Carbon and silicon background impurity control in undoped GaN layers grown with trimethylgallium and triethylgallium via metalorganic chemical vapor deposition

Abstract

The unintentional impurity incorporation in GaN epitaxial layers impacts the electrical conductivity and optical properties of the films grown by metalorganic chemical vapor deposition (MOCVD). It is critical to control impurity-related states for device structure development. The aim of this work is to contribute to the understanding of the reasons for the presence of certain background impurities. In this paper, the unintentional impurity incorporation of carbon, hydrogen, oxygen, and silicon in undoped (u-) GaN films grown by low-pressure MOCVD were studied. Background impurity concentrations were evaluated by secondary ion mass spectroscopy (SIMS) to optimize growth parameters including V/III ratio, growth temperature (Tg), growth pressure (Pg), and gallium (Ga) precursors of trimethylgallium (TMG) or triethylgallium (TEG). Unintentional [C] and [Si] incorporations are found to be highly dependent on the growth parameters. For the same growth conditions, u-GaN films grown with a TEG precursor exhibited a lower background concentration of C compared to that of GaN grown with TMG. However, the lowest background [C] achieved was grown with TMG using optimized conditions and exhibited [C] < 4 × 1015 cm−3 which was at the detection limit of the SIMS measurement. These results were measured for a u-GaN layer grown with TMG at 200 Torr, 1030 °C, and a V/III of 3700. The lowest background [Si] of 4 × 1015 cm−3 was achieved by growing with TMG at 200 Torr, 1000 °C, and V/III of 650.