M. Chmielowska

Power Performance of AlGaN/GaN High-Electron-Mobility Transistors on (110) Silicon Substrate at 40 GHz

This letter reports the first millimeter-wave power demonstration of AlGaN/GaN high-electron-mobility transistors grown on a (110) silicon substrate. Owing to an AlN/AlGaN stress-mitigating stack and in spite of the twofold surface symmetry of Si (110), it is possible to obtain crack-free GaN layers for the fabrication of millimeter-wave power devices with high performance. The device exhibits a maximum dc drain current density of 1.55 A/mm at VGS = 0 V with an extrinsic transconductance of 476 mS/mm. An extrinsic current gain cutoff frequency of 81 GHz and a maximum oscillation frequency of 106 GHz are deduced from Sij parameters. At 40 GHz, an output power density of 3.3