Mechanisms in thermal stress aided electroless etching of GaN grown on sapphire and approaches to vertical devices

Abstract

A thermal stress aided electroless etching (TSEE) process of epitaxial GaN on sapphire has been demonstrated experimentally and theoretically. The sapphire has been successfully separated from the epitaxial GaN by electroless etching assisted by the thermal peeling stress at the GaN/sapphire interface. ANSYS simulation indicates a sharp increase in peeling stress at the edge of the chip. The mechanism of the TSEE process has been elucidated in macro- and micro-interpretation in this paper, which is based on a charge transfer reaction model with a thermodynamic cycle and an Arrhenius equation. The influences of etching temperature (ET) and etchant concentration (EC) on the TSEE process were quantitatively analyzed based on experimental results. X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) results show an improvement in the epitaxial GaN crystallinity with the TSEE process. Analysis of the mechanisms of the TSEE process will undoubtedly deepen our understanding of semiconductor etching and facilitate more potential applications.