JP5200829B2 - Method for manufacturing group III nitride compound semiconductor light emitting device - Google Patents

Description

  The present invention relates to a method for producing a group III nitride compound semiconductor light emitting device.

In order to control the wavelength of light emitted from a group III nitride compound semiconductor light emitting device used as a semiconductor light emitting device for a short wavelength, InGaN containing In in its active layer may be used.
When a group III nitride compound semiconductor layer containing In (hereinafter sometimes simply referred to as “semiconductor layer”) is grown by MOCVD, the growth temperature is maintained at a lower temperature (800 ° C. or lower) than GaN and AlGaN. Is done. This is because InGaN has a low dissociated vapor pressure, so that it is difficult to incorporate In into the crystal when grown at a high temperature.
A p-type layer made of GaN or the like formed on the active layer generally has a relatively high temperature (900 regardless of the composition of the active layer (that is, even if In is included in the active layer)). ˜1000 ° C.). Therefore, in order to prevent InGaN from sublimating from the active layer during the formation of the p-type layer, measures such as providing an uppermost cap layer in the active layer including a semiconductor layer containing In have been taken.

Patent Document 1 discloses a technique for improving the light emission output by controlling the growth conditions of a p-type layer formed on an active layer including an In-containing semiconductor layer severely so that the active layer has high quality. Is disclosed.
Reference should be made to Patent Document 2 and Patent Document 3 as documents disclosing techniques related to the present invention.
JP 2008-47774 A JP 2005-136421 A JP 2006-303259 A

In the technique disclosed in Patent Document 1, since the thermal conditions (growth temperature and time) must be strictly managed during the growth of the p-type layer, it takes time to manufacture and may increase the manufacturing cost of the light emitting element. is there.
Accordingly, an object of the present invention is to improve the crystallinity of a semiconductor layer containing In in an active layer while relaxing the heat treatment conditions of the p-type layer.

As a result of intensive studies to achieve the above object, the present inventors have found that there is the following relationship between the growth temperature of the p-type layer and the crystal quality of the semiconductor layer containing In in the active layer. .
When the growth temperature of the p-type layer is high (about 1000 ° C.), the crystallinity of the semiconductor layer containing In (which was poor in crystallinity due to low-temperature growth) is improved (capped by the p-type layer and In Mg, which is a dopant of the p-type layer, diffuses into the active layer (provided that there is no sublimation), and this causes the crystallinity of the active layer to decrease.
When the growth temperature of the p-type layer is low (less than 900 ° C.), diffusion of Mg, which is a dopant of the p-type layer, into the active layer can be prevented, but a semiconductor containing In that is originally grown at a low temperature and a good crystal structure cannot be obtained The crystallinity of the layer is not improved as during the high temperature growth.
In the manufacturing process of the semiconductor light emitting device so far, without knowing the above-mentioned knowledge, the growth condition of the p-type layer is finely adjusted to improve the crystal structure of the semiconductor layer containing In and the trade-off between Mg diffusion. It was something to balance.

The present invention has been made based on the above findings, and the first aspect thereof is defined as follows. That is,
A method of manufacturing a semiconductor light emitting device comprising a group III nitride compound semiconductor,
A p-clad layer growth step of growing a p-clad layer on an active layer including a semiconductor layer containing In at a first temperature (800 to 900 ° C.);
A heat treatment step of heat-treating the laminate obtained in the p-cladding layer growth step at a second temperature higher than the first temperature;
A p-contact layer growth step for growing a p-contact layer on the p-cladding layer at a third temperature lower than the second temperature;
A method for producing a Group III nitride compound semiconductor light-emitting device.

According to the method for manufacturing a group III nitride compound semiconductor light emitting device as defined above, a p-cladding layer with a relatively small amount of Mg, which is a p-type dopant, is formed at a relatively low temperature (first temperature). Form. Therefore, it is possible to prevent Mg supplied during the formation of the p-clad layer from diffusing into the active layer. Although heat treatment is performed at a relatively high second temperature after the formation of the p-clad layer, the amount of Mg contained in the p-clad layer is very small, and Mg hardly diffuses from the p-clad layer to the active layer. On the other hand, this heat treatment temperature is sufficient to improve the crystallinity of the semiconductor layer containing In and the p-type cladding layer.
The p-contact layer having a relatively large Mg doping amount is grown at a relatively low temperature (third temperature) after the heat treatment. Therefore, Mg diffusion due to the p contact layer hardly occurs.
Here, the second temperature and the third temperature can be fixed to a constant temperature and do not need to be adjusted precisely. Therefore, a large margin can be taken in the heat treatment conditions when forming the p-type layer, and the manufacturing conditions of the semiconductor light emitting element are relaxed.

