Vertical Current Transport in AlGaN/GaN HEMTs on Silicon: Experimental Investigation and Analytical Model

Abstract

We investigate the vertical leakage mechanism in metal–organic chemical vapor deposition-grown carbon (C)-doped AlGaN/GaN High Electron Mobility Transistors (HEMTs) on 6-in silicon wafer. Substrate bias polarity-dependent ${I}$ – ${V}_{s}$ , temperature-dependent fitting, and band diagram analysis pointed to the Poole–Frenkel (P–F) type of conduction mechanism for vertical transport in the devices with breakdown as high as 580 V for a buffer of $\textsf {4}~\mu \text{m}$ . Trap activation energy of 0.61 eV was estimated from the P–F fitting which matches well with values reported in the literature. We propose that higher dislocation density leads to shallower traps in the buffer and build an analytical model of dislocation-mediated vertical leakage around this. The variation in leakage as a function of dislocation density at a given field is predicted and is found to be the most abrupt in the range from $\sim 10^{\textsf {7}}$ to $\sim 10^{\textsf {9}}$ cm $^{-\textsf {2}}$ of dislocation density. This can be attributed to a sharp decrease in trap activation energy in the above range of dislocation density, possibly due to complex formation between point defects and dislocations.