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


The influence of dislocation density on the transport properties of HEMT structures is reported. Experimental results, obtained on HEMT structures prepared in the same growth run on templates with different dislocation densities (DD), 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 DD. To suppress this phenomenon, the addition of an AlGaN back barrier (BB) beneath 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 DD was possible. We show that DD lowering considerably increases the electron mobility in 2DEG. DD also has a significant influence on the Fermi level position in GaN. Reduction of DD can improve the performance of high-frequency GaN HEMT applications.