Intrinsic Transconductance Research Articles

1W/mm power pseudomorphic HFET with optimised recess technology

The authors report record DC characteristics and RF performance of a power double heterostructure (DH) pseudomorphic (PM) InGaAs quantum well HFET. The device, with a 0.3*70 mu m/sup 2/ gate, exhibits an intrinsic transconductance as high as 720 mS/mm, a maximum current density of approximately 1 A/mm and delivers a state-of-the-art output power density of 1 W/mm with 5.7 dB linear gain and 38% power added efficiency at 33 GHz. A detailed analysis of the technological aspects and electrical characteristics of the device is proposed to explain these excellent performances. >

In0.49Ga0.51P/GaAs heterostructures grown by low-pressure metalorganic chemical vapor deposition

We have successfully grown In0.49Ga0.51P/GaAs heterostructures and made InGaP-based high electron mobility transistors (HEMTs) by low-pressure metalorganic chemical vapor deposition. We have found the epitaxial layer of InGaP with a Hall mobility of 4073 cm2/V s (300 K) and the photoluminescence full width at half-maximum of 1 meV (4.2 K) for GaAs, 12 meV (4.2 K) for In0.49Ga0.51P. Zinc-induced disordering phenomenon was examined by transmission electron microscope. By Shubnikov-de Haas measurement, we demonstrated the existence of a two-dimensional electron gas in InGaP/GaAs heterojunctions. The sheet carrier concentration of 2DEG is around 8.8×1011 cm−2 at 1.5 K. A HEMT device with 1 μm×40 μm gate (pattern) shows an extrinsic transconductance of 65.5 mS/mm and an intrinsic transconductance of 266 mS/mm at 300 K.

Fabrication and performance of 1-dim MODFETs

We fabricated GaAs/AlGaAs MODFETs having extremely small channels in parallel perpendicular to the gate. The single channel width was varied from 250 nm down to 40 nm, and the pitch was 500 nm. These devices show an intrinsic transconductance up to 1000 mS/mm. We studied the saturation drift velocity at 300 K and found there is a strong limitation due to additional lateral interface scattering.

GaAs/sub x/Sb/sub 1-x//In/sub y/Al/sub 1-y/As p-channel heterostructure FETs with high transconductance and low gate leakage current

The first known p-channel GaAs/sub x/Sb/sub 1-x//In/sub y/Al/sub 1-y/As HFETs on InP are reported. The devices, using a strained-layer GaAs/sub x/Sb/sub 1-x/ channel, have achieved extrinsic transconductances of 40 mS/mm and intrinsic transconductances of 100 mS/mm. In addition to high transconductance, the devices exhibit excellent pinchoff and demonstrate a record gate turn-on voltage of -3 V as a result of extremely low gate leakage currents, making them exceptional candidates for complementary technologies. These outstanding gate characteristics are attributed to the valence band-edge discontinuity of 0.64 eV.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A pseudomorphic GaInP/InP MESFET with improved device performance

A high-bandgap GaInP epitaxial material grown on InP to increase the Schottky barrier height of the InP MESFET is discussed. The Schottky gate materials used in this study were Au and Pt/sub 2/Si. The pseudomorphic GaInP/InP MESFET with an Au gate has a Schottky barrier height of 0.54 eV, and the reverse leakage current of the device is 10/sup -2/ times lower than that of the conventional InP MESFET. The extrinsic and intrinsic transconductance of the pseudomorphic MESFET are 66.7 and 104.2 mS/mm respectively for the 5- mu m-gate-length GaInP/InP MESFET. >

Electric parameter evolutions against gatelength and bias in ultrashort gate AlGaAs/GaAs HEMTs

The electric parameter evolutions of state of the art ultrashort gate planar doped AlGaAs/GaAs HEMTs are studied against gatelength l/sub g/=0.4-0.1 mu m and bias. The best value of maximum intrinsic transconductance obtained is g/sub m0max/=800 mS/mm at l/sub g/=0.15 mu m and the measured cutoff frequency is f/sub t/=125 GHz at l/sub g/=0.1 mu m.

Cryogenic behavior of Ultrashort gate AlGaAs/GaAs and pseudomorphic AlGaAs/InGaAs/GaAs HEMT's

High performance ?-doped double recess 0.1-0.4?m AlGaAs-GaAs S-HEMTs[1] and ?-doped single-recess 0.1-0.7?m AlGaAs/GaInAs/GaAs PM-HEMTs [2-3] are studied from 300K down to 60K. DC and 0.1-40GHz HF measurements followed by electric parameter extractions give extensive evolutions of HEMT electric parameters versus temperature T, gatelength 1 g . The results are interpreted in terms of the transition regime from diffusive to strong overshoot/near ballistic carrier transport under the gate. In the longer devices (1 g =0.4-0.7?m), the latter effects become important at low temperatures and bring frequency intrinsic performance improvement mainly in terms of an increase of maximum intrinsic transconductance g mo . The shorter devices (0.1-0.2?m) appear to be already well in the overshoot regime at 300K due to the high quality epitaxial layers, and their frequency performance improvement upon cooling comes mainly from a reduction of intrinsic capacitance C gsint . The relative increase of intrinsic unity current gain cut-off frequency f tint upon cooling rates at a similar value of 30-40% for all investigated gatelengths(0.1-0.7?m).

