Pseudomorphic Modulation-doped Field Effect Research Articles

Characteristics of InxGa1−xAs/GaAs pseudomorphic modulation doped field effect transistor

High performance pseudomorphic InxGa1−xAs/GaAs modulation doped field effect transistors (MODFETs) grown by metalorganic chemical vapor deposition have been characterized at dc using modulation spectroscopy. A transconductance as high as 175 and 253 mS/mm was obtained at 30% and 40% indium content, respectively. In order to identify the origin of the MODFETs’ features we have performed a self-consistent Schrodinger–Poisson calculation of the subband and intersubband energies. The photoreflectance spectra can be divided into two parts by the photon energy; one belongs to the GaAs bulk transition and the other belongs to the InxGa1−xAs/GaAs quantum well transition including two-dimensional electron gas (2DEG) signals. The built-in electric fields are 20.6×104 V/cm and 22.6×104 V/cm. From photoreflectance spectra peaks at 1.035 and 1.06 eV show that their energies agree with line shape fitting and 2DEG theory.

Monolithic millimeter wave optical receivers

A single stage monolithic millimeter wave optical receiver circuit was designed and fabricated using a metal-semiconductor-metal (MSM) photodetector and a pSeudomorphic Modulation Doped Field Effect Transistors (SMODFET) on a GaAs substrate for possible applications in chip-to-chip and free space communications. The MSM photodetector and the SMODFET epitaxial material were grown by molecular beam epitaxy (MBE). Device isolation was achieved using an epitaxially grown buffer between the MSM detector layers and SMODFET. The photodetector was designed for maximum absorption at optical wavelength of 770 nm light and the SMODFET impedance matching network was optimized for 44 GHz. The monolithic millimeter wave optical receiver circuit achieved 3 dB gain over a photodetector at 39 GHz, which was the limit of the measurement system. TOUCHSTONE model of the circuit indicated 6.6 dB gain over the photodetector and 5.7 dB total gain including the insertion loss of the photodetector at 44 GHz.

Fabrication of High Breakdown Pseudomorphic Modulation Doped Field Effect Transistors Using Double Dry Etched Gate Recess Technology in Combination with E-Beam T-Gate Lithography

We have developed a technology to fabricate pseudomorphic 0.3 µ m gatelength modulation doped field-effect transistors (MODFETs) having a breakdown voltage up to 20 Volts. This technology uses molecular beam epitaxy (MBE) to grow the InGaAs/AlGaAs/GaAs heterostructure with two pulse doping layers on 3 inch semiisolating GaAs wafers. A mix and match lithography was applied using an i-line stepper and an electron beam direct write process to define the mushroom shaped gates (T-gates). The breakdown enhancement is achieved by a self aligned selective double dry etched gate recess using AlGaAs etch stop layers. We investigated the heterostructure doping and the influence of the gate recess process to the device performance.

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.

Electrical characterization of pseudomorphic GaAs/InGaAs/AlGaAs and AlGaAs/InGaAs/AlGaAs modulation doped field effect transistor-type heterostructures grown by molecular-beam epitaxy

We studied the influence of the indium composition y, growth temperature Ts and InGaAs quantum-well channel thickness dch on the 300 and 77 K Hall electrical properties of pseudomorphic modulation doped field effect transistor (MODFET)-type heterostructures grown by molecular-beam epitaxy. In agreement with Nguyen et al., we find an optimum channel thickness of 90 Å for an indium composition y=0.25 of the channel. Significant improvements in sheet resistivity ρs and in carrier concentration nso were obtained by using AlGaAs doped barriers on both sides of the pseudomorphic channel. We were thus able to obtain a two-dimensional electron gas sheet density nso as high as 4.0×1012 cm−2 at 77 K, which is among the highest values ever reported for MODFETs on GaAs.

CH4/H2 reactive ion etching for gate recessing of pseudomorphic modulation doped field effect transistors

Pseudomorphic AlGaAs/InGaAs modulation doped field effect transistors have been fabricated by using methane/hydrogen (CH4/H2) reactive ion etching for gate recessing. Source-drain resistance and Hall measurements on as etched and annealed samples are presented. The electrical degradation introduced by the plasma can be recovered after annealing at 400 °C. A threshold voltage (Vth) standard deviation of 14 mV over a 5 cm (2 in.) wafer was obtained.

Vertical integration of an In 0.15 Ga 0.85 As modulation-doped field effect transistor and GaAs laser grown by molecular beam epitaxy

A vertically integrated structure consisting of an In/sub 0.15/Ga/sub 0.85/As pseudomorphic modulation doped field effect transistor (MODFET) and a GaAs graded index separate confinement heterostructure single quantum well (GRINSCH SQW) laser was grown by molecular beam epitaxy. Wafers containing integrated MODFET/laser layers produced MODFETs with DC and microwave performance comparable to wafers containing only MODFET layers, indicating that the modulation doping and the strained In/sub 0.15/Ga/sub 0.85/As channel were largely unaffected by the long, high temperature laser growth. The lasers had threshold currents similar to identical structures grown on n-type substrates and the integrated structures had a -3dB modulation bandwidth of 3.5 GHz. >