Al(As,Sb) heterobarriers on InAs: growth, structural properties and electrical transport

Abstract

We discuss structural and electrical properties of AlAs_xSb_1-x bulk layers and InAs/AlAs_xSb_1-x heterostructures grown by molecular beam epitaxy over a wide range of composition (0≤x≤0.4). We demonstrate the strong sensitivity of the structural quality and the composition of Al(As,Sb) on growth parameters such as substrate temperature, As : Sb flux ratio, as well as total group-V flux, and discuss the influence of a miscibility gap on the molecular beam epitaxial growth of Al(As,Sb). We also find that both the composition and the growth temperature strongly influence the surface morphology: Al(As,Sb) - especially when grown at low substrate temperature - appears to grow in an island-coalescence mode rather than in a two-dimensional manner as it does for pure AlAs or AlSb. The electrical transport along AlSb/InAs/Al(As,Sb) quantum wells is strongly influenced by the growth temperature of Al(As,Sb) and we observe the formation of additional defects when the top barrier was grown at low substrate temperature. The transport across InAs/Al(As,Sb) heterojunctions was found to depend on both the growth temperature and the arsenic composition. An increase in arsenic composition results in a strongly decreased current across the heterojunction. From ballistic electron emission spectroscopy experiments, we confirm the transition from a staggered band lineup for InAs/AlSb to a straddled band lineup for InAs/AlAs_xSb_1-x for x=0.16.