Metamorphic [formula omitted] HEMT on GaAs: MBE growth and device performance

A new HEMT using InAlAs/InGaAs grown on GaAs has been realized. This structure, with an In content close to 27%, presents high electron mobility with high 2DEG density (20700 cm 2/V.s with 4×10 12 cm -2 at 77K) and high Schottky barrier quality (Vb=0.68V with η=1.1). A 3 μm gate length device has shown intrinsic transconductance as high as 530 mS /mm.

Metamorphic In0.3Ga0.7As/In0.29Al0.71As layer on GaAs: A new structure for high performance high electron mobility transistor realization

A new high electron mobility transistor (HEMT) using InAlAs/InGaAs grown on GaAs has been successfully realized. This structure, with an In content close to 30%, presents several advantages over conventional pseudomorphic HEMT on GaAs and lattice matched HEMT on InP. To accommodate the mismatch between the active layer and the GaAs substrate, a metamorphic buffer has been grown. High electron mobility with high two-dimensional electron gas density (20 700 cm2/V s with 4×1012 cm−2) and high Schottky barrier quality (Vb=0.68 V with η=1.1) have been obtained. A 3 μm gate length device has shown intrinsic transconductance as high as 530 mS/mm.

Improved InAlAs/InGaAs HEMT characteristics by inserting an InAs layer into the InGaAs channel

An InAlAs/InGaAs HEMT with a thin InAs layer inserted into the InGaAs channel is proposed and its electron transport properties and device performances have been investigated. By optimizing the thickness and the exact point of insertion in the InAs layer, the mobility and electron velocity at 300 K have been increased by 30% and 15%, respectively, compared to the conventional heterostructure. In addition, a maximum intrinsic transconductance of 970 mS/mm and a maximum current gain cutoff frequency of 58.1 GHz have been attained by a 0.6 mu m-gate-length device.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A δ-doped GaAs/In 0.37Ga 0.63As/GaAs high electron mobility transistor prepared by low-pressure metalorganic chemical vapor deposition

A high mobility and high performance δ-doped GaAs/In 0.37Ga 0.63As/GaAs high electron mobility transistor (δ-HEMT) grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) was studied. The electron mobility of this structure at 300 and 77 K were 5500 and 33,000 cm 2/v's, respectively, which were comparable with those of similar structures reported previously. With a gate geometry of 5 × 250 μm 2, the estimated extrinsic transconductance and saturation current density at 300 K (77 K) of the proposed δ-HEMT are 56 mS/mm (78 mS/mm) and 116 mA/mm (140 mA/mm) respectively, can be achieved. The intrinsic transconductance is estimated to be 109 mS/mm (245 mS/mm) at 300 K (77 K). Furthermore, the relationships between transconductance, gate breakdown voltage, and cap-layer thickness are also investigated.

Relationship between measured and intrinsic transconductances for FETs with gate conduction

A relationship between measured and intrinsic transconductances for field-effect transistors (FETs) with non-negligible gate conduction is derived. The equation shows that gate-source/drain conductances further reduce the measured transconductance besides the effects of R S and R D. An example demonstrating the importance of this reduction is given for an AlGaAs/GaAs submicron MODFET.

Single and dual p-doped channel In/sub 0.52/Al/sub 0.48/ As/In/sub x/Ga/sub 1-x/As (x=0.53, 0.65) FET's and the role of doping

The properties of lattice-matched (x=0.53) and strained (x=0.65) In/sub 0.52/Al/sub 0.48/As/In/sub x/Ga/sub 1-x/As p-doped channel FETs are reported. The role of doping density is studied with the help of two designs (dual-channel with low doping and single-channel with high doping). The strained dual-channel devices demonstrated an improvement of mobility from 108 cm/sup 2//V-s (53% In) to 265 cm/sup 2//V-s (65% In) at 300 K. The corresponding intrinsic transconductance enhancement is from 23 Ms/mm (53% In) to 46.5 mS/mm (65% In) using 1.0 mu m-long gates. The cutoff frequency (f/sub t/) also improves from 1.0 to 1.4 GHz. The impact of strain in the highly-doped single-channel device is small. The band structure under lattice-matched and strained conditions and the position of the Fermi level according to doping seem to be the main factors determining the reported features.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Enhancement mode n-channel Si/SiGe MODFET with high intrinsic transconductance

n-channel Si/SiGe MODFETs with quantum wells grown on a thick (1.5μm) graded buffer (Ge 5–30%) are realised. MODFETs with a surface gate work in the depletion mode due to a large gate-to-2-DEG channel distance of 75 nm. MODFETs with a recessed gate 10–15 nm above the channel exhibit enhancement mode operation with significantly high extrinsic transconductances of 340 mS/mm or 670 mS/mm at 300 K or 77 K and corresponding intrinsic transconductances of 38O mS/mm or 800 m S7/mm. The performance indicates the improved layer quality on graded buffers.

