MQW and the growth step of the gallium nitride based semiconductor layer are repeated twice or more.
[0008]
According to the above configuration, dislocation propagation to the GaN layer can be further prevented.
[0009]
Also, a method of manufacturing a gallium nitride based semiconductor device having a gallium nitride based semiconductor layer in which dislocation termination does not occur on the surface, wherein InGaN / GaN MQW is formed at a growth temperature T1, and the temperature is set to T1 in an atmosphere containing ammonia. from the temperature was raised to the growth temperature T2 of the gallium nitride-based semiconductor layer, then, and forming the InGaN / GaN MQW as the base layer of the device structure by growing a device structure.
[0010]
According to the above configuration, by annealing InGaN / GaN MQW at the growth temperature of the gallium nitride based semiconductor layer in an atmosphere containing ammonia, a gallium nitride based semiconductor layer is formed in the V-groove defect generated on the surface of the InGaN / GaN MQW. Thus, it is possible to prevent the occurrence of termination of dislocations on the surface of the semiconductor layer formed thereon.
[0011]
In the method for manufacturing a gallium nitride semiconductor device, the gallium nitride semiconductor is GaN.
[0012]
In the method for manufacturing a gallium nitride based semiconductor device, the gallium nitride based semiconductor is AlGaN.
[0013]
In the method for manufacturing a gallium nitride based semiconductor device , the temperature T1 is 650 to 800 ° C.
[0014]
In the method for manufacturing a gallium nitride based semiconductor device , the temperature T2 is 800 to 1100 ° C. The present invention also relates to a gallium nitride based semiconductor device formed on a substrate, an InGaN / GaN MQW layer formed on the substrate and having a V-groove defect on the surface, and the InGaN / GaN MQW layer. A gallium nitride based semiconductor layer and a device structure formed on the gallium nitride based semiconductor layer, wherein the InGaN / GaN MQW layer and the gallium nitride based semiconductor layer serve as a base layer of the device structure. And
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0016]
FIGS. 1A and 1B are explanatory views of a method for forming a gallium nitride based semiconductor layer according to the present invention. In FIG. 1A, when the GaN layer 12 is formed on the substrate 10 by MOCVD, dislocations 14 are generated as described above. When InGaN / GaN MQW 18 is further grown continuously on the GaN layer 12, a V-groove defect 20 may be generated on the surface thereof. When the V-groove defect 20 does not occur, the end 15 of the dislocation 14 is generated on the surface 16 of the InGaN / GaN MQW 18. On the other hand, when the V-groove defect 20 is generated, V-shaped pits are generated on the surface 16. The V-groove defect 20 is selectively generated only at the terminal portion of the surface 16 of the dislocation 14. The probability of occurrence of the V-groove defect 20 increases as the number of InGaN / GaN MQW18 layers increases, the indium composition of InGaN in the InGaN / GaN MQW18 increases, and the thickness of the InGaN increases.
[0017]
As described above, when the growth conditions of the InGaN / GaN MQW 18 are optimized, the V-groove defect 20 can be generated at the terminal portion of the surface 16 of almost all the dislocations 14. As a growth condition of such InGaN / GaN MQW18, it is preferable to set the growth temperature in the range of 650 to 800 ° C. The growth temperature 650 to 800 ° C. of the InGaN / GaN MQW 18 corresponds to the growth temperature T1 according to the present invention.
[0018]
A characteristic point in the present invention is that the growth of InGaN / GaN MQW 18 is performed under the condition that the V-groove defect 20 is likely to be generated as described above, and the temperature is set to gallium nitride based semiconductor layer such as GaN in a nitrogen atmosphere. The growth temperature is 800 ° C. or higher and 1100 ° C. or lower, and the gallium nitride based semiconductor layer 22 is grown as shown in FIG. The growth temperature of the gallium nitride based semiconductor layer 22 in this case corresponds to the growth temperature T2 according to the present invention. In this way, the dislocations 14 are bent in the lateral direction at the V-groove defect 20 portion, and the termination of the dislocations on the surface of the gallium nitride based semiconductor layer 22 can be prevented. This is because dislocations 14 propagating from the GaN layer 12 formed on the substrate 10 proceed along the V-groove surface 24 of the V-groove defect 20 and thus proceed from the adjacent V-groove surface 24 in the same manner. This is probably because the dislocations 14 are associated with each other at the interface between the InGaN / GaN MQW 18 and the gallium nitride based semiconductor layer 22 to form a loop. The loop formed in this way is indicated by 26 in FIG.
