Broadening of near-band-gap photoluminescence in n-GaN films

This letter addresses the broadening mechanism of the near-band-gap photoluminescence in GaN films doped n type with silicon. The films were produced by plasma assisted molecular beam epitaxy and their carrier concentration was varied systematically from 10(15) to 10(20) cm(-3). The photoluminescence was excited with a 10 mW He-Cd laser at 77 K. At low carrier concentration (<10(17) cm(-3)) the photoluminescence peak has a full width at half maximum of about 18 meV, while at high carrier concentration (>10(18) cm(-3)) the full width at half maximum increases monotonically with carrier concentration up to about 120 meV. The broadening of the line at high carrier concentration is attributed to tailing of the density of states caused by potential fluctuations due to randomly distributed impurities, The data were quantitatively analyzed, as a function of carrier concentration and compensation ratio, using the impurity band broadening model of Morgan [Phys. Rev. 139, A343 (1965)], and the agreement between model and experimental data supports the model's validity and suggests a potential method of determining the compensation in degenerate nitride semiconductors. (C) 1998 American Institute of Physics.