Pulsed Laser Deposition and Electrical Properties of Zinc Selenide Based Thin Film Structures for Integration with Mid-infrared Applications

Abstract

Thin films of chlorine (Cl) and copper (Cu) doped zinc selenide (Cl:ZnSe and Cu:ZnSe) were fabricated by pulsed laser deposition (PLD) with the goal of enabling a multilayered semiconductor structure for a mid-infrared (mid-IR) electrically excited laser. Doping of ZnSe is achieved by varying the mass ratio of zinc chloride (ZnCl₂) or copper selenide (Cu₂Se) to ZnSe precursors in starting pressed powder targets. Appropriate adjustment of the fraction of dopant precursor in the mixtures allows for the control of the dopant concentration, N_D–N _A for N_D >> N_A (or N_A-N_D for N _A >> N_D) in the thin films, where N_D is the donor concentration and N _A is the acceptor concentration. PLD is used to ablate the Cl:ZnSe or Cu:ZnSe targets, to produce thin films on gallium arsenide (GaAs) substrates. Impedance spectroscopy allows current-voltage and capacitance-voltage (C-V) characterization. Specifically Mott-Schottky measurements determine N_D-N_A (or N _A-N_D) of the fabricated thin film samples with comparisons to the nominal dopant concentration of the targets. The Mott-Schottky, 1/C² vs. V, measurements for determining N_D-N_A were calibrated against well-characterized silicon wafers with known values of N _D. The goal of this project was to demonstrate a reliable method for controlling the dopant concentration in PLD-deposited Cl:ZnSe and Cu:ZnSe thin films. The results obtained allows for the fabrication of Cl:ZnSe and Cu:ZnSe thin films with known N_D-N _A for use in a mid-IR electrically-excited laser devices under development in our research group.