Comparison of electrical properties and deep traps in p-AlxGa1−xN grown by molecular beam epitaxy and metal organic chemical vapor deposition

Abstract

The electrical properties, admittance spectra, microcathodoluminescence, and deep trap spectra of p-AlGaN films with an Al mole fraction up to 45% grown by both metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were compared. The ionization energy of Mg increases from 0.15 to 0.17 eV in p-GaN to 0.3 eV in 45% Al p-AlGaN. In p-GaN films grown by MBE and MOCVD and in MOCVD grown p-AlGaN, we observed additional acceptors with a concentration an order lower than that of Mg acceptors, with a higher hole capture cross section and an ionization energy close to that of Mg. For some of the MBE grown p-AlGaN, we also detected the presence of additional acceptor centers, but in that case the centers were located near the p-AlGaN layer interface with the semi-insulating AlGaN buffer and showed activation energies considerably lower than those of Mg.

Deep traps in GaN-based structures as affecting the performance of GaN devices

“…In most cases the activation energies for both peaks are close to each other and to the Mg ionization energy determined from Hall/van der Pauw measurements, but the pre-exponential factor for the low temperature peak yields the apparent hole capture cross section of 10 À16 to 10 À15 cm 2 , while the high temperature peak is characterized by a very much lower apparent hole capture cross section of 10 À20 to 10 À19 cm 2 [115][116][117][118]. It has been reported that the magnitude of the capacitance step and the admittance peak related to the low temperature feature is greatly increased by hydrogen plasma treatment (and proton irradiation) of p-GaN:Mg samples [115,116]. The relative magnitude of the low temperature step was also found to be lower in MBE growth or HVPE growth in Ar atmosphere as opposed to MOCVD growth [115] (in both cases the hydrogen concentration is very considerably lower than the Mg concentration, see e.g.…”

“…In the second case, the activation energy is that of the temperature dependence of conductivity [111]. In many cases experimentally measured admittance spectra show two distinct peaks in admittance/steps in capacitance [112][113][114][115][116]. This is illustrated by Fig.…”

“…15 for p-GaN films grown by MBE [115], but similar features have been observed in p-GaN films grown by MOCVD and HVPE [114][115][116]. In most cases the activation energies for both peaks are close to each other and to the Mg ionization energy determined from Hall/van der Pauw measurements, but the pre-exponential factor for the low temperature peak yields the apparent hole capture cross section of 10 À16 to 10 À15 cm 2 , while the high temperature peak is characterized by a very much lower apparent hole capture cross section of 10 À20 to 10 À19 cm 2 [115][116][117][118]. It has been reported that the magnitude of the capacitance step and the admittance peak related to the low temperature feature is greatly increased by hydrogen plasma treatment (and proton irradiation) of p-GaN:Mg samples [115,116].…”

“…It has been reported that the magnitude of the capacitance step and the admittance peak related to the low temperature feature is greatly increased by hydrogen plasma treatment (and proton irradiation) of p-GaN:Mg samples [115,116]. The relative magnitude of the low temperature step was also found to be lower in MBE growth or HVPE growth in Ar atmosphere as opposed to MOCVD growth [115] (in both cases the hydrogen concentration is very considerably lower than the Mg concentration, see e.g. Ref.…”

“…In some samples the introduction of Mg causes the appearance of a broad blue luminescence band near 2.9 eV, in other it gives rise to a sharp transition near 3.2 eV with a series of phonon replicas. It was reported that the treatment of the samples in hydrogen plasma can convert the broad blue PL or MCL line into the sharp transition near 3.2 eV or into a mixture of both types of PL features [115,116]. However, cases where the sharp UV line dominates over the broad blue band in MBE samples have been reported in contrast to the predominance of the broad blue line in MOCVD pGaN (see e.g.…”