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Optical Studies of Wide Band Gap III-Nitride Semiconductor Quantum Wells and Superlattices
|Hamid Haratizadeh 1,2, Bo Monemar 2, Plamen P. Paskov 2, Per Olof Holtz 2, Peder Bergman 2, H. Amano 3, Isamu Akasaki 3
1. Shahrood University of Technology, University Bolvd., Shahrood 3619995161, Iran
A detailed optical study of several sets of AlN/GaN superlattice (SL) as well as AlGaN/GaN multiple quantum well (MQW) structures has been reported. In this study all materials were grown by MOCVD, as opposed to most previous studies where MBE was employed. Doublet excitonic features are observed in the PL spectra. They are explained in terms of discrete well width variations by one c-lattice parameter, i.e. two GaN monolayers. The residual photoluminescence (PL) line width in MQW structures is varying from about 10 meV for 15 Å QWs to > 15 meV for 45 Å QWs, also comparable to the best MBE structures reported. While the recombination process in undoped samples is excitonic, in MQWs doped with Si above about 5×1018 cm-3 free electrons (a 2DEG) are dominant, and the PL process is a free electrons-localized hole transition at low temperatures. The hole localization prevails up to very high n-doping, as was previously observed in bulk GaN. The hole localization is demonstrated via several experiments, including results on PL transient decay times and LO phonon coupling. Near surface band bending, due mainly to dopant depletion in doped structures or interaction with surface states in case of higher Al content in barriers, influence the distribution of electron filling among the QWs, making a detailed modeling of the spectral shape somewhat ambiguous. It is found that AlN barriers promote a strong room temperature PL signal from the QWs, as opposed to the case with AlGaN barriers.
Presentation: Oral at E-MRS Fall Meeting 2006, Symposium F, by Hamid Haratizadeh
See On-line Journal of E-MRS Fall Meeting 2006
Submitted: 2006-06-14 12:07 Revised: 2009-06-07 00:44