Biased Photoresponse Analysis of Al–ZnO Heterojunctions with n- and p-Type Silicon

Al-ZnO/(n)Si and Al-ZnO/(p)Si heterojunction structures were fabricated by RF-sputtering of Al-ZnO thin film on Si substrates and their electrical and photoresponse properties were comparatively analyzed. The Al-ZnO/(n)Si heterojunction exhibited excellent diode behavior with an equivalent barrier height of 0.72 eV and an rectification ratio of 6.7 × 10 ³ at ±0.5 V, while no rectifying behavior was observed for Al-ZnO/(p)Si device. Illuminated I-V analysis performed with different light intensities revealed excellent photoresponse properties and the strong dependence of the photocurrent on external bias for both Al-ZnO/(n)Si and Al-ZnO/(p)Si structures. The Al-ZnO/(n)Si structure requires smaller reverse bias than Al-ZnO/(p)Si for similar photoresponse. Based on dark I-V, illuminated I-V, and the energy band diagrams, photoresponse mechanisms were explained. In order to further understand the photoresponse mechanisms, quantum efficiency measurements were carried out, with applied external voltage bias. A general descriptive model was presented for the first time for the photogenerated current density in both Al-ZnO/(n)Si and Al-ZnO/(p)Si heterojunctions at different voltage bias.