Doped-channel HFETs Research Articles

K-Band Monolithic InGaP–InGaAs DCFET Amplifier Using BCB Coplanar Waveguide Technology

A K-band (20 GHz) monolithic amplifier was developed and fabricated by adopting a low-/spl kappa/ benzocyclobutene (BCB) coplanar waveguide (CPW) line and InGaP-InGaAs doped-channel HFETs (DCFETs). This monolithic microwave integrated circuit (MMIC) utilizes a high impedance BCB CPW microstrip line (Z/sub 0/=70 /spl Omega/) for the biasing circuits, and a Z/sub 0/=50 /spl Omega/ line for the RF signal transmission. The low dielectric constant characteristic of the BCB interlayer is beneficial for a common-ground bridge process, which reduces the parasitics. The calculated loss tan/spl delta/ is 0.036 for the BCB at 20 GHz. The one-stage MMIC amplifier achieves an S/sub 21/ of 5 dB at 20 GHz, which is the first demonstration of the K-band InGaP-InGaAs DCFET monolithic circuit.

Study of InGaP/InGaAs double doped channel heterostructure field-effect transistors (DDCHFETs)

InGaP/InGaAs double doped channel heterostructure field-effect transistors (DDCHFETs) with δ-doped channels and uniformly doped channels are comprehensively studied and demonstrated. From the simulation results, based on a two-dimensional simulator of Atlas, the band diagrams, DC and RF characteristics of studied devices are compared and studied. The better drain current drivability, higher transconductance and microwave performances are obtained in the studied device with δ-doped channel. In addition, experimentally, the DDCHFET with δ-doped quantum well channel is fabricated successfully. Due to the employed InGaAs double δ-doped channel structure and Schottky behaviours of InGaP ‘insulator’, good DC properties including pinch-off and saturation characteristics, higher and linear transconductance, and good RF properties are obtained. Moreover, the experimental results are consistent with simulated data.

Investigation of a new InGaP-InGaAs pseudomorphic double doped-channel heterostructure field-effect transistor (PDDCHFET)

An interesting new InGaP-InGaAs pseudomorphic double doped-channel heterostructure field-effect transistor (PDDCHFET) is fabricated and demonstrated. Due to the employed InGaAs double doped channel (DDC) structure and Schottky behaviors of InGaP insulator, good dc properties including higher turn-on voltage, lower leakage current, better linearity, and good RF performances are obtained. In addition, the experimental results are fitted well with theoretical simulation data based on a two-dimensional (2-D) simulator. Moreover, the studied device exhibits relatively negligible temperature-dependent characteristics over a wide operating temperature region (300<T<450 K). Therefore, the studied PDDCHFET provides the promise for high-temperature and high-performance microwave electronic applications.

Submicron RIE recessed InGaP/InGaAs doped-channel FETs

High performance submicron In/sub 0.49/Ga/sub 0.51/P/In/sub 0.15/Ga/sub 0.85/As doped-channel heterostructure field effect transistors (HFETs) have been developed and characterized. In order to achieve a high uniformity of device characteristics crossing the wafer, BCl/sub 3/+CHF/sub 3/ reactive ion etching technology in gate-recessed process is applied to fabricate the InGaP/InGaAs doped-channel FETs. The unity current gain cut-off frequency (f/sub T/), maximum frequency of oscillation (f/sub max/), and threshold voltage have been investigated versus the gate-length. The improved microwave performance in smaller gate-length devices is mainly associated with the reduction of the input capacitance. The 0.2 /spl times/ 200-/spl mu/m/sup 2/ gate-dimension DCFET exhibits a saturated P/sub out/ of 18.9 dBm, a power density of 388 mW/mm, a PAE of 35%, and an associated gain of 14 dB at 2.4 GHz.

