Mark H. Jaffe

Design and experimental characteristics of strained In/sub 0.52/Al/sub 0.48/As/In/sub x/Ga/sub 1-x/As (x>0.53) HEMTs

Strained In/sub 0.52/Al/sub 0.48/ As/In/sub x/Ga/sub 1-x/As (x>0.53) HEMTs (high electron mobility transistors) are studied theoretically and experimentally. A device design procedure is reported that is based on band structure and charge control self-consistent calculations. It predicts the sheet carrier density and electron confinement as a function of doping and thickness of layers. The DC performance at 300 K is presented. Wafer statistics demonstrate improvement of device characteristics with excess indium in the channel (g/sub m,/ /sub intr/=500 and 700 mS/mm for x=0.60 and 0.65). Microwave characterization shows the f/sub T/ improvement (f/sub T/=40 and 45 GHz for x=0.60 and 0.65, respectively) and the R/sub ds/ limitations of the 1- mu m-long-gate HEMTs. >

Band structure and charge control studies of n‐ and p‐type pseudomorphic modulation‐doped field‐effect transistors

We present results of a numerical formalism developed to address the band structure and the charge control problem in pseudomorphic n‐ and p‐type modulation‐doped field‐effect transistors (MODFETs), which are created by adding excess indium in the active channel region. For n‐type structures, the tight‐bonding formalism is used to study the effect of strain on the crystal electronic properties. A finite‐difference technique to solve the Schrodinger equation simultaneously with the Poisson equation is used to model the MODFET. The enhanced performance in n‐type pseudomorphic devices has been shown to be primarily due to better charge confinement. Results are also presented as a function of channel strain. For p‐type structures, the Kohn–Luttinger formulation is used together with deformation potential theory to describe the hole states. Significant reductions in the mass of the hole gas due to biaxial compressive strain are demonstrated, suggesting dramatic potential improvement in the operation characteri...

Theoretical studies of optical modulation in lattice matched and strained quantum wells due to transverse electric fields

Electrooptical modulators based on quantum well structures have become an important area of research due to potential applications in high-speed optical modulation and image processing. In this paper, we examine the physics of a quantum well modulator within the generalized Kohn-Luttinger Hamiltonian. Issues of importance for the modulator structure are the excitonic absorption shift, exciton binding energy, line broadening, tunneling rates for electrons and holes in the presence of a transverse electric field, and changes in optical absorption coefficients as a function of electric field. A formalism to study these effects for both lattice matched and nonlattice matched quantum well structures is provided and the potential of material tailoring for specific optical response is discussed. It is shown that the reliability of this technology is critically related to the fabrication of high-quality interfaces and alloys since even a one-monolayer variation in quantum well size can have a substantial effect on the modulation properties.

Ultrasonographic Diagnosis of Extremity Masses

Radiographic examination of soft tissue extremity masses is frequently inconclusive. In 18 patients with normal or nonspecifically abnormal radiographs, gray scale ultrasonography provided useful additional information. It was possible to distinguish fluid collections from solid masses, and recurrent venous thrombosis from hematoma in anticoagulated patients. Occasionally, specific diagnoses were suggested on the basis of ultrasonic morphologic characteristics. Diagnoses included soft tissue neoplasms, hematomas, aneurysms, synovial cysts, abscesses, and a lymphocele.Ultrasonically guided percutaneous needle aspiration was diagnostic in two cases. Features of differential diagnostic value relative to extremity solid masses and fluid collections are discussed. Ultrasonography is useful in evaluating these soft tissue masses.

In‐plane hole effective masses in InxGa1−xAs/Al0.15Ga0.85As modulation‐doped heterostructures

We have determined the strain dependence of the in‐plane hole effective mass in pseudomorphic Inx Ga1−x As/Al0.15 Ga0.85As modulation‐doped heterostructures by low‐temperature Shubnikov–de Haas measurements. An effective mass equal to 0.18m0 is measured for x=0.2. The measured values are in good agreement with theoretical calculations.

Theoretical formalism to understand the role of strain in the tailoring of hole masses in p-type InxGa1-xAs (on GaAs substrates) and In0.53+xGa0.47-xAs (on InP substrates) modulation-doped field-effect transistors

Recently, experimental studies have suggested that strained p‐channel modulation‐doped field‐effect transistors (MODFET’s) display enhanced characteristics due to a decrease in hole masses. In this letter, we examine the potential of using biaxial compressive strain to lower the effective mass of the hole gas. The Kohn–Luttinger Hamiltonian is used to describe the hole states in a strained channel. Using this, the Schrodinger equation is solved self‐consistently with the Poisson equation. The coupling between light‐ and heavy‐hole states is found to be critical to get accurate properties of the hole gas. A decrease in the effective hole mass of more than three times is found at low temperatures in the presence of the biaxial strain. The theoretical technique described here is not variational in nature and can be applied to an arbitrarily shaped confining potential profile with different material parameters across interfaces. This technique should be quite useful in designing and understanding strained p‐M...

Perirenal cobwebs: the expanding CT differential diagnosis.

Although initially described as representing collateral venous structures, perirenal cobwebs may be due to a variety of benign and malignant conditions. Six representative cases illustrating the broad differential diagnosis are presente.

A comparison of the electronic properties of thin-period (InAs)(GaAs) and (InAs)(AlAs) superlattices with compositionally similar random alloys

A comparison is made between the electronic properties of the (InAs) (GaAs) and (InAs) (AlAs) superlattices with their compositionally similar random alloys. While the long range order in the superlattice can dramatically reduce the effect of alloy scattering on both transport and excitonic linewidth, the electronic properties of the thin period superlattice are similar to the alloy with major differences occurring only in the hole states. Since the band-edge lineup at strained heterointerfaces is largely unknown, we present the dependence of the bandgap, the electron and hole effective masses and the separation between the heavy and light hole bands at the center of the Brillouin zone with respect to the band-edge lineup. Our calculations show that thin period strained superlattices using these systems could have excellent potential for high-speed devices.

Computed tomography of acute renal failure secondary to rhabdomyolysis

Two patients with rhabdomyolysis and renal failure were imaged with CT. The presence of a striate nephrogram, nephromegaly, and perinephric fluid has not previously been described on CT. Although nonspecific, these findings suggest the diagnosis of acute tubular blockade, and, once identified, administration of additional urographic contrast medium should be avoided.

Gestational trophoblastic neoplasia: Computed tomographic appearance

Abstract The authors present the computed tomographic findings in a patient with malignant gestational trophoblastic neoplasia. No similar case has been described on computed tomography. The interesting aspects of the case and a brief review of this clinical entity is discussed.