Deep-Level Characterization of Free-Standing HVPE-grown GaN Substrates Using Transparent Conductive Polyaniline Schottky Contacts

We have investigated electronic deep levels in free-standing n-GaN substrates grown by hydride vapor phase epitaxy (HVPE), by means of a steady-state photo-capacitance spectroscopy technique, using transparent conductive polyaniline Schottky contacts. Two specific deep levels located at ~1.7 and ~3.1 eV below the conduction band were revealed to be significantly reduced compared to those in n-GaN layers grown by metal-organic chemical vapor deposition. This difference between them is probably due to extremely low concentrations of threading dislocations and residual C impurities in the HVPE-grown n-GaN substrates.