The optimum value of the second temperature at which the heat treatment is performed varies depending on the growth temperature of the semiconductor layer containing In in the light emitting layer, but is preferably about 100 to 200 ° C. higher than the growth temperature of the semiconductor layer containing In. . This corresponds to 900 to 1000 ° C. in the case of a blue light emitting element, for example. If it is lower than 900 ° C., the crystal structure of the semiconductor layer containing In cannot be improved. On the other hand, heat treatment at a temperature exceeding 1000 ° C. is not preferable because the crystal quality of the semiconductor layer containing In deteriorates.
The heat treatment time can be arbitrarily selected according to the composition and thickness of the semiconductor, but is preferably about 100 to 300 seconds.
On the other hand, the third temperature for forming the p-contact layer is preferably 800 to 900 ° C. If the temperature exceeds 900 ° C., Mg may be diffused. On the other hand, if it is less than 800 ° C., sufficient crystallinity may not be obtained in the p-contact layer, which may result in high resistance and low translucency. Absent.

  After forming the p-cladding layer, it is preferable to perform heat treatment in a so-called as-grown state from the viewpoint of simplifying the manufacturing process. That is, in a series of processes for growing a semiconductor layer using an MOCVD apparatus, when the growth of the p-clad layer is completed, the supply of the group III material and dopant gas of the group III nitride compound semiconductor is stopped, and nitrogen gas and ammonia Only gas is distributed. Then, the temperature of the MOCVD apparatus (for example, the temperature given to the workpiece substrate) is raised to the second temperature.

In this specification, the group III nitride compound semiconductor means Al _X Ga _Y In _1- XYN (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ X + Y ≦ 1) as a general formula. A so-called binary system of AlN, GaN and InN, Al _x Ga _1-x N, Al _x In _1-x N and Ga _x In _1-x N (in the above, 0 <x <1 ) Of the so-called ternary system. At least a part of the group III element may be substituted with boron (B), thallium (Tl), etc., and at least a part of the nitrogen (N) is also phosphorus (P), arsenic (As), antimony (Sb) , Bismuth (Bi) or the like. The group III nitride compound semiconductor layer may contain an arbitrary dopant. Si, Ge, Se, Te, C, or the like can be used as the n-type impurity. Mg, Zn, Be, Ca, Sr, Ba, or the like can be used as the p-type impurity.
Further, the semiconductor layer containing In is Al _X Ga _Y In _1- XYN (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ X + Y <1 in the definition of the group III nitride compound semiconductor described above. ).
Group III nitride compound semiconductor layers are formed by well-known metal organic chemical vapor deposition (MOCVD), molecular beam crystal growth (MBE), halide vapor deposition (HVPE), sputtering, ion plating. It can be formed by a method or the like.
It is also possible to expose the group III nitride compound semiconductor to electron beam irradiation, plasma irradiation or heating by a furnace after doping with a p-type impurity.

  When performance (film quality) is important, a p-clad layer growth step for growing at the first temperature, a heat treatment step for heat treatment at the second temperature, and a p-contact layer growth step for growth at the third temperature. These may be performed separately in separate chambers or apparatuses. By dividing and processing, Mg contamination can be reduced, and in the heat treatment, it is possible to minimize the diffusion of Mg using an RTA (rapid heat treatment apparatus).

  The light emitting element is formed by stacking such group III nitride compound semiconductors. A quantum well structure (multiple quantum well structure or single quantum well structure) can be adopted as the layer structure of the active layer for light emission. In addition, a single hetero type, a double hetero type, and a homozygous type can also be adopted.

Hereinafter, an example of the semiconductor light emitting device 100 according to an embodiment of the present invention will be described.
1 shows a basic semiconductor multilayer structure of a semiconductor light emitting device 100 of the embodiment of the invention of FIG.
A buffer layer 2 made of aluminum nitride (AlN) is formed on the sapphire substrate 1, and an n-contact layer 3 made of GaN doped with silicon (Si) is formed thereon.

On the n-contact layer 3, an n-clad layer 4 in which an undoped InGaN layer 1041 and a Si-doped n-GaN layer 1042 are repeatedly stacked is formed.
On the n-cladding layer 4, an active layer 5 having a multiple quantum well structure in which a well layer made of undoped InGaN and a barrier layer made of undoped GaN are repeatedly stacked is formed.
On the active layer 5, a p-cladding layer 6 is formed in which an AlGaN layer doped with Mg and an InGaN layer doped with Mg are repeatedly laminated.

A p-contact layer 7 made of a GaN layer doped with Mg is formed on the p-cladding layer 6, and a p-GaN layer having a higher Mg concentration than the p-contact layer is formed on the p ^- contact layer 7. A p ⁺ contact layer 8 is formed.
A translucent thin film p-electrode 10 by metal vapor deposition is formed on the p ⁺ contact layer 8, and an n-electrode 40 is formed on the n-contact layer 3. The translucent thin film p-electrode 10 includes a first layer 11 made of cobalt (Co) directly bonded to the p ⁺ contact layer 8 and a second layer 12 made of (Au) bonded to the cobalt film. . The translucent thin film p-electrode can be made of a nickel-gold alloy or can be formed of ITO.

