Fabrication and characterization of ZnO:Zn(n$^{+}$)/Porous-Silicon/Si(p) heterojunctions for white light emitting diodes

Abstract

The fabrication and characterization of electroluminescent ZnO:Zn(n$^{+}$)/Porous Silicon/Si(p) heterojunctions is presented. Highly conductive ZnO films (ZnO:Zn(n$^{+}$)) were produced by applying a temperature annealing at 400$^{\circ}$C by 5 min to the ZnO/Zn/ZnO arrange formed by DC sputtering, and the Porous Silicon (PS) films were prepared on p-type (100) Si wafers by anodic etching. The ZnO:Zn(n$^{+}$)/PS/Si(p) heterojunction is accomplished by applying a brief temperature annealing stage to the entire ZnO/Zn/ZnO/PS/Si structure to preserve the PS luminescent characteristics. The ZnO:Zn(n$^{+}$) films were characterized by X-ray diffraction and Hall-van der Pauw measurements. The PS and ZnO:Zn(n$^{+}$) films were also studied by photoluminescence (PL) measurements. The current-voltage characteristics of the heterojunctions showed well defined rectifying behavior with a turn-on voltage of 1.5 V and ideality factor of 5.4. The high ideality factor is explained by the presence of electron tunneling transport aided by energy levels related to the defects at the heterojunction interface and into the PS film. The saturation current and the series resistance of the heterostructure were $4 \times 10^{-7}$ A/cm$^2$ and 16 $\Omega$-cm$^{2}$, respectively. White color electroluminescence is easily observed at the naked eye when excited with square wave pulses of 8 V and 1 KHz.