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

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, ND--N A for ND >> NA (or NA-ND for N A >> ND) in the thin films, where ND 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 ND-NA (or N A-ND) 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 ND-NA 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 ND-N A for use in a mid-IR electrically-excited laser devices under development in our research group.