Incorporation of Mg in GaN grown by molecular beam epitaxy

We report Mg doping experiments in GaN grown by plasma-enhanced molecular beam epitaxy on sapphire and GaAs substrates. Secondary ion mass spectrometry was used to measure the Mg concentration as a function of Mg flux. Our data show a linear dependence at low fluxes and then tend to saturate, in agreement with the measurements at higher fluxes by Guha et al, We model this in terms of two interacting layers of Mg atoms on the GaN surface, one chemisorbed, the other physisorbed. We suggest that surface stoichiometry is an essential factor in determining doping efficiency and is responsible for the observed temperature-dependence of Mg incorporation. (C) 1999 Elsevier Science B.V. All rights reserved.