Physics-based explanation of kink dynamics in AlGaAs/GaAs HFETs

The physical origin of the kink and its dynamics are investigated in AlGaAs/GaAs doped-channel heterostructure field-effect transistors (HFETs) both through measurements and two-dimensional (2D) device simulations. The kink is shown to arise from the interaction of surface deep acceptors with impact-ionization-generated holes, the latter partially discharging the deep levels and therefore leading to conductive-channel widening and to drain-current increase. Under pulsed operation, kink dynamics is governed by hole emission and capture phenomena, prevailing at low and high drain-source voltages, respectively.

Investigation of temperature-dependent characteristics of an n/sup +/-InGaAs/n-GaAs composite doped channel HFET

The temperature-dependent characteristics of an n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InGaAs/n-GaAs composite doped channel (CDC) heterostructure field-effect transistor (HFET) have been studied. Due to the reduction of leakage current and good carrier confinement in the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -InGaAs/n-GaAs CDC structure, the degradation of device performances with increasing the temperature is insignificant. Experimentally, for a 1 x 100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> device, the gate-drain breakdown voltage of 24.5 (22.0) V, turn-on voltage of 2.05 (1.70) V, off-state drain-source breakdown voltage of 24.4 (18.7) V, transconductance of 161 (138) mS/mm, output conductance of 0.60 (0.60) mS/mm, and voltage gain of 268 (230) are obtained at 300 (450) K, respectively. The shift of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> from 300 to 450 K is only 13 mV. In addition, the studied device also shows good microwave performances with flat and wide operation regime.

High Schottky barrier Al0.5In0.5P/InGaAs doped-channel HFETs with superior microwave power performance

Al/sub 0.5/In/sub 0.5/P/In/sub 0.15/Ga/sub 0.85/As doped-channel HFETs (DCFETs) are expected to have a high linearity and a high breakdown voltage for microwave power device applications due to the improvement of a larger /spl Delta/E/sub c/ (0.45eV) and a wide bandgap AlInP Schottky layer. The device, biased at V/sub ds/=3.0 V and operated at 2.4 GHz, provided an output power density of 209 mW/mm. A power-added efficiency of 59% and a linear power gain of 17 dB. Two-tone measurement reveals that third-order intermodulation at an input power of 0 dBm is -29 dBc and the output intercept point (OIP/sub 3/) is 30.4 dSm for devices with a 1 mm wide gate.

188 GHz doped-channel In0.8Ga0.2P/In0.53Ga0.47As/InP HFETs

The authors have fabricated 0.14 /spl mu/m T-gate, doped-channel In/sub 0.8/Ga/sub 0.2/P/In/sub 0.53/Ga/sub 0.47/As/InP HFETs. An extrinsic peak transconductance of 722 mS/mm and a maximum current density of 761 mA/mm were obtained. The doped-channel HFET exhibits excellent RF performance with f/sub T/=188 GHz and f/sub max/=225 GHz at V/sub ds/=1.5 V. These are state-of-the-art results for doped-channel HFETs and are comparable to the best reported performance of InP p-HEMTs with similar gate length.

Comparison of single- and double-barrier pseudomorphic InGaP/InGaAs HFETs

We report the growth and fabrication of pseudomorphic InGaP/InGaAs/GaAs doped-channel heterostructure field effect transistors (HFETs). A direct comparison between single and double barrier HFETs of otherwise nominally identical devices shows that the use of a double barrier structure reduces the output conductance and enhances both the current gain cutoff frequency f T and the maximum oscillation frequency f max. The maximum drain current reaches 630 mA/mm for highly strained In 0.30Ga 0.70As channel devices compared with 360 mA/mm for comparably doped In 0.15Ga 0.85As channel HFETs. Compared to that of In 0.15Ga 0.85As channel devices, the In 0.30Ga 0.70As channel HFETs yield a higher maximum oscillation frequency while having a comparable current gain cutoff frequency. Double barrier HFETs with an In 0.15Ga 0.85As channel yield f T=19 GHz and f max=63 GHz, while those with an In 0.30Ga 0.70As channel show a result of 18 and 78 GHz, respectively. These results demonstrate that the use of highly strained InGaAs channels and double InGaP barriers significantly improves device performance.

