Short-circuit Current Gain Cutoff Research Articles

High-frequency AlGaN/GaN T-gate HEMTs on extreme low resistivity silicon substrates

The T-gate high frequency AlGaN/GaN high electron mobility transistors (HEMTs) are demonstrated on an 8 inch extremely-low resistivity (ELR) silicon substrate with a resistivity of ∼2.5 mΩ cm to investigate the potential of using the ELR Si substrate for RF applications. The devices are also fabricated on the 60 Ω cm substrate for comparison. The 0.1 μm T-gate is realized by e-beam lithography to improve the high frequency characteristics of the devices. The short-circuit current gain cutoff frequency (fT), the maximum oscillation frequency (fmax), and maximum transconductance (gm,max) of 27 GHz, 71 GHz and 247 mS mm−1 can be achieved, respectively. The obtained high frequency performance is among the best reported to date for the GaN HEMTs on such low resistivity silicon substrates.

Radio Frequency Transistors and Circuits Based on CVD MoS2.

We report on the gigahertz radio frequency (RF) performance of chemical vapor deposited (CVD) monolayer MoS2 field-effect transistors (FETs). Initial DC characterizations of fabricated MoS2 FETs yielded current densities exceeding 200 μA/μm and maximum transconductance of 38 μS/μm. A contact resistance corrected low-field mobility of 55 cm(2)/(V s) was achieved. Radio frequency FETs were fabricated in the ground-signal-ground (GSG) layout, and standard de-embedding techniques were applied. Operating at the peak transconductance, we obtain short-circuit current-gain intrinsic cutoff frequency, fT, of 6.7 GHz and maximum intrinsic oscillation frequency, fmax, of 5.3 GHz for a device with a gate length of 250 nm. The MoS2 device afforded an extrinsic voltage gain Av of 6 dB at 100 MHz with voltage amplification until 3 GHz. With the as-measured frequency performance of CVD MoS2, we provide the first demonstration of a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS2 may be suitable for industrial-scale electronic applications.

Black phosphorus radio-frequency transistors.

Few-layer and thin film forms of layered black phosphorus (BP) have recently emerged as a promising material for applications in high performance nanoelectronics and infrared optoelectronics. Layered BP thin films offer a moderate bandgap of around 0.3 eV and high carrier mobility, which lead to transistors with decent on-off ratios and high on-state current densities. Here, we demonstrate the gigahertz frequency operation of BP field-effect transistors for the first time. The BP transistors demonstrated here show respectable current saturation with an on-off ratio that exceeds 2 × 10(3). We achieved a current density in excess of 270 mA/mm and DC transconductance above 180 mS/mm for hole conduction. Using standard high frequency characterization techniques, we measured a short-circuit current-gain cutoff frequency fT of 12 GHz and a maximum oscillation frequency fmax of 20 GHz in 300 nm channel length devices. BP devices may offer advantages over graphene transistors for high frequency electronics in terms of voltage and power gain due to the good current saturation properties arising from their finite bandgap, thus can be considered as a promising candidate for the future high performance thin film electronics technology for operation in the multi-GHz frequency range and beyond.

A High Performance In0.7Ga0.3As MOSFET with an InP Barrier Layer for Radio-Frequency Application

We demonstrate a high performance implant-free n-type In0.7Ga0.3As channel MOSFET with a 4-nm InP barrier layer fabricated on a semi-insulating substrate employing a 10-nm Al2O3 as gate dielectric. The maximum effective channel mobility is 1862 cm2/V·s extracted by the split C—V method. Devices with 0.8 μm gate length exhibit a peak extrinsic transconductance of 85 mS/mm and a drive current of more than 200 mA/mm. A short-circuit current gain cutoff frequency fT of 24.5 GHz and a maximum oscillation frequency fmax of 54 GHz are achieved for the 0.8 μm gate-length device. The research is helpful to obtain higher performance In0.7Ga0.3As MOSFETs for radio-frequency applications.

205-GHz (Al,In)N/GaN HEMTs

We report 55-nm gate AlInN/GaN high-electron-mobility transistors (HEMTs) featuring a short-circuit current gain cutoff frequency of fT = 205 GHz at room temperature, a new record for GaN-based HEMTs. The devices source a maximum current density of 2.3 A/mm at VGS = 0 V and show a measured transconductance of 575 mS/mm, which is the highest value reported to date for nonrecessed gate nitride HEMTs. Comparison to state-of-the-art thin-barrier AlGaN/GaN HEMTs suggests that AlInN/GaN devices benefit from an advantageous channel velocity under high-field transport conditions.

