This paper describes cryogenic broad-band amplifiers with very low power consumption and very low noise for the 4-8-GHz frequency range. At room temperature, the two-stage InP-based amplifier has a gain of 27 dB and a noise temperature of 31 K with a power consumption of 14.4 mW per stage, including bias circuitry. When cooled to 15 K, an input noise temperature of 1.4 K is obtained at 5.7 mW per stage. At 0.51 mW per stage, the input noise increases to 2.4 K. The noise measurements have been repeated at different laboratories using different methods and are found consistent.

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Herein we report the wafer-scale synthesis of thin-film black arsenic–phosphorus (b-AsP) alloys via two-step solid-source molecular beam deposition (MBD) and subsequent hermetic thermal annealing. We characterize our thin films with a variety of compositional and structural metrology techniques. X-ray photoelectron spectroscopy and energy dispersive spectroscopy determine compositions of As0.78P0.22 for our thin films, while X-ray reflectivity measurements indicate film thicknesses of 6–9 nm. High-resolution transmission electron spectroscopy images reveal a nanocrystalline morphology with orthorhombic b-AsP grains on the order of ∼5 nm. Raman scattering spectroscopy is employed to characterize the vibrational spectra of our thin films, and the results obtained are in agreement with previously reported b-AsP spectra. Evidence of uniform wafer-scale growth is substantiated by Raman mapping. We simulate crystal structure, band gaps, and Raman spectra from first-principles DFT-based computations and find excellent agreement with our experimental results. This work is the first demonstration of on-wafer synthesis of b-AsP. Our large-area growth technique enables the development of next-generation b-AsP devices for optoelectronic, digital, and radio frequency (RF) applications.

We have studied the electroreflectance and photoreflectance spectra from a pseudomorphic Ga0.78Al0.22As/In0.21Ga0.79As/GaAs modulation-doped quantum well (MDQW) structure in the temperature range 79<T<304 K. The features from the InGaAs MDQW can be accounted for on the basis of a two-dimensional density of states and a Fermi level filling factor. A detailed line shape fit makes it possible to evaluate the Fermi energy, and hence the two-dimensional electron gas concentration (Ns), as well as other important parameters of the structure. Our value for Ns is in good agreement with a Hall measurement.

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We have measured the kinetic parameters for the removal of SiO2 films from silicon in ultrahigh vacuum using Auger electron spectroscopy and low-energy electron diffraction, both with and without a beam of atomic silicon incident on the surface. Due to the very low vapor pressure of SiO2, it is removed only through reduction to SiO by excess silicon. We find that the activation energy for the rate limiting step in the thermal desorption of SiO2 is 3.54±0.2 eV, so that at temperatures below ∼900 °C, thick films (∼25 Å) can scarcely be removed by thermal desorption alone, in agreement with earlier work. Very thin oxide films (∼5Å) can be readily removed at lower temperatures, since SiO formed at the Si-SiO2 interface encounters a negligible diffusion barrier and sublimes directly into vacuum. With a beam of silicon incident, SiO forms at the oxide surface and desorbs with an activation energy of only 0.84±0.2 eV. Oxide films on silicon can be removed at temperatures as low as 700 °C using an incident silicon beam flux of 3×1013 cm−2 s−1.

We report electrical measurements on four different metal contacts which formed Schottky barriers to lightly doped complementary n-and p-type Alo.,,Ino.,2 As epitaxial material grown by molecular beam epitaxy on semi-insulating InP substrates. The Schottky contact metals studied were Au, Al, Pt, and the tri-layer Ti/Pt/Au. The Schottky barrier heights varied from 0.560 eV for A1 on n-type AlInAs to 0.905 eV for Al on p-type AlInAs, with intermediate values for the other metals studied. The sum of the n-and p-type Schottky barrier heights for each metal contact ranged from 1.440 to 1.465 eV, in good agreement with the accepted A1,.,InO.,,As bandgap value of 1.45 eV.ATTICE-matched AlInAs/InGaAs/InP devices are very L attractive for high-speed, high-frequency transistor applications [ 11 - [3]. As such, the characteristics of Schottky barriers to AlJn, -,As ( x = 0.48) are of fundamental interest for device applications. AlInAs epitaxial layers have been the subject of numerous investigations in the last decade [ 11 -[ 121. These studies have included AlInAs energy bandgap dependence on alloy composition by optical methods [4]; growth and characterization of MBE-grown AlInAs [5]; photoemission studies [6]; AlInAs Schottky barrier height compositional dependence work [7]; further investigations of the Schottky barrier height of AlInAs [8] -[ 101 ; and barrier height studies [ll], [12]. Similar work on the Schottky barrier height of AlGaAs has also been performed [ 131.In this work we present new data on the fundamental electronic properties of the Schottky barrier height of complementary p-and n-type A10,481n0,52 As Schottky barriers grown by molecular beam epitaxy. The n-type and p-type A10,4,1no,5, As samples consisted of a 3000-8, heavily doped 1 X 1019 cm-3 buried ohmic contact layer followed by approximately 4000 8, of a lightly doped surface layer. The group 111 fluxes were calibrated using W E E D intensity oscillations and the layers were determined to be within f 1 % of lattice-matched composition using double-crystal X-ray diffraction. The uniform low doping concentration for both the p-and n-type Alo,481no,52As samples was chosen to be roughly 2 X 10l6 ~m -~, and was determined by capacitance versus voltage ( C V ) measurements to be approximately 1.4 x 10l6 cm-3 f 3% and 2.4 x 10l6 cm-3 f 2% for the . Streit are with TRW, Inc., Redondo Beach, CA IEEE Log Number 9104126.Engineering, University of Utah, Salt Lake City, UT 84112. 92072.w n + or p + InAlAs ( 1 00) InP Substrate Fig. 1. Device structure of Alo,481no,52 As samples.p-and n-type devices, respectively. The 4.15-mil-diameter metal dots were evaporated following a 7-mil-diameter mesa etching to expose the buried heavily-doped layer. An illustrative schematic of the device structure is shown in Fig. 1.One benefit of studying complementary p-and n-type Schottky devices is that the sum of the Schottky barrier heights, 4, and +n, should be equal to the energy bandgap E, of the semiconductor material [13]- [15]. This equality is known as the barrier heig...

X-ray diffuse scattering in (001) InGaAs/(AlGa)As transistor structures of high electron mobility was observed for structures whose InGaAs channel thickness substantially exceeded the critical thickness for misfit dislocation formation. The diffuse scattering was determined to originate from misfit dislocations, as confirmed by plan-view transmission electron microscopy. Diffuse scattering was measured using triple-axis X-ray diffraction, which showed that the diffuse scattering was sensitive to the density and direction of the misfit dislocations. Using transmission electron microscopy for calibration, we determined that the diffuse scattered intensity was directly proportional to the dislocation density. For samples with misfit dislocations along only (110), diffuse scattering was confined to a crystallographic direction that was perpendicular to the misfit segments, but for samples with thicker InGaAs layers (and with misfit segments in both (110) directions) diffuse scattering extended along all azimuthal directions. We also determined that observation of directional diffuse scattering provided a more sensitive means of detecting misfit segments than other commonly used techniques.