SEMICONDUCTOR THEORY

Direct or indirect band gap



Phys. Rev. B, 98, 245203 (2018)



The direct or indirect nature to the bandgap of a semiconductor is a fundamental property. Despite the extensive research and broad applications of the conventional semiconductors, the understanding of the mechanisms determining their direct or indirect nature to the bandgap remains a challenge. Lack of fundamental understanding of the mechanism controlling the indirect bandgap nature of Si might be the main reason for the difficulty of developing Si-based direct bandgap materials.



Yuan et al. resolved this long-standing puzzle by presenting a unified theory for understanding the direct or indirect nature of bandgap in conventional group II?VI, group III?V, and group IV semiconductors unambiguously. They found that the occupied cation d bands play a prime role in forming the direct or indirect bandgap of semiconductors via the s?d and p?d coupling with the states of the X- and L-valley, which remarkably pushes their energy levels up, but leaves the Γ-valley intact. The either lacking or low-lying of the occupied d orbitals in cations of Diamond, Si, Ge, and Al-containing group III?V semiconductors explains their nature of indirect bandgap.



Junyi Zhu (The Chinese University of Hong Kong, Hong Kong, China)



doi: 10.1088/1674-4926/40/3/030202