Temperature dependence of photoluminescence of an n-i-p-i GaAs superlattice

Since the concept of doping superlattice was proposed by Esak and Tsu, the electronic properties of it were intensively investigated both theoretically and experimentally. Doping 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 ~PL! experiments. 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 GaAs superlattice. Both PL peaks from indirect transitions and direct transitions are clearly observed, the redshifts of the two peaks with increasing temperature are discussed in terms of the competition of the direct and indirect transitions in the n-i-p-i GaAs superlattice. The sample was grown by molecular-beam epitaxy ~MBE! on a ~001! N GaAs substrate, after deposition of 1 mm semi-insulating GaAs buffer layer, ten periods of n GaAs (40 nm)/p GaAs (40 nm! was grown. n GaAs was Si doped and p GaAs was Be doped, both n and p doping concentration is 1310 cm. The overall structures were grown at 520 °C. The PL was performed in a Fourier transform spectrometer equipped with an InGaAs detector. The spectra were obtained under excitation with the 514.5-nm line of an argon-ion laser.