Defects Created by 25 keV Hydrogen Implantation in n -type GaN
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Defects Created by 25 keV Hydrogen Implantation in n-type GaN F. D. Auret, W. E. Meyer, H. A. van Laarhoven, S. A. Goodman, M. J. Legodi, B. Beaumont1 and P. Gibart1 Physics Department, University of Pretoria, Pretoria 0002, South Africa. 1 CRHEA-CNRS, Valbonne, France. ABSTRACT We have studied defects introduced in n-GaN during 25 keV hydrogen and 40 keV He implantation using deep level transient spectroscopy (DLTS). These measurements revealed that 25 keV hydrogen implantation introduces a complex set of electron traps, of which most are different to the defects observed after high-energy (MeV) electron and proton implantation. At least three of the defects detected after 25 keV proton implantation exhibit a metastable character in that they can be reproducibly removed and re-introduced during reverse and zero bias anneal cycles. Isochronal and isothermal annealing experiments yielded low activation energies of approximately 0.1 – 0.2 eV for both processes. By comparison, 40 keV He ion implantation introduced the same metastable defects, but in different relative concentrations. INTRODUCTION Hydrogen plays an important role in determining the properties of semiconductors. In the case of GaN, hydrogen is present in large concentrations during crystal growth and thereafter [1]. Up to now, most investigations of hydrogen in GaN focussed on Mg passivation and limited information is available about the influence of hydrogen on defects in n-type GaN [2]. Methods of introducing hydrogen into semiconductors include low-energy implantation and hydrogen plasma processing. When hydrogen is implanted into GaN, defects are introduced. The electronic properties of defects introduced by high-energy (2 MeV) hydrogen bombardment in n-GaN have already been reported [3]. However, 2 MeV hydrogen ions penetrate about 25 microns into GaN and thus the region probed by DLTS (approximately the first micron below the GaN surface) does not contain significant concentrations of hydrogen to investigate its passivation effect on other defects. Consequently, the interaction of hydrogen with defects induced during GaN crystal growth and subsequent particle implantation cannot easily be investigated by DLTS for implantation with high-energy hydrogen ions. In this paper, we report DLTS results obtained after implanting n-GaN with 25 keV hydrogen-ions, for which both the implantation induced defects and the implanted H are present in the region analysed by DLTS. We show that this implantation introduces several defects not observed after 2 MeV hydrogen implantation and that some of these defects exhibit a metastable character. In addition, we demonstrate that 40 keV He ion implantation also introduces the same metastable defects that H-implantation does, but in different relative concentrations. EXPERIMENTAL PROCEDURE For this investigation, we have used GaN with a free carrier density of (2–3)×1016 cm–3, grown by epitaxial lateral overgrowth organo-metallic vapor phase epitaxy (ELOG-OMVPE) on I4.3.1
sapphire. After cleaning the samples using con
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