Both the photoluminescence peaks corresponding to the vertical transitions and the nonvertical transitions in an n-i-p-i GaAs superlattice are clearly observed. The redshifts of the two peaks with increasing temperature are discussed in terms of the temperature-dependent carrier separation effect.Since the concept of doping superlattice was proposed by Esak and Tsu, 1 the electronic properties of it were intensively investigated both theoretically and experimentally.
2-11Doping superlattices are structures which contain alternatively n-type and p-type doped regions of one semiconductor material and have a number of unique properties, such as tunable electronic structures, indirect band gap in real space, and large recombination lifetimes. These properties are originated from the spatial separation of electrons and holes due to the periodic impurity space charge potential and can be utilized in semiconductor devices such as light-intensity modulators. Great efforts have been put on the tunable and indirect band-gap transitions of n-i-p-i superlattices. The possible vertical optical transitions in n-i-p-i superlattices are also investigated by temperature-dependent photoluminescence ͑PL͒ experiments.7-9 However, these reports only discussed the overall PL intensity dependence on temperature and the critical temperature point at which vertical transitions will prevail in intensity according to the sample parameters. To our surprise, no discussions on the PL peak energy dependence on temperature were performed in the large body of previous research in this field. In this paper, we investigate the temperature-dependent PL properties of an n-i-p-i
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