Studies on low‐leakage surface‐undoped InAlAs/InGaAs‐doped channel HFETs

Studies on low‐leakage surface‐undoped InAlAs/InGaAs‐doped channel HFETs

Low-frequency noise in AlGaN-GaN doped-channel heterostructure field effect transistors grown on insulating SiC substrates

The authors report low-frequency noise measurements of doped-channel GaN/AlGaN heterostructure field-effect transistors grown on insulating silicon carbide substrates. In the frequency range 1 Hz – 100 kHz the observed noise is of the 1/f type, and the estimated value of the Hooge constant αH is ~10–3.

GaN based heterostructure for high power devices

We discuss the potential of GaN-based field effect transistor for high-power, high-temperature operation. At room temperature, the GaN/AlGaN doped channel HFETs (DC-HFETs) demonstrated highest frequency operation among all wide band gap semiconductor devices because of excellent transport properties of two dimensional electron gas at the AlGaN/GaN heterointerface and a large sheet carrier concentration in the device channel. CW operation at 10 and 15 GHz was also recently reported. Monte Carlo simulations indicate that short-channel GaN devices should have transported superior even to GaAs. However, improved thermal and microwave designs are required in order to take advantage of these material properties for applications in high power devices.

AlGaN/GaN doped channel heterostructure field effect transistors

AlGaN/GaN Heterostructure Field Effect Transistors (HFETs) are expected to have a high transconductance and a high saturation current because of the relatively high electron mobility and high saturation velocity of the two dimensional electron gas (2DEG) in AlGaN/GaN modulation doped structures. Our experimental results revealed that, in the fabricated devices, the transconductance is limited by a large source series resistance, Rs, and by a small sheet carrier concentration, ns, of the 2DEG in the device channel. In order to increase ns, we recently proposed to use a Doped Channel HFET (DC-HFET) design, similar to that used in AlGaAs/GaAs DC-HFETs. In AlGaN/GaN structures, an additional impurity scattering caused by the channel doping has relatively less of an effect on the electron mobility than in AlGaAs/GaAs devices, due to a much higher electron effective mass in GaN. One micron gate AlGaN/GaN Doped Channel HFETs reached the cutoff frequency fT of 18.3 GHz. Short channel AlGaN/GaN Doped HFETs with 0.25 micron gates demonstrated the cutoff frequency fT up to 36.1 GHz and the maximum oscillation frequency, fmax ≈ 97.3 GHz. These values of fT and fmax are the highest value reported for any wide band gap semiconductor device. Our simulations of AlGaN/GaN Doped Channel HFETs show that transconductances in access of 1000 mS/mm may be obtained for very thin AlGaN layers, a large gate voltage swing, and for a large surface sheet density of the 2D electron gas.

CW operation of short-channel GaN/AlGaN doped channel heterostructure field effect transistors at 10 GHz and 15 GHz

We report on a 0.15-/spl mu/m gate length AlGaN/GaN doped channel heterostructure field effect transistor (DC-HFET) with maximum frequency of oscillation in excess of 97 GHz. HFETs based on our doped channel design exhibited CW microwave operation up to 15 GHz with a maximum output power of approximately 270 mW/mm at 10 GHz. These values are still limited by parasitics and can be significantly improved by optimizing the device design.

Recent Progress in Gan Based Field Effect Transistors

ABSTRACTMost types of GaN based Field Effect Transistors – MESFETs, MISFETs, Heterostructure FETs (HFETs), and Doped Channel HFETs (DC-HFETs) have demonstrated a good performance at both room temperature and elevated temperatures. The DC-HFETs demonstrated the best direct current and microwave characteristics among all wide band gap semiconductor devices because of excellent transport properties of two dimensional electron gas at the AlGaN/GaN heterointerface and a large sheet carrier concentration in the device channel. Other advantages of GaN-based materials for FET applications include a very high breakdown field, a very high saturation field, a high peak velocity, a large conduction and valence band discontinuities at the AlN-GaN heterointerface, and a reasonable thermal conductivity (comparable to that of Si). In this paper, we review our recent results obtained for different types of GaN-based transistors.

