Gordon C. Osbourn

A GaAsxP1−x/GaP strained‐layer superlattice

Strained−layer superlattices form a broad new class of semiconductor materials with tailorable electronic properties. We have succeeded in growing a GaAsxP1−x/GaP(100) strained−layer superlattice (SLS). The structure was grown by alternate metalorganic chemical vapor deposition of thin (60 A)layers (20 each) of GaAs0.4P0.6 and GaP. These layers were grown onto a GaAsxP1−x layer which was graded in composition from x = 0 (composition of underlying GaP substrate)to x = 0 (average composition of the SLS). Photoluminescense studies of the SLS were carried out to determine the optical band gap. At T = 78 K, the spectrum shows a dominant band−edge peak at 2.03 eV as well as weaker peaks at higher energies. Tight binding and effective mass calculations, also carried out, predict a direct band gap (due to zone folding) of 2.02 eV and higher lying transition energies which are in good agreement with these data.

Systems and methods for biometric identification using the acoustic properties of the ear canal

The present invention teaches systems and methods for verifying or recognizing a persons identity based on measurements of the acoustic response of the individuals ear canal. The system comprises an acoustic emission device, which emits an acoustic source signal s(t), designated by a computer, into the ear canal of an individual, and an acoustic response detection device, which detects the acoustic response signal f(t). A computer digitizes the response (detected) signal f(t) and stores the data. Computer-implemented algorithms analyze the response signal f(t) to produce ear-canal feature data. The ear-canal feature data obtained during enrollment is stored on the computer, or some other recording medium, to compare the enrollment data with ear-canal feature data produced in a subsequent access attempt, to determine if the individual has previously been enrolled. The system can also be adapted for remote access applications.

The preparation and characterization of strained-layer superlattices in the GaAs + GaP System

The technique of metal organic chemical vapor deposi-tion has been used to prepare strained-layer superlattices in the GaAs + GaP system. The superlattices consist of alternating layers of GaP and GaAsxP1−x for x = 0.2 to 1.0, which vary in thickness from 30 to 400 Å. The layers were grown by the decomposition of trlmethylgallium and various mixtures of ASH3 and PH3 in H2 at 800δC. The thickness and uniformity of the layers were determined by optical and transmission electron microscopy and x-ray diffraction. The composition of the layers was determined from x-ray diffraction. A new analysis has been developed to determine the layer strain as well as the composition of thick layers (∼ 300 Å). Transmission electron microscopy has been used to yield direct evidence that strained-layer superlattices can be used to remove the misfit dislocations generated during the epitaxial growth of a GaAsxP1-x alloy on a lattice mismatched GaP substrate. These results are in agreement with the previous work of Matthews and Blakeslee. Optical absorption, photocurrent spectroscopy and photoluminescence have been used to deter-mine the band gap energy as well as the energies for other optical transitions. The values are in excellent agreement with the values predicted by tight binding and effective mass calculations.

Extended infrared response of InAsSb strained-layer superlattices

Strained‐layer superlattices of InAsSb were grown with low densities of dislocations and microcracks for optical characterization to determine the suitability of these structures for infrared photodetectors. Infrared transmission measurements revealed absorption throughout the 8–12 μm region and extended to longer wavelengths than predicted from consideration of the tensile strain‐induced band‐gap shift in a type‐I superlattice. We conclude that a type‐II superlattice occurs in the InAsSb system for alloy compositions >60% Sb.

Ion channeling studies of InGaAs/GaAs strained‐layer superlattices

The first ion channeling studies of the InxGa1−xAs/GaAs strained‐layer superlattice (SLS) system are reported. The strong orientation dependence of the dechanneling for both axial and planar directions relative to the [100] growth axis indicates that the ≊1% lattice mismatch is accommodated by lattice strain. Tetragonal distortions along the growth direction give rise to alternating tilts for inclined crystal directions which result in significant [110] and (110) dechanneling. Measurements for 40‐layer structures with different In concentrations demonstrate that the channeling technique is a depth‐sensitive probe of the degree of strain in SLS systems.

Photoluminescence and the band structure of InAsSb strained‐layer superlattices

Infrared photoluminescence measurements were performed on InAs0.13Sb0.87 /InSb strained‐layer superlattices. In thick layered structures we observed very low energy transitions proving that a type II superlattice occurs in the InAsSb system. Band structures were calculated based on estimates of the band offsets and strain shifts obtained from the photoluminescence data.

Large valence-band nonparabolicity and tailorable hole masses in strained-layer superlattices

The two‐dimensional, strain‐induced light‐hole masses in InGaAs strained‐layer superlattices are shown to have large nonparabolicity contributions. Calculated hole masses agree with experimental values to within the 20% scatter. The results indicate that these tailorable hole masses could be useful tools for studying two‐dimensional valence transport.

Electrical transport of holes in GaAs/InGaAs/GaAs single strained quantum wells

We report electrical transport data for holes in single strained quantum well structures of the type GaAs/InxGa1−xAs/GaAs with x≊0.2. With modulation doping, 4 K mobilities of ∼3×104 cm2/V s have been achieved. This value is near that attained for electrons in comparable structures, illustrating the enhanced transport possible due to the strain‐induced light‐hole planar mass.

Independently variable band gaps and lattice constants in GaAsP strained‐layer superlattices

The capability of independently varying band gaps and lattice constants in ternary strained‐layer superlattices has been experimentally demonstrated for the first time. High‐quality GaAsxP1−x/GaP superlattices (0<x≤0.62, lattice mismatches up to 2.3%) were grown by metalorganic chemical vapor deposition and their band gaps and lattice constants were measured. The band gaps at each composition agree with calculated values, and differ significantly from the band gaps of bulk alloys with the same lattice constant. This newly demonstrated capability could allow high‐quality heterojunction devices to be grown in a variety of lattice‐mismatched ternary systems.

Empirically defined regions of influence for clustering analyses

We present a simple but effective clustering algorithm for non-hierarchical k-dimensional data which is also useful for pattern recognition applications. The method uses a visually-empirical region of influence (VERI) that we have discovered. Our approach enables us to use human cluster judgments as the cluster criteria, and to extend these criteria in a natural way to k-dimensional data. The VERI algorithm requires no user input (e.g. the number of clusters in the final result) or user adjustments beyond providing the data itself. The algorithm computes clusterings based on the local k-dimensional neighbors of each point, and thus handles arbitrary numbers of clusters and arbitrary global cluster shapes. We demonstrate that the method works well for a variety of 2D cluster configurations which popular methods cannot treat (despite requiring the number of clusters as input), and illustrate that the performance is maintained for k-dimensional problems. The application of the method to pattern recognition problems is outlined, and efficient implementations of the VERI algorithm are presented.