Optimization of fabrication processes of the mesa-type GaAs:Te blocked-impurity-band detector
In this work, the device structure of the mesa-type GaAs:Te blocked-impurity-band detector was designed. The fabrication processes were presented briefly, and optimization of the fabrication processes was investigated. A 3-micron-thick SiO2 film was deposited as resist to substitute for photoresist in the 50-micron-deep mesa etching process. In addition, a bi-layer photoresist lithography technique was adopted to optimize the process of electrode fabrication. It is demonstrated that the device quality can be improved significantly after optimization.
GaAs BIB photodetector development for far-infrared astronomy
GaAs photoconductive detectors offer an extended spectral response in the far-infrared (FIR) compared to presently available stressed Ge photoconductors. Furthermore, responsivity at wavelengths up to 330 microns can be reached without having to apply uniaxial stress close to the breaking limit on each pixel. This would greatly simplify the production of detector arrays and therefore allow much larger numbers of pixels. Such arrays are highly demanded for upcoming far-infrared astronomy missions with space and airborne telescopes. However, bulk GaAs photoconductors have only limited sensitivity, due to low absorption and high dark currents. Considerable improvement of the detector performance can be expected from the development of GaAs blocked impurity band (BIB) devices. Our recent crystal growth experiments show that the liquid phase epitaxial (LPE) technique is capable of producing the required purity for the blocking layer. We have also performed far-infrared absorption measurements of doped GaAs layers which demonstrate the spectral range extension to about 330 microns and the enlarged absorption coefficient for the more highly doped absorption layer. Experimental work is supported by numerical modeling of BIB devices done in our group.
Far-field dispersal modeling for fuel-air-explosive devices
A computer model for simulating the explosive dispersal of a fuel agent in the far-field regime is described and is applied to a wide variety of initial conditions to judge their effect upon the resulting fuel/air cloud. This work was directed toward modeling the dispersal process associated with Fuel-Air-Explosives devices. The far-field dispersal regime is taken to be that time after the initial burster charge detonation in which the shock forces no longer dominate the flow field and initial canister and fuel mass breakup has occurred. The model was applied to a low vapor pressure fuel, a high vapor pressure fuel and a solid fuel. A strong dependence of the final cloud characteristics upon the initial droplet size distribution was demonstrated. The predicted fuel-air clouds were highly non-uniform in concentration. 18 refs., 86 figs., 4 tabs.