Pseudomorphic Modulation-doped Field-effect Transistors Research Articles

Investigation of InGaP/InGaAs n- and p-channel pseudomorphic modulation-doped field effect transistors with high gate turn-on voltages

The performances of InGaP/InGaAs camel-gate n- and p-channel pseudomorphic modulation-doped field effect transistors (MODFETs) are demonstrated and compared. In the n-channel (p-channel) device, an extremely high gate turn-on voltage of 1.7 (2.0) V is measured due to the pn depletion in the camel-like gate region and the presence of a large conduction (valence) band discontinuity at the InGaP/InGaAs heterostructure. In addition, a maximum drain saturation current of 425 mA/mm (−345 mA/mm) and a maximum transconductance of 85 mS/mm (63 mS/mm) are obtained for the n-channel (p-channel) device. These excellent characteristics indicate that the devices that are studied are promising for signal amplifiers and inverter circuit applications.

High performances of InGaP∕InGaAs∕GaAs pseudomorphic modulation-doped field effect transistors using camel-gate structure

In this article, high-performance InGaP∕InGaAs∕GaAs δ-doped pseudomorphic modulation-doped field effect transistors (pMODFETs) employing n+-GaAs∕p+-InGaP∕n-InGaP camel-gate structure are characterized. Because of the depleted p-n junction in the gate region and the presence of the large conduction-band discontinuity of the InGaP∕InGaAs heterostructure, a large gate turn-on voltage is obtained. The dc and microwave characteristics of single- and double-δ-doped pMODFETs are demonstrated. The double-δ-doped pMODFET exhibits a higher drain saturation current, a larger transconductance, a broader gate voltage swing, and better high-frequency responses than the single-δ-doped device. The excellent performance of the studied devices is promising for linear and large signal amplifiers and high-frequency circuit applications.

InGaP/InGaAs/GaAs camel-gate p -channel pseudomorphic modulation-doped field effect transistor

A novel InGaP/InGaAs/GaAs p-channel pseudomorphic modulation-doped field effect transistor based on p+-GaAs/n+-InGaP/p-InGaP camel-like gate structure is reported for the first time. Owing to the p–n depletion of the camel-like gate and the presence of relatively large ΔEv at InGaP/InGaAs heterostructure, an extremely large gate turn-on voltage, greater than 2 V, is measured. For a 1×100 µm2 device, the experimental results show a maximum saturation current density of −345 mA/mm and a widely broad gate voltage swing, greater than 4 V, with 80% maximum transconductance. Furthermore, the fT and fmax values are 3.1 and 4.8 GHz, respectively.

A Novel GaAs/InGaAs/AlGaAs Structure of Modulation-DopedField-Effect Transistors with High Transconductances

Novel structure GaAs/InGaAs/AlGaAs pseudomorphicmodulation-doped field-effect transistors (MODFETs) with a buried p-i-n dipolelayer and a 200 nm buffer layer have been fabricated. According tothe calculation, the dipole buried layer not only results in the very thinbuffer layer required, but also enhances the density of two-dimensionalelectron gas. The measured transconductances of these MODFETs, with a gatelength of 2 µm and a drain-source spacing of 5 µm, are as high as320 mS/mm and the measured maximum drain currents of the typical devices arehigher than 500 mA/mm.

Frequency optimization of pseudomorphic modulation-doped field-effect transistor (AlGaAs/InGaAs) for microwave and millimeter-wave applications

The results of an analysis based on the solution of the 2-D Poisson equation are presented to investigate the dependence of the small-signal parameters on biasing conditions. The switching parameters are calculated simply from the charge variations, and it is found that the characteristics depend only on the basic device parameters and terminal voltages. The high value of ft proves the utility of the model in the design of low-power MMICs. A maximum frequency of 101.42 GHz at 0.25 μm is obtained, and the results show close agreement with the experimental data, thereby proving the validity of the proposed model. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 377–383, 2000.

Current-voltage characteristics and field distribution of pseudomorphic (AlGaAs/InGaAs) modulation-doped field-effect transistor for microwave circuit applications

A two-dimensional analytical model for the current–voltage characteristics of a pseudomorphic AlGaAs/InGaAs modulation-doped field-effect transistor is developed using charge-control analysis for its microwave circuit applications. The two-dimensional potential, field, electron concentration, and velocity profiles are expressed explicitly in the saturation region. The results so obtained are compared with the experimental data, and show excellent agreement, thereby proving the validity of the model. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 407–412, 2000.

