The impacts of variable Ag doping content on the characteristics of p-Ag x :NiO/n-Si heterojunction diodes

Abstract P-Ag x :nickel oxide (Ag x :NiO)/n-silicon (Si) heterojunction diodes (HJDs) were fabricated, and the impacts of various Ag doping content on the characteristics of p-Ag x :NiO/n-Si HJDs were studied. The crystallinity, hole concentration, and conductivity of the Ag x :NiO film improved with increasing of Ag content. The Ag atoms passivated the defects of NiO grain boundaries, decreasing the leakage current from 9.5 × 10 −4 A for the p-Ag x :NiO/n-Si HJD without Ag (Ag = 0) to 2.2 × 10 −5 A for that with Ag molar ratio of 1. However, excess Ag doping (Ag molar ratio of 1.6) caused a large leakage current, resulted by the rougher interface between Ag x :NiO and Si. The p-Ag x :NiO/n-Si HJD with Ag = 1 had the highest rectification ratio of 2976 at ±2 V than those with Ag = 0 (rectification ratio: 33.5) and Ag = 1.6 (rectification ratio: 677). The p-Ag x :NiO/n-Si HJD with Ag = 1 exhibited the lowest ideality factor among all the HJDs. With increasing of Ag content, the barrier height of the p-Ag x :NiO/n-Si HJDs increased from 0.58 to 0.84 eV for the Ag molar ratio of 0 and 1, respectively. However, the barrier height was decreased to 0.66 eV in the HJDs with Ag molar ratio of 1.6. The carrier-transport mechanisms of the prepared HJDs were studied using Ln(I) versus Ln(V) plots. The p-Ag x :NiO/n-Si HJDs with Ag = 0 and 1.6 exhibited only one carrier transport in the space–charge-limited current (SCLC) mode. Most of the injected electrons did not contribute to the current; instead, they occupied most of the traps, leading to only the holes participating in current flow. Nevertheless, the HJDs with Ag = 0.5 and 1 exhibited two distinct conduction mechanisms. At a low bias voltage of V ⩽ 0.6 V, the diffusion–recombination mechanism dominated the conduction. However, the SCLC controlled the carrier transport at a high bias voltage of V ⩾ 0.6 V.