[0019]
FIGS. 2A and 2B are explanatory views of the principle that the dislocations 14 are bent in the lateral direction by the V-groove defect 20. FIG. 2A is an enlarged view of the vicinity of the V-groove defect 20. In this case, the dislocation 14 that has propagated from the GaN layer 12 (not shown) terminates at the bottom 28 of the V-groove defect 20. On both sides of such a dislocation 14, the crystal phase of InGaN / GaN MQW18 is shifted. Therefore, when crystal growth of the gallium nitride based semiconductor layer 22 starts from both side surfaces 30 and 32 of the V-groove defect 20 (V-groove surface 24 in FIG. 1B), crystals grown from the side surfaces 30 and 32, respectively. As shown in FIG. 2A, a new dislocation 14a should be generated at the interface.
[0020]
However, since there are irregularities on the surface having the V-groove defect 20, when a gallium nitride based semiconductor layer 22 such as GaN is grown thereon, the growth starts at the recess. Since the apex of the bottom 28 of the V-groove defect 20 is a point, crystal growth does not start from both side surfaces 30 and 32 at the bottom 28 of the V-groove defect 20 at the same time. The generated nucleus grows. In this case, the phase of the crystal grown inside the V-groove defect 20 grows by taking over the phase of the surface on which the growth has started, that is, the side surface 32 of FIG. As a result, the dislocations 14 propagate along the side surface 30 opposite to the side surface 32 where crystal growth has started. This state is indicated by a mark (2) in FIG. Based on such a principle, the dislocation 14 propagating from the lower side of the figure reaches the interface 34 between the InGaN / GaN MQW 18 and the gallium nitride based semiconductor layer 22 along one side surface 30 of the V-groove defect 20, and then the interface. It progresses in the horizontal direction of the figure along 34. For this reason, the dislocations 14 and the interface 34 that have traveled the interface 34 between the InGaN / GaN MQW 18 and the gallium nitride based semiconductor layer 22 in the same manner from the adjacent V-groove defect 20 not shown in FIG. To meet. Thus, when the two dislocations 14 meet on the interface 34, the dislocation loop is completed, and the dislocations 14 cannot move thereafter. Therefore, propagation of the dislocation 14 to the gallium nitride based semiconductor layer 22 formed on the InGaN / GaN MQW 18 can be avoided, and the termination 15 of the dislocation 14 on the surface of the gallium nitride based semiconductor layer 22 can be prevented.
[0021]
As described above, in this embodiment, after growing InGaN / GaN MQW18 at a temperature of about 650 to 800 ° C. and forming the V-groove defect 20 on the surface thereof, the growth temperature of the gallium nitride based semiconductor layer such as GaN Then, the growth of the gallium nitride based semiconductor layer 22 is continued at the growth temperature until the dislocation 14 can be prevented from propagating into the gallium nitride based semiconductor layer 22 according to the above-described principle. As a result, the end 15 of the dislocation 14 does not occur on the surface of the gallium nitride based semiconductor layer 20.
[0022]
The above-described growth step of InGaN / GaN MQW 18 and the growth step of the gallium nitride based semiconductor layer are each performed once, but these steps may be repeated a plurality of times (two or more times). An example in which these steps are repeated twice is shown in FIG. 3, first, a GaN layer 12, an InGaN / GaN MQW 18, and a gallium nitride based semiconductor layer 22 are formed on the substrate 10 under the same conditions as in FIG. Next, the InGaN / GaN MQW 36 is formed with the temperature set to the growth temperature (T1) of InGaN / GaN MQW, and the temperature is increased again to T2 under a nitrogen atmosphere to form the gallium nitride based semiconductor layer 38.