Delta-doped GaAs grown by chloride CVD

It is expected that delta-doped FETs have the following advantages: (1) large gate-breakdown voltage; (2) high intrinsic transconductance; (3) high controllability of the threshold voltage. Since it is necessary to control the epitaxial growth at the atomic layer level, delta-doped epitaxial layers have been grown by MBE or MOCVD. In the present work, Si delta-doping which was previously believed to be impossible to realize by chloride CVD is reported for the first time. Crystal growth and doping were carried out by using a conventional AsCl 3/Ga/H 2 chemical vapor deposition system. For realizing the Si delta-doping, an abrupt GaAs growth interruption technique which we have newly found was applied. The free carrier concentration was measured by the C-V method. The delta-doped layer has a maximum carrier concentration of 2.2 x 10 18 cm -3 and a full width at half-maximum of 120 Å. Delta-doped layers with good uniformity and high reproducibility could be obtained. The fact that the delta-doping technique can be realized by chloride CVD is very promising to grow low cost epitaxial layers for high-quality low noise FETs.

Fabrication of electroplated T gates with 60 nm gate length for pseudomorphic high electron mobility transistor devices

We have fabricated and electrically characterized mm-wave high electron mobility transistors (HEMTs) on pseudomorphic heterostructure GaAs/InGaAs samples. The T- and Γ-shaped gates were produced using electroplating and a conventional single resist-layer lift-off process. High frequency measurements of the same device before and after plating demonstrate the reduction in gate resistance. Direct current and high frequency properties of the HEMTs depend strongly on gate length and gate recess depth. Characterization of parallel conducting layers, low field mobility, and sheet carrier concentration depth profiles were obtained with gated Hall measurements. Best HEMT performance was obtained at a gate length of 60 nm, giving an extrinsic (intrinsic) transconductance of 620 mS/mm (840 mS/mm) and a cutoff frequency ft of 135 GHz.

Bulk and interfacial properties of the compositionally graded InxAl1−xAs (x≤0.52) quasi-insulator and its applications

We have investigated the first in a series of compositionally graded quasi‐insulator/semiconductor heterojunction (HJ) capacitors, intended to provide low interface state densities, low dc leakage currents, and high effective surface barriers. Molecular‐beam epitaxy (MBE) was used to grow compositionally graded InxAl1−xAs quasi‐insulators with x≤0.52 deposited on semiconducting In0.53Ga0.47As layers lattice matched to n+ ‐InP substrates. Interface states derived from electric field and temperature‐dependent capacitance‐voltage measurements have densities in the order of ≊1011/cm2 eV and have time constant distributions which are strongly dependent on compositional gradient. The surface barrier height also depends on the compositional gradient and the leakage current is decreased by three orders of magnitude from 10−6 to 10−9 A for a reverse bias of 1 V. Heterojunction insulated gate field‐effect transistors (HIGFETs) with an intrinsic transconductance gm=125 mS/mm were obtained on a 5‐μm‐long gate structure.

InAlAs/InGaAs/InP HEMTs with high breakdown voltages using double-recess gate process

The DC and RF performance of InAlAs/InGaAs/InP HEMTs fabricated using a double-recess gate process are reported. A gate-drain breakdown voltage as high as 16 V was observed. The HEMTs also exhibited a high sourcedrain breakdown voltage near pinchoff of 16 V and a low RF output conductance of 6mS/mm. For a 1.4 μm gate length, an intrinsic transconductance of 560 mS/mm and fr and fmax values of 16 and 40 GHz, respectively, were achieved.

Ultra-submicrometer-gate AlGaAs/GaAs HEMTs

Ultra-submicrometer-gate AlGaAs/GaAs high-electron-mobility transistors (HEMTs) that have gate lengths ranging from 25 to 85 nm and were fabricated using electron-beam lithographic techniques on epitaxial wafers grown by molecular beam epitaxy are discussed. These devices show that velocity overshoot and short-gate geometry effects play an important role for the gate lengths less than 100 nm. The maximum intrinsic transconductance is 215 mS/mm, and the effective saturated electron velocity reaches 3*10/sup 7/ cm/s for a 30-nm HEMT. >

Experimental verification of the impact of mosfet series resistance on device miniaturization down to source-drain areas as small as 0.2 μm by 0.3 μm

The contact and sheet resistance contributions to the series resistance of MOSFETs for silicided n + and p + source drain areas ≥ 0.2×0.3 μ 2 , have been measured. For S/D sizes < 0.7 μm (i.e. shorter than transfer length), the current flow is multi dimensional and the resistance increases rapidly; for 0.5×0.5 μm 2 , R s is 500 ω, and for 0.2×0.3 μm 2 it increases to 4.6 kω. For a maximum intrinsic transconductance degradation of 10% due to the total series resistance, which includes analytical results for the access resistance, the minimum S/D area that can be tolerated is 0.5×0.5 μm 2 .