The application of the Methods of Cathodoluminescence and Photoluminescence for Non-destructive Testing of AlGaN Heterostructures

Abstract

Abstract. This paper examines cathodoluminescence spectra of samples on sapphire substrates to develop methods of non-destructive testing of wafers with AlGaN/GaN heterostructures. It has been determined that the cathodoluminescence peak of AlGaN compound was demonstrated for decreased energy of excitation electrons (at 0.5 eV and 1 keV) only. Cathodoluminescence peak of AlN compound with energy of 6.15 eV was demonstrated at any excitation energy of 0.5 to 6.15 eV. It has been demonstrated that cathodoluminescence spectrum analysis allowed determining aluminum percentage in AlGaN, which was essential for inward testing of wafers for microwave transistors production. Data on the intensity distribution of "yellow" photoluminescence over the wafer surface has been obtained, and it has been demonstrated that these measurements were a prospective method of non-destructive testing to sorting wafers by defects. IntroductionThere are a number of publications which state that in order to obtain high-quality AlGaN/GaN-based high electron mobility transistors, Al content in the AlGaN layer should be within the range of 20 to 35 %. The main purpose of this work is to develop cathodoluminescence methods as implements for non-destructive testing in order to determine aluminum content in heterostructures before their production is started. Methods of cathodoluminescence and photoluminescence are effectively used for examination of properties of wide-band gap materials and structures, in particular, for examination of dislocation nature in GaN thin films and for control of self-radiation related to a band-to-band junction [1][2][3]. Cathodoluminescence and photoluminescence allow detecting the defects related to luminescence in the visible spectrum. The relation between the so-called "yellow" cathodoluminescence excited by electrons of various energy and resistance of ohmic contacts of a GaN source and drain of microwave transistors has been ascertained. Aluminum content in AlGaN layers has been examined, in particular, in the work [3], however, thick layers of specified material (hundreds of nanometers thick) have been used. In this work, AlGaN layers with a thickness of 20nm have been examined.