M. J. Manfra

New MBE buffer used to eliminate backgating in GaAs MESFETs

The buffer is grown by molecular beam epitaxy (MBE) at low substrate temperatures (150-300 degrees C) using Ga and As/sub 4/ beam fluxes. It is highly resistive, optically inactive, and crystalline, and high-quality GaAs active layers can be grown on top of the buffer. MESFETs fabricated in active layers grown on top of this new buffer show improved output resistance and breakdown voltages; the DC and RF characteristics are otherwise comparable to MESFETs fabricated by alternative means and with other buffer layers.<<ETX>>

Ultralow-threshold (50 A/cm2) strained single-quantum-well GaInAsSb/AlGaAsSb lasers emitting at 2.05 μm

Strained single-quantum-well, broadened-waveguide GaInAsSb/AlGaAsSb diode lasers have exhibited room-temperature threshold current densities as low as 50 A/cm2, one of the lowest values reported for diode lasers at room temperature. These lasers, grown by molecular beam epitaxy, have emission wavelengths of ∼2.05 μm, characteristic temperature of 65 K, internal quantum efficiency of 95%, and internal loss coefficient of 7 cm−1. Single-ended cw power of 1 W is obtained for a 100-μm aperture.

175 K continuous wave operation of InAsSb/InAlAsSb quantum‐well diode lasers emitting at 3.5 μm

Multiple quantum‐well diode lasers incorporating compressively strained InAs0.935Sb0.065 wells and tensile‐strained In0.15Al0.85As0.9Sb0.1 barriers are reported. These lasers, grown on InAs substrates by molecular beam epitaxy, have emission wavelengths between 3.2 and 3.55 μm. Broad‐stripe lasers have exhibited pulsed threshold current density as low as 30 A/cm2 at 80 K and the characteristic temperatures between 30 and 40 K. The maximum pulsed operating temperature is 225 K. Ridge‐waveguide lasers have cw threshold current of 12 mA at 100 K, and the maximum cw operating temperature is 175 K.

High-power-density GaAs MISFETs with a low-temperature-grown epitaxial layer as the insulator

A GaAs layer grown by molecular beam epitaxy at 200 degrees C is used as the gate insulator for GaAs MISFETs. The gate reverse breakdown and forward turn-on voltages, are improved substantially by using the high-resistivity GaAs layer between the gate metal and the conducting channel. It is shown that a reverse bias of 42 V or forward bias of 9,3 V is needed to reach a gate current of 1 mA/mm of gate width. A MISFET having a gate of 1.5*600 mu m delivers an output power of 940 mW (1.57-W/mm power density) with 4.4-dB gain and 27.3% power added efficiency at 1.1 GHz. This is the highest power density reported for GaAs-based FETs.<<ETX>>

High-breakdown-voltage MESFET with a low-temperature-grown GaAs passivation layer and overlapping gate structure

GaAs MESFETs were fabricated using a low-temperature-grown (LTG) high-resistivity GaAs layer to passivate the doped channel between the gate and source and between the gate and the drain. The gate was fabricated such that the source and drain edges of the metal gate overlapped the LTG GaAs passivation layer. The electric fields at the edges of the gate were reduced by this special combination of LTG GaAs passivation and gate geometry, resulting in a gate-drain breakdown voltage of 42 V. This value is over 60% higher than that of similar MESFETs fabricated without the gate overlap.<<ETX>>

HIGH-PERFORMANCE GAINASSB THERMOPHOTOVOLTAIC DEVICES WITH AN ALGAASSB WINDOW

A large increase in the quantum efficiency (QE) and open-circuit voltage Voc of GaInAsSb thermophotovoltaic (TPV) devices is obtained by the use of an AlGaAsSb window layer compared with devices without a window layer. The TPV structure, grown on GaSb substrates by organometallic vapor phase epitaxy or molecular beam epitaxy, consists of a 1-μm-thick n-GaInAsSb base layer, a 3-μm-thick p-GaInAsSb emitter layer, a 100-nm-thick AlGaAsSb window layer, and a 25-nm-thick GaSb contacting layer. The band-gap energy of the lattice-matched GaInAsSb is 0.53–0.55 eV. The peak internal QE of the TPV cells with the window is >90%, compared with less than 60% for those without the window. At a short-circuit current density of ∼1000 mA/cm2, Voc of ∼300 meV is obtained for cells with the window layer, compared with less than 220 meV without the window layer. These increases are attributed to a substantial decrease in the surface recombination velocity with the window layer. Based on a standard calculation, the electron d...

Thermal conductivity of AlAs0.07Sb0.93 and Al0.9Ga0.1As0.07Sb0.93 alloys and (AlAs)1/(AlSb)11 digital-alloy superlattices

A differential 3ω technique is employed to determine the thermal conductivity of the AlAs0.07Sb0.93 ternary alloy, the Al0.9Ga0.1As0.07Sb0.93 quaternary alloy, and an (AlAs)1/(AlSb)11 digital-alloy superlattice. Between 80 and 300 K, the thermal conductivities for all three samples are relatively insensitive to temperature. The thermal conductivity of the (AlAs)1/(AlSb)11 superlattice is smaller than that of the AlAs0.07Sb0.93 ternary alloy, but much larger than the predictions of a model for phonon transport across the superlattice interfaces.

Hydroplane polishing of semiconductor crystals

A new technique for obtaining optically flat, damage‐free surfaces on semiconductor crystals has been developed. The polishing is very fast, being capable of removing over 30 μm of materials per minute in the case of GaAs and InP. Initial results indicate that the technique can also be used in the polishing of HgCdTe.

Optical heterodyne detection and microwave rectification up to 26 GHz using quantum well infrared photodetectors

We have demonstrated heterodyne detection up to an intermediate frequency of 26.5 GHz using quantum well infrared photodetectors. A CO/sub 2/ laser and a lead-salt tunable diode laser were used as the infrared sources. Heterodyne detection experiments measure the high frequency behavior of photoexcited electrons and their transport properties. We have also carried out microwave rectification experiments which measure the high frequency behavior associated with the dark-current electron-transport processes.

Low-resistance ohmic contacts to p-type GaAs using Zn/Pd/Au metallization

We have fabricated the low resistance ohmic contacts to p-type GaAs. Specific contact resistances as low as 7 × 10^-7Ω.cm²have been obtained for contacts prepared by heat treating Zn/Pd/Au metallizations deposited on p-type epitaxial GaAs layers with an acceptor concentration of 1.5 × 10¹⁹cm^-3. These contacts are reproducible, simple to fabricate, exhibit excellent adhesion, and have a uniformly smooth surface morphology.