C. R. Bolognesi

Interface roughness scattering in InAs/AlSb quantum wells

We present a study of interface roughness scattering in not‐intentionally‐doped AlSb/InAs/AlSb quantum wells grown by molecular beam epitaxy on [001] GaAs semi‐insulating substrates. The low‐temperature mobility is found to be limited by interface roughness scattering for well widths below 100 A. The measured mobilities are well accounted for by Gold’s theoretical treatment [A. Gold, Phys. Rev. B 35, 723 (1987)], once it is suitably modified to account for the band nonparabolicity of InAs. The experimental electron density dependence of the mobility indicates a lateral correlation length for the interface roughness Λ≊62 A for interface fluctuations approximately 1 monolayer high. We believe this roughness scale is characteristic of the bottom (InAs‐on‐AlSb) interface.

High-transconductance InAs/AlSb heterojunction field-effect transistors with delta -doped AlSb upper barriers

The authors report the fabrication and temperature-dependent characterization of InAs/AlSb quantum-well heterojunction field-effect transistors (HFETs). Devices with electron sheet concentrations of 3.8*10/sup 12/ cm/sup -2/ and low-field electron mobilities of 21000 cm/sup 2//V-s have been realized through the use of Te delta -doping sheets in the upper AlSb barrier. One device with a 2.0- mu m gate length showed a peak extrinsic transconductance of 473 mS/mm at room temperature. Gate leakage current, operating current density, and extrinsic transconductance were found to decrease with decreasing temperature.<<ETX>>

Growth of InAs-AlSb quantum wells having both high mobilities and high concentrations

Low-temperature mobilities in InAs-AlSb quantum wells depend sensitively on the buffer layer structures. Reflection high energy electron diffraction and x-ray diffraction show that the highest crystalline quality and best InAs transport properties are obtained by a buffer layer sequence GaAs → AlAs → AlSb → GaSb, with a final GaSb layer thickness of at least 1 μm. Using the improved buffer scheme, mobilities exceeding 600,000 cm2/Vs at 10 K are routinely obtained. Modulation δ-doping with tellurium has yielded electron sheet concentrations up to 8 × 1012 cm−2 while maintaining mobilities approaching 100,000 cm2/Vs at low temperatures.

Microwave performance of a digital alloy barrier Al(Sb,As)/AlSb/InAs heterostructure field-effect transistor

High-speed, digital alloy barrier-based, Al(Sb,As)/AlSb/InAs heterostructure field-effect transistors (HFETs) fabricated using a standard mesa process are demonstrated. Current gain cutoff frequencies f/sub T/ of 38.5 GHz were extracted from the measured scattering parameters for devices with a 0.6- mu m gate length and a 3- mu m source-to-drain separation. A significant output conductance depressed f/sub max/ to 40 GHz. The results show the feasibility and potential of InAs/AlSb-based HFETs for high-speed electronics applications.<<ETX>>

Study of interface composition and quality in AlSb/InAs/AlSb quantum wells by Raman scattering from interface modes

We have studied the interface structure and the quality of molecular‐beam‐epitaxy grown AlSb/InAs/AlSb quantum wells through Raman scattering from interface vibrational modes from single quantum wells. A series of samples was grown by varying the growth temperature and the interface composition (by forcing either a light AlAs or a heavy InSb interface bond configuration at each InAs/AlSb interface). We have observed the InSb modes for all the samples and related the intensity and shape of the interface modes to the structure and quality of the interfaces. This work demonstrates that a single interface heterostructure can be probed by Raman scattering.

Quantized conductance of ballistic constrictions in InAs/AlSb quantum wells

Split‐gate ballistic constrictions have been fabricated on InAs/AlSb quantum‐well heterostructures. Sharp conductance steps of 2e2/h are observed at 4.2 K, while conductance plateaus persist up to 30 K. The sharp features and high temperature operation are made possible by the low effective mass (m*Γ= 0.023me) of InAs, and the closeness of the quantum well (20 nm) to the wafer surface.