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Results of an Advanced Research Projects Agency (ARPA) sponsored project to demonstrate the operational benefits of incorporating advanced structural ceramic ball elements into the F117–PW–100 aircraft gas turbine engine high rotor thrust bearings is described. This program consists of design, fabrication and experimental evaluation of candidate hybrid ball bearing designs in Pratt & Whitney and MRC Bearings test facilities. The bearing design criteria and development test conditions utilized for the project are compatible with the requirements of the F117–PW–100 engine system application. Two hybrid bearing designs were produced by analytically varying internal geometry features such as M–50 race curvatures and contact angles to optimize for the modulus of elasticity of the ceramic balls. One–and–one–eighth inch size CERBEC grade NBD 200 silicon nitride ceramic balls demonstrated integrity and a quadruple rolling contact fatigue life improvement versus state–of–the–art M–50 steel balls in single ball test rigs. Thermal performance data obtained in full scale bearing rig performance testing with one–hundred–seventy–eight millimeter size hybrid and all–steel baseline bearings shows comparable characteristics. The hybrid bearing displayed a distinct survivability benefit in bearing liquid lubricant starvation testing. Two dozen hybrid bearings will be fabricated for full–scale bearing rig endurance tests to be conducted in 1995–1996 as a prerequisite to validation in operating F117–PW–100 engines in 1996–1997.

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A new, nondestructive junction depth measurement technique for HgCdTe photovoltaic devices is investigated. The technique uses a scanning laser microscope to obtain laser beam induced current (LBIC) data from which information regarding the junction depth is extracted, and is applicable to both homojunction and heterojunction diodes. For implanted heterojunction photodiodes, the position of the n-p junction relative to the heterojunction is an important factor determining completed device performance, with blind photodiodes resulting if the n-p junction is incorrectly placed. At present, the only methods available for junction depth determination (e.g., secondary ion mass spectroscopy and differential Hall) are destructive and not applicable as routine process monitoring techniques. It is envisaged that the development of a nondestructive routine process monitoring procedure will help improve yield and reduce the cost of HgCdTe photovoltaic devices. In this paper, experimental and theoretical results are presented in order to assess the sensitivity of the new technique to the effects of junction doping density, illumination wavelength, frontside/backside illumination, and test structure geometry.

Both wet chemical and dry plasma etching techniques have been investigated for mesa structuring in n- and p-type HgCdTe. Scanning electron microscopy (SEM) confirms the isotropic nature of a bromine-based wet chemical etching solution, and the anisotropic profile that results from reactive ion etching. Laser-beam-induced-current (LBIC) measurements reveal no significant modifications to the electrical properties for chemically etched HgCdTe material, but clearly demonstrate a p- to n-type conversion in p-type samples and n+ doping in n-type samples for reactive ion etching (RIE) (processing conditions: 400 mTorr, CH4/5H2, 0.4 W/cm2). LBIC measurements following low-temperature (200 °C) mercury annealing of RIE-processed samples indicate the full restoration of electrical properties to that of the initial as-grown wafers, thus preserving the beneficial aspects of RIE for anisotropic mesa structuring in HgCdTe.

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