[0023]
Thus, by forming two or more layers of InGaN / GaN MQW, it is possible to better prevent dislocation propagation to the gallium nitride based semiconductor layer 38 formed as the uppermost layer.
[0024]
Further, when the process of raising the temperature to the growth temperature of the gallium nitride based semiconductor layer 22 after the growth of the InGaN / GaN MQW 18 is performed in an atmosphere containing ammonia, the gallium nitride based semiconductor layer at the growth temperature of the gallium nitride based semiconductor layer Even if the growth process 22 is not performed, the propagation of the dislocation 14 from the bottom 28 of the V-groove defect 20 can be prevented. This is because the nitride semiconductor of InGaN / GaN MQW 18 evaporates by raising the temperature to the growth temperature of the gallium nitride based semiconductor layer 22, and this reacts with ammonia to form a gallium nitride based semiconductor layer in the V-groove defect 20. This is because the direction of the dislocations 14 is bent in the direction of the interface 34 between the InGaN / GaN MQW 18 and the gallium nitride based semiconductor layer 22 in the same manner as described above.
[0025]
As described above, in this embodiment, the InGaN / GaN MQW 18 is grown at a relatively low temperature, for example, 650 to 800 ° C. to intentionally generate the V-groove defect 20, and the InGaN / GaN in which the V-groove defect 20 is generated. The gallium nitride semiconductor layers 22 and 38 are grown on the MQWs 18 and 36 at a relatively high temperature, thereby reducing the dislocations 14 in the gallium nitride semiconductor layers 22 and 38 grown at a high temperature. In this way, as shown in FIGS. 1B and 3, if the gallium nitride semiconductor layers 22 and 38 without the dislocations 14 are formed, the gallium nitride semiconductor layers 22 and 38 are formed on the gallium nitride semiconductor layers 22 and 38 thereafter. Even when a semiconductor crystal is grown, the dislocation 14 does not propagate. Therefore, an efficient device such as a light-emitting element can be formed by growing a device structure on the gallium nitride based semiconductor layers 22 and 38 where such dislocations 14 are not present.
[0026]
As a result of various experiments, the present inventors have found the following conditions for efficiently generating the V-groove defect 20 at the position of the dislocation 14 on the surface of the InGaN / GaN MQW 18, 36.
[0027]
Number of InGaN / GaN MQW stacks: 3 to 20 cycles, preferably 5 to 15 cycles. One cycle thickness is 10 nm.
[0028]
Total thickness of InGaN / GaN MQW: 50 to 200 nm, preferably 10 to 500 nm.
[0029]
In composition in InGaN / GaN MQW: 5 to 15%, preferably 7 to 13%.
[0030]
Growth temperature of InGaN / GaN MQW: 650 to 800 ° C., preferably 700 to 750 ° C.
[0031]
Growth temperature of gallium nitride based semiconductor layer grown on InGaN / GaN MQW: 800 to 1100 ° C., preferably 1000 to 1080 ° C.
[0032]
According to the above conditions, the dislocations 14 generated in the gallium nitride based semiconductor layers 22 and 38 formed on the InGaN / GaN MQW can be greatly reduced. In addition, as a material of the gallium nitride based semiconductor layers 22 and 38 described above, there is GaN as described above, but AlGaN can also be used under the same conditions.
[0033]
When an AlGaN / GaN-based LED that emits light at a wavelength of 350 nm is fabricated on the gallium nitride-based semiconductor layer 22 formed as described above, the luminous efficiency is approximately doubled compared to the case where the present invention is not used. I was able to.
[0034]
【The invention's effect】
As described above, according to the present invention, it is possible to form a gallium nitride based semiconductor layer in which dislocation termination does not occur on the surface.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a method for forming a gallium nitride based semiconductor layer according to the present invention.
FIG. 2 is an explanatory diagram of the principle that dislocations in a gallium nitride based semiconductor layer are reduced by the method for forming a gallium nitride based semiconductor layer shown in FIG.
FIG. 3 is a diagram showing an example in which an InGaN / GaN MQW growth step and a gallium nitride based semiconductor layer growth step are repeated twice.
FIG. 4 is a diagram showing an example of a conventional gallium nitride based semiconductor layer.
