Effect of uniaxial stress on the excitation spectrum of Si and S donors in GaP

Infrared transmission measurements of GaP with sulfur and silicon donors using a difference absorption method have revealed two excitation lines due to sulfur not previously reported. The effects of uniaxial compression along the [100] and [110] directions were used to identify the symmetry of the final states of the observed transitions. Most of the lines due to sulfur donors were seen to split into two components, but the lines due to silicon donors were seen to shift slightly, rather than to split. The difference in behavior between the two impurities is explained in terms of the different symmetries of the silicon and sulfur ground states. The observed energy levels of both donors were fit to the effective-mass theory using masses $m_{\perp }=(0.17\mathrm{}\pm 0.01)m_0$ and $m_{\parallel }=(21\mathrm{}\pm 2)m_0$, and ionization energies 105 ± 1 meV for sulfur, and 83 ± 1 meV for silicon donors.