J.B. Boos

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.

Fermi level unpinning of GaSb (100) using plasma enhanced atomic layer deposition of Al2O3

N-type and p-type GaSb metal-oxide-semiconductor capacitors (MOSCAPs) with atomic-layer-deposited (ALD) and plasma-enhanced-ALD (PEALD) Al2O3 dielectrics are studied to identify the optimum surface preparation and oxide deposition conditions for a high quality oxide-semiconductor interface. The ALD Al2O3/GaSb MOSCAPs exhibit strongly pinned C-V characteristics with high interface state density (Dit) whereas the PEALD Al2O3/GaSb MOSCAPs show unpinned C-V characteristics (low Dit). The reduction in Sb2O3 to metallic Sb is suppressed for the PEALD samples due to lower process temperature, identified by x-ray photoelectron spectroscopy analysis. Absence of elemental Sb is attributed to unpinning of Fermi level at the PEALD Al2O3/GaSb interface.N-type and p-type GaSb metal-oxide-semiconductor capacitors (MOSCAPs) with atomic-layer-deposited (ALD) and plasma-enhanced-ALD (PEALD) Al2O3 dielectrics are studied to identify the optimum surface preparation and oxide deposition conditions for a high quality oxide-semiconductor interface. The ALD Al2O3/GaSb MOSCAPs exhibit strongly pinned C-V characteristics with high interface state density (Dit) whereas the PEALD Al2O3/GaSb MOSCAPs show unpinned C-V characteristics (low Dit). The reduction in Sb2O3 to metallic Sb is suppressed for the PEALD samples due to lower process temperature, identified by x-ray photoelectron spectroscopy analysis. Absence of elemental Sb is attributed to unpinning of Fermi level at the PEALD Al2O3/GaSb interface.

Optimization of the

While there have been many demonstrations on n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) in III-V semiconductors showing excellent electron mobility and high drive currents, hole mobility in III-V p-channel MOSFETs (pMOSFETs) has traditionally lagged in comparison to silicon. GaSb is an attractive candidate for high-performance III-V pMOSFETs due to its high bulk hole mobility. We fabricate and study GaSb pMOSFETs with an atomic layer deposition Al₂O₃ gate dielectric and a self-aligned source/drain formed by ion implantation. The band offsets of Al₂O₃ on GaSb were measured using synchrotron radiation photoemission spectroscopy. The use of a forming gas anneal to passivate the dangling bonds in the bulk of the dielectric was demonstrated. The density of interface states <i>D</i>_it was measured across the GaSb band gap using conductance measurements, and a midband-gap <i>D</i>_it of 3 × 10¹¹/cm² eV was achieved. This enabled pMOSFETs with a peak hole mobility value of 290 cm²/Vs.

\hbox{Al}_{2}\hbox{O}_{3}/ \hbox{GaSb}

Recent progress in high-current photodiodes now makes it possible to efficiently generate over 26 dBm of RF power directly from the output of a photodiode. This paper describes two photodetector designs which demonstrate excellent large- and small-signal behavior. Maximum small-signal compression currents have increased to over 700 mA at 300 MHz. Output RF power amplifier stage efficiencies of over 45% (class AB operation) and 35% (class A) have been achieved from 0.3 to 6 GHz with RF power outputs over 26 dBm. The linearity figure of merit (LFOM) is also shown to be greater than 50, leading to the possibility of implementing very high linearity RF power amplifiers in the future.

Interface and a High-Mobility GaSb pMOSFET

We describe a new class of micro-opto-mechanical chemical sensors: A photonic microharp chemical sensor is an array of closely spaced microbridges, each differing slightly in length and coated with a different sorbent polymer. They are optically interrogated using microcavity interferometry and photothermal actuation, and are coupled directly to an optical fiber. Simultaneous measurements of the fundamental flexural resonant frequency of each microbridge allow the real-time detection and discrimination of a variety of vapor-phase analytes, including DMMP at concentrations as low as 17 ppb.

High-Current Photodetectors as Efficient, Linear, and High-Power RF Output Stages

Sheet carrier concentrations in quantum wells of InAs clad by AlSb were enhanced by modulation doping with very thin (9–12 A) remote InAs(Si) donor layers. The growth temperature of the donor layers was a key parameter, with relatively low temperatures required to minimize Si segregation into the AlSb. Sheet carrier concentrations as high as 3.2×1012/cm2 and 5.6×1012/cm2 were achieved by single- and double-sided modulation doping, respectively. High electron mobility transistors fabricated using the modulation doped structure exhibited a unity current gain cut-off frequency of 60 GHz for a 0.5 μm gate length at a source-drain voltage of 0.5 V.

Photonic microharp chemical sensors

This letter reports on the fabrication and performance of planar all ion-implanted 1.0-µm gate length InP power junction field effect transistors (JFETs). The devices were fabricated utilizing n+ implantation, a AuZn/TiW/Au gate metallization, and an n+ drain ledge. At 4.5 GHz, the 300-µm gate width JFETs exhibited maximum insertion gains of up to 13 dB and scaled output powers as high as 1 W/mm with 3-dB gain.

Modulation doping of InAs/AlSb quantum wells using remote InAs donor layers

The authors describe experimental results from micromechanical resonators coated with a chemoselective polymer that detect chemical vapors from volatile organic compounds using all-optical interrogation. The shift in the resonant frequency of the gold microbeam is read out using photothermal actuation and microcavity interferometry. Response times of less than 5s are achieved for vapor concentrations as low as 60ppm using optical powers of a few megawatts.

Planar fully ion implanted InP power junction FET's

InAs∕AlSb-based high-electron-mobility transistors (HEMTs) were irradiated with 2MeV protons. Radiation damage caused the source-drain current Ids to decrease nearly linearly with fluence Φ at a rate of Δ[Ids(Φ)∕Ids(0)]∕ΔΦ≈7×10−16cm2. Radiation-induced decreases in Ids have been observed for other HEMT material systems, and have been attributed to high-efficiency defect-induced scattering of carriers out of the two-dimensional electron gas. However, in the InAs∕AlSb system the rate of decrease of Ids is about 140 times less than that for typical GaAs∕AlGaAs HEMTs. An explanation is presented in which the high radiation tolerance of InAs∕AlSb HEMTs is related to carrier reinjection and the unusually large energy offset between the AlSb barriers and the InAs quantum well.

All-optical micromechanical chemical sensors

A comprehensive examination of the low-frequency noise characteristics of AlSb/InAs and related high-electron mobility transistors (HEMTs) in the 6.1-Aring-lattice-constant material system is reported. The effect of gate bias on the noise of devices in this technology is reported for the first time. The slope of the noise level in all the devices examined is nearly 1/f below 100 Hz, but some have significant generation-recombination Lorentzian components at higher frequencies, with an activation energy between 0.30 and 0.40 eV. The Hooge parameter alphaH for open-channel measurements is in the range between 5times10-4 and 5times10-3 based on measurements at low drain voltage. Comparisons are made to the noise performance of several earlier InAs-based HEMTs with considerably different layer structure and channel composition