Deep centres in bulk MOCVD n‐type hexagonal GaN thin films and near their interface

Abstract

Deep level transient spectroscopy (DLTS) is performed in metal organic chemical vapour deposition (MOCVD) hexagonal GaN doped with silicon either intentionally or not. Capacitance transients are measured in junctions and analysed with the help of several techniques. In these samples, the main contribution due to deep levels appears as a prominent peak in the Fourier transform DLTS (FTDLTS) spectrum with an apparent ionisation energy of 0.95 eV and a capture cross section close to 5 × 10–15 cm2. However, these values must be considered as apparent ones. Isothermal transient spectroscopy (ITS) and a high resolution method based on the analysis of the transients recorded over five decades of time show that several sub-levels exist with ionisation energies between 0.40 and 0.76 eV, and capture cross sections in the range 5 × 10–20– 5 × 10–17 cm2. Capture kinetics confirms this fact, indicating that at least three charge states (either +, 0, – or 0, –, 2–) are involved. The possible origins of long-term instabilities and reversible evolutions of the current–voltage characteristics of the diodes which are also detected, are discussed in relation with these deep states.