Low Output Conductance Research Articles

Depletion mode GaAs metal–oxide–semiconductor field effect transistors with Ga2O3(Gd2O3) as the gate oxide

We have successfully fabricated depletion mode GaAs metal–oxide–semiconductor field effect transistors using Ga2O3(Gd2O3) as the gate oxide and an oxygen implant isolation technique. Growth of the device structure including the deposition of Ga2O3(Gd2O3) was performed in a multichamber molecular beam epitaxy system. A 1 μm×100 μm device shows excellent dc and microwave characteristics with low output conductance. Complete pinchoff at Vg=−2.5 V and operation in the accumulation mode of up to Vg=2.5 V were measured. The maximum transconductance was 100 mS/mm, with a high drain current density of 315 mA/mm. Microwave testing yielded a fT of 14 GHz and a fmax of 35 GHz.

Breakdown behavior of low-power pseudomorphic AlGaAs/InGaAs 2-D MESFET's

We report the breakdown behavior of the two-dimensional (2-D) MESFET, which is a low-power heterodimensional transistor having dual side gates that contact the edge of the two-dimensional electron gas (2-DEG) channel in a double-side planar-doped pseudomorphic Al/sub 0.24/Ga/sub 0.76/As/In/sub 0.17/Ga/sub 0.83/As material structure. Low output conductance (less than 6 mS/mm for V/sub GS/=0 V) and low gate leakage current (less than 100 nA) are measured out to a drain-source bias of 20 V, indicating that the effects of impact ionization are reduced in the 2-D MESFET. Excellent off-state drain-source and drain-gate breakdown voltages are experimentally measured to be 20 and 21 V, respectively. We attribute these high breakdown values to the electric and geometric properties of the heterodimensional Schottky metal/2-DEG junction.

Characteristics of fully quaternary In0.52(Al0.8Ga0.2)0.48As/In0.53(Al0.2Ga0.8)0.47As heterostructures in doped-channel FETs

A fully quaternary In/sub 0.52/(Al/sub 0.8/Ga/sub 0.2/)/sub 0.48/As/In/sub 0.53/(Al/sub 0.2/Ga/sub 0.8/)/sub 0.47/As heterostructure was introduced into doped-channel FETs (fully-Q DCFETs) on InP substrates for the first time. Combining the advantages of high quality quaternary InAlGaAs Schottky and channel layers, the authors were able to enhance device gate-to-drain and channel breakdown voltages, and to eliminate the kink effect. This results in an extremely low output conductance (g/sub 0/=0.6 mS/mm), and a high DC gain ratio (g/sub m//g/sub 0//spl sime/350).

Enhanced breakdown voltage in InP-HEMTs by using an In0.53(AlxGa1–x)0.47As (x = 0.1, 0.2) quaternary channel

An In0.53(AlxGa1–x)0.47As quaternary channel has been introduced into n+-InAlAs/InGaAs HEMTs. By adding a small amount of Al to the InGaAs channel, the bandgap can be enhanced, which provides a higher reversed gate-drain breakdown voltage. In addition, the associated impact ionisation process can be suppressed in these quaternary channels. These HEMTs have been demonstrated with a very low output conductance (4 mS/mm for x = 0.2) and a much smaller gate leakage current than conventional InP-HEMTs.

Utilization of an electron beam resist process to examine the effects of asymmetric gate recess on the device characteristics of AlGaAs/InGaAs PHEMTs

The DC and microwave characteristics of two sets of AlGaAs/InGaAs PHEMTs having a gate length of 0.2 /spl mu/m are compared. The first set is composed of devices fabricated using a trilayer electron beam resist process for T-gate recess and metallization. The second set is composed of devices fabricated using a new four-layer electron beam resist process which enables the asymmetric placement of a T-gate in a wide recess trench. Devices fabricated using the four-layer resist process showed improved breakdown voltage, lower gate-drain feedback capacitance, lower output conductance, and higher f/sub max/ with only slight reduction of drain current and transconductance. For example, the off-state drain-source breakdown voltage increased from 5.2 to 12.5 V, and the f/sub max/, increased from 133 to 158 GHz as the drain side cap recess, L/sub ud/, was increased from 0 to 0.55 /spl mu/m.

