Infrared studies on GaN single crystals and homoepitaxial layers

We performed an infrared study on the highly n-type and semi-insulating GaN single crystals. We also studied epitaxial layers (homoepitaxy) grown on t he (0 0 0 (1) over bar)N and (0 0 0 1)Ga faces of these crystals. For the n -type GaN single crystals, we show that the (0 0 0 (1) over bar)N faces alw ays possess much higher free carrier concentration than the (0 0 0 1)Ga fac e. Moreover, infrared reflectivity of the layers deposited on both polarity of semi-insulating and highly conducting bulk GaN substrates shows that th e incorporation of impurities (most probably oxygen and silicon) is systema tically higher in the layers grown on the (0 0 0 (1) over bar)N faces. Thes e results clearly indicate that the growth of epitaxial layers on the bulk GaN substrates should be done on the (0 0 0 1)Ca faces of the GaN crystals. (C) 2000 Elsevier Science B.V. All rights reserved.