Effect of silicon doping on performance of 30-pair In_xGa _1-xN/GaN quantum well solar cells

Silicon doping in a barrier layer has been demonstrated to improve crystal quality and the interfacial quality of InGaN/GaN quantum wells. Furthermore, it also reduces piezoelectric field with heavy silicon doping. In this work, the characteristics of 30-pair In_xGa_1-xN/GaN quantum well solar cells with undoped wells/undoped barriers (UWUB), Si-doped wells/Si-doped barriers (DWDB), and undoped wells/Si-doped barriers (UWDB) are compared and investigated. The short circuit currents (J_sc) of the solar cells with UWUB, DWDB, and UWDB are 0.54, 0.16, and 0.23 mA/cm², respectively. This indicates that the electric field in quantum wells dominates the collected current capability. The open circuit voltages (V_oc) of the solar cells with UWUB, DWDB, and UWDB are 2.18, 1.38, and 1.91 V, respectively. Recombination rate determines V_oc. The solar cell with UWUB exhibits the highest efficiency among the three solar cells. The temperature dependences of solar efficiency differ in three cases. As temperature increases, solar efficiency decreases in the UWUB sample, and increases in the DWDB and UWDB samples owing to the competition between the increasing J_sc and the decreasing V_oc.