Carrier diffusion length measured by optical method in GaN epilayers grown by MOCVD on sapphire substrates

Abstract

The carrier ambipolar diffusion length L of optically excited carriers in GaN epitaxial layers grown on sapphire substrate was estimated by an optical method using fitting of the experimental photoluminescence spectra recorded from the front and back sides of the samples by the theoretical equation describing light reflection, light absorption and carrier profile in the medium. The estimations were carried out in the range of excitation intensities from 5 W/cm 2 CW up to 1 MW/cm 2 (pulsed), using excitation at the wavelengths of 325, and 337.1 nm in order to vary the excited layer depth. It has been found that in the samples under study the value of L is about 120–130 nm and does not depend significantly on the excitation intensity up to 200 kW/cm 2. Further increase of excitation level leads to higher values of L about 150–170 nm, probably because of the electron-hole plasma expansion.