In0.227GaAs/GaAsN0.011 was introduced as a 1.2-eV multiple quantum well (MQW) with a flat conduction band (FCB) in which a conduction band edge of GaAsN was adjusted to be equal to that of InGaAs. This MQW was established as a candidate material for a middle absorption layer of three-junction solar cell since electron confinement was eliminated and a short electron lifetime in GaNAs was compensated by InGaAs layer. The band alignment of MQW was characterized by the power-dependent photoluminescence (PL) measurement under low temperature. According to the band-anti crossing model, the FCB is possibly constructed since a small amount of incorporated N can drastically reduce the energy of the conduction band edge of GaAsN. The PL results demonstrated that In0.227GaAs/GaAsN MQW was a type-I structure when N content was below 1.1%, and became a type-II structure when N content was above 1.1%. The type-II MQW was characterized by the observation of blueshift of PL peak when increasing excitation power. This blueshift is a result of band-bending effect due to the accumulation of excited carriers at the interface between two materials, which is unique for the type-II MQW. In addition, it was observed that the activation energy estimated from the Arrhenius plot provided a minimum value in the structure with 1.1%N; the lowest activation energy indicated the weakest confinement energy of carriers in the structure. These results approved that a transition from type-I to type-II occurred when N content surpassed 1.1%, and our designed In0.227GaAs/GaAsN0.011 MQW was potentially the FCB structure.
W. Yanwachirakul, N. Miyashita, H. Sodabanlu, K. Watanabe, Y. Okada, M. Sugiyama, and Y. Nakano, "Characterization of InGaAs/GaAsN multiple quantum well with flat conduction band for improving carrier transport in multijuction solar cell," Proc. SPIE 10527, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VII, 105270E (Presented at SPIE OPTO: January 31, 2018; Published: 16 February 2018); https://doi.org/10.1117/12.2296574.
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