Impact Of Growth Parameters On The Background Doping Of Gan Films Grown By Ammonia And Plasma-Assisted Molecular Beam Epitaxy For High-Voltage Vertical Power Switches

We report on ammonia and plasma-assisted molecular beam epitaxy (NH3-MBE and PAMBE) grown GaN layers with a low net carrier concentration (N-net). Growth parameters, such as growth rate, V-III ratio, and plasma power, were investigated on different substrates to study their impact on surface morphology and background doping levels using atomic force microscopy and capacitance-voltage (C-V) measurements, respectively. The elevated growth rates are especially interesting for vertical power switches, requiring very thick drift regions (over 10 mu m) with low background concentrations. For our NH3-MBE-grown layers, N-net shows an almost linear increase with the growth rate. Using a freestanding substrate and at a fast growth rate of 1.4 mu m hr(-1), a N-net value as low as 1 x 10(15) cm(-3) was achieved. For samples grown via PAMBE, the lowest N-net among samples grown under a Ga adlayer was 2 x 10(16) cm(-3) for a growth rate of 0.32 mu m h(-1) on a GaN-on-sapphire template. The results support the use of MBE for growing high-quality GaN material with reasonably fast growth rates maintaining low background doping levels for high-voltage vertical power electronic devices.