[Explanation of symbols]
10 substrate, 12 GaN layer, 14 dislocation, 16 surface, 18, 36 InGaN / GaN MQW, 20 V groove defect, 22, 38 gallium nitride semiconductor layer, 24 V groove surface, 26 loop, 28 bottom, 30, 32 side , 34 interface.

Claims (9)

A method for manufacturing a gallium nitride based semiconductor device having a gallium nitride based semiconductor layer in which dislocation termination does not occur on the surface as an underlying buffer layer ,
InGaN / GaN MQW is grown on the substrate at a growth temperature T1 to generate V-groove defects on the surface ,
Raising the temperature from T1 to the growth temperature T2 of the gallium nitride based semiconductor layer in a nitrogen atmosphere,
A gallium nitride based semiconductor layer is grown on the InGaN / GaN MQW at the temperature T2, and dislocations in the InGaN / GaN MQW are formed on the side surface of the V-groove defect and between the InGaN / GaN MQW and the gallium nitride based semiconductor layer. Proceed along the interface ,
A gallium nitride based semiconductor device is produced by growing a light emitting device device structure on the substrate and the buffer layer using the InGaN / GaN MQW and the gallium nitride based semiconductor layer as a base buffer layer. Device manufacturing method. The method of claim 1, wherein
A method of manufacturing a gallium nitride semiconductor device, wherein the growth step of the InGaN / GaN MQW and the growth step of the gallium nitride semiconductor layer are repeated twice or more. A method of manufacturing a gallium nitride semiconductor device having a gallium nitride semiconductor layer having no dislocation termination on the surface as an underlying buffer layer ,
An InGaN / GaN MQW is formed on the substrate at a growth temperature T1, and a V-groove defect is generated on the surface .
In an atmosphere containing ammonia, the temperature is increased from T1 to the growth temperature T2 of the gallium nitride semiconductor layer , and the dislocations in the InGaN / GaN MQW are changed to the side surfaces of the V-groove defects and the InGaN / GaN MQW and gallium nitride semiconductor. Proceed along the interface with the layer,
Thereafter, a light emitting device device structure is grown on the substrate and the buffer layer using the InGaN / GaN MQW and the gallium nitride based semiconductor layer as a base buffer layer, thereby forming the InGaN / MQW and nitride as the base buffer layer of the device structure. A method of manufacturing a gallium nitride based semiconductor device, comprising forming a gallium based semiconductor layer to manufacture a gallium nitride based semiconductor device. The method according to any one of claims 1 to 3, wherein
The method of manufacturing a gallium nitride semiconductor device, wherein the gallium nitride semiconductor is GaN. The method according to any one of claims 1 to 3, wherein
The method of manufacturing a gallium nitride semiconductor device, wherein the gallium nitride semiconductor is AlGaN. The method according to any one of claims 1 to 5, wherein
The method of manufacturing a gallium nitride based semiconductor device, wherein the temperature T1 is 650 to 800 ° C. The method according to any one of claims 1 to 6, wherein
The method of manufacturing a gallium nitride based semiconductor device, wherein the temperature T2 is 800 to 1100 ° C. A gallium nitride based semiconductor device having a gallium nitride based semiconductor layer as an underlying buffer layer ,
A substrate,
An InGaN / GaN MQW layer formed on the substrate and having V-groove defects on its surface;
The gallium nitride based semiconductor layer formed on the InGaN / GaN MQW layer causes dislocations in the InGaN / GaN MQW layer to be formed on the side surface of the V-groove defect and at the interface between the InGaN / GaN MQW and the gallium nitride based semiconductor layer. Proceed along,
A light emitting device structure formed on the gallium nitride based semiconductor layer;
A gallium nitride based semiconductor device, wherein the InGaN / GaN MQW layer and the gallium nitride based semiconductor layer are used as a buffer layer as a base of the device structure. The apparatus of claim 8.
The InGaN / GaN MQW layer is
The stacking cycle is 3 to 20 cycles,
The layer thickness is 50 to 200 nm,
A gallium nitride semiconductor device characterized in that the In composition is 5 to 15%.

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