Effect of AlN nucleation layer growth conditions on buffer leakage in AlGaN∕GaN high electron mobility transistors grown by molecular beam epitaxy (MBE)

The effect of the AIN nucleation layer growth conditions on buffer leakage in unintentionally doped AlGaN/GaN high electron mobility transistors was investigated. The samples were grown by rf-plasma assisted molecular beam epitaxy on 4H-SiC (0001). Drain-source leakage cur-rents were found to be markedly different for samples grown with different Al/N flux ratios during the AIN nucleation layer. Growth of N-rich nucleation layers (Al/N < 1) resulted in a significant reduction in buffer leakage. Secondary ion mass spectroscopy results showed that Si incorporation into Al-rich AIN layers (Al/N > 1) grown on SiC was as high as similar to 1-2 x 10(18) atoms/cm(3). In contrast, Si incorporation into N-rich AIN layers was two orders of magnitude lower, similar to 2 x 10(16) atoms/cm(3). Initial devices grown on low-leakage material realized via N-rich nucleation yielded output power densities at 4 GHz of 4.8 W/mm with a power added efficiency (PAE) of 62% at a drain bias of 30 V, and 8.1 W/mm with a PAE of 38% at a drain bias of 50 V. (c) 2005 American Vacuum Society.