Photo-Induced conductivity of heterojunction GaAs/Rare-Earth doped SnO2

Rare-earth doped (Eu3+ or Ce3+) thin layers of SnO2 were deposited by sol-gel-dip-coating, along with GaAs films, deposited by resistive evaporation. The as-built heterojunction has potential application in optoelectronic devices, because it may combine the emission from the rare-earth-doped transparent oxide, with a high mobility semiconductor. Trivalent rare-earth-doped SnO2 has very efficient emission in a wide wavelength range, including red (in the case of Eu3+) or blue (Ce3+). The advantage of this structure is the possibility of separation of the rare-earth emission centres, from the electron scattering, leading to an indicated combination for electroluminescence. Electrical characterisation of the heterojunction SnO2:Eu/GaAs showed a significant conductivity increase compared to the conductivity of the individual films. Monochromatic light excitation indicated the role of the most external layer, which may act as a shield (top GaAs), or a UV light absorber sink (top RE-doped SnO2). The observed improvement on the electrical transport properties is probably related to the formation of short conduction channels in the semiconductor junction with two-dimensional electron gas (2DEG) behaviour, which was evaluated by excitation with distinct monochromatic light sources, where the samples were deposited by varying the order of layer deposition.