Abstract
A series of double heterojunction AlGaN/GaN/AlGaN high electron mobility transistor (HEMT) heterostructures are grown by ammonia MBE on sapphire substrates using AlN buffer layers with varying thicknesses and growth conditions. The grown heterostructures are investigated by atomic force microscopy as well as photoluminescence (PL), stimulated emission (SE), and photoreflectance (PR) measurements. It is shown that PL intensity cannot be used as a reliable criterion for quality control of HEMT heterostructures because of an influence of surface roughness. A new method of quality control of the active GaN layer in HEMTs is proposed based on determination of the SE threshold excitation level. An advantage of the method is that no reference sample is needed for comparison of different HEMT structures. Internal electric field strength values are determined from PR spectra and their correlation with 2DEG density is demonstrated.
Radiative and 2DEG properties of AlGaN/GaN/AlGaN high electron mobility transistor (HEMT) heterostructures are investigated. It is shown that photoluminescence intensity cannot be used as a reliable criterion for comparison of HEMT heterostructures because of an influence of surface roughness. In contrast, a strong correlation between stimulated emission threshold and 2DEG mobility is observed. Based on the result, a new method of quality control for HEMT heterostructures is proposed.