The Backside Pulse Doped Channel Heterostructure Field-Effect Transistor: Design, DC, and RF Performance

We report about a theoretical and experimental study of AlGaAs/InGaAs modulation doped field-effect transistors (MODFETs) having doped channels. On the basis of self consistent calculations we suggest design rules of where to introduce the channel doping into the channel to obtain high speed devices with high saturation currents and reasonable low noise performance. For a 0.35 µm gate length backside pulse doped channel device (BSPDC-HFET) with 120 µm gate width a maximum transconductance of 625 mS/mm and a maximum saturation current at VGS=+0.8 V of 720 mA/mm have been measured. The cut-off frequencies are fT=80 GHz, fmax=195 GHz. At 18 GHz a minimum noise figure of NF=1.1 dB with 17 dB associated gain were measured.

39 GHz monolithic coplanar waveguide amplifier using doped channel HFET technology on InP

A single-state amplifier has been designed and fabricated using 0.25 mu m gate length, doped-channel HFET technology on InP substrates. Coplanar waveguide (CPW) was used for impedance matching. A gain of 14.4 dB was measured at 39 GHz. >

Effect of p-i-p/sup +/ buffer on characteristics of n-channel heterostructure field-effect transistors

The carrier concentration in heterostructure FETs (HFETs) with a p-i-p/sup +/ buffer is presented as a function of the gate bias, obtained by self-consistent one-dimensional calculation of 2-D electron density, subband levels, and electrostatic potential. These results quantify certain limitations on the range of geometrical and doping parameters and make it possible to optimize the HFET design and to compare modulation doped FET (MODFET) and doped channel HFET (DCHFET) structures. Monte Carlo simulations demonstrate that this p-i-p/sup +/ buffer drastically reduces the short-channel effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

AlGaAs/InGaAs/GaAs quantum well doped channel heterostructure field effect transistors

The results of experimental and theoretical studies of pseudomorphic AlGaAs/InGaAs/GaAs quantum-well doped-channel heterostructure field effect transistors (QW-DCHFETs) are presented. The channel doping was introduced in two ways: during growth by molecular beam epitaxy or by direct ion implantation. The latter technique may be advantageous for fabrication of complementary DCHFET circuits. Peak transconductances of 471 mS/mm and peak drain currents of 660 mA/mm in 0.6- mu m-gate doped-channel devices were measured. The results show the advantages of the DCHFET over standard heterostructure FET structures and their potential for high-speed IC applications. Self-consisted calculations of the subband structure show that the potential barrier between the quasi-Fermi level in the channel and the bottom of the conduction band in the barrier layer is considerably larger for the doped channel structure than for the structure with an undoped channel. This lowers the thermionic emission gate current of the doped channel device compared to the undoped channel device.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A self-aligned gate III-V heterostructure FET process for ultrahigh-speed digital and mixed analog/digital LSI/VLSI circuits

A planar ion-implanted self-aligned gate process for the fabrication of high-speed digital and mixed analog/digital LSI/VLSI integrated circuits is reported. A 4-b analog-to-digital converter, a 2500-gate 8*8 multiplier/accumulator, and a 4500-gate 16*16 complex multiplier have been demonstrated using enhancement-mode n/sup +/-(Al,Ga)As/MODFETs, superlattice MODFETs, and doped channel heterostructure field-effect transistors (FETs) whose epitaxial layers were grown by molecular-beam epitaxy. With nominal 1- mu m gate-length devices, direct-coupled FET logic ring oscillators with realistic circuit structures have propagation delays of 30 ps/stage at a power dissipation of 1.2 mW/stage. In LSI circuit operation, these gates have delays of 89 ps/gate at a power dissipation of 1.38 mW/gate when loaded with an average fan-out of 2.5 gates and about 1000 mu m of high-density interconnects. High-performance voltage comparator circuits operated at sampling rates greater than 2.5 GHz at Nyquist analog input rates and with static hysteresis of less than 1 mV at room temperature. Fully functional 4-b analog-to-digital circuits operating at frequencies up to 2 GHz were obtained. >