Magneto-optical studies of n-GaAs under high hydrostatic pressure

Far-infrared laser spectroscopy and Fourier spectroscopy are used in order to study the influence of hydrostatic pressure on shallow donor and cyclotron resonance spectra in high-purity epitaxial films of n-GaAs. Accurate pressure variations for the effective mass and dielectric constant are obtained at a temperature of 4.2K and pressures of up to 17.3kbar. These parameters are subsequently used to interpret the pressure variation of the chemical shifts of the 1s and 2s levels. It is shown that the dependence of these chemical shifts on magnetic field at fixed pressure can be described well by lowest-order perturbation theory. The ratio of the chemical shifts of the 1s level to the corresponding chemical shifts of the 2s level at zero magnetic field is found to be pressure independent and equal to 7.2+or-0.3 for all donors. A much stronger increase of chemical shifts than that predicted by lowest-order perturbation theory is observed on increasing pressure. In addition, a resonant interaction of the 1s level of the deepest shallow donor with a strongly localised level of the same impurity centre is observed on increasing pressure. A qualitative interpretation of all these phenomena is given.