First-principle calculations of electronic and optical properties of CdCr₂Te₄ spinel: use of mBJ + U potential in narrow band gap semiconductors

In this study, we report the theoretical investigation of electronic structure and frequency-dependent optical properties of narrow band gap CdCr₂Te₄ normal spinel. While GGA + U and TB-mBJ schemes fail to show the semiconducting nature of CdCr₂Te₄ spinel, combining the mBJ potential with the Hubbard U correction obtains a narrow band gap of 0.04 eV. The indirect band gap using mBJ + U scheme occurs due to the shifting of spin-up Cr-e_g and Cr-t_2g states of conduction band towards higher energy. This reflects the better suitability of mBJ + U scheme to study the band structure of CdCr₂Te₄ as compared to the GGA + U, TB-mBJ, and expensive hybrid functional methods. The asymmetrical nature of spin-up and spin-down states in total DOS indicates them to be magnetic compounds. The integer value of total magnetic moment per formula unit rules out the metallic nature of this compound. We studied the optical spectra in terms of the band to band transitions for their possible use in optoelectronic applications.