Localized vibrational modes in GaN:O tracing the formation of oxygenDX-like centers under hydrostatic pressure

Abstract

Vibrational modes are observed at ambient pressure in O-doped GaN at 544 cm Ϫ1 using Raman spectroscopy. Investigation of these modes with applied hydrostatic pressure reveals the existence of three closely spaced modes that shift in relative intensity with increasing pressure. Notably, transitions between the different modes occur at previously observed electronic transitions associated with the DX-like center behavior of substitutional O on the N site. A simple one-dimensional oscillator model is used to extract approximate force constants; these are consistent with the assignment of the 544 cm Ϫ1 mode to O N and with force constants for C and B dopants in GaP. The relative intensity changes observed at 11 and 17 GPa are assigned to changes in the charge state due to the merging of the ϩ/0 ionization level and the Fermi energy and the transition to DX Ϫ that causes a previously observed drop in free electron concentration, respectively.

Optical studies of the effect of oxidation on GaN

“…3, show the expected E 2 2 and A 1 (LO) symmetry phonons superimposed on the band gap related PL emission. 25 Our results show no evidence of this band. We see that the intensities of the E 2 2 and A 1 (LO) bands are comparable in each spectrum.…”

Calculated properties of point defects in Be-doped GaN

“…The measured frequency for O N is 544 cm Ϫ1 . 48 Figure 5 shows how the calculated LVM's for Be Ga , (Be-Be) Ga , and Be Ga -O N compare with the modes observed in heavily Be-doped GaN.…”

Tunable local polariton modes in semiconductors

“…1,[38][39][40] The charge-state dependent LVM's, which can be considered as precursors of tunable LPM's, remain relatively unstudied. In a recent paper by Wetzel et al, 13 the charge-state dependent triplet of LVM's generated by oxygen in GaN has been reported, which is similar to the GaP:O deep center. Even though this defect does not satisfy our condition for LPM's, Eq.…”

“…The energy lost by the captured carrier can be transferred either to photon(s) in the radiative transition, 2 or to nearby carrier in the Auger effect, 3 or to a series of long-wavelength acoustic phonons when the carrier descends a staircase of the excited states in the cascade mechanism, 4 or to the local vibration quanta when multi-phonon emission 5 takes place. There are some indirect [6][7][8] and direct [9][10][11][12][13][14][15][16][17][18] evidence that capture or release of the charge carrier is associated not only with the lattice relaxation but, more importantly with the alteration of local vibrational modes (LVM's), i.e. with changes in the local elastic constants.…”