On the study of antimony incorporation in InAs/InAsSb superlattices for infrared sensing

Abstract

Advanced infrared detector materials utilizing InAs/InAsSb superlattices (SLs) are emerging due to the long minority carrier lifetimes observed in this material system. However, compositional and dimensional changes through Sb segregation alter the detector properties from the original design, and precise compositional control of the Sb in the SL is crucial to advance the state-of-the-art of this novel material system. In this study, epitaxial conditions that can mitigate Sb segregation during growth are explored in order to achieve high-quality SL materials. A nominal SL structure of 77 Å InAs/35 Å InAs0.7Sb0.3 tailored for a midinfrared gap was used to optimize our epitaxial parameters. Since the growth of mixed anion alloys is complicated by the potential reaction of Asx with Sb surfaces, the substrate temperature (Ts), and arsenic cracker temperature (TAs) was varied in order to control the Asx surface kinetics on a Sb surface. Experimental results indicate that the SL sample grown at the lowest investigated Ts of 400 °C produces the highest Sb mole fraction x of ∼0.3 in InAs1-xSbx layers, which is then decreased by 14% as the Ts increases from 400 to 440 °C. This reduction originates from Sb surface segregation during InAsSb growth through the As-Sb exchange process. Although this incorporation was increased with a lower TAs, the crystalline quality of SL layers quickly degraded with the TAs below 850 °C due to the poor adsorption coefficient of As4 at the growth front. Since a change in the designed compositions and effective layer widths related to Sb segregation disrupts strain balance and also significantly impacts the detector performance, further studies to prevent Sb segregation are needed.