Vibrational Spectroscopy of GaN:Mg Under Pressure

Abstract

The microscopic structure of Mg-H complexes in GaN has been a subject of intense theoretical and experimental investigation. In order to probe the Mg-H structure, we have studied the effect of hydrostatic pressure on the local vibrational mode (LVM) frequency. At ambient pressure, the LVM frequency is 3125 cm -1 , which corresponds to a N-H stretching mode. In this study, Fourier-transform spectroscopy was performed on free-standing GaN:Mg,H samples in a diamond-anvil cell, with nitrogen as a pressure-transmitting fluid. The samples had been removed from their sapphire substrate by the laser-liftoff technique. The LVM frequency was measured, at liquid helium temperatures, for pressures ranging from 0 to 5 GPa. The pressure dependence of the frequency is nonlinear: first it decreases with pressure, then it increases. Comparison with first-principles calculations allows us to derive information about the microscopic structure of the Mg-H complex. The calculated stable configuration indeed gives rise to a frequency shift consistent with experiment. Based on the comparison between theory and experiment, we can exclude the bond-center configuration, which would result in a much larger pressure derivative than experimentally observed.

Hydrogen-impurity complexes in III–V semiconductors

“…was not yet detected. The investigated shift of the stretching mode frequency with hydrostatic pressure is consistent with the configuration of figure 11(b), even though the discontinuity in the slope of the shift at 1.6 GPa is not yet explained [76]. The monitoring of the H-and D-line intensities of the Mg Ga -H complex has been used to clarify a series of technological relevant problems of Mg-doped p-type GaN ( [77] and references therein).…”

Local Vibrational Mode Spectroscopy of Hydrogen in Compound Semiconductors

“…3). The experimental pressure shift was compared with predictions from first-principles calculations [23]. For the bondcentered configuration, the calculated frequency shift was 15 cm -1 /GPa, much larger than the experimentally observed shift.…”