Engineering direct-indirect band gap transition in wurtzite GaAs nanowires through size and uniaxial strain

One dimensional semiconductor nanowires have been extensively researched in the past years because of their unique characteristics. Group III-V semiconductors show special promise in a wide range of applications, such as field-effect transistors, light-emitting diodes, and optical sensors. The fundamental properties of these materials are essential to their applications, particularly the electronic properties. In this presentation, we report first principles density-functional theory study on the electronic properties of wurtzite GaAs nanowires along the (0001) direction, with the diameter of the wires up to 3.0 nm [1]. It was found that the band gap of GaAs nanowires experience a direct-to-indirect transition when the diameter of the nanowires is smaller than $\sim $2.8 nm. For those thin GaAs nanowires with an indirect band gap, it was found that the gap can be tuned to be direct if a moderate external uniaxial strain is applied. Both tensile and compressive strain can trigger the indirect-to-direct gap transition. The critical strains for the gap-transition are determined by the energy crossover of two states in conduction bands. \\[4pt] [1] A. Copple, N. Ralston, X.-H. Peng, Appl. Phys. Lett.100, 193108 (2012).