InAs/AlSb dual-gate HFETs

We report the first implementation of InAs/AlSb dual-gate (DG) HFETs. The devices were fabricated by conventional optical lithography and consist of two electrically distinct 1-μm gates, with a 1-μm intergate separation. The DG-HFETs feature well-behaved, kink-free drain characteristics, and exhibit both high transconductance and low output conductance. We find that DG operation significantly reduces the short-channel effects that have so far plagued InAs/AlSb devices, and increases the maximum allowable drain bias. We estimate that cutoff frequencies as high as 30 GHz-μm may be possible for such devices based on simple equivalent circuit models and previously published experimental data on single-gate InAs/AlSb HFETs.

Metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with a novel composite channels design

We report on fabrication and performance of novel 0.13 μm T-gate metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with composite InGaAs channels, combining the superior transport properties of In/sub 0.52/Ga/sub 0.48/As with low-impact ionization in the In/sub 0.32/Ga/sub 0.68/As subchannel. These devices exhibit excellent DC characteristics, high drain currents of 750 mA/mm, extrinsic transconductances of 600 mS/mm, combined with still very low output conductance values of 20 mS/mm, and high channel and gate breakdown voltages. The use of a composite InGaAs channels leads to excellent cut-off frequencies: f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 350 GHz and an f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> 160 GHz at V/sub DS/=1.5 V. These are the best microwave frequency results ever reported for any FET on GaAs substrate.

Novel heterodimensional diodes and transistors

We describe novel heterodimensional devices which utilize Schottky barriers to a two-dimensional (2D) electron gas. These devices include a 2D–3D Schottky diode, an AlGaAs GaAs Schottky Gated Resonant Tunneling Transistor (SGRTT), an AlGaAs InGaAs 2D Metal Semiconductor Field Effect Transistor (2D MESFET), and a Coaxial MESFET. These devices hold promise of ultra low power, high speed operation. The 1 micron wide 2D MESFET, which has a very low output conductance and a steep subthreshold slope, exhibited the highest transconductance of any 1 μm wide device.

DC and RF characteristics of double recessed and double pulse doped AlInAs/GaInAs/InP HEMTs

The effects of gate recess etch profiles on DC and RF characteristics of passivated, double pulse doped AlInAs/GaInAs/InP HEMTs were investigated. On-wafer characterisation has revealed that double recessed devices have higher breakdown voltage, lower output conductance, input capacitance, and feedback capacitance compared to conventional single recessed devices.

Microwave performance of a 0.25 μm gate AlGaN/GaN heterostructure field effect transistor

We fabricated a 0.25 μm gate length AlGaN/GaN heterostructure field effect transistor (HFET) with a maximum extrinsic transconductance of 27 mS/mm (at room temperature) limited by the source series resistance. The device exhibited an excellent pinch-off and a low parasitic output conductance in the saturation regime. We measured the cutoff frequency fT and the maximum oscillation frequency fmax as 11 and 35 GHz, respectively. These values are superior to the highest reported values for field effect transistors based on other wide band-gap semiconductors such as SiC. These results demonstrate an excellent potential of AlGaN/GaN HFETs for microwave and millimeter wave applications.

