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.

In this work, we compare the luminescence results obtained on InGaN/GaN multiple quantum well (QW) structures with different numbers of QWs. Structures are designed for scintillating applications, where large QW number covering particle penetration depth is necessary, and fast luminescence response is required. Special attention is devoted to increase the intensity of fast excitonic QW emission and to decrease the luminescence of the QW defect band, which has slower luminescence response and is undesired for fast scintillator applications. We found that increasing the In content in QWs suppresses the defect band luminescence and decreasing the QW growth rate increases the photoluminescence (PL) intensity of excitonic luminescence. We also show that increasing the number of InGaN further improves the PL properties of InGaN QWs. The photoluminescence and cathodoluminescence characteristics are compared and discussed.