GaAs-based High Electron Mobility Transistors Research Articles

Neutral beam process in AlGaN/GaN HEMTs: Impact on current collapse

In this paper, we report a promising approach for the gate recess process with a suppressed current collapse in GaN-based high electron mobility transistors (HEMTs) by means of neutral beam (NB). A recessed gate structure has been widely studied as a way to realize normally-off operation in GaN, InP, and GaAs-based HEMTs. Since GaN-based materials are usually etched by dry process, plasma-induced damage is a serious concern. NB is free from electrical charges and UV photons, resulting in an accurate control of etching depth and less plasma-induced damages. In this work, we introduce NB irradiation to the gate interface and measured DC and gate-pulsed output characteristics. The results suggest that NB is applicable for the gate recess etching with suppressing the current collapse.

A Review of Raman Thermography for Electronic and Opto-Electronic Device Measurement With Submicron Spatial and Nanosecond Temporal Resolution

We review the Raman thermography technique, which has been developed to determine the temperature in and around the active area of semiconductor devices with submicron spatial and nanosecond temporal resolution. This is critical for the qualification of device technology, including for accelerated lifetime reliability testing and device design optimization. Its practical use is illustrated for GaN and GaAs-based high electron mobility transistors and opto-electronic devices. We also discuss how Raman thermography is used to validate device thermal models, as well as determining the thermal conductivity of materials relevant for electronic and opto-electronic devices.

Ultra-high-throughput Production of III-V/Si Wafer for Electronic and Photonic Applications.

Si-based integrated circuits have been intensively developed over the past several decades through ultimate device scaling. However, the Si technology has reached the physical limitations of the scaling. These limitations have fuelled the search for alternative active materials (for transistors) and the introduction of optical interconnects (called “Si photonics”). A series of attempts to circumvent the Si technology limits are based on the use of III-V compound semiconductor due to their superior benefits, such as high electron mobility and direct bandgap. To use their physical properties on a Si platform, the formation of high-quality III-V films on the Si (III-V/Si) is the basic technology ; however, implementing this technology using a high-throughput process is not easy. Here, we report new concepts for an ultra-high-throughput heterogeneous integration of high-quality III-V films on the Si using the wafer bonding and epitaxial lift off (ELO) technique. We describe the ultra-fast ELO and also the re-use of the III-V donor wafer after III-V/Si formation. These approaches provide an ultra-high-throughput fabrication of III-V/Si substrates with a high-quality film, which leads to a dramatic cost reduction. As proof-of-concept devices, this paper demonstrates GaAs-based high electron mobility transistors (HEMTs), solar cells, and hetero-junction phototransistors on Si substrates.

Editors' Choice—On the Radiation Tolerance of AlGaN/GaN HEMTs

The radiation tolerance of AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on high quality, low threading dislocation density (TDD) ammonothermal GaN and hydride vapor phase epitaxy GaN substrates was studied and compared to the radiation response of devices on SiC substrates where the TDD is 104 times higher. Hall and transport measurements were performed as a function of 2 MeV proton fluence. The threading dislocation density had no effect on the radiation response. Comparing the results with published data reveals that almost all irradiated GaN-based HEMTs respond to radiation damage similarly regardless of differences in initial film quality, device structure, aluminum mole fraction, etc. AlGaAs/GaAs HEMTs are also shown to behave similarly but are around ten times more sensitive to radiation damage than GaN-based HEMTs. Known values of the displacement energy thresholds in GaN and GaAs are used to calculate that 36% fewer defects are created in GaN than in GaAs, which is too small to cause a 1000% difference in radiation sensitivity between GaN- and GaAs-based HEMTs. An alternative explanation is proposed in which the piezoelectric field at the AlGaN/GaN interface causes scattered carriers to be reinjected into the 2DEG channel, thereby mitigating some of the harmful radiation effects.

High speed electrically-controlled terahertz modulator

We have developed an electrically-controlled terahertz modulator which can be used to realize amplitude modulation of terahertz waves at an extremely high speed. The terahertz modulator is made on GaAs-based high electron mobility transistors (HEMTs) array on which numerous split-ring resonators (SRRs) are formed. The device exhibits the capability of dynamical response to incident terahertz waves under a fast time-varying voltage. Our measurement results reveal that an ultrafast modulation speed over 11MHz under an applied AC gate voltage can be achieved. With the resistance and the capacitance of HEMTs further optimized, it was demonstrated that the HEMT/SRR-based modulator may operate at an even higher modulation frequency.

Graphene-GaAs/AlxGa1−xAs heterostructure dual-function field-effect transistor

We have integrated chemical vapor-deposited graphene and GaAs/AlxGa1−xAs heterostructure into a hybrid field effect transistor (FET). Depending on the operation scheme, graphene can be utilized either as a gate electrode for a GaAs-based high electron mobility transistor (HEMT) or as a channel material gated by two dimensional electron gas (2DEG) formed in the interface of a heterojunction. Our studies reveal that 2DEG can function as an effective back-electrode to tune the ambipolar effect of graphene. The performance of graphene FET (GFET) is limited by the interface band bending of the heterojunction associated with the gating voltages and the intrinsic surface morphology of GaAs substrate. Our results bode a way to implement HEMT/GEFT-based bi-FET integrated circuits.

