A survey of ohmic contact materials and properties to GaAs, InP, GaN will be presented along with critical issues pertaining to each semiconductor material. Au-based alloys (e.g. GeAuNi for n-type GaAs) are the most commonly used contacts for GaAs and InP materials for both n-and p-type contacts due to the excellent contact resistivity, reliability, and usefulness over a wide range of doping levels. Research into new contacting schemes for these materials has focused on addressing limitations of the conventional Au-alloys in thermal stability, propensity for spiking, poor edge definition, and new approaches for a non-alloyed contact. The alternative contacts to GaAs and InP include alloys with higher temperature stability, contacts based on solid phase regrowth, and contacts that react with the substrate to form lower bandgap semiconductors alloys at the interface. A

Unpassivated AlGaN/GaN high-electron-mobility transistors show significant gate lag effects due to the presence of surface states in the region between the gate and drain contact. Low-temperature (100 °C) layers of MgO or Sc2O3 deposited by plasma-assisted molecular-beam epitaxy are shown to effectively mitigate the collapse in drain current through passivation of the surface traps. These dielectrics may have advantages over the more conventional SiNX passivation in terms of long-term device stability.

We have successfully demonstrated an integrated optical system for collecting the fluorescence from a trapped ion. The system, consisting of an array of transmissive, dielectric micro-optics and an optical fiber array, has been intimately incorporated into the ion-trapping chip without negatively impacting trapping performance. Epoxies, vacuum feedthrough, and optical component materials were carefully chosen so that they did not degrade the vacuum environment, and we have demonstrated light detection as well as ion trapping and shuttling behavior comparable to trapping chips without integrated optics, with no modification to the control voltages of the trapping chip.Integration of fluorescence collection optics with a microfabricated surface electrode ion trap

We modeled population growth from 1990 to 2000 in the north Dallas-Fort Worth Metroplex using two different methods: a conventional model based on remote sensing land-use change detection, and a newly devised approach using GIS-derived road development measurements. These methods were applied at both city and census-tract levels and were evaluated against the actual population growth. It was found that accurate population growth estimates are achieved by both methods. At the census-tract level, our models yielded a comparable result with that obtained from a more complex commercial demographics model. At both city and census-tract levels, models using road development were better than those using land-use change detection. In addition to being efficient in cost and time, our models provide direct visualization of the distribution of the actual population growth within cities and census tracts when compared to commercial demographic models.

Inductively coupled plasma (ICP) etching of GaAs, GaP, and InP is reported as a function of plasma chemistry, chamber pressure, rf power, and source power. Etches were characterized in terms of rate and anisotropy using scanning electron microscopy, and root-mean-square surface roughness using atomic force microscopy. ICP etch rates were compared to electron cyclotron resonance etch rates for Cl2/Ar, Cl2/N2, BCl3/Ar, and BCl3/N2 plasmas under similar plasma conditions. High GaAs and GaP etch rates (exceeding 1500 nm/min) were obtained in Cl2-based plasmas due to the high concentration of reactive Cl neutrals and ions generated as compared to BCl3-based plasmas. InP etch rates were much slower and independent of plasma chemistry due to the low volatility of the InClx etch products. The surface morphology for all three materials was smooth over a wide range of etch conditions.