BGaN micro-islands as novel buffers for GaN hetero-epitaxy

B_xGa_1-xN (x ∼ 0.02) micro-islands provide novel buffers for growing GaN films and AlGaN/GaN heterostructures on sapphire substrates. These films and heterostructures show low threading dislocation density (TDD), low residual carrier concentration, and high two-dimensional electron gas (2DEG) mobility: Non-doped GaN films had the TDD of 2 × 10⁸ cm^-2 and the residual electron concentration of 9.4 × 10⁹ cm^-3 at 433 K. AlGaN/GaN heterostructures exhibited 2DEG Hall mobility of 1720 and 13100 cm² V^-1 s^-1 at 300 and 77 K, respectively. An almost constant sheet electron density (2.9-4.2 × 10¹² cm^-2) was obtained in the wide temperature range from 500 to 77 K, indicating the absence of parallel conduction in the GaN buffer layers.