Effect of Capping on Electrical and Optical Properties of GaN Layers Grown by HVPE

Gallium nitride, grown by hydride vapor phase epitaxy and capped with a thin AlGaN layer, was studied by photoluminescence (PL) methods. The concentration of free electrons in GaN was found from the time-resolved PL data, and the concentrations of point defects were estimated from the steady-state PL measurements. The intensity of PL from GaN decreases moderately after capping it with Si-doped AlGaN, and it decreases dramatically after capping with Mg-doped AlGaN. At the same time, the concentration of free electrons and the concentrations of main radiative defects in GaN are not affected by the AlGaN capping. We demonstrate that PL is a powerful tool for nondestructive characterization of semiconductor layers buried under overlying device structures.