The effect of low-energy Ga ions on GaAs/AlGaAs heterostructures

A high-mobility two-dimensional electron gas at a GaAs/AlGaAs heterojunction has been exposed to low-energy Ga ion beams. The authors report the reduction in both the sheet carrier density and mobility at 44 K for ion doses and energies in the range 10¹¹-10¹² cm^-2 and 1-6 keV respectively. The sheet resistivity can be increased by a factor of 10¹⁰ with a dose of 2*10¹² cm^-2 ions at 6 keV. The ion irradiation also reduces the persistence of the low temperature photo-induced conduction and increases the amount of ionised impurity scattering. Reduced photoluminescence from wells close to the surface of a multiple quantum well structure extends the transport data to suggest a range of approximately=70 nm from the surface over which electronic properties are modified. An ultra-high vacuum compatible method for altering the surface electronic properties therefore seems viable.