Electron heating and huge positive magnetoresistance in an AlGaAs∕GaAs high electron mobility transistor structure at high temperatures

We have performed magnetoresistivity measurements ρxx(B) on an AlGaAs∕GaAs high electron mobility transistor (HEMT) structure at high temperatures T. The observed positive magnetoresistance (MR) in the HEMT structure can be greatly enhanced simply by increasing the driving current. At T=80K and B=6T, the MR value can be increased from ∼150% to 4000%, almost a 30-fold increase when a large current of 40μA is applied. Such results are due to electron heating effects and our data lay the foundation for practical magnetic device applications which can be readily combined with high-speed electronics, high-frequency amplifiers, and radar using the mature GaAs-based HEMT technology.

Huge positive magnetoresistance in a gated AlGaAs∕GaAs high electron mobility transistor structure at high temperatures

Magnetoresistivity measurements on a gated AlGaAs∕GaAs high electron mobility transistor (HEMT) structure were performed at high temperatures T. By changing the applied gate voltage Vg, we can investigate the observed huge positive magnetoresistance (PMR) at different effective disorder and density inhomogeneity within the same HEMT structure. The observed PMR value increases with increasing disorder in the depletion mode (Vg⩽0). Moreover, the PMR value is not limited by the quality of the HEMT structure at T=80K. Such results pave the way for low-cost, high-throughput GaAs-based HEMT fabrication for future magnetic sensing and recording devices fully compatible with the mature HEMT technology.

Novel structure of GaAs-based interdigital-gated HEMT plasma devices for solid-state THz wave amplifier

Theoretical analysis of potential distribution in the interdigital-gated high electron mobility transistor (HEMT) plasma wave device was carried out. The dc I–V characteristics of capacitively coupled interdigital structure showed that uniformity of electric field under the interdigital gates was improved compared to the dc-connected interdigital gate structure. Admittance measurements of capacitively coupled interdigital gate structure in the microwave region of 10–40GHz showed the conductance modulation by drain–source voltage. These results indicate the existence of plasma wave interactions.

Huge positive magnetoresistance of GaAs∕AlGaAs high electron mobility transistor structures at high temperatures

The authors have performed magnetoresistivity measurements ρxx(B) on GaAs∕AlGaAs high electron mobility transistor (HEMT) structures at high temperatures T. These HEMT structures show huge positive magnetoresistance (MR). For B=±6T, the MR values are >1300% and >200% at T=20 and 80K, respectively. Since a GaAs-based HEMT structure is not susceptible to ferromagnetic noise which appears to represent a fundamental challenge to the scalability of magnetic MR devices to ultrahigh area densities, the experimental results pave the way for the integration of scalable nonmagnetic MR devices with the mature HEMT technology using the same material system.

Room temperature generation of terahertz radiation from a grating-bicoupled plasmon-resonant emitter: Size effect

A doubly interdigitated grating gates structure was incorporated into a GaAs-based high-electron mobility transistor to configure a plasmon-resonant emitter. Two dimensional electrons are then periodically confined in 100nm regions. The devices exhibit a plasma-wave signature under 1.5μm cw laser illumination. Two devices with different geometries have been subjected to an impulsive laser at room temperature. The authors observed clear generation of terahertz radiation from both devices.

Strain-Relaxed In0.1Al0.25Ga0.65As ∕ In0.22Ga0.78As ∕ In0.1Al0.25Ga0.65As HEMT

A GaAs-based high-electron mobility transistor with a quaternary strain-relaxed layer (SR-HEMT) has been fabricated successfully. The lower lattice mismatch between and yields high-electron mobility and good carrier confinement. Experimental results indicate that the SR-HEMT exhibits a peak of , a maximum drain-current density of , a high breakdown voltage of , a cut-off frequency of , a maximum oscillation frequency of , a small-signal power gain of , and a saturated power of at with the gate dimension of . Furthermore, the SR-HEMT exhibits a temperature-insensitive threshold voltage shift of .

High switching performance 0.1-/spl mu/m metamorphic HEMTs for low conversion loss 94-GHz resistive mixers

We report high switching performance of 0.1-μm metamorphic high-electron mobility transistors (HEMTs) for microwave/millimeter-wave monolithic integrated circuit (MMIC) resistive mixer applications. Very low source/drain resistances and gate capacitances, which are 56 and 31% lower than those of conventional pseudomorphic HEMTs, are due to the optimized epitaxial and device structure. Based on these high-performance metamorphic HEMTs, a 94-GHz MMIC resistive mixer was designed and fabricated, and a very low conversion loss of 8.2 dB at a local oscillator power of 7 dBm was obtained. This is the best performing W-band resistive field-effect transistor mixer in terms of conversion loss utilizing GaAs-based HEMTs reported to date.

