Journal of Crystal Growth 248 (2003) 513–517 Growth and characteristics of Fe-doped GaN S. Heikman*, S. Keller, T. Mates, S.P. DenBaars, U.K. Mishra Department of Electrical and Computer Engineering and Materials Department, University of California, Santa Barbara, CA 93106, USA Abstract The Fe doping of GaN by metalorganic chemical vapor deposition was studied. Si–Fe co-doping experiments revealed that the compensation activity of Fe was 34%. The Fe-doping response was investigated in detail by secondary ion mass spectroscopy. The observed slow Fe concentration turn-on and turn-off was found to be related to the sample surface, rather than to the reactor environment. Improved turn-off was demonstrated by etching a GaN:Fe surface in acids before the GaN regrowth. Fe segregation on the growth surface was proposed to explain the observed Fe-doping response. r 2002 Elsevier Science B.V. All rights reserved. PACS: 81.10.Bk; 72.80.Ey Keywords: A1. Doping; A1. Segregation; A3. Metalorganic vapor phase epitaxy; B1. Nitrides 1. Introduction Semi-insulating GaN is important for many nitride-based device structures. In vertical devices, semi-insulating material may be used for current confinement, as demonstrated in the AlGaN/GaN current aperture vertical transistor [1]. Lateral conduction devices, such as the AlGaN/GaN high electron mobility transistor (HEMT), require semi-insulating material beneath the device struc- ture to enable sharp current pinch-off. Moreover, semi-insulating material can simplify electrical characterization structures, for instance Hall effect measurement structures. Nominally undoped GaN grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrate typically shows n-type conductivity, presumably due to doping by residual oxygen impurities, originating from the substrate [2,3]. To grow semi-insulating material the residual donors have to be compensated by acceptor states, commonly done either by introdu- cing high densities of threading dislocations, or by choosing growth conditions that result in high levels of carbon impurities, leading to the forma- tion of deep acceptor states [4,5]. These methods have undesired side-effects: High threading dis- location densities inevitably propagate into the device structure, and compensation with carbon requires growth conditions that typically leads to high dislocation densities. Clearly, for the growth of semi-insulating GaN films on sapphire substrate there is a need for a stable point-defect acceptor that can be incorporated readily regardless of growth conditions. We recently demonstrated growth of semi- insulating GaN films on sapphire by MOCVD, by means of Fe-doping [6]. The deep acceptor *Corresponding author. E-mail address: sten@ece.ucsb.edu (S. Heikman). 0022-0248/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0248(02)01926-7