Characterization of hole traps in MOVPE-grown p-type GaN layers using low-frequency capacitance deep-level transient spectroscopy

Traps in MOVPE-grown Mg-doped GaN samples composed of p+/p−/n+ structures were investigated using low-frequency capacitance deep-level transient spectroscopy (DLTS). A drop-off in capacitance with decreasing temperature was observed. This is caused by the longer RC time constant of the diode with lower temperature, which is due to a decrease in the number of ionized Mg acceptors (which have a high ionization energy). This limits the use of lower temperatures in DLTS measurements. To extend DLTS to a lower temperature (105 K), DLTS using a capacitance measurement frequency of 1 kHz was applied. Thus, we can quantitatively discuss concentrations of traps with shallow energy levels. We obtained a nearly one-to-one relation between Ha (EV +0.29 eV) and Hd (EV +0.88 eV) in the p-type layer, which strongly supports the theoretical calculation that a carbon on a nitrogen site forms donor-like (Ha) and acceptor-like (Hd) states.