Study of hydrogen-sensing characteristics of a Pt-oxide-AlGaAs metal-oxide-semiconductor high electron mobility transistor

A new hydrogen sensor based on a GaAs-based high electron mobility transistor (HEMT) with a catalytic Pt-oxide-Al0.24Ga0.76As (MOS) gate structure is fabricated and demonstrated. The threshold voltage shift, hydrogen detection sensitivity, and transient responses of the device under different hydrogen concentrations and temperature are measured and studied. Based on the transistor amplification action, even at an extremely low hydrogen concentration of 14ppm H2/air, the studied device shows significant drain current variation (about 0.12mA). Furthermore, the studied device can be operated under wider operating temperature regimes with remarkable hydrogen-sensing properties. The decreased hydrogen detection capability with increasing operating temperature demonstrates the exothermic reaction of the hydrogen adsorption and desorption processes.

A W-band subharmonically pumped monolithic GaAs-based HEMT gate mixer

A W-band high electron mobility transistor (HEMT) subharmonically pumped (SHP) gate mixer is designed with fixed LO frequency operation. it is fabricated on a 4-mil substrate using 0.15-/spl mu/m GaAs pHEMT monolithic microwave integrated circuit (MMIC) process. the on-wafer measurement results show that the best conversion loss is about 4.7 dB in the W-band, as a 11-dbm 42-GHz low observable (LO) signal is pumped. To our knowledge, this is the first result on low conversion-loss W-band MMIC SHP HEMT gate mixer.

FACTORS LIMITING THE MAXIMUM OPERATING VOLTAGE OF MICROWAVE DEVICES

The operating voltage of advanced microwave devices is currently limited by impact-ionization and breakdown effects. An extended study of the effects of hot carriers on the breakdown behavior and reliability of GaAs-based and InP-based HEMTs (high electron mobility transistors) has been carried out by means of pulsed measurements, electroluminescence spectroscopy and microscopy and Monte Carlo simulations. We show that the parasitic bipolar effect, which explains kink effects in HEMTs, can also induce regenerative phenomena eventually leading to on-state breakdown. Results concerning the effects of hot carrier aging on GaAs-based and InP-based HEMTs are summarized.

Low phase noise millimeter-wave frequency sources using InP-based HBT MMIC technology

A family of millimeter-wave sources based on InP heterojunction bipolar transistor (HBT) monolithic microwave/millimeter-wave integrated circuit (MMIC) technology has been developed. These sources include 40-GHz, 46-GHz, 62-GHz MMIC fundamental mode oscillators, and a 95-GHz frequency source module using a 23.8-GHz InP HBT MMIC dielectric resonator oscillator (DRO) in conjunction with a GaAs-based high electron mobility transistor (HEMT) MMIC frequency quadrupler and W-band output amplifiers. Good phase noise performance was achieved due to the low 1/f noise of the InP-based HBT devices. To our knowledge, this is the first demonstration of millimeter-wave sources using InP-based HBT MMIC's.

Refinement of low-resistance Ni–Ge–Au ohmic contacts to n+ GaAs using screening and response surface experiments

Multivariable screening and response surface experiments have been performed to model ohmic contact resistance (Rc) of a Ni–Ge–Au ohmic metal process for n+ GaAs-based high electron mobility transistors (HEMTs). Seven variables were examined via a fractional factorial screening experiment to rank the effects of each process variable. The results of the screening experiment indicated that the most significant variables were total Ge and Au evaporated thickness, Ge-to-Au ratio, and the post-alloy cooling time. Response surface experiments were designed around these three variables to examine the first- and second-order effects. The results enabled the development of an empirical model of ohmic contact resistance from which a new low value of 0.03 ± 0.03 Ω · mm (one-sigma) was predicted. Twenty confirmation runs on the new process indicated an average Rc of 0.06 ± 0.02 Ω · mm (one-sigma), with a range of 0.02 Ω · mm to 0.11 Ω · mm, a reduction from the previous average process value of 0.14 ± 0.07 Ω · mm (one-sigma).

GaAs and InP selective molecular-beam epitaxy

We present here the selective molecular-beam epitaxy (MBE) techniques used to achieve high quality material that integrates multiple device technologies on the same GaAs or InP substrate. We have successfully demonstrated selective MBE for both GaAs-based high electron mobility transistor (HEMT)—heterojunction bipolar transistor (HBT) integration and InP-based PIN diode—HEMT integration. New merged processing technologies have been developed to achieve high performance monolithic microwave and optoelectronic HEMT-HBT and PIN-HEMT integrated circuits. In each case the performance potential of discrete devices has been maintained throughout the monolithic integration process.