The effects of monolayer thickness and sheet doping density on dark current and noise current in quantum dot infrared photodetectors

Abstract

Abstract We report measurements on a series of quantum dot infrared photodetectors grown with different combinations of monolayer thicknesses (2.2. 2.55 and 2.9 ML) and quantum dot layer sheet doping densities (6 u 10 10 cm -2 and 12u 10cm -2 ). The dark current and noise current were higher in devices grown with sheet doping density of 12 u 10 10 cm -2 . At a given bias voltage the dark current and the noise current was found to be lowest in devices having 2.55 ML and sheet doping density of 6 u 10 10 cm -2 . This combination gives a sheet doping density to dot density ratio of approximately unity. Highest gain was achieved in devices with 2.55 ML and sheet doping density of 6 u 10 10 cm -2 . Keywords: QDIP, monolayer, sheet doping density, noise gain. Introduction Quantum Dot Infrared Photodetector (QDIP) has been investigated as potential infrared (IR) photodetectors for large area arrays, normal incident operation and high operating temp erature. However its predicte d advantages over Quantum Well Infrared Photodetector (QWIP) an d the current market leading technology, Mercury Cadmium Telluride (CMT), have not been fully demonstrated to date. For instance the operating temperatures of QDIP s are still lower than those of CMT. Although the CMT has high detectivity, there are still si gnificant challenges in the growth and fabrication of CMT for large area Focal Plane Arrays (FPAs) [1]. On the other hand QDIPs grown and fabricated using the relatively mature III-V technologies can potentially overcome these limitations to provide low cost large area high performance FPA. The detectivity which is used as a figure of merit to characterize performance of IR detectors is defined as,