The electronic band structure of GaBiAs/GaAs layers: Influence of strain and band anti-crossing

Abstract

The GaBi As bismide III-V semiconductor system remains a relatively underexplored alloy particularly with regards to its detailed electronic band structure. Of particular importance to understanding the physics of this system is how the bandgap energy E and spin-orbit splitting energy Δ vary relative to one another as a function of Bi content, since in this alloy it becomes possible for Δ to exceed E for higher Bi fractions, which occurrence would have important implications for minimising non-radiative Auger recombination losses in such structures. However, this situation had not so far been realised in this system. Here, we study a set of epitaxial layers of GaBi As (2.3 x 10.4), of thickness 30-40 nm, grown compressively strained onto GaAs (100) substrates. Using room temperature photomodulated reflectance, we observe a reduction in E , together with an increase in Δ , with increasing Bi content. In these strained samples, it is found that the transition energy between the conduction and heavy-hole valence band edges is equal with that between the heavy-hole and spin-orbit split-off valence band edges at ∼9.0 ± 0.2 Bi. Furthermore, we observe that the strained valence band heavy-hole/light-hole splitting increases with Bi fraction at a rate of ∼15 (±1) meV/Bi, from which we are able to deduce the shear deformation potential. By application of an iterative strain theory, we decouple the strain effects from our experimental measurements and deduce E and Δ of free standing GaBiAs; we find that Δ indeed does come into resonance with E at ∼10.5 ± 0.2 Bi. We also conclude that the conduction/valence band alignment of dilute-Bi GaBiAs on GaAs is most likely to be type-I.

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