Enhancing the photo-to-dark current ratio by inserting a thin MgO layer in p-NiO/i-NiO/n-Si photodiodes.

A thin magnesium oxide (MgO) layer was inserted at the i-NiO/n-Si interface of p -NiO/i-NiO/n-Si (p-i-n) photodiodes (PDs) to enhance the photo-to-dark current ratio of the prepared ultraviolet (UV) PDs. Both types of p-i-n PDs (with and without the MgO layer) exhibited clear rectifying behaviours. However, the p-i-n PDs with MgO insertion demonstrated an ideality factor (5.3) smaller than that of the p-i-n PDs without MgO (13.9), suggesting that MgO passivated the interface defects between NiO and Si. The p-i-n PDs with the MgO layer exhibited a lower dark current at a low reverse-bias voltage because carriers were blocked by the insulating MgO layer. However, the photo-generated carriers penetrated the thin MgO layer at high reverse-bias voltages. Therefore, the photo-to-dark current ratio was high at both low and high bias voltages. The p-i-n PDs with MgO have a higher photo-to-dark current ratio of approximately 12 times that of p-i-n PDs without MgO at 1-V reverse bias voltage. The detectivity of p-i-n PDs with MgO increased with bias voltage, reaching a peak value of 9.2 x 1013 Jones at a reverse-bias voltage of 8 V. However, the detectivity of the p-i-n PDs without MgO was approximately nine times lower and less dependent on the bias voltage. Carrier transport mechanism showed that at a small forward bias voltage, both the p-i-n PDs exhibited Ohmic conduction. The p-i-n PDs without MgO exhibited a diffusion-recombination model at a high forward bias voltage. In contrast, in the p-i-n PDs with the MgO layer, a space-charge-limited current dominated carrier transport. [ABSTRACT FROM AUTHOR]