Fabrication and characterization of all-oxide heterojunction p-CuAlO2 + x/n-Zn1 − xAlxO transparent diode for potential application in “invisible electronics”

Transparent p–n heterojunction diodes have been fabricated by p-type copper aluminum oxide (p-CuAlO2 + x) and n-type aluminum doped zinc oxide (n-Zn1 − xAlxO) thin films on glass substrates. The n-layers are deposited by sol-gel-dip-coating process from zinc acetate dihydrate (Zn(CH3COO)2·2H2O) and aluminum nitrate (Al(NO3)3·9H2O). Al concentration in the nominal solution is taken as 1.62 at %. P-layers are deposited onto the ZnO:Al-coated glass substrates by direct current sputtering process from a prefabricated CuAlO2 sintered target. The sputtering is performed in oxygen-diluted argon atmosphere with an elevated substrate temperature. Post-deposition oxygen annealing induces excess oxygen within the p-CuAlO2 + x films, which in turn enhances p-type conductivity of the layers. The device characterization shows rectifying current–voltage characteristics, confirming the proper formation of the p–n junction. The turn-on voltage is obtained around 0.8 V, with a forward-to-reverse current ratio around 30 at ± 4 V. The diode structure has a total thickness of 1.1 μm and the optical transmission spectra of the diode show almost 60% transmittance in the visible region, indicating its potential application in ‘invisible electronics’. Also the cost-effective procedures enable the large-scale production of these transparent diodes for diverse device applications.