Black-Silicon Ultraviolet Photodiodes Achieve External Quantum Efficiency above 130%

At present, ultraviolet sensors are utilized in numerous fields ranging from various spectroscopy applications via biotechnical innovations to industrial process control. Despite this, the performance of current UV sensors is surprisingly poor. Here, we break the theoretical one-photon–one-electron barrier and demonstrate a device with a certified external quantum efficiency above 130% in UV range without external amplification. The record high performance is obtained using a nanostructured silicon photodiode with self-induced junction. We show that the high efficiency is based on effective utilization of multiple carrier generation by impact ionization taking place in the nanostructures. While the results can readily have a significant impact on the UV-sensor industry, the underlying technological concept can be applied to other semiconductor materials, thereby extending above unity response to longer wavelengths and offering new perspectives for improving efficiencies beyond the Shockley-Queisser limit.

Figure 1

(a) External (blue circles) and internal (yellow dashed) quantum efficiency of the induced-junction black-Si photodiode measured at zero bias. The inset shows schematically the structure of the device. (b),(c) Bird’s eye view SEM image of black-Si nanotexture with conelike and columnarlike morphology, respectively.

Figure 2

Simulated electrical field distribution ($E$) and electrostatic potential ($\mathrm{\Psi }$) in a single black-Si nanoneedle with a conelike shape (top) and a columnarlike shape (bottom).

Figure 3

(a) Comparison of both IQE and EQE of our two similar induced-junction photodiodes, one with black-Si texturing (black curves) and another with planar surface (blue curves). Additionally, the IQEs reported for different silicon photodetectors with planar surface are shown as comparison (WFG stands for Wilkinson, Farmer, and Geist). The purple curve shows our Silvaco Atlas simulation of black-Si photodiode. (b) Schematic of the band diagram for silicon.