Capacitance-voltage characteristics and cutoff frequency of pseudomorphic (AlGaAs/InGaAs) modulation-doped field-effect transistor for microwave and high-speed circuit applications

A two-dimensional analytical model for the capacitance–voltage characteristics of a pseudomorphic AlGaAs/InGaAs modulation-doped field-effect transistor is developed using charge-control analysis for its microwave frequency applications. The model includes the effect of various fringing field capacitances, and a cutoff frequency of 94.8 GHz is obtained for an L=0.25 μm device. The effect of traps has been included, which decreases the cutoff frequency. The results so obtained are compared with experimental data, and show excellent agreement, thereby proving the validity of the model. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 312–318, 1999.

Band-bending effect of low temperature GaAs on a pseudomorphic modulation-doped field-effect transistor

Low temperature photoluminescence (PL) measurements on pseudomorphic modulation-doped transistors with a low-temperature (LT) GaAs layer in the GaAs buffer layer clearly show a decrease in the quantum well PL transition energies compared to a structure with no LT GaAs. Self-consistent calculations of the electron and hole bandstructure suggest that the observed increase in the redshift in PL energies with increasing quantum well-LT GaAs spacing can be attributed to band bending induced by the Fermi level pinning at the undoped GaAs/LT GaAs interface and a novel carrier compensation effect of LT GaAs.

Transconductance extraction for pseudomorphic modulation-doped field-effect transistor (AlGaAs/InGaAs) for microwave and millimeter-wave applications

Transconductance extraction for pseudomorphic modulation-doped field-effect transistor (AlGaAs/InGaAs) for microwave and millimeter-wave applications

High photoresponsivity of a p-channel InGaP/GaAs/InGaAs double heterojunction pseudomorphic modulation-doped field effect transistor

In this letter, we report the electrical and optical characteristics of p-channel In0.13Ga0.87As double heterojunction pseudomorphic modulation-doped field effect transistor (MODFET) structure grown by gas source molecular beam epitaxy. The Hall mobility and the density of 2-DHGs (two-dimensional hole gases) in the pseudomorphic In0.13Ga0.87As channel were measured to be 250 cm2/V s and 1.9×1012 cm−2 at 300 K, and 5800 cm2/V s and 1.5×1012 cm−2 at 23 K, respectively. The fabricated p-channel MODFET shows a good mobility property which is due to high valence band discontinuity of InGaP/GaAs/InGaAs double barriers. The peak energy in the photoluminescence spectrum from the p-channel pseudomorphic MODFET structure was found to be 1.4 eV (λ=881 nm). The photoresponsivity with this modified pseudomorphic MODFET structure shows outstandingly better than that of a pin photodiode, particularly at low incident optical power.

Back-gating effect of low-temperature GaAs on a pseudomorphic modulation-doped field-effect transistor

Low-temperature (LT) photoluminescence (PL) measurements on pseudomorphic modulation-doped transistors with a (LT) GaAs layer in the GaAs substrate have revealed the existence of a substrate voltage. The substrate voltage is manifested by a decrease in the PL transition energies of the quantum-well subbands due to the quantum confined Stark effect. Our results indicate that the substrate voltage is generated by the trapping of holes from the undoped molecular-beam-epitaxy-grown GaAs at the GaAs/LT GaAs interface by the high concentration of arsenic antisite defects in the LT GaAs layer.

MBE growth and device applications of lattice-matched and strained heterostructures on (n11)-oriented and patterned substrates

