Optical constants of evaporated amorphous zinc arsenide (Zn₃As₂) via spectroscopic ellipsometry

We have used spectroscopic ellipsometry to measure the optical constants of evaporated amorphous zinc arsenide (Zn₃As₂). A five parameter model using a Tauc-Lorentz oscillator was found to fit well each of six amorphous samples deposited on Si₃N₄/silicon, allowing the layer thicknesses and optical constants to be deduced. Layer thicknesses varied from 20 to 70 nm. The fitted value of the optical gap (Tauc gap) is 0.95 eV, close to the 1.0 eV band gap for crystalline bulk zinc arsenide. A single set of parameters from an ensemble Tauc-Lorentz model can be used to determine the thicknesses of amorphous Zn₃As₂ layers as long as the layers are ≳ 25 nm thick. Measured film thicknesses do not correlate with targeted thicknesses, likely due to low sticking coefficients of evaporated zinc arsenide.