Minority carrier diffusion lengths and optical self‐absorption coefficient in undoped GaN

In this paper we report electron beam induced current (EBIC) measurements on Schottky diodes on undoped GaN samples grown by the metal organic vapor phase epitaxy method on porous silicon substrates. A 2D simulation model was applied to perform the theoretical EBIC profiles and to compare with the experimental one. A minority carrier diffusion length ( L ) for holes of 0.72 μm was measured in the space charge region, indicating constant diffusivity of 6.48 cm 2 /s and a lifetime coefficient of 0.8 ns. An increase of L is observed as the probe source is moved from the Schottky junction to the bulk material. This increase was related to the polarization effects that are preponderant in group III–nitride devices. Far from the depletion layer (greater than 0.91 μm) the measured current is produced by the reabsorbed recombination radiation process. This corresponds to an optical self‐absorption coefficient of a p = 0.112 μm −1 . The results show that the transport parameters depend on the growth technology. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)