The epitaxy of lattice-matched and strained semi-conducting films on patterned and misoriented substrates has led to new growth phenomena, material properties and device applications. Our work on InP- and GaAs-based heterostructures on (111)- and (311)-oriented substrates and strained heterostructures on planar and patterned (small area) substrates is described in this paper. The possibility of reliable and reproducible p-type doping of (311)A GaAs by Si during molecular-beam epitaxial growth and the application of such doping in the realization of high-performance electronic devices have been investigated. It is seen that p-type doping up to a free hole concentration of 4 × 10 19 cm −3 is obtained at low (⪕ 500°C) growth temperature and high As 4 flux. The incorporation of Si atoms into electrically active As sites is at least 95%. n-p-n heterojunction bipolar transistors grown by all-Si doping exhibit excellent current voltage characteristics and a common emitter current gain β = 240. Doped channel p-type heterojunction field-effect transistors have transconductance g m = 25 mS/mm. We have experimentally and theoretically studied piezo-electric field effects in InP-based In xGa 1 − xAs/In 0.52Al 0.48As pseudomorphic quantum wells grown by molecular-beam epitaxy on (111)B InP substrates. The electro-optic coefficients of this material were measured and found to be much larger than that of GaAs. We have also investigated the consequences of altered growth modes on the epitaxy of highly strained InGaAs on patterned small area (001) GaAs substrates. Al 0.15Ga 0.85As/In 0.25Ga 0.75As pseudomorphic modulation-doped field-effect transistors and strained In xGa 1 − xAs/GaAs p-i-n photodiodes have been fabricated on patterned (100)-GaAs substrates and characterized. Compared with devices made on planar substrates, small area growth improves the dc transconductance by 40% and current gain cutoff frequency by 50% in the transistors. Photodiodes grown in small recesses (∼30 μm) exhibit 2–4 times higher quantum efficiency than those on planar substrates.

Analytical Model to Determine the Gate Leakage Current in In0.52Al0.48As/InxGa1-xAs Pseudomorphic Modulation Doped Field-Effect Transistors Caused by Thermionic Field Emission

The gate leakage current of pulse doped In0.52Al0.48As/Inx Ga1-x As pseudomorphic modulation doped field-effect transistors (MODFETs) is analysed by thermionic field emission theory. For the first time, a theoretically based investigation of the leakage current for this type of device is carried out. The influence of parameters of the layer structure design on the gate leakage current such as the thickness of the barrier layer or the doping concentration in the supply layer is predicted. The model adequately predicts the experimental decrease in leakage current with increased thickness of the barrier layer and reduced doping concentration.

The Applications of Citric Acid/Hydrogen Peroxide Etching Solutions in the Processing of Pseudomorphic MODFETs

The etching characteristics of and in citric acid/hydrogen peroxide etching solution were studied. The etch rate and the selectivity were measured over a wide concentration range from room temperature down to 0°C. The results show that by changing the concentration of the solution we can vary the selectivity ( etch rate: etch rate) from over 80:1 to reverse selectivity of 1:1.4; the etch rate can also be varied from over 4000 Å/min to less than 150 Å/min. However, high selectivity process consistently shows high etch rate. We have developed mesa and gate recess etch processes for pseudomorphic modulation doped field effect transistor (MODFET) structures based on these results. Using a two‐step mesa etch process, we can produce a recessed sidewall profile of the channel layer and hence avoid the parasitic gate leakage path caused by the contact of Schottky gate to the exposed channel layer at the sidewall. A nonselective low etch rate process was chosen for gate recess etch since the selective etch shows high etch rate and causes excessive undercut in the cap layer. Using the citric acid/hydrogen peroxide etch process with low etch rate, very uniform threshold voltage (with a standard deviation of 25 mV across a 2 in. wafer) can be achieved. This is the best result reported using nonselective wet etch and compares very favorably to published results using dry etch.

A MODFET process for micrometer scale strained layer islands

Previous studies have demonstrated that the density of misfit dislocations can be reduced by growth of strained layers on patterned substrates. In this paper, a new process sequence for the fabrication of pseudomorphic modulation-doped field effect transistors (MODFETs) on pattened GaAs substrates is presented. Semi-insulating GaAs substrates were patterned and dry etched using chemically assisted ion beam etching (CAIBE) to define a series of mesas prior to epitaxial layer growth. Double-doped, pseudomorphic MODFET layers were then grown on the substrates by molecular beam epitaxy. Using a planarization technique based on SiO 2/photoresist, MODFETs with vacuum-passivated T-gates which bridge across up to 20 mesas were fabricated. Current-voltage measurements of these MODFETs show high output currents and good pinc-off characteristics.

