Photodetector performance limitations: Recombination or trapping—Power exponent variation with the applied bias to rescue

The presence of defects and impurities causes recombination that hampers the effectiveness of photodetectors (PDs) and influences the photodetection capabilities of the device. Based on the value of the exponent in power-law fitting led to the conclusion whether trap/defect are dominating or not. However, sometimes it may lead to contradictory results when one sees the photocurrent behavior and the exponent’s value in power law fitting. The value of exponent less than unity always does not reflect trap/defect dominion in the device. Also, the decaying of photocurrent must be accompanied by the results of whether traps are dominated or not. The applied bias potential plays a significant role in distinguishing between the mechanism of recombination and trapping. By varying the applied potential and observing the behavior of the photocurrent and power exponent, it can be possible to distinguish between these two mechanisms (recombination/trapping). This study will help to understand recombination and trapping mechanisms and the role of bias potential on device performance, especially on metal–semiconductor-metal (MSM)-based PDs. For a conclusive view, it is better to go with the variation of exponent value with voltage in power-law fitting and photocurrent behavior (particularly decay behavior). Moreover, this study will help identify preliminary recombination and trapping mechanisms where only the defect/trap state or recombination is required over existing techniques like DLTS, ultrafast spectroscopy, and PL. Graphical abstract Transit length variation with the applied bias in photodetector can be seen in the power exponent in the power-law fitting. Defect or trap states are generated when perfect crystallinity or periodicity is broken. Suppose defect or trap states dominate the dynamics of the excited carriers. In that case, the value of exponent in power-law fitting remains almost the same with a variation of applied bias, as seen in the left section of the figure. Also, suppose defects of trap states are not dominating the dynamics. In that case, the value of the exponent increases with the applied bias up to saturation level, as can be seen in the right section of the figure.