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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.

For the first time, fundamental read-range limitations are calculated for two major types of "passive" (i.e. batteryless) RFID systems. Many applications require large read range. But, in shorter range applications excess read range provides read-path signal margin which enhances reading reliability, signal penetration, and/or flexibility in RFID system design, layout, and installation. Analysis was restricted to passive technologies because passive tags are required for the majority of future RFID applications. The analysis shows 2.44 GHz Surface Acoustic Wave (SAW) based RFID potentially has a 30X read range superiority compared to passive semiconductor IC-based RFID operating near 900 MHz.

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Detailed information concerning the anisotropy of the effective limiting superconducting energy gap A(0) of doped Sn has been obtained from measurements of the temperature dependence of the attenuation of compressional ultrasonic waves. Earlier results for the In-doped Sn system have been confirmed for other impurities, and analysis of the results has been made in terms of recent developments in the theory of dirty superconductivity. Measurements have been made for the sound-propagation vector q parallel to the [001], [110], and [100] directions in single crystals of In-, Cd-, Sb-, and Bi-doped Sn with impurity concentrations ranging from ^1 to 5 000 parts per million (ppm). The measured anisotropy between the [110] and [001] directions for pure Sn is ^20% of the average energy gap. It is found that this anisotropy is reduced to ~2% for values of the inverse resistivity ratio p >10"~2 and for AF C >15 mdegK. BCS theory, which was developed for isotropic, weak-coupling superconductors, is applicable to the most heavily doped samples; it is found that the energy gap (^1.76ksT c ) and the temperature dependence of ultrasonic attenuation are in agreement with the predictions of the theory. By comparing the energy-gap measurements from tunneling data with the energy gap obtained from ultrasonic-attenuation data, it is possible to demonstrate that the temperature dependence of the attenuation gives a measure of more than one energy gap. In addition to the gap obtained from the attenuation data at low temperatures, a larger gap can be observed near 2Y From tunneling data, the larger gap for q| [[001] is (1.9db0.05)foT , c ; the ultrasonic determination yields (1.92 ±0.02)ksT c . In addition, the temperature dependence of the larger gap is obtained near T c and is compared with BCS theory. For [1-T/rj ranging from ~4X10~2 to ^4X10^, it is found that the BCS-predicted approximation, A(r)/A(0) = 1.74[l~r/r c ] 1 / 2 , is accurate to ~2%.