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

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 under-standing of the reasons for the presence of certain background impurities. In this paper, the unintentional im-purity 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] in-corporations 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 con-ditions and exhibited [C] < 4 x 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 degrees C, and a V/III of 3700. The lowest background [Si] of 4 x 1015 cm-3 was achieved by growing with TMG at 200 Torr, 1000 degrees C, and V/III of 650.

Automated summary

This study aims to investigate the unintentional impurity incorporation in GaN epitaxial layers and optimize the growth conditions to reduce background impurity concentrations. The results show that the unintentional incorporation of carbon and silicon impurities is highly dependent on the growth parameters. The use of TEG precursor can reduce the carbon concentration, while the lowest concentration can be achieved with TMG precursor under optimized conditions. Similarly, the lowest background silicon concentration can be achieved with TMG precursor under specific conditions.