Impact Ionization In Quantum Well Infrared Photodetectors With Different Number Of Periods

This paper presents the detailed investigation of the photocurrent accompanied with impact ionization effect in In0.15Ga0.85As/GaAs multiple quantum well infrared photodetectors (QWIPs) with 10 and 50 periods. The sample with 50 periods exhibits remarkable enhancement at high electric field while a negative differential conductivity (NDC) phenomenon is observed in the sample with 10 periods. The enhancement at high electric field is attributed to impact ionization across the conduction-band-edge discontinuity between incident hot electrons and the electrons confined in the wells. The different behavior of these two samples indicates that the length of the multiplication region strongly affects the multiplication factor M. We also measured the photocurrent of GaAs/Al0.15Ga0.85As QWIPs, which do not show an obvious multiplication phenomenon. This is attributed to a different impact ionization coefficient alpha. A theoretical model of the multiplication factor M varying with impact ionization coefficient alpha, capture probability p(e), and well number N is provided to clarify these phenomena and compared with experimental result. (C) 2012 American Institute of Physics. [doi :10.1063/1.3681284]