Compensation effects in GaN:Mg probed by Raman spectroscopy and photoluminescence measurements

Abstract

Compensation effects in metal organic chemical vapour deposition grown GaN doped with magnesium are investigated with Raman spectroscopy and photoluminescence measurements. Examining the strain sensitive E 2 (high) mode, an increasing compressive strain is revealed for samples with Mg-concentrations lower than 7 Â 10 18 cm À3. For higher Mg-concentrations, this strain is monotonically reduced. This relaxation is accompanied by a sudden decrease in crystal quality. Luminescence measurements reveal a well defined near band edge luminescence with free, donor bound, and acceptor bound excitons as well as a characteristic donor acceptor pair (DAP) luminescence. Following recent results, three acceptor bound excitons and donor acceptor pairs are identified. Along with the change of the strain, a strong modification in the luminescence of the dominating acceptor bound exciton and DAP luminescence is observed. The results from Raman spectroscopy and luminescence measurements are interpreted as fingerprints of compensation effects in GaN:Mg leading to the conclusion that compensation due to defect incorporation triggered by Mg-doping already affects the crystal properties at doping levels of around 7 Â 10 18 cm À3. Thereby, the generation of nitrogen vacancies is introduced as the driving force for the change of the strain state and the near band edge luminescence. V

Incorporation of Mg into thick free-standing HVPE GaN

“…The Raman E 2 high mode, a vibration which is particularly sensitive to strain, appeared at 569.6 cm -1 and was identical to that measured in an unintentionally doped free-standing GaN HVPE sample of similar thickness. Furthermore, the position of the line is within the range typically reported for free-standing GaN reported by others [13], and is only 2 cm -1 greater than the predicted value [14]. The results are also consistent with those of HVPE GaN heteroepitaxial films, which show a decreasing compressive stress with thickness [15].…”

Tuning the surface Fermi level on p-type gallium nitride nanowires for efficient overall water splitting

“…Consequently, the reduction of E F À E V in the nearsurface region, as shown in Fig. 2c, can be directly correlated to the reduction in the downward surface band bending with increasing Mg-dopant incorporation 30,31 . In addition, our detailed analysis reveals that variations in the surface band bending have a very small, or negligible dependence on the morphology of GaN nanowires.…”

Defect-engineered GaN:Mg nanowire arrays for overall water splitting under violet light

“…This increased tensile strain is further identified as a fingerprint of the formation of V N in GaN:Mg nanowires. 21 The degradation in the crystal quality of the GaN:Mg nanowires is also confirmed from the increment of full-width-at-half-maximum (FWHM) of the E 2 Raman line. 24 At very high Mg flux (T Mg ¼ 280 C), the DAP emission ( Fig.…”

“…This suggests that V N related donor type native defects are most likely present in GaN at high Mg doping level, and act as compensating centers in p-type GaN. 21 Despite the N-rich growth conditions, the V N related defects can be formed along the growth direction due to higher diffusion lengths of Ga compared to N adatoms on the nonpolar surfaces which forms the nanowire sidewalls. 12 Additionally, the presence of Mg may limit the availability of active nitrogen on the nanowire sidewalls.…”