10 GHz bandwidth monolithic p-i-n modulation-doped field effect transistor photoreceiver

A photoreceiver circuit using an InGaAs p-i-n photodiode and InGaAs/InAlAs pseudomorphic modulation-doped field effect transistor (MODFET) based preamplifier has been fabricated. The 18 μm diam photodiode has a bandwidth of 29 GHz and the ft and fmax of the MODFET are 26 and 30 GHz, respectively. The photoreceiver circuits have bandwidths of 10 GHz and 17 dB gain. The sensitivity at 2.5 Gb/s is −26.4 dBm.

Gas source molecular beam epitaxial growth and device applications in In 0.5Ga 0.5P and In 0.5Al 0.5P heterostructures

This article reviews briefly the recent progress in the In 0.5Ga 0.5P and In 0.5Al 0.5P epilayers lattice-matched to GaAs grown by gas source molecular beam rpitaxy (GSMBE). It covers the growth conditions, and the structural, electrical, and optical properties. Important research results on the electronic and photonic device applications of these materials grown by GSMBE are also reviewed and discussed. We focus on the InGaP/InGaAs and InAlP/InGaAs pseudomorphic modulation-doped field-effect transistors, InGaP/GaAs and InAlP/GaAs heterojunction bipolar transistors, short wavelength visible laser diodes, and 0.98 μm lasers using In 0.5Ga 0.5P as the cladding layers. The results clearly demonstrate that high quality In 0.5Ga 0.5P and In 0.5Al 0.5P heterostructures prepared by GSMBE are suitable for state-of-the-art device applications.

Modulation-doped In0.48Al0.52P/In0.2Ga0.8As field-effect transistors

In0.48Al0.52P/In0.2Ga0.8As pseudomorphic modulation-doped field-effect transistors (MODFETs) were realized for the first time by gas-source molecular beam epitaxy on GaAs substrates. Extrinsic transconductances of 173 and 283 mS/mm at 300 and 77 K, respectively, were measured for MODFETs with a 1 μm long and 75 μm wide gate. The devices showed very good pinch-off characteristics, and the output conductance was only 1.3 mS/mm. Extremely high Schottky barrier height (0.92 eV) and low gate leakage current (Irev<250 nA at VGS=−5 V) were achieved. The gate breakdown voltage was −17 V. No I-V collapse was observed at 77 K. Microwave measurements showed that the current gain cutoff frequency fT of the devices was 11.5 GHz and the maximum frequency of oscillation fmax, was 26 GHz. These results demonstrate the promising potential of pseudomorphic In0.48Al0.52P/InGaAs MODFETs as high frequency and high power devices.

Photoluminescence From 2D Electron Gas and Many Body Effects as a Probe of the Crystalline Quality of Pseudomorphic GaAs/InGaAs/AlGaAs and GaAs/N(GaAs)10(N+l)(InAs)m/AlGaAs Modfet Structures

We have performed low temperature (5K) photoluminescence (PL) measurements in order to study the crystalline quality of pseudomorphic modulation-doped field effect transistors (MODFET's) grown by MBE. MODFET's based on GaAs/AlGaAs with either an InGaAs or a (GaAs)n(InAs)m short period superlattice (SPS) channel have been studied. On modulation doped structures, the presence of free carriers into the channel strongly affects the PL emission,. In this paper, we present a study of PL line shape of MODFET structures with different channel thicknesses and growth conditions. A correlation between the PL line shape and these parameters is clearly observed.

Submicron modulation-doped field-effect transistor/metal–semiconductor–metal-based optoelectronic integrated circuit receiver fabricated by direct-write electron-beam lithography

An all direct-write electron-beam fabrication process has been developed for the fabrication of monolithic optoelectronic integrated circuits (OEICs). Various electron-beam resist technologies are investigated including image reversed AZ5214, PMMA/P[MMA−MAA] bilayer, and PMMA/P[MMA−MAA]/PMMA trilayer. A novel single-step air-bridge formation process utilizing selective development is described. These processes are demonstrated in the fabrication of a 0.85-μm sensitive OEIC receiver comprised of a metal–semiconductor–metal (MSM) detector integrated with a submicron GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistor based transimpedance amplifier. A 3-dB transimpedance bandwidth of 5.6 GHz and a transimpedance bandwidth product of 4.8 THz Ω are measured for the amplifier. Discrete high-resolution MSM photodetectors with finger/gap spacings ranging from 0.1 to 1.0 μm have been fabricated and characterized.