Thin films of the phase transition material vanadium dioxide (VO2) were deposited by thermal oxidation of e-beam evaporated vanadium on a variety of bulk materials. Substrate effects on transition temperature are confirmed as being due to a mismatch between film and substrate thermal expansion coefficients. Decreasing tensile stress results in a lowering of VO2 transition temperature. Effects of low-energy Ar+ bombardment on the electrical and optical properties of these predeposited VO2 films were investigated. Bombardment energies in the range 138–500 eV at 1.0–1.3 mA/cm2 for 120–180 s were provided by a Commonwealth Millatron. The higher Ar+ energies resulted in collapse of the VO2 optical transmittance hysteresis loop, while low-energy Ar+ ions caused both a downward shift in the transition temperature and a decrease in hysteresis loop width, suggesting a dependence of these quantities on intrinsic stress. In addition, large decreases in cold-state resistivity are reported and attributed to a reduction of the surface oxide by the low energy argon beam.

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An enhanced quantum well infrared photodetector (EQWIP) with lower dark current and improved performance relative to a conventional QWIP is described. Dark current reduction and external quantum efficiency improvements are achieved by novel structural enhancements that involve patterning the GaAs/AlGaAs multiple quantum well into a diffraction grating and reducing the number of wells. A 64×64 long wave infrared EQWIP array with 60 μm pixel pitch and peak D*∼8×1010 cm Hz1/2/W was demonstrated at 77 K. The low bias current permits hybridization to conventional readout circuits. Test results for pixel pitches down to 30 μm show that high EQWIP performance is achievable in the small pixels required for large focal plane array formats.