L. Buckle

85nm gate length enhancement and depletion mode InSb quantum well transistors for ultra high speed and very low power digital logic applications

We demonstrate for the first time 85nm gate length enhancement and depletion mode InSb quantum well transistors with unity gain cutoff frequency, fT, of 305 GHz and 256 GHz, respectively, at 0.5V VDS, suitable for high speed, very low power logic applications. The InSb transistors demonstrate 50% higher unity gain cutoff frequency, fT, than silicon NMOS transistors while consuming 10 times less active power

Novel InSb-based quantum well transistors for ultra-high speed, low power logic applications

InSb-based quantum well field-effect transistors, with gate length down to 0.2 /spl mu/m, are fabricated for the first time. Hall measurements show that room temperature electron mobilities over 30,000 cm /sup 2/V/sup -1/s/sup -1/ are achieved with a sheet carrier density over 1/spl times/10/sup 12/ cm/sup -2/ in a modulation doped InSb quantum well with Al/sub x/In/sub 1-x/Sb barrier layers. Devices with 0.2 /spl mu/m gate length and 20% Al barrier exhibit DC transconductance of 625 /spl mu/S//spl mu/m and f/sub T/ of 150 GHz at V/sub DS/ =0.5V. 0.2 /spl mu/m devices fabricated on 30% Al barrier material show DC transconductance of 920 /spl mu/S//spl mu/m at V/sub DS/ = 0.5 V. Benchmarking against state-of-the-art Si MOSFETs indicates that InSb QW transistors can achieve equivalent high speed performance with 5-10 times lower dynamic power dissipation and therefore are a promising device technology to complement scaled silicon-based devices for very low power, ultra-high speed logic applications.

High-performance long-wavelength HgCdTe infrared detectors grownon silicon substrates

Long-wavelength HgCdTe heterostructures on silicon (100) substrates have been grown using metal-organic vapor phase epitaxy. Test diodes have been fabricated from this material using mesa technology and flip-chip bonding. We have demonstrated excellent resistance-area product characteristics for diodes with a 10.2μm cutoff wavelength. R0A values approaching 103Ωcm2 at 80K have been measured and the resistance-area product maintained above 102Ωcm2 at 1V reverse bias. Variable temperature R0A values correspond to expected generation-recombination loss mechanisms between 60 and 120K. Current-voltage characteristics of two diodes at opposite sides of an array indicate that a very uniform imaging long-wavelength infrared array could be fabricated from this material.

Mid-infrared AlxIn1−xSb light-emitting diodes

The properties of AlxIn1−xSb light-emitting diodes (LEDs) have been investigated as a function of aluminum concentrations between 0% and 8.8%. By varying the aluminum concentration it is possible to tailor the peak emission wavelength to match the characteristic absorption of CO2, CO, CH4, NO, and NO2, making these diodes suitable for use in infrared gas sensing applications. The total emitted power and internal quantum efficiency were found to have maxima of 27mW∕cm2 and 4.2%, respectively, at a composition of 2.5%, where the peak emission was found to be 5.3μm, making LEDs of this composition particularly suited to the detection of NO.

Midinfrared GaInSb/AlGaInSb quantum well laser diodes operating above 200 K

Electroluminescence from GaInSb/AlGaInSb type I quantum well diode lasers, grown on GaAs, has been investigated as a function of strain in the quantum wells. Lasing was observed, in pulsed operation, up to temperatures of 161, 208, 219, and 202 K for structures containing 0.55%, 0.62%, 0.78%, and 1.1% strain, respectively, with lasing occurring at ∼3.3 μm at 200 K for the 1.1% structure.

InSb/AlInSb quantum-well light-emitting diodes

We have investigated the room-temperature electroluminescent properties of InSb∕AlxIn1−xSb quantum-well light-emitting diodes. The maximum emission from diodes containing quantum wells occurred at significantly higher energies than the band gap of InSb. Close agreement between experimental and theoretical data confirms that recombination occurs within the quantum well.

Optical absorption by dilute GaNSb alloys: Influence of N pair states

The optical properties of GaNSb alloys with N contents of up to 2.5% have been investigated at room temperature using infrared absorption spectroscopy. The evolution of the absorption onsets with N content has been described using a three level band anticrossing model of the N localized states interactions with the GaSb conduction band. This approach includes the effect of N pair states, which is critical to reproduce the observed optical properties. This confirms theoretical predictions that N pair states have a more pronounced effect on the band dispersion in GaNSb than in GaNAs.

Optimizing indium aluminum antimonide LEDs and photodiodes for gas sensing applications

We have developed a range of un-cooled mid-IR LEDs and photodiodes for IR gas sensing applications. Varying the composition of MBE grown Indium Aluminium Antimonide (In(1-x)AlxSb) epi-layers on GaAs allows us to engineer the emission/detection wavelength for a particular gas up to λmax≈6μm. The relatively high series resistance, LED drive requirements, and the non-optimised impedance matching of the un-biased photodiodes restricts the market for these components. Sub-dividing single element devices into N smaller devices connected in series enable the LED current and voltage requirements to be tailored to match the source, and improves the photodiode impedance matching. We report the development of the necessary growth and photolithography technologies for series-connecting InAlSb diodes on GaAs substrates. We include results from multi-element Co2 (Al(x)=4.5%) and CH4 (Al(x)=8.5%) sensing LEDs and photodiodes. These impedance matched LEDs represent a 9-fold improvement in the wall-plug efficiency compared with single element LEDs with the same light output. The impedance of the multi-element photodiodes is increased significantly with respect to the series resistance, which gives up to a 5-fold improvement in sensitivity since the noise contributions from the external amplifier and series resistance are minimised. These advances have greatly improved the suitability of these components for gas sensing, and further improvements in the performance are expected through optimisation of the epi-layer design and the device geometry.

Recombination processes in midinfrared AlxIn1−xSb light-emitting diodes

Emission characteristics, spectral properties, and quantum efficiencies of AlxIn1−xSb light-emitting diodes, with aluminum compositions between 0% and 8.75%, have been investigated as a function of temperature from 25 to 300 K, and a function of current from 1 to 100 mA. As both current and temperature are varied a change in the dominant recombination mechanism is observed as indicated by changes in the measured emission. An analysis of the light-current characteristics shows that Auger processes become important in all devices at temperatures above 100 K, implying an activation energy of approximately 7–13 meV depending on the aluminum composition.

Dilute Antimonide Nitrides for Very Long Wavelength Infrared Applications

The addition of small amounts of nitrogen to III-V semiconductors leads to a large degree of band-gap bowing, giving rise to band-gaps smaller than in the associated binary materials. The addition of a small percentage of nitrogen to GaSb or InSb is predicted to move their response wavelengths into the long or even very long wavelength IR ranges. We report the growth of GaNxSb1-x by MBE, using an r.f. plasma nitrogen source, examining the influence of plasma power, substrate temperature and growth rate. We demonstrate high structural quality, as determined by x-ray diffraction, and show a reduction in band-gap by over 300meV, compared with GaSb, based on FTIR transmission spectroscopy. We also report initial experiments on the growth of InNxSb1-x and Ga1-yInyNxSb1-x, with a view to extending the response into the long and very long wavelength IR ranges.