Aluminum nitride crystal-based photodetector with bias polarity-dependent spectral selectivity

Visible-blind ultraviolet-selective photodetection and ultraviolet-visible broad spectral photodetection are two essential functions eagerly pursued in each application area. However, they usually cannot be realized simultaneously in a bare photodetector because their different underlying photoexcitation processes would interfere with each other. In this work, a photodetector integrating the two distinct photodetector characteristics is presented. The device is prepared based on the heterojunction of a large-scale aluminum nitride bulk crystal and monolayer graphene. The visible-blind ultraviolet-selective photodetection and the ultraviolet-visible broad spectral photodetection are separately manifested in the device depending on the bias polarity. Under a negative bias, the device is a visible-blind deep-ultraviolet photodetector, demonstrating a 193/785 nm rejection ratio of over 106 for the photocurrent and a 193/405 nm rejection ratio of over 103 for the signal/noise ratio. Under a positive bias, the device performs as a broad spectral photodetector responding to light from 193 to 785 nm. Systematical characterization reveals that different photodetection manners are the synergistical results of the different photon energies of the incident light, wavelength-dependent penetration depths in AlN, and the different working modes of the device under different bias conditions. This work provides a particular dual-functional photodetector, which is of great significance in terms of both application and device physics.