Realisation of doped-channel MISFETs with high breakdown voltage in AlGaAs/InGaAs based material system

The authors report the realisation of a doped-channel MISFET with high drain-source and gate-drain breakdown voltages of 41 and -37 V, respectively, and a record low output conductance of 150 mu S/mm. These characteristics are achieved through the use of n-type highly doped In/sub 0.26/Ga/sub 0.74/As as the channel material and a short period (AlAs)/sub 3/(GaAs)/sub 4/ superlattice as the gate insulator and the lower barrier grown on GaAs

Series-parallel association of FET's for high gain and high frequency applications

This paper presents a simple approach in the design of composite field effect transistors with low output conductance. These transistors consist of the series association of two transistors, with the transistor connected to the drain terminal wider than the transistor connected to the source terminal. It is shown that this composite transistor has the same DC characteristics as a long-channel transistor of uniform width. A composite transistor has two main advantages over its "DC equivalent" transistor of uniform width: significant area savings and a higher cutoff frequency. The main application is low-voltage, high-frequency analog circuits. The proposed technique is particularly suited for analog design in gate arrays.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Realization of high performance doped-channel MISFETs in highly strained AlGaAs/InGaAs/AlGaAs based quantum wells

Doped channel metal-insulator-semiconductor field effect transistors (DC-MISFETs) in the highly strained Al x Ga 1- x As/ In 0.26Ga 0.74As/Al y Ga 1- y As (0< x, y≤1.0) and ((AlAs) m (GaAs) n )/In 0.26Ga 0.74As/( (AlAs) p (GaAs) q ) single quantum wells grown via MBE on GaAs (100) substrates have been examined with a view towards improved performance via control of growth using RHEED behavior of static and dynamic surfaces. Breakdown voltages over 20 V and over 40 V have been realized in structures containing AlGaAs alloy and equivalent Al content short period superlattice (SPSL) barriers, respectively. Low gate leakage currents and output conductance as low as 150 μS/mm have been realized. Increasing the In content to 30% and using heavy Si doping in the well, DC-MISFETs containing SPSL barriers have yielded drain currents of 1.2 A/mm and breakdown voltages of ∼10 V.

High-speed, high breakdown voltage InP/InGaAs double-heterojunction bipolar transistors grown by MOMBE

The authors report very-high-performance InP/InGaAs double-heterojunction bipolar transistors (DHBTs) with low output conductance and high breakdown voltage of at least 5.5 V at high current densities, with measured BV/sub CEO/ and BV/sub CBO/ of >7.5 V and 10.6 V, respectively. The 11 mu m/sup 2/ devices exhibited f/sub T/ of 134 GHz and f/sub max/ of 113 GHz at V/sub CE/=1.57 V and I/sub C/=16.22 mA. The epitaxial structure was grown by metal-organic molecular beam epitaxy (MOMBE) using tertiarybutylarsine and tertiarybutylphosphine as the group-V sources.

Improved charge control and the frequency performance in InAs/AlSb HFET's

It is shown how the well thickness and the buffer layers influence the charge control properties of InAs/AlSb HFETs (heterostructure field-effect transistors) and how the kink can be eliminated from the drain characteristics of micron-sized HFETs, resulting in low output conductances and well-behaved drain characteristics. It is also demonstrated that a proper buffer layer structure is most beneficial in submicron devices, and results in great improvements in operational range and frequency performance.

Temperature dependence of common-emitter I-V and collector breakdown voltage characteristics in AlGaAs/GaAs and AlInAs/GaInAs HBT's grown by MBE

Temperature-dependent measurements from 25 to 125 degrees C have been made of the DC I-V characteristics of HBTs with GaAs and In/sub 0.53/Ga/sub 0.47/As collector regions. It was found that the GaAs HBTs have very low output conductance and high collector breakdown voltage BV/sub CEO/>10 V at 25 degrees C, which increases with temperature. In striking contrast, the In/sub 0.53/Ga/sub 0.47/As HBTs have very high output conductance and low BV/sub CEO/ approximately 2.5 V at 25 degrees C, which actually decreases with temperature. This different behavior is explained by the >10/sup 4/ higher collector leakage current, I/sub CO/, in In/sub 0.53/Ga/sub 0.47/As compared to GaAs due to bandgap differences. It is also shown that device self-heating plays a role in the I-V characteristics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Direct-current and radio-frequency characterization of submicron striped-channel field effect transistor structures using focused ion beam and electron-beam lithography

