Abstract: Disclosed is an optical semiconductor device which has a quantum well structure comprising a quantum well made of a zinc oxide or a zinc oxide mixed crystal thin film, and utilizes optical transition between subbands in the quantum well structure. An element of this device can be formed as a film on a transparent substrate or a plastic substrate at a temperature of 200° C. or lower. The quatum well structure includes a barrier layer made of an insulating material such as ZnMgO; a homologous compound expressed by the following general formula: RMO3(AO)m, wherein R=Sc or In, M=Fe, Cr, Ga or Al, A=Zn, Mg, Cu, Mn, Fe, Co, Ni or Cd, and m=a natural number; or (Li, Na)(Ga, Al)O2.

Abstract: Disclosed is an optical semiconductor device which has a quantum well structure comprising a quantum well made of a zinc oxide or a zinc oxide mixed crystal thin film, and utilizes optical transitions between subbands in the quantum well structure. An element of this device can be formed as a film on a transparent substrate or a plastic substrate at a temperature of 200° C. or lower. The quantum well structure includes a barrier layer made of an insulating material such as ZnMgO; a homologous compound expressed by the following general formula: RMO3(AO)m, wherein R=Sc or In, M=In, Fe, Cr, Ga or Al, A=Zn, Mg, Cu, Mn, Fe, Co, Ni or Cd, and m=a natural number; or (Li, Na)(Ga, Al)O2.

Abstract: A spin filter is composed of a first magnetic semiconductor multi-quantum well structure, a second magnetic semiconductor multi-quantum well structure and a non-magnetic semiconductor quantum well structure which is located between the first magnetic semiconductor multi-quantum well structure and the second magnetic semiconductor multi-quantum well structure. The first magnetic semiconductor multi-quantum well structure and the second magnetic semiconductor multi-quantum well structure are split in spin state. Carriers in down-spin state are penetrated through the first magnetic semiconductor multi-quantum well structure and carriers in up-spin state are penetrated through the second magnetic semiconductor multi-quantum well structure.

Abstract: A spin filter is composed of a first magnetic semiconductor multi-quantum well structure, a second magnetic semiconductor multi-quantum well structure and a non-magnetic semiconductor quantum well structure which is located between the first magnetic semiconductor multi-quantum well structure and the second magnetic semiconductor multi-quantum well structure. The first magnetic semiconductor multi-quantum well structure and the second magnetic semiconductor multi-quantum well structure are split in spin state. Carriers in down-spin state are penetrated through the first magnetic semiconductor multi-quantum well structure and carriers in up-spin state are penetrated through the second magnetic semiconductor multi-quantum well structure.

Abstract: An intersubband light emitting element includes a semiconducting substrate, a first layer composed of a first semiconducting material, and a second layer composed of second semiconducting material. The first layer makes a heterojunction with the second layer. The top of a valence band of the first semiconducting material is higher in energy than the bottom of a conduction band of the second semiconducting material. The element further includes a third layer making a heterojunction with the first or second layer. The third layer has a superlattice structure. One of the first and second layer is provided on the semiconducting substrate directly or through at least one semiconducting layer.