Negative Differential Resistance Observation and a New Fitting Model for Electron Drift Velocity in GaN-Based Heterostructures

The aim of this paper is an investigation of electric field-dependent drift velocity characteristics for Al
_0.3
Ga
_0.7
N/AlN/GaN heterostructures without and with in situ Si
₃
N
₄
passivation. The nanosecond-pulsed current- voltage (I-V) measurements were performed using a 20-ns applied pulse. Electron drift velocity depending on the electric field was obtained from the I-V measurements. These measurements show that a reduction in peak electron velocity from 2.01 × 10
⁷
to 1.39 × 10
⁷
cm/s after in situ Si
₃
N
₄
passivation. Also, negative differential resistance regime was observed which begins at lower fields with the implementation of in situ Si
₃
N
₄
passivation. In our samples, the electric field dependence of drift velocity was measured over 400 kV/cm due to smaller sample lengths. Then, a wellknown fitting model was fitted to our experimental results. This fitting model was improved in order to provide an adequate description of the field dependence of drift velocity. It gives reasonable agreement with the experimental drift velocity data up to 475 kV/cm of the electric field and could be used in the device simulators.