Optical properties of C-doped bulk GaN wafers grown by halide vapor phase epitaxy

Abstract

Optical and structural studies of homoepitaxially grown m-plane GaN Appl. Phys. Lett. 100, 172108 (2012) Freestanding bulk C-doped GaN wafers grown by halide vapor phase epitaxy are studied by optical spectroscopy and electron microscopy. Significant changes of the near band gap (NBG) emission as well as an enhancement of yellow luminescence have been found with increasing C doping from 5 Â 10 16 cm À3 to 6 Â 10 17 cm À3. Cathodoluminescence mapping reveals hexagonal domain structures (pits) with high oxygen concentrations formed during the growth. NBG emission within the pits even at high C concentration is dominated by a rather broad line at $3.47 eV typical for n-type GaN. In the area without pits, quenching of the donor bound exciton (DBE) spectrum at moderate C doping levels of 1-2 Â 10 17 cm À3 is observed along with the appearance of two acceptor bound exciton lines typical for Mg-doped GaN. The DBE ionization due to local electric fields in compensated GaN may explain the transformation of the NBG emission. V C 2014 AIP Publishing LLC.

Carbon doped GaN layers grown by Pseudo‐Halide Vapour Phase Epitaxy

“…These defects, negative growth pyramids, are shortly discussed in the following section. The observed increase of impurity absorption and incorporation conforms to Khromov et al …”

“…In comparison to studies at dislocation etched GaAs surfaces, the pit`s facets reflect emitted photons and direct them to the sensor. But more probably it is caused by the increased yellow band (YL) intensity around 2.2 eV (figure c), due to the enhanced impurity incorporation on facetted areas . In figure d the near band gap spectra taken at different sample points (1) red – between pits, 2) blue ‐ undisturbed surface, 3) green – edge of pit and 4) black – inside a pit) are shown.…”

“…SI GaN layers were produced also by carbon doping by a number of epitaxial methods. Recently, carbon was doped up to 6 × 10 17 cm −3 during HVPE growth of thick GaN layers by using acetylene gas . Another paper, published after our first submission, deals with carbon doping during HVPE growth by using methane and a carbon concentration of 10 19 cm −3 was achieved.…”

Study of optical properties of bulk GaN crystals grown by HVPE

“…5(a). These results confirm the high quality of these bulk samples and indirectly prove that the O and C impurities are not the main factor in the YL band of these samples, as the YL band in GaN films resulting from C N eO N complexes is always stable at low temperature [5]. The details of the PL spectrum near the D 0 X A emission of each sample are also shown in Fig.…”

“…Although GaNbased devices are widely available on the market, there is still substantial interest in the fundamental material properties. Special attention is focused on the yellow luminescence (YL) band due to its limitation on the overall efficiency of optoelectronic devices [5], and several research groups have presented experimental evidence to elucidate the possible reasons for the YL band from different aspects. The ubiquitous YL band observed from photoluminescence (PL) spectra at approximately 2.2 eV is widely believed to be related to deep states in GaN [6e9].…”