Observation of persistent photoconductivity in delta -doped GaAs

Capacitance-voltage (C-V) profiles have been measured for single delta -doped GaAs(Si) samples at various 2D sheet electron concentrations. The effect of temperature and incident light on the profiles has been monitored. In a heavily doped sample the authors have observed persistent photoconductivity, which they believe confirms the existence of the DX centre in delta -doped GaAs(Si). They have also noted a freeze-out of the equivalent 3D electron distribution with decreasing temperature, leading to an effective increase in the full width at half maximum (FWHM) of the C-V profile which can be attributed to electron trapping by DX centres. Using deep level transient spectroscopy they have observed a trap with activation energy approximately 350 meV in the heavily doped sample that exhibited persistent photoconductivity; this trap was not present in the lower doped delta -layers.