Fourier transform spectroscopy at diamond anvil cell pressures

The high pressure diamond anvil cell can be used for Fourier Transform Magneto-Spectroscopy of impurity levels in semiconductors at far infrared wavelengths. The performance of the diamond anvil cell for this type of spectroscopy is evaluated. In the present measurements we investigate the non-metastable impurity states in n-type Al_xGa_1-xAs materials in the frequency range 80-300 cm^-1up to a maximum pressure of 45 kbar. A shallow to deep transition of an impurity in undoped n-type Al_0.03Ga_0.97As was observed at approximately 22kbar. This non-metastable state is either non-lattice relaxed or is weakly relaxed and is resonant with the conduction band at atmospheric pressure. In lightly silicon doped n-type GaAs the crossover from the shallow donor state to the non-metastable silicon A₁antibonding level occurred at 25 kbar.