Enhanced SWIR Photodetection in Colloidal Quantum Dot Photodiodes via Tunneling Current Suppression

Achieving high detectivity in photodiodes requires the effective suppression of the dark current under operational conditions. In this study, we investigate colloidal quantum dot short-wavelength infrared (SWIR) photodiodes and demonstrate a significant reduction in dark current under external bias conditions. This reduction is achieved through the incorporation of injection-blocking layers (IBLs), specifically molybdenum oxide (MoO_x), at the electrode interfaces. This approach helps maintain flat dark current-voltage (J-V) characteristics, even under high applied biases. Our detailed analysis reveals that the dark J-V characteristics of our photodiodes adhere to the Simmons model, which describes metal-semiconductor contact behavior influenced by applied bias. This indicates that the observed current behavior in our diode can be primarily attributed to tunneling current dynamics. Importantly, the IBL effectively suppresses electron tunneling from the electrode, as demonstrated by the increase of threshold voltage for Fowler-Nordheim tunneling (FNT) with IBL thickness increase. We achieved a 16-fold decrease in dark current density to 4.4 × 10^-3 mA/cm², resulting in enhanced photodetection performance with a specific detectivity of 8.6 × 10¹¹ Jones, coupled with a record-high external quantum efficiency of 84% at −1 V. These findings pave the way for the development of highly sensitive and reliable photodetection systems in the SWIR range.