Characteristics of Cl-doped ZnSe layers grown by molecular-beam epitaxy

High-quality n-type ZnSe layers have been grown by molecular-beam epitaxy using chlorine (Cl) as a dopant. The Cl-doped ZnSe layers showed mirrorlike morphology and good crystallinity, although some degrade in crystallinity is observed at a heavy doping. The carrier concentration of the layer could be widely controlled by a ZnCl₂ Knudsen cell temperature. The carrier concentration attained 1×10¹⁹ cm^{- 3}, where the resistivity was as low as 3×10^{- 3} Ω cm, indicating a remarkable improvement compared to the previous work using group-III elements as a dopant. Hall mobilities at room temperature were in the range of 200-400 cm²/(V s), depending on the doping level. The Cl-doped ZnSe layer exhibited strong blue near-band-gap photoluminescence (PL) with suppressed deep-level emission at room temperature. The 4.2-K PL of the layer was dominated by strong emission of excitons bound to neutral donors originating from substitutional Cl atoms. It was found by a secondary ion-mass-spectroscopy analysis that diffusion of Cl atoms in the ZnSe layer during growth was negligible (<370 Å).