Deep electron and hole traps in freestanding n-GaN grown by hydride vapor phase epitaxy

Abstract

Deep level electron and hole traps were studied by means of deep level transient spectroscopy with electrical and optical injection on a freestanding thick n-GaN sample with low dislocation density. It is shown that at both the upper and the lower surface of the sample there exists a thin, ϳ0.5 m layer of damaged material with lowered concentration of electrons and enhanced density of deep centers. Deep in the bulk of the film the densities of the majority of the electron and hole traps are shown to be very low, but measurably higher on the lower face ͑N face͒, which was originally closer to the Al 2 O 3 substrate. The two faces are also shown to similarly differ in the density of deep hole traps whose concentration is deduced from low-temperature capacitance-voltage measurements in the dark and after illumination ͑such traps were previously associated with dislocation states͒. The concentration of persistent photocapacitance centers is shown to be very low on both sides and considerably lower than previously reported for other n-GaN samples with higher dislocation densities. Electron beam induced current measurements on both sides of the sample reveal the presence of dark spots whose density roughly correlates with the density of dislocations at the upper and lower faces. The reverse current at high voltages is shown to be considerably higher on the N face. The possible relationship of the observed phenomena to dislocations is discussed.

Electrical and recombination properties and deep traps spectra in MOCVD ELOG GaN layers

“…4). These observations are similar to the ones we have reported for HVPE-grown GaN samples with different thickness and different dislocation density [5,6]. We attributed the 0.9 eV traps to some native defects whose concentration is enhanced in tune with the increased dislocation density, whilst the extended states were associated with the dislocations per se [5].…”

“…The 0.6 eV traps are commonly observed in n-GaN samples grown by various techniques and are believed to be due to some intrinsic defects [8]. The results of deep spectra measurements on the ELOG sample are very similar to our earlier measurements for free-standing low-dislocation-density thick HVPE samples [6]. The only significant differences are the absence in the latter of the 0.25 eV traps (which makes sense if those are dislocations-related).…”

“…This is in stark contrast with our results obtained for undoped n-GaN films grown by hydride vapour phase epitaxy (HVPE) with the thickness varying from 2 µm to 100 µm and corresponding strong change of dislocation density from some 10 9 cm -2 to 10 8 cm -2 [5]. Measurements performed on free-standing thick HVPE-grown n-GaN samples with dislocation density on the order of 10 6 cm -2 [6,7] also indicated a strong change in deep levels spectra and allowed to observe features due to individual dislocations in microcathodoluminescence (MCL) and electron beam induced current (EBIC) images of such structures.…”

“…Schottky diodes for these measurements were prepared by shadow mask deposition of Au. More detailed descriptions of setups can be found in [5][6][7].…”

Microcathodoluminescence and electron beam induced current observation of dislocations in freestanding thick n-GaN sample grown by hydride vapor phase epitaxy

“…The properties of the Schottky diodes will be described in a separate article. 10 The experimental setups are described in detail, …”