The thick film p-electrode 20 includes a first layer 21 made of vanadium (V), a second layer 22 made of gold (Au), and a third layer 23 made of aluminum (Al). It is comprised by laminating sequentially from the top.
The n-electrode 40 having a multilayer structure is formed by laminating a first layer 41 made of vanadium (V) and a second layer 42 made of aluminum (Al) on a part of the n-contact layer 3 that is partially exposed. Composed.
A protective film 30 made of a SiO ₂ film is formed on the top.
Note that a reflective metal layer made of aluminum (Al) having a thickness of about 500 nm can be formed by metal vapor deposition on the outermost lowermost portion corresponding to the bottom surface of the sapphire substrate 1. In addition, you may form this reflective metal layer with nitrides, such as TiN and HfN other than metals, such as Rh, Ti, and W.

The group III nitride compound semiconductor light emitting device 100 shown in FIG. 1 is formed as follows.
First, the buffer layer 2, the n contact layer 3, the n clad layer 4, the active layer 5, and the p clad layer 6 are formed on the sapphire substrate. Thereafter, heat treatment is performed by supplying only nitrogen gas and ammonia gas into the reaction vessel of the MOCVD apparatus. After the heat treatment, the p ⁻ contact layer 7 and the p ⁺ contact layer 8 are grown.
In the above process, the growth temperature of the p-clad layer 6 was 850 ° C., and the heat treatment conditions were 1000 ° C. and 120 seconds. The subsequent growth of the p ⁻ contact layer 7 and the p ⁺ contact layer 8 was performed at 900 ° C.
Note that the growth temperature of the semiconductor layer containing In in the active layer is about 770 ° C.

According to the semiconductor light emitting device 100 manufactured as described above, the crystal quality of the active layer is increased. As a result, a light emitting element with high luminous efficiency is obtained.
In order to verify the improvement in luminous efficiency, the heat treatment conditions of the above examples were changed. In Comparative Example 1, no heat treatment was performed. In Comparative Example 2, heat treatment (1000 ° C. × 120 seconds) was performed after the formation of the active layer and before the growth of the p-clad layer. In Comparative Example 3, the heat treatment temperature in the example was 1100 ° C. × 120 seconds.
The results of the PL test are shown in FIG.
It can be seen from Comparative Example 1 that the PL strength is increased by the effect of the heat treatment.
From Comparative Example 2, it can be seen that it is effective to perform the heat treatment with the p-cladding layer grown. This is presumably because the p-cladding layer functions as a cap layer for the light-emitting layer, and thermal decomposition of InGaN is suppressed.
From Comparative Example 3, it can be seen that if the heat treatment temperature is too high, the thermal decomposition of InGaN cannot be suppressed and the effect of the heat treatment is reduced.

  According to the study by the present inventors, even when the substrate of the light emitting element is made of GaN, the effect of the heat treatment was confirmed as described above. However, the degree of effect (PL intensity increase rate) was smaller for GaN substrates than for sapphire substrates. This is presumably because when sapphire is used as the substrate, lattice defects generated in the semiconductor layer containing In in the active layer are larger, and the effect of improving the lattice defects by heat treatment appears more greatly.

  The present invention is not limited to the description of the embodiments and examples of the invention described above. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

It is a schematic diagram which shows the structure of the light emitting element of the Example of this invention. It is a graph which shows PL intensity | strength of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 Buffer layer 3 n contact layer 4 n clad layer 5 active layer 6 p clad layers 7 and 8 p contact layer

Claims (5)

A method of manufacturing a semiconductor light emitting device comprising a group III nitride compound semiconductor,
A p-clad layer growth step of growing a p-clad layer on an active layer including a semiconductor layer containing In at a first temperature (800 to 900 ° C.);
A heat treatment step of heat-treating the laminate obtained in the p-cladding layer growth step at a second temperature higher than the first temperature;
A p-contact layer growth step for growing a p-contact layer on the p-cladding layer at a third temperature lower than the second temperature;
And a method of manufacturing a group III nitride compound semiconductor light emitting device, wherein the doping amount of Mg in the p contact layer is larger than the doping amount of Mg in the p clad layer .   2. The manufacturing method according to claim 1, wherein the second temperature is 900 to 1000 ° C., and the third temperature is 800 to 900 ° C. 3.   3. The manufacturing method according to claim 1, wherein the p-clad layer growth step is executed by an MOCVD apparatus, and the heat treatment step is executed in the MOCVD apparatus.   4. In the heat treatment step, a gas mixture of nitrogen gas and ammonia gas is circulated in the MOCVD apparatus, and a dopant gas for converting the group III nitride compound semiconductor into p-type is not circulated. The manufacturing method as described in. The manufacturing method according to claim 1, wherein the substrate of the semiconductor element is made of sapphire.

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