Enhancing performance of Au-hyperdoped Si photodetectors for infrared detection

Abstract

Hyperdoping Si with transition metals to form intermediate bands for infrared absorption has attracted attention recently for producing sub-bandgap photoconductivity. In particular, Si hyperdoped with Au has been demonstrated to exhibit optoelectronic response at 1550 nm. However, the reported external quantum efficiencies (EQEs) are low, and the device fabrication processes had not been optimized. In this paper, we demonstrate a significant improvement in sub-bandgap EQE through modification of the material and device fabrication processes. By increasing the Si:Au layer thickness, modification of device design, and formation of Ohmic contacts, the EQE was measured to be as high as 0.44% at 1550 nm, nearly two orders of magnitude higher than previous reports from similar devices. Additionally, the EQE was measured to be in the 10-3 range for wavelengths as long as 2.4 μm. The EQE spectrum showed features that were attributed to defect levels from a substitutional Au acceptor defect. The above bandgap EQE showed gain in one device. Thermal annealing at 300 °C does not improve the efficiency of Si:Au photodiodes. These results demonstrate the viability of Au-hyperdoped Si for infrared detection below the bandgap of Si.