Brian R. Bennett

Electrooptical effects in silicon

A numerical Kramers-Kronig analysis is used to predict the refractive-index perturbations produced in crystalline silicon by applied electric fields or by charge carriers. Results are obtained over the 1.0-2.0 \mu m optical wavelength range. The analysis makes use of experimental electroabsorption spectra and impurity-doping spectra taken from the literature. For electrorefraction at the indirect gap, we find \Delta n = 1.3 \times 10^{5} at \lambda = 1.07 \mu m when E = 10^{5} V/cm, while the Kerr effect gives \Delta n = 10^{-6} at that field strength. The charge-carrier effects are larger, and a depletion or injection of 1018carriers/cm3produces an index change of \pm1.5 \times 10^{-3} at \lambda = 1.3 \mu m.

Carrier-induced change in refractive index of InP, GaAs and InGaAsP

The change in refractive index Delta n produced by injection of free carriers in InP, GaAs, and InGaAsP is theoretically estimated. Bandfilling (Burstein-Moss effect), bandgap shrinkage, and free-carrier absorption (plasma effect) are included. Carrier concentrations of 10/sup 16//cm/sup 3/ to 10/sup 19//cm/sup 3/ and photon energies of 0.8 to 2.0 eV are considered. Predictions for Delta n are in reasonably good agreement with the limited experimental data available. Refractive index changes as large as 10/sup -2/ are predicted for carrier concentrations of 10/sup 8//cm/sup 3/ suggested that low-loss optical phase modulators and switches using carrier injection are feasible in these materials. >

Hybrid Hall effect device

A novel magnetoelectronic device incorporating a single microstructured ferromagnetic film and a micron scale Hall cross was fabricated and characterized at room temperature. Magnetic fringe fields from the edge of the ferromagnet generate a Hall voltage in a thin film semiconducting Hall bar. The sign of the fringe field, as well as the sign of the output Hall voltage, is switched by reversing the magnetization of the ferromagnet. This new device has excellent output characteristics and scaling properties, and may find application as a magnetic field sensor, nonvolatile storage cell, or logic gate.

AlSb/InAs HEMT's for low-voltage, high-speed applications

The design, fabrication, and characterization of 0.1 /spl mu/m AlSb/InAs HEMTs are reported. These devices have an In/sub 0.4/Al/sub 0.6/As/AlSb composite barrier above the InAs channel and a p/sup +/ GaSb layer within the AlSb buffer layer. The HEMTs exhibit a transconductance of 600 mS/mm and an f/sub T/ of 120 GHz at V/sub Ds/=0.6 V. An intrinsic f/sub T/ of 160 GHz is obtained after the gate bonding pad capacitance is removed from an equivalent circuit. The present HEMTs have a noise figure of 1 dB with 14 dB associated gain at 4 GHz and V/sub Ds/=0.4 V. Noise equivalent circuit simulation indicates that this noise figure is primarily limited by gate leakage current and that a noise figure of 0.3 dB at 4 GHz is achievable with expected technological improvements. HEMTs with a 0.5 /spl mu/m gate length on the same wafer exhibit a transconductance of 1 S/mm and an intrinsic f/sub T/L/sub g/, product of 50 GHz-/spl mu/m.

Photoluminescence studies of self‐assembled InSb, GaSb, and AlSb quantum dot heterostructures

Photoluminescence (PL) spectroscopy has been performed on a set of self‐assembled InSb, GaSb, and AlSb quantum dot (QD) heterostructures grown on GaAs. Strong emission bands with peak energies near 1.15 eV and linewidths of ∼80 meV are observed at 1.6 K from 3 monolayer (ML) InSb and GaSb QDs capped with GaAs. The PL from a capped 4 ML AlSb QD sample is weaker with peak energy at 1.26 eV. The PL bands from these Sb‐based QD samples shift to lower energy by 20–50 meV with decreasing excitation power density. This behavior suggests a type II band lineup. Support for this assignment, with electrons in the GaAs and holes in the (In,Ga,Al)Sb QDs, is found from the observed shift of GaSb QD emission to higher energies when the GaAs barrier layers are replaced by Al0.1Ga0.9As.

Molecular beam epitaxial growth of InSb, GaSb, and AlSb nanometer‐scale dots on GaAs

Thin layers of InSb, GaSb, and AlSb were grown on GaAs substrates by molecular beam epitaxy. Atomic force microscopy was used to examine surface morphology as a function of growth temperature and monolayer coverage. For each material, conditions were found which resulted in Stranski–Krastanov growth with the strain‐induced formation of nanometer‐scale dots. Relatively uniform distributions of dots form in a temperature window near the congruent sublimation temperature for both InSb and GaSb. In the case of InSb, deposition of 2 monolayers at 430 °C produced a surface with 3×109/cm2 dots with heights of 58±5 A and diameters of 600±50 A.

Surface reconstruction phase diagrams for InAs, AlSb, and GaSb

Abstract : We present experimental flux-temperature phase diagrams for surface reconstruction transitions on the 6.1As compound semiconductors. The phase transitions occur within or near typical substrate temperature ranges for growth of these materials by molecular beam epitaxy and therefore provide a convenient temperature standard for optimizing growth conditions. Phase boundaries for InAs (0 0 1) [(2*4)->(4*2)], AlSb (0 0 1) [c(4*4)->(1*3)], and GaSb (0 0 1) [(2*5)_>(1*3)] are presented as a function of substrate temperature and Group V-limited growth rate (proportional to flux), for both cracked and uncracked Group V species. We discuss differences between materials in the slopes and offsets of the phase boundaries for both types of Group V species.

Auger coefficients in type-II InAs/Ga1−xInxSb quantum wells

Two different approaches, a photoconductive response technique and a correlation of lasing thresholds with theoretical threshold carrier concentrations have been used to determine Auger lifetimes in InAs/GaInSb quantum wells. For energy gaps corresponding to 3.1–4.8 μm, the room-temperature Auger coefficients for seven different samples are found to be nearly an order-of-magnitude lower than typical type-I results for the same wavelength. The data imply that at this temperature, the Auger rate is relatively insensitive to details of the band structure.

Mobility enhancement in strained p-InGaSb quantum wells

Quantum wells of InGaSb clad by AlGaSb were grown by molecular beam epitaxy. The InGaSb is in compressive strain, resulting in a splitting of the heavy- and light-hole valence bands and an enhancement of the mobility. The mobility was found to increase with increasing InSb mole fraction for values of strain up to 2%. Room-temperature mobilities as high as 1500cm2∕Vs were reached for 7.5nm channels of In0.40Ga0.60Sb. These results are an important step toward the goal of high-performance p-channel field-effect transistors for complementary circuits operating at extremely low power.

NANOSTRUCTURE PATTERNS WRITTEN IN III-V SEMICONDUCTORS BY AN ATOMIC FORCE MICROSCOPE

An atomic force microscope has been used to pattern nanometer-scale features in III–V semiconductors by cutting through a thin surface layer of a different semiconductor, which is then used as an etch mask. Cuts up to 10 nm deep, which pass through 2–5 nm thick epilayers of both GaSb and InSb, have been formed. Lines as narrow as 20 and 2 nm deep have been made. Selective etchants and a 5 nm GaSb etch mask are used to transfer patterns into an InAs epilayer. The results are promising for applications requiring trench isolation, such as quantum wires and in-plane gated structures.