Identification of GaN Buffer Traps in Microwave Power AlGaN/GaN HEMTs Through Low Frequency S-Parameters Measurements and TCAD-Based Physical Device Simulations

In this paper, the type, activation energy (E
_a
) and cross section (σ
_n
) of the GaN buffer traps existing in the AlGaN/GaN high-electron mobility transistors are investigated through low frequency (LF) S-parameters measurements. Furthermore, we present the 2-D physics based TCAD numerical simulation analysis of this device. The dc simulation results are calibrated to match with the experimentally measured I-V characteristics and this allows to qualitatively estimate the concentration of traps (N
_T
) present in the GaN buffer. Knowing the measured trap energy level and the estimated trap concentration N
_T
, TCAD physical simulations are performed at various temperatures in order to extract the LF-Y
₂₂
admittance parameter. Interestingly, the LF-Y
₂₂
simulation results are found to be in good agreement with the measurements and this result strongly suggests that LF admittance dispersion is an effective tool in identifying the traps present in the GaN buffer. Moreover, this paper reveals that acceptor-like traps with an apparent concentration of 5.0 × 10
¹⁶
cm
^-3
and with the apparent trap energy level of 0.4 eV below the conduction band are located in the GaN buffer.