Transport properties of AlGaN/GaN HEMT structures with back barrier: impact of dislocation density and improved design

Abstract

The influence of dislocation density on the transport properties of high electron mobility transistor (HEMT) structures is reported in this work. Experimental results, obtained on HEMT structures prepared in the same growth run on templates with different dislocation densities, are compared. However, the direct comparison of structures is complicated, since parallel parasitic currents through deeper parts of the heterostructure were observed in samples with lower dislocation density. To suppress this phenomenon, the addition of an AlGaN back barrier (BB) beneath the two dimensional electron gas (2DEG) channel is proposed and optimized and the most suitable design based on both modeling and experimental results is suggested. Subsequently, the comparison of electron mobility in 2DEG for structures with AlGaN BB and different dislocation densities was possible. We show experimentally that lowering the dislocation density considerably increases the electron mobility in 2DEG. It is shown that the dislocation density also has a significant influence on the Fermi level position in GaN. The presented results suggest that reduction of dislocation density can improve the performance of high-frequency GaN HEMT applications.