Non Destructive Evaluation of AlGaN/GaN HEMT structure by cathodoluminescence spectroscopy

Highlights: • Cathodoluminescence investigation of radiative defects in AlGaN/GaN HEMT. • Estimation of ultra thin GaN cap thickness and its interface quality with barrier. • The quantum well emission from the GaN cap of AlGaN/GaN HEMT. • Band edge peak intensity of AlGaN barrier relates to its YL defects concentration. • Use of low e-beam accelerating voltage to probe cap as well as barrier layer. We have investigated radiative defects in various component layers in an AlGaN/GaN HEMT structure by measuring Cathodoluminescence (CL) spectrum as a function of accelerating voltage. Low electron beam accelerating voltages (below 1 kV) CL spectra are used to get information about defects in the cap layer and the barrier layer. Samples with good quality GaN cap layer showed surface quantum well (SQW) transition in the CL spectrum. The cap layer thickness and its quality can be determined from the SQW emission energy and its integrated intensity. We show that low intensity electron beam provides information about the defects in the cap layer as well as barrier layer through the intensity and energy of the yellow luminescence peak. The observed changes in the CL intensity of the barrier layer towards the surface have been correlated to the formation of aluminium oxide, giving rise to higher concentration of deep acceptor defects probably related to the adsorbed oxygen on the uncapped AlGaN barrier layer samples. The results are supported by X-ray photoelectron spectroscopy (XPS), High resolution X-ray diffraction (HRXRD) and Secondary ion mass spectrometry (SIMS) techniques.