Undoped and Si-doped GaN epitaxial films have been grown on sapphire substrates by metal-organic chemical vapor deposition. Variable angle spectroscopic ellipsometry (VASE) and surface photovoltage (SPV) spectroscopy were used to determine the minority carrier diffusion lengths of the films. Both the reflectivity and absorption coefficient (α) could be calculated from the VASE measurements. In SPV spectra at room temperature, a strong transition with a threshold at 3.42 eV was observed in both films, while an exciton-related absorption was observed only in the undoped GaN. The minority carrier diffusion lengths were calculated to be about 200 nm for the undoped GaN and about 20 nm for the Si-doped GaN. Moreover, a large divergence in the range of 1/α in the undoped GaN was found and attributed to its high surface barrier energy.
Citation: Physica Status Solidi
Pub Type: Journals
Electron states at surfaces and interfaces, III-V semiconductors, Photoconduction and photovoltaic effects