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

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-Vs, 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 580V for a buffer of 4 μm. 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 ~107 to ~109 cm-2of 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.