In0.69Al0.31As0.41Sb0.59/In0.27Ga0.73Sb double-heterojunction bipolar transistors with InAs0.66Sb0.34 contact layers

Presented are the first DC and RF results for a double heterojunction bipolar transistor, at a 6.2 Å lattice constant, incorporating InAs0.66Sb0.34. These devices show excellent performance with a high collector current density of 1.9×105 A/cm2, high breakdown voltage over 2.5 V, high short-circuit current gain cutoff frequency of 59 GHz, and maximum frequency of oscillation of 34 GHz.

AlGaN/GaN HEMT‐based fully monolithic X‐band low noise amplifier

A fully monolithic AlGaN/GaN HEMT-based low noise amplifier is reported. The circuit demonstrated a noise figure of 3.5 dB, gain of 7.5 dB, input return loss of –7.5 dB, and output return loss of –15 dB at 8.5 GHz. The dc characteristics of individual 0.25-μm × 150-μm transistors were: maximum current density of 1.0 A/mm, maximum transconductance of 170 mS/mm and a threshold voltage of –6.8 V. The devices have a typical short circuit current gain cutoff frequency of 24.5 GHz and a maximum oscillating frequency of 48 GHz. The devices demonstrated a minimum noise figure of 1.6 dB with an associated gain of 10.6 dB at 10 GHz. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effects of isoelectronic Al doping and process optimization for the fabrication of high-power AlGaN-GaN HEMTs

In order to improve the electrical characteristics of AlGaN-GaN heterostructures for applications in high electron mobility transistors (HEMTs), high-quality AlGaN-GaN was grown by way of metal-organic chemical vapor deposition on sapphire. We applied isoelectronic Al doping into the GaN-channel layers of modified AlGaN-Al-doped GaN channel-GaN heterostructures. We then compared the electrical performance of the fabricated heterostructures with those of conventional AlGaN-GaN heterostructures. The AlGaN-GaN HEMTs that were fabricated achieved power densities of up to 4.2 W/mm, some of the highest values ever reported for 0.25-/spl mu/m gate length AlGaN-GaN HEMTs. These devices exhibited a maximum drain current density of 1370 mA/mm, a high transconductance of 230 mS/mm, a short-circuit current gain cutoff frequency (f/sub T/) of 67 GHz, and a maximum frequency of oscillation (f/sub max/) of 102 GHz.

High power 0.25 [micro sign]m gate GaN HEMTs on sapphire with power density 4.2 W∕mm at 10 GHz

Metal organic chemical vapour deposition-grown AlGaN/GaN high electron mobility transistors (HEMTs) with power density up to 4.2 W/mm, one of the highest values ever reported for 0.25 µm gate-length AlGaN/GaN HEMTs, were fabricated on sapphire substrates. The devices exhibited maximum drain current density as high as 1370 mA/mm, high transconductance up to 223 mS/mm, short-circuit current gain cutoff frequency (fT) of 67 GHz, and maximum frequency of oscillation (fmax) of 102 GHz.

Small signal RF performance of AlGaN∕GaN heterojunction bipolar transistors

Small signal RF characteristics of an AlGaN/GaN HBT are presented. The devices had a short circuit current gain cutoff frequency of 2 GHz. The roll off of the short-circuit current gain (H/sub 21/) of the device was less than 20 dB/decade. We propose that this is due to the distributed nature of the base-collector parasitic resistance-capacitance network caused by a high sheet resistance in the base (100 k/spl Omega///spl square/) and high base contact resistances. Finite element small signal equivalent circuit simulations support this explanation.

Properties of GaAs MOSFET with gate dielectric grown by liquid-phase selective oxidation method

The effects of operating temperature and thickness of gate dielectric on the electrical characteristics of a GaAs MOSFET have been investigated. We fabricated the GaAs MOSFET using Ga 2O 3(As 2O 3) as the gate dielectric prepared by a liquid-phase chemically enhanced oxidation method. By reducing the temperature from 150°C to −50°C, the transconductance can be enhanced about 100% for a 1 μm gate-length MOSFET with oxide thickness of 35 nm. An increasing trend of transconductance can also be observed by reducing the gate-oxide thickness. In addition, the short-circuit current gain cutoff frequency f T and the maximum oscillation frequency f max as a function of temperature and gate-oxide thickness are discussed for different values of gate length.

