Investigation of deep trap states at the negative polarization interface of N-polar HEMT through capacitance-conductance measurements

N-polar high electron mobility transistors (HEMTs) will play a crucial role in the future high frequency and high power GaN based technology due to their inherent advantages over Ga-polar technology. However, still, there are some fundamental questions about N-polar technology that need to be addressed. One of the questions that remained unanswered or regaining interest recently is the nature of the negative polarization interface of N-polar HEMTs. Two contradicting views exist regarding the nature of the negative polarization interface at the barrier/buffer interface of N-polar HEMT: one view suggests that hole-like trap states exist at this interface while the other view suggests that two-dimensional hole gas exists at this interface. To give a possible solution to this fundamental question, in this study, two N-polar HEMT heterostructures were investigated, one without any Si delta-doping at the barrier/buffer interface and the other with Si delta-doping at the same interface. Through capacitance-conductance measurements, existence of deep trap states at the negative polarization interface at barrier/buffer interface is demonstrated for the sample without Si delta-doping, which indirectly contradicts the idea of existence of hole gas at this interface. Moreover, in the capacitance-conductance measurements, Si delta-doping is shown to eliminate the presence of deep trap states.