High pressure far-infrared magneto-spectroscopy of impurity and free electron states in silicon-doped gallium arsenide using a novel diamond-anvil apparatus

This thesis contains two parts. In the first part, a novel diamond-anvil cell (DAC) probe for far-infrared (FIR) magneto-spectroscopy in a small-bore magnet is designed and built. A miniature multi-bellows ram is invented to generate amplified force for in situ pressure tuning of the DAC. A constructed 26-mm diameter double-bellows ram is capable of producing 5kN force (scalable to 10kN with four bellows) when driven by {dollar}sp4{dollar}He at 4.2K. Signals are enhanced using paraboloidal cones to focus the FIR radiation on the sample and collect the transmitted signal. FIR magneto-transmission down to 80cm{dollar}sp{lcub}-1{rcub}{dollar}, and photoluminescence can be measured on the same sample under the same pressure-field-temperature conditions, independently tunable in the ranges 0-20GPa (in steps as small as 0.05GPa), 0-15T, and 2-300K.; In the second part, Si impurity states in nondegenerate GaAs are investigated under pressure via observing the 1s-2p{dollar}sb{lcub}+{rcub}{dollar} transition of Si-donors at 4.2K by FIR Fourier transform magneto-spectroscopy (FTMS) and laser magneto-spectroscopy using the novel probe. When DX-centers are never populated under visible illumination, the Si-donors retain their effective-mass nature up to 36.6kbar, above which the 1s-2p{dollar}sb{lcub}+{rcub}{dollar} peak is quenched due to the crossover of 1s({dollar}Gamma{dollar}) and 1s(X) Si-levels. The A{dollar}sb1{dollar} localized Si-level remains a high energy resonance for the entire direct-gap regime. When DX-centers are populated by cooling (200K {dollar}to{dollar} 4.2K) in the dark under 55kbar, photoionizing the DX-center forms a new Si-center that does not revert to the shallow donor configuration and can not be persistently photoionized at low temperatures. The new center competes with the shallow Si-donors at different Si-sites via the conduction band, and begins to quench the 1s-2p{dollar}sb{lcub}+{rcub}{dollar} intensity at {dollar}sim{dollar}30kbar without anticrossing. Possible defect reactions are proposed to explain the new center. The pressure dependence of the electron effective mass (at {dollar}{lcub}bf k{rcub}=0{dollar}) in GaAs is measured via cyclotron resonance (CR) by FTMS at 17K up to 36.8kbar, above which the CR peak is quenched again due to the 1s({dollar}Gamma{dollar})-1s(X) crossover. The data are corrected for the band nonparabolicity using a three-band k{dollar}cdot{dollar}p calculation. Our results agree well with prior measurements extending only to 17kbar and with the prediction of the three-band k{dollar}cdot{dollar}p model.