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.

No abstract

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.

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.