Search

The physical and electrical properties of GaAs show it to be an important semiconductor material for use in various electronic devices associated with advanced military systems. However, the realization of enhanced device performance has been delayed, partly due to the lack of consistent, high quality, semi-insulating GaAs substrate material. A modified liquid-encapsulated Czochralski technique employing pressure-assisted, in-situ compounding is described. This process, first demonstrated in the United States by the US Army Electronics Technology and Devices Laboratory, consistently yields high resistivity (to 10 to the 9th power ohm-cm) GaAs without the intentional addition of charge compensators. This approach is now becoming the basis for U.S. volume production of large diameter, high quality, semi-insulating GaAs material. An automated system for the measurement of transport properties by use of the van der Pauw method is described. A mixed conduction analysis allows the direct determination of individual carrier concentrations and mobilities, intrinsic carrier concentration and Fermi level. Applied to ET&DL's non-Cr-doped GaAs, this analysis yields electron mobilities higher than Cr-doped material and Fermi levels which are nearly intrinsic. (Author)

Conductivity and Hall measurements were made on semi-insulating GaAs samples grown with a recently developed process using in-situ compounding with liquid encapsulated (B2O3) Czochralski growth techniques. Mixed conduction analysis in combination with a nomographic analysis of charge balance and conduction was used to elucidate compensation in this material. Given the Cr concentration in one sample, the use of an iterative self-consistent procedure allowed the deduction of total donor and acceptor concentrations for identically prepared Cr-doped and undoped samples. Further analysis yielded the compensation ratio and energy level of the dominant acceptor of a third specimen. A subsequent spark source analysis confirmed the high purity of this in-situ compounded material, as well as the conclusions and utility of the nomographic analysis. (Author)

A wide variety of semiconductor devices utilizing gallium arsenide are currently under development by the military for use in secure communication, improved surveillance, and high speed digital logic systems. The GaAs field effect transistor, a critical component in these systems, is experiencing a rapidly expanding use in oscillator, mixer, logic element, power amplification, and low-noise/high-gain applications. However, the full potential of this device has not been realized, partly because of poor and unpredictable quality semi-insulating GaAs substrates. More specifically, native defects, electrically active impurities, and diffusing charge traps are problems associated with commercial substrates. A silicon- and carbon-free modification of the liquid encapsulated Czochralski technique is described which yields high purity semi-insulating GaAs (approximately 10 to the 8th ohm-cm) without the intentional addition of charge compensators. The technique employs liquid encapsulated compounding of GaAs at nitrogen pressures to 100 atm, ultrapure elements, and pyrolytic boron nitride crucibles. A high pressure (135 atm) Varian HPCZ Czochralski crystal puller is employed for both compounding and crystal growth. (Author)

The requirement for low-threshold high-efficiency laser sources for miniaturized rangefinder and fiber optic communication applications has led to the study of rare earth pentaphosphate compounds. Neodymium pentaphosphate (NdPP) has recently emerged as a promising 1.05 micrometer laser material operating in pulsed and cw modes, with thresholds of the latter reported less than 1 milliwatt. In contrast to doped lasers such as Nd:YAG, NdPP is a stoichiometric compound (NdP5O14) which accommodates up to thirty times more Nd than YAG. The evaluation and testing of NdPP lasers in prototype components using transverse and longitudinal optical pumping has been hindered due to the limited size (several mm), availabilty, and quality of the single crystals. We have devised unique modifications of conventional solution growth techniques in order to control reaction kinetics and precipitation rates. The largest bulk single crystals (greater than 1 cm) of yttrium and lanthanum substituted NdPP presently available were grown by these modified techniques. We have observed laser action in as-grown 90% Nd 10% Y pentaphosphate crystals with dimensions typically 4.5x3 mm in diamond-shaped cross section by 2 mm thick.

This patent application describes a passive millimeter wave image guide power limiter comprising a length of dielectric transmission line or waveguide for millimeter wave frequencies located on a relatively thin conductive ground plane forming thereby an image guide and including a planar doped barrier diode structure formed in the dielectric transmission line with the planar doped barrier structure being integrally grown in a slot milled in the constituent material, i.e. gallium arsenide, of the waveguide transversely across the width dimension thereof so as to be orientated perpendicular to the flow of RF power being propagated along its length dimension. The planar doped barrier structure becomes conductive at a predetermined power level to reflect any further incident RF power back toward the power source.

This invention relates generally to semiconductive devices and more particularly to planar doped barrier and superlattice devices. An electronic oscillator being operable to detect millimeter wave and infrared frequency output signals over the range of 1-1000GHz consists of a semiconductor device having a structure comprised of a first planar doped barrier region separated from a second planar doped barrier region by a superlattice region. Upon the application of a uniform electric field, the first planar doped barrier region operates as a means for injecting electrons into the superlattice region which then traverse to the second planar doped barrier region which operates as means for receiving the electrons. During transit through the superlattice region, the electrons undergo an oscillatory motion thereby making possible the detection of signals whose frequency is a function of the applied voltage and the periodic spacing of the superlattice.