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

Abstract

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 (E V +0.29 eV) and Hd (E V +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.

GaN-based power devices: Physics, reliability, and perspectives

“…Trap states detected near the valence band edge at EC -3.2 eV [363], EC -3.22 eV [346], [357], EC -3.25 eV [359] and EC -3.28 eV [339], even if nominally assigned to other physical origins, can reasonably be ascribed to the shallow level of the dopant, which is known to be typically located from 0.15 eV to 0.2 eV above the valence band edge [381], [382]. A shallower level at EC -3.36 eV [364] was tentatively ascribed to Mg-H complexes, and a similar origin was assigned to the EC -0.62 eV level in [357]. Additional levels at EC -0.355 eV [340] and at EC -0.597 eV [365] were ascribed to generic Mg-related defects, whereas the EC -0.44 eV level in [349] was associated with Mg-VN complexes.…”

“…and experimentally associated with a band of allowed states between EC -2.64 eV and EC -2.49 eV [329], [330], [364], [375]- [377]. Being a deep acceptor, the CN level does not generate large free hole density and strong p-type conductivity; large concentrations of CN can pin the Fermi level at EV+0.9 eV, leading to semi-insulating layers.…”

“…Being a deep acceptor, the CN level does not generate large free hole density and strong p-type conductivity; large concentrations of CN can pin the Fermi level at EV+0.9 eV, leading to semi-insulating layers. CN may also induce the formation of shallow acceptor-like levels in the EC -3.31 eV to EC -3.15 eV band [330], [346], [348], [352], [353], [356]- [358], [364], [373]- [376]. On the other hand, if C occupies interstitial positions, the resulting CI sites are believed to introduce a deep donor level in the upper part of the gap, with typical energies ranging from EC -1.35 eV to EC -1.2 eV [346], [348], [352], [357].…”

Capacitance Temperature Dependence Analysis of GaN-on-Si Power Transistors

“…The obtained hole cross-sections combined with the trap energies allow building an exponential relationship, shown in Figure 9. Then, by comparing the exponential relationship with the deep acceptor traps properties reported in the literature [35][36][37][38][39][40][41][42][43][44][45] (see Figure 9) in the energy 0.8 to 1.0 eV energy range, it seems that hypothesis involving only carbon on the N-site: C N or gallium vacancy alone: V Ga or tied to a silicon atom on the Ga-site: V Ga -Si Ga can be discarded because the trap hole cross section mismatch is too large. The remaining hypotheses involve oxygen as the gallium vacancy with oxygen atom(s) on the N-site: V Ga -(O N ) x traps proposed by Polyakov et al [43] and Lee et al [45].…”

“…Figure 9. Acceptor traps' cross-section as a function of their energy with respect to the valence band.Colors refer to the hypothesis proposed by the authors[35][36][37][38][39][40][41][42][43][44][45] (C N : carbon on the N-site; V Ga -(O N ) x : gallium vacancy with oxygen atom(s) on the N-site; V Ga : gallium vacancy; V Ga -Si Ga : gallium vacancy with a silicon atom on the Ga-site; C N -O N : carbon on the N-site with an oxygen atom on the N-site).…”