Submicrometere-gate GaAs metal–semiconductor field effect transistors (MESFETs) have been fabricated using focused ion beam (FIB) and electron-beam lithography. The channels of these devices are composed of several high conductance implanted stripes of 1 μm width, connecting source to drain. These conductive stripes are formed by Si implantation using FIB and annealed for 30 s at 850 °C. The region between the conductive stripes are semi-insulating GaAs having width of ‘‘S.’’ MESFETs with stripe width of 1 μm and stripe separation of 0.1, 1, and 2 μm were fabricated and characterized. The device with 0.1 μm separation represents the control sample with a uniformly doped channel due to overlap of conductive stripes upon the postimplant annealing. Devices with higher stripe separations showed higher effective transconductance (gm), lower output conductance (go), higher breakdown (Vbr), and higher current gain cut-off frequency (fT). All transistor showed well behaved direct-current output performance with excellent pinch-off characteristics and low leakage currents as small as 50 μA for source-drain voltage of 4 V and gate bias of −9 V without any soft breakdown. Transconductance of 200 mS/mm, gate-drain breakdown voltage as high as 20 V, output conductance of 4 mS/mm, and fT of 9 GHz from a device with 0.35 μm gate length with stripe separation of 2 μm.

Magnesium as p Dopant in InGaAs / InP Heterojunction Bipolar Transistors Grown by Metalorganic Vapor Phase Epitaxy

Magnesium has been used as p dopant for the base in heterojunction bipolar transistors during growth by metalorganic vapor phase epitaxy. Very sharp and well controlled Mg profiles were achieved resulting in excellent dc‐characteristics of the device. With a layer sequence suitable for high frequency applications, the transistors show a common emitter current gain of about 100 with very weak dependence on collector current, low offset voltage, low output conductance, and high breakdown voltage.

Optimization of buffer layers for AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors by atmospheric pressure metalorganic chemical vapor deposition

Pseudomorphic AlGaAs/InGaAs/GaAs high electron mobility transistors (HEMT) incorporating various types of buffer layers were fabricated (D = 0.50 × 100μm) and characterized by Hall-effect measurements, low temperature photoluminescence (PL), and room temperature IV characteristics. The devices fabricated with a thick (5000A) undoped high purity GaAs buffer layer grown at 650° C showed poor pinch-off characteristics, high output conductance and large leakage currents (>2 mA at pinch-off). Devices incorporating an undoped high purity GaAs (3000A) buffer layer grown at 550° C showed sharp pinch-off characteristics, low output conductance, and low leakage currents (1.3 mA at pinch-off). Low temperature growth of GaAs (550° C) enhanced carbon incorporation resulting in increasedp-type characteristics. This type of buffer layer provided additional barrier height between the active layer and the substrate reducing the injection of electrons into the substrate.

In0.5Ga0.5As/InAlAs Modulation-doped Field Effect Transistors on GaAs Substrates Grown by Low-Temperature Molecular Beam Epitaxy

We report on the lattice-mismatched growth and electrical properties of In0.5Ga0.5As/InAlAs modulation-doped heterostructures on GaAs substrates by molecular beam epitaxy using a wide-gap InAlAs graded buffer layer and low-temperature Molecular Beam Epitaxial growth at about 350°C. A drastic reduction in residual carrier accumulation has been achieved, and a high electron mobility at room temperature of 11100 cm2/V·s was obtained with an electron concentration of 3×1012/cm2. It was found that the cause of residual carrier accumulation is related to the growth interruption or temperature rise after the growth of the graded buffer layer. The fabricated Modulation-doped Field Effect Transistors showed low output conductance, good pinch-off characteristics and no kink effect. The higher transconductance of 270 mS/mm was also obtained.