Nitride semiconductor multilayer film reflector and light-emitting device using the same

A nitride semiconductor multilayer film reflector comprising a first semiconductor layer comprised of a group III nitride semiconductor, a second semiconductor layer, a first composition-graded layer and a second composition-graded layer, the nitride semiconductor multilayer film reflector being fabricated by repeatedly stacking the second composition-graded layer, the first semiconductor layer, the first composition-graded layer and the second semiconductor layer sequentially on a Ga surface,

• wherein the first semiconductor layer has a higher Al composition than the second semiconductor layer;
• wherein the first composition-graded layer is interposed between the first and second semiconductor layers so as to be located at a group III element face side of the first semiconductor layer, the first composition-graded layer being adjusted so that the Al composition thereof becomes lower as the first composition-graded layer comes close to the second semiconductor layer;
• wherein the second composition-graded layer is interposed between the first and second semiconductor layers so as to be located at a nitride face side of the first semiconductor layer, the second composition-graded layer being adjusted so that the Al composition thereof becomes lower as the second composition-graded layer comes close to the second semiconductor layer;
• wherein energy levels of electrons at bottoms of conduction bands of the first and second semiconductor layers and the first and second composition-graded layers are continuous without band offset;
• wherein the first composition-graded layer on which an antinode of a standing light wave having a predetermined wavelength is formed has an n-type impurity concentration of not less than 5×1019 cm−3, another region including the second composition-graded layer on which a node of the standing light wave having the predetermined wavelength is formed has an n-type impurity concentration of not more than 1×1019 cm−3, and a negative fixed charge due to polarization repels electrons in the first composition-grade layer and a positive fixed charge due to polarization attracts electrons in the second composition-graded layer;
• wherein the first and second semiconductor layers are an AlInN layer and a GaN layer respectively and the AlInN layer has an Al composition value ranging from 0.82 to 0.85;
• and
• wherein the first and second composition-graded layers are AlInN layers having Al compositions graded from 0.6 to the Al composition values respectively.