There are conventionally-known nitride semiconductor light emitting devices in each of which a p-type Mg-doped AlGaN layer as an electron barrier layer to trap electrons in an active layer is formed on an active layer including an In-containing nitride semiconductor (see the description of Japanese Patent No. 3446660 and Japanese Patent Application Publication No. 2006-261392, for example).
In the nitride semiconductor light emitting device disclosed in the description of Japanese Patent No. 3446660, the p-type AlGaN layer includes a first p-type AlGaN layer and a second p-type AlGaN layer. The first p-type AlGaN layer is formed by MOCVD (Metal Organic Chemical Vapor Deposition) which uses a N2 gas to inhibit the deterioration of the active layer. The second p-type AlGaN layer is formed by MOCVD which uses a H2 gas to form barrier potential.
In the nitride semiconductor light emitting device, however, the Al composition ratio of the first p-type AlGaN layer is almost the same as that of the second p-type AlGaN layer, and is set at 0.1 or greater. In addition, the first p-type AlGaN layer is doped with a large amount of Mg for decreasing the bulk resistance.
As a result, the nitride semiconductor light emitting device entails a problem that the quality of the active layer is deteriorated due to excessive diffusion of Mg into the active layer in the process of forming the second p-type AlGaN layer.
The nitride semiconductor light emitting device disclosed in Japanese Patent Application Publication No. 2006-261392 has an intermediate layer between the active layer and the p-type AlGaN layer for the purpose of inhibiting excessive diffusion of Mg into the active layer. The intermediate layer includes an undoped GaN layer, an undoped AlGaN layer and the like.
In the case of the nitride semiconductor light emitting device, however, the temperature of the substrate is raised while the intermediate layer is being grown on the active layer. As a result, the nitride semiconductor light emitting device has a problem that the active layer thermally deteriorates during the temperature rise, and accordingly entails the quality degradation.
In short, the nitride semiconductor light emitting devices have problems such as the decrease in the light-emission efficiency and the incapability of producing sufficient light output.
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