Analysis of the carbon-related “blue” luminescence in GaN

Abstract

The properties of a broad 2.86 eV photoluminescence band in carbon-doped GaN were studied as a function of C-doping level, temperature, and excitation density. The results are consistent with a C Ga -C N deep donor-deep acceptor recombination mechanism as proposed by Seager et al. For GaN:C grown by molecular-beam epitaxy (MBE) the 2.86 eV band is observed in Si co-doped layers exhibiting high n-type conductivity as well as in semi-insulating material. For low excitation density (4 W/cm 2 ) the 2.86 eV band intensity decreases as a function of cw-laser exposure time over a period of many minutes. The transient behavior is consistent with a model based on carrier diffusion and charge trapping-induced Coulomb barriers. The temperature dependence of the blue luminescence below 150 K was different for carbon-contaminated GaN grown by metalorganic vapor phase epitaxy (MOVPE) compared to C-doped MBE GaN.

Carbon defects as sources of the green and yellow luminescence bands in undoped GaN

“…Lyons et al [9] calculated that optical transitions of electrons from the conduction band to this level would cause a blue band with a maximum at about 2.7 eV. These authors noticed that in C-doped GaN, a blue band is often observed when the carbon concentration is high [10,11], or at high excitation intensity [12,13], which, in their opinion, supported the existence of the 0/+ level of the C N defect. In contrast, there is only one optically active transition level for the C N O N complex in the band gap of GaN.…”

“…A careful analysis suggests that this is unlikely. Indeed, a blue band is often observed in C-doped GaN, along with the YL band [10][11][12][13]46]. However, closer inspection of the luminescence spectra in these papers allows us to conclude that at least two different defect-related blue bands were observed.…”

“…However, closer inspection of the luminescence spectra in these papers allows us to conclude that at least two different defect-related blue bands were observed. A band with a maximum at 2.85-2.86 eV (the BL band) was observed in GaN grown by molecular beam epitaxy (MBE) [12,13], and a broader band with a maximum at 3.0 eV (the BL2 band) was observed in GaN grown by MOCVD [10,11]. In Ref.…”

“…Indeed, the intensity of the YL band should be much lower than that the BL band since the defect is almost completely saturated with holes in such experimental conditions. At lower excitation intensities (20 W/cm 2 ), the intensity of the BL band (relative to the YL band) decreased with increasing concentration of C from 2 × 10 18 to 2 × 10 19 cm −3 [13]. We assume that the BL band observed in Refs.…”

Impact of Surface Treatment on Interface States of ALD Al2O3/GaN Interfaces

“…Previous DLOS and photoluminescence studies of defects in bulk GaN have correlated defect levels near mid-gap and near the valence band to carbon-related defects. [23][24][25][26][27] Carbon is an expected interface impurity due to exposure to atmosphere before the ALD process, and due to the presence of carbon in the aluminum precursor (i.e. TMAl).…”