Electronic structure and optical properties of NaSi

The electronic structure and optical properties of NaSi were investigated using first-principles calculations and diffuse reflectance measurements. The calculation indicates that NaSi is an indirect band gap semiconductor whose valence band maxima and conduction band minima are located at a k-point between the Γ and X points and at the Y point, respectively. NaSi has several direct band gaps, which are approximately 0.1 eV larger than the indirect band gap, leading to its large optical absorption coefficient near the indirect band gap. The valence bands originate from Si-3p states and the conduction bands from the Si-3s, Si-3p, Na-3s, and Na-3p states. Diffuse reflectance measurements revealed that NaSi has a band gap of 1.63 eV, which is comparable to the band gap calculated using HSE06 (1.68 eV).