Controllable terahertz intersubband absorptions in ZnO/(Sb,N) co-doped ZnO quantum wells: First-principles study

Abstract

ZnO-based heterostructures have emerged as promising materials for infrared and terahertz (THz) optoelectronic technologies capable of operating at room temperatures. This is attributed to the intrinsically high longitudinal-optical (LO) phonon energy which suppresses the phonon scattering to boost the temperature performance. Numerous high-performance THz sources rely on single doping (e.g., ZnO/MgxZn1–xO, ZnO/CdxZn1–xO hybrids). Herein, the combined theoretical approaches based on density functional theory (DFT) and the numerical matrix method were employed to unravel the electronic and optical properties of a quantum well made from ZnO/(Sb,N) co-doped ZnO heterostructures. The findings reveal that (Sb,N) co-doped relatively requires the lower formation energy than the single doping counterparts. Both un-doped and (Sb,N) co-doped ZnO are characterized as semiconductors of which the energy gap of the latter is relatively lower. The combination of these materials consequently creates type-I band lineups with the valence and conduction band offsets of 1.03 eV and 0.61 eV, respectively. Intriguingly, a confined electron in the resultant quantum well derived from the conduction band offset exhibits the intersubband optical transitions in the energy range of 6.0–10.0 THz which is the challenging regime in THz technology. Moreover, the optical absorptions can be effectively modulated by the width of the quantum well and the external electric fields. Specifically, the increases in the well width and field strength result in the redshift and blueshift in the absorption spectrum, respectively. Hence, ZnO/(Sb,N) co-doped ZnO/ZnO heterostructure is conclusively a potential candidate for THz optoelectronic devices.