Electron concentration dependence of exciton localization and freeze-out at local potential fluctuations in InN films

InN films with electron concentration ranging from n similar to 10(17) to 10(20) cm(-3) grown by metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were investigated by variable-temperature photoluminescence and absorption measurements. The energy positions of absorption edge as well as photoluminescence peak of these InN samples with electron concentration above 10(18) cm(-3) show a distinct S-shape temperature dependence. With a model of potential fluctuations caused by electron-impurity interactions, the behavior can be quantitatively explained in terms of exciton freeze-out in local potential minima at sufficiently low temperatures, followed by thermal redistribution of the localized excitons when the band gap shrinks with increasing temperature. The exciton localization energy sigma (loc) is found to follow the n (5/12) power relation, which testifies to the observed strong localization effects in InN with high electron concentrations.

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Special Funds for Major State Basic Research Project 973 2006CB6049 National Nature Science Foundation of China 60721063 60731160628 60676057 60820106003 60906025 60990311 Nature Science Foundation of Jiangsu province BK2008019 BK2009255 NJU- Yangzhou Institute of Opto-electronics

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Special Funds for Major State Basic Research Project 973 2006CB6049 National Nature Science Foundation of China 60721063 60731160628 60676057 60820106003 60906025 60990311 Nature Science Foundation of Jiangsu province BK2008019 BK2009255 NJU- Yangzhou Institute of Opto-electronics