Fabrication of depletion-mode GaAs MOSFET with a selective oxidation process by using metal as the mask

The n-channel depletion-mode GaAs MOSFETs with a selective liquid phase chemical-enhanced oxidation method at low temperature by using metal as the mask (M-SLPCEO) are demonstrated. The proposed process can simplify one mask to fabricate GaAs MOSFET and grow reliable gate oxide films as well as side-wall passivation layers at the same time. The 1 μm gate-length MOSFET with a gate oxide thickness of 35 nm shows a transconductance of 90 mS/mm and a maximum drain current density larger than 350 mA/mm. In addition, a short-circuit current gain cutoff frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 6.5 GHz and a maximum oscillation frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 18.3 GHz have been achieved from the 1 μm×100 μm GaAs MOSFET.

Fabrication of high performance GaN modulation doped field effect transistors

Fabrication of GaN devices presents a number of processing issues. Since the AlGaN/GaN material and sapphire substrates are transparent in the ultraviolet, light scattering can degrade the quality of the lithography. GaN and AlGaN are chemically inert materials, highly resistant to wet etching. Schottky contacts are fabricated with noble metals (Pt, Au) which present adhesion problems. The approaches to solving these difficulties and the routes to fabrication of high performance GaN-based modulation doped field effect transistors are presented. The light scattering has been addressed by the deposition of amorphous Si on the backside of the wafers. Mesa etching for device isolation has been performed with both chemically assisted ion beam etching and a newly developed wet etching technique. Finally, metal adhesion has been greatly improved by the initial deposition of a thin sputtered Pt layer, followed by a thick layer of Pt/Au by e-beam evaporation. A 100 μm wide device showed a maximum dc current density of 946 mA/mm, a peak transconductance of 160 mS/mm, a short circuit current gain cutoff frequency of 15.6 GHz, and a maximum oscillation frequency of 49.4 GHz.

Demonstration of submicron depletion-mode GaAs MOSFETs with negligible drain current drift and hysteresis

We successfully fabricated submicron depletion-mode GaAs MOSFETs with negligible hysteresis and drift in drain current using Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) as the gate oxide. The 0.8-μm gate-length device shows a maximum drain current density of 450 mA/mm and a peak extrinsic transconductance of 130 mS/mm. A short-circuit current gain cutoff frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) of 17 GHz and a maximum oscillation frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 60 GHz were obtained from the 0.8 μm×60 μm device. The absence of drain current drift and hysteresis along with excellent characteristics in the submicron devices is a significant advance toward the manufacture of commercially useful GaAs MOSFETs.

Single- and double-heterojunction pseudomorphic In/sub 0.5/(Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/P/In/sub 0.2/Ga/sub 0.8/As high electron mobility transistors grown by gas source molecular beam epitaxy

In/sub 0.5/(Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/P/In/sub 0.2/Ga/sub 0.8/As single- and double-heterojunction pseudomorphic high electron mobility transistors (SH-PHEMTs and DH-PHEMTs) on GaAs grown by gas-source molecular beam epitaxy (GSMBE) were demonstrated for the first time. SH-PHEMTs with a 1-μm gate-length showed a peak extrinsic transconductance g/sub m/ of 293 mS/mm and a full channel current density I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 350 mA/mm. The corresponding values of g/sub m/ and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> were 320 mS/mm and 550 mA/mm, respectively, for the DH-PHEMTs. A short-circuit current gain (H/sub 21/) cutoff frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 21 GHz and a maximum oscillation frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 64 GHz were obtained from a 1 μm DH device. The improved device performance is attributed to the large /spl Delta/E/sub c/ provided by the In/sub 0.5/(Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/P/In/sub 0.2/Ga/sub 0.8/As heterojunctions. These results demonstrated that In/sub 0.5/(Al/sub 0.3/Ga/sub 0.7/)/sub 0.5/P/In/sub 0.2/Ga/sub 0.8/As PHEMT's are promising candidates for microwave power applications.

Functional devices based on real space transfer in Si/SiGe structure

A charge injection transistor, which operates as an exclusive-OR logic gate, and a monolithic multiterminal device, electrically reprogrammable between OR and NAND logic function, have been successfully implemented in a Si-Si/sub 0.7/Ge/sub 0.3/ heterostructure grown by rapid thermal epitaxy on a Si substrate. Room temperature operation of the charge injection transistor is demonstrated, with 10 dB on/off ratio for the exclusive-OR logic function. Microwave measurements indicate a short circuit current gain cutoff of 6 GHz, for a device with a source-drain distance of 0.5 /spl mu/m. Device simulations were used to identify primary dependencies of the device performance on the parameters used in the design of the structure. Further structural improvements are suggested.

High-breakdown AlGaAs/InGaAs/GaAs PHEMT with tellurium doping

The authors report the fabrication and characterisation of an Al0.43Ga0.57As/In0.2Ga0.8As/GaAs pseudomorphic HEMT (PHEMT) with high channel conductivity grown by solid source MBE. The high conductivity of the channel is a direct consequence of the high sheet charge and high mobility that has recently been obtained by using tellurium as the n-type dopant in 43% AlGaAs. The device characteristics reflect the resulting reduction in the parasitic resistances of the high channel conductivity. Microwave measurements yield a short-circuit current gain cutoff frequency fT of 11 GHz and maximum oscillation frequency fmax of 25 GHz. A high gate-drain breakdown voltage of 26 V along with a maximum drain current density of 400 mA/mm obtained in the device illustrate the applicability of this technology in microwave power field effect transistors.

Rapid Thermal Epitaxy for Device Applications

AbstractRapid thermal epitaxy (RTE) is studied for a variety of applications including transistors as well as optoelectronic devices. Two transistor applications are discussed here. First, the growth of n-type epitaxial layers over n+ buried layers for low power BiCMOS, and second, the growth and fabrication of charge injection transistors (CHINTs) from a multi-layer structure including strained Si1−xGex layers.Scaled bipolar transistors for BiCMOS integrated circuits require low collector-substrate capacitance in order to minimize power consumption. The unintentional incorporation of dopant into a growing epitaxial layer, known as autodoping, can affect the ultimate lower limit of the collector-substrate capacitance. In this work, we studied the effects of epitaxial layer growth rate, arsenic buried layer implant dose, and pre-epitaxial bake temperature on autodoping using RTE. To begin, we experimented with the buried layer implant dose to check its affect on lateral autodoping. The amount of autodoping increased when the buried layer implant dose increased, confirming the source of the arsenic autodoping as the buried layer. Also, in contrast to data from conventional reactors, we found the peak interface concentration and integrated dose in regions adjacent to the buried layer to be linearly dependent on the growth rate (i.e. low growth rates trap less arsenic at the substrate/epi layer interface). Next, by adjusting the pre-bake temperature over a range from 800 to 1050°C without changing the growth conditions, we first observed a rise in autodoping with temperature to 950°C at which point the incorporated autodoping dose and peak concentration began to fall. Through simulation of the evaporated arsenic from the buried layer and data for arsenic desorption from the silicon surface, we explain this behavior. Finally, using the data gathered on the autodoping characteristics of RTE, we show a process using two growth rate steps and a low temperature pre-bake step which completely eliminates the lateral autodoping peak. Using this new growth process, epitaxial silicon films over arsenic doped buried layers for low power BiCMOS are possible.Charge injection transistors and logic elements have been successfully implemented in a Si/Si0.7Ge0.3 heterostructure grown by RTE on a Si substrate. Shallow p+ source and drain ohmic contacts are obtained by a boron diffusion from a selectively deposited boron doped Ge layer. Room temperature operation of the charge injection transistor is demonstrated for the first time. High frequency measurements indicate a short circuit current gain cutoff frequency of 6 GHz.

Selfaligned AlGaAs/GaAs HBT grown by MOMBE

The very low parasitic resistance n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBT) grown by metal organic molecular beam epitaxy (MOMBE) using all gaseous source dopants are reported. The carbon and tin dopants were introduced through the uses of trimethygallium (TMGa) and tetraethyltin (TESn). To achieve the low parasitics, the graded InGaAs emitter cap layer was doped with tin to 5*10/sup 19/ cm/sup -3/ and the doping level in the subcollector was 3*10/sup 18/ cm/sup -3/. The emitter and collector sheet resistances were 25 Omega / Square Operator and 10 Omega / Square Operator , respectively. The 800 AA thick base layer was carbon doped to a level of 7*10/sup 19/ cm/sup -3/. The base contact resistance and sheet resistance were 0.1 Omega mm and 180 Omega / Square Operator , respectively. With a thin AlGaAs surface passivation layer for the emitter-base junction, the common emitter DC current gain was maintained up to 25, even for 2*5 mu m/sup 2/ emitter size devices. The unity short circuit current gain cutoff frequency f/sub T/, and maximum oscillation frequency f/sub max/, were 48 and 63 GHz, respectively.

High-speed InP/InGaAsP metal-semiconductor field-effect transistors grown by chloride vapor phase epitaxy

We report the fabrication of enhancement mode InGaAsP/InP metal-semiconductor field-effect transistors having gate lengths of 2 μm. The epitaxial layers for this structure have been grown by chloride vapor phase epitaxy. The devices show extrinsic transconductances as high as 220 mS/mm, a short-circuit current gain cutoff frequency of fT=5.2 GHz, and a maximum available power gain cutoff frequency of fmax=9.5 GHz. A novel gate technology has been utilized where a lower band-gap quaternary InGaAsP layer of about 350 Å thickness is grown on the top of the InP channel layer.