Photoionisation spectroscopy of negatively charged muonium in GaAs

Here we propose a photoexcited muon spin spectroscopy experiment to ionise a negatively charged muonium in GaAs. The muonium state behaves as an acceptor level in GaAs, which is estimated to be 0.9 eV below the conduction band minimum. Its resonant photoionisation is measurable in the MuSR spectrum, as demonstrated by a pilot experiment in ARGUS. The resonant energy allows us to measure the defect level, which is otherwise available only from the Arrhenius activation energy. The measurement is therefore extremely accurate and athermal, and a temperature dependent measurement tells us the shift of the defect level relative to the band edges. This study helps understanding the behaviour of a hydrogen atom in GaAs, which has a wide range of uses in semiconductor industries.