Modulation of polarization field by fluorine ions in AlGaN/GaN heterostructures revealed by positron annihilation spectroscopy

Abstract

Modulations of energy band and polarization field by fluorine ions in fluorine plasma treated AlGaN/GaN heterostructures were revealed by positron annihilation spectroscopy (PAS). It is found that the annihilation probability is mainly governed by the electric field in the AlGaN/GaN heterostructure, which could be modulated by charged ions, opposite to what was first expected from the large number of plasma-induced defects such as Ga-vacancies. The modulation of electric field is successfully observed through the opposite changes in the S parameters on the two sides of the hetero-interface after fluorine plasma treatment due to the opposite E-field directions. Fluorine is experimentally proved to be negatively charged in GaN related materials, which is consistent with the operation principle of enhancement-mode AlGaN/GaN HEMT fabricated by fluorine plasma treatment. It is also suggested that PAS is a useful tool to probe the intrinsic electric field in AlGaN/GaN system. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.