Growth of short-period InAs/GaSb superlattices for mid-infrared photodetectors

摘要

The purpose of this work is to explore mid-infrared (IR) photodetector materials that can operate at room temperature. Shorter-period InAs/GaSb superlattices (SLs) have larger intervalance band seperations, which is beneficial for reducing Auger recombination and tunneling current, thus making room temperature operation possible. To test these possibilities, several short-period SLs ranging from 50 to 11 A were designed for 4 μm detection threshold and molecular beam epitaxy was used to grow specially designed structures. Since morphological degradation is generally expected in shorter-period SLs, their structural qualities were monitored by transmission electron microscopy. The effect of layer properties on the optical and electrical properties was studied using low temperature photoconductivity measurements and magnetic field dependent Hall measurements. The samples with larger-periods (50 to 31 A) showed excellent structural qualities, leading to sharper photoresponse band edge (5 meV) and lower residual background carrier concentrations (8x10~(10) cm~(-2)). As the period approached 24 A, slight layer thickness undulations within the SLs were observed and these undulations intensified as the period further reduced to 17 A. Evidently, these structural degradations strongly influence their optical properties causing significant broadening in photoresponse band edge (9 meV). In the thinner samples with the period below 17 A, no optical signal was detected. With slower growth rates, samples with periods as thin as 19 A were grown without significant layer thickness variations.