Abstract
As important functional materials, the electronic structure and physical properties of (GaAs)m(AlAs)n superlattices (SLs) have been extensively studied. However, due to limitations of computational methods and computational resources, it is sometimes difficult to thoroughly understand how and why the modification of their structural parameters affects their electronic structure and physical properties. In this article, a high-throughput study based on density functional theory calculations has been carried out to obtain detailed information and to further provide the underlying intrinsic mechanisms. The band gap variations of (GaAs)m(AlAs)n superlattices have been systematically investigated and summarized. They are very consistent with the available reported experimental measurements. Furthermore, the direct-to-indirect-gap transition of (GaAs)m(AlAs)n superlattices has been predicted and explained. For certain thicknesses of the GaAs well (m), the band gap value of (GaAs)m(AlAs)n SLs exponentially increases (increasing n), while for certain thicknesses of the AlAs barrier (n), the band gap value of (GaAs)m(AlAs)n SLs exponentially decreases (increasing m). In both cases, the band gap values converge to certain values. Furthermore, owing to the energy eigenvalues at different k-points showing different variation trends, (GaAs)m(AlAs)n SLs transform from a Γ-Γ direct band gap to Γ-M indirect band gap when the AlAs barrier is thick enough. The intrinsic reason for these variations is that the contributions and positions of the electronic states of the GaAs well and the AlAs barrier change under altered thickness conditions. Moreover, we have found that the binding energy can be used as a detector to estimate the band gap value in the design of (GaAs)m(AlAs)n devices. Our findings are useful for the design of novel (GaAs)m(AlAs)n superlattices-based optoelectronic devices.
Highlights
The artificial semiconductor superlattice (SL) is a specific form of layered fine composite, in which the nanoscale thin layers with different band gaps are alternately grown by the strict periods
When the aluminum arsenide (AlAs) barrier is ultrathin (i.e.; n < 4), the wave function of gap value in the design of (GaAs) in adjacent wells could be overlapping each other, resulting in a narrowing of the band gap caused by the quantum size effect
When the monolayer number m is larger than 10, Eg(m) gradually converges to a certain value of Eg,b. This trend is consistent in all (GaAs)m(AlAs)n SLs, except for the values of A and k
Summary
The artificial semiconductor superlattice (SL) is a specific form of layered fine composite, in which the nanoscale thin layers with different band gaps are alternately grown by the strict periods. For certain thicknesses of the GaAs well as shown, the band gap value of (GaAs)m(AlAs)n SLs exponentially increased according to the function Eg(n) = Eg,GaAs + Aekn (where Eg,GaAs is band gap value of bulk GaAs, 1.508 eV, which is very close to the experimental measurements) as the thickness of AlAs barrier increases.
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