Possible impact of surface morphology on stimulated emission in GaN–AlGaN double heterostructures

Abstract

Stimulated emission is studied in a hexagonal AlGaN/GaN/AlGaN double heterostructure grown on a (0 0 0 1) sapphire substrate by low pressure (200 mbar) metallorganic vapor phase epitaxy. A sharp increase in the edge emitted luminescence intensity is obtained above a threshold excitation density of 40 kW/cm 2 and is accompanied by a strong narrowing of the luminescence line width. The specific surface morphology of the heterostructure is suspected to be responsible for an optical feedback in the sample. Although the surface is extremely smooth yielding roughness values of σ RMS<0.36 nm an almost perfectly periodic corrugation is superimposed reflecting the columnar growth mode of the nitrides. The measured quasi-periodic corrugation of λ=110–120 nm periodicity perfectly matches the stimulated emission wavelength in the dielectric material.