Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride

Abstract

Time-dependent cathodoluminescence (CL) and specimen current (SC) are monitored to evaluate trapping behaviour and evolution of charge storage. Examination of CL and SC suggests that the near band edge emission in GaN is reduced primarily by the activation of traps upon irradiation, and Gallium vacancies are prime candidates. At the steady state, measurement of the stored charge by empiric-analytical methods, suggests that all available traps within the interaction volume have been filled, and that additional charge is being stored interstitially, necessarily beyond the interaction volume. Once established, the space charge region is responsible for the steady state CL emission and prior to build up, it is responsible for the generation of diffusion currents. Since the non-recombination effects resulting from diffusion currents that develop early on are analogous to those leading to device failure upon aging, this study is fundamental towards a holistic insight into optical properties in GaN. I. INTRODUCTION: The dynamics behind electrical stress that results in optical malfunction and failure remain unresolved despite the urgency to determine mechanisms leading to electronically fatigue-resilient GaN devices. 1 Similarly, the study of charging mechanisms upon electron beam bombardment in poorly conductive materials is an active field of research. 2 And in fact, a grounded stage in an electron microscope can serve as a simulation platform, where prolonged irradiation by electron beams promote device aging and simultaneous and in-situ cathodoluminescence (CL) monitors impact from the inflicted electrical stress on optical properties. 3,4 This is achieved by selecting current densities in the electron beam analogous to operational currents in nitride-based laser diode devices, 5 which is conducive to the CL dynamics elucidation of aging and breakdown. In this scheme, understanding electron beam derived charging mechanisms will enable improved device operation, as it offers qualitative insight into operational aging in GaN.