Preparation and properties of Ni/InGaN/GaN Schottky barrier photovoltaic cells

Ni/In_xGa_1-xN/GaN Schottky barrier solar cells with different In contents (x = 0.07/0.13) and two types of Schottky patterns (semitransparent current spreading layer and grid contact) are fabricated and the dependences of photovoltaic performances of these solar cells on In contents and Schottky patterns are studied. Solar cells with semitransparent contact have almost the same open-circuit voltages (V _oc) as solar cells with grid contact and exhibit a higher fill factor (FF). However, solar cells with grid contact exhibit a higher maximum output power density (P_max) than semitransparent contact due to their larger short-circuit current density (J_sc). On the other hand, V _oc and FF decrease significantly with increasing In content (beyond the decrease expected from the band gap of InGaN). By comparing the X-ray rocking curves, AFM images, dark current characteristics and spectral responsivities, it could be concluded that the deterioration of InGaN crystal quality with increasing In content is the dominant reason accounting for the strong decrease of V_oc and FF. In addition, using AMPS simulation, the band structure and ideal spectral responsivities are obtained. Comparison of the experimental and simulated results also shows that high crystal quality is a key factor to obtain high performance InGaN-based Schottky barrier photovoltaic cells.