Accumulation hole layer in p-GaN/AlGaN heterostructures

We present the results on piezoelectric and pyroelectric doping in AlGaN-on -GaN and GaN-on-AlGaN heterostructures and demonstrate p-GaN/AlGaN structur es with accumulation hole layer. Our results indicate that polarization cha rge can induce up to 5x10(13) cm(-2) holes at the AlGaN/GaN heterointerface s. We show that the transition from three-dimensional (3D) to two-dimension al (2D) hole gas can be only achieved for hole sheet densities on the order of 10(13) cm(-2) or higher. At lower densities, only 3D-hole accumulation layer may exist. These results suggest that a piezoelectrically induced 2D- hole gas can be used for the reduction of the base spreading resistance in AlGaN/GaN-based heterostructure bipolar transistors. (C) 2000 American Inst itute of Physics. [S0003-6951(00)00421-6].