Nanometer-Thin Pure B Layers Grown by MBE as Metal Diffusion Barrier on GaN Diodes

Pure boron layers, deposited by molecular beam epitaxy (MBE) on AlGaN/GaN/p-Si substrates to a thickness of ~ 7 nm, were applied as barriers to aluminum metallization. For low-temperature deposition from 250°C - 400°C, low-saturation-current diodes to the n-type GaN were fabricated that all tolerated alloying at 400°C. After alloying, the relatively high current level of the 250°C diode was reduced to that of the other low temperature diodes, whereas 700°C B deposition resulted in high-current diode characteristics. The results suggest a favorable B-to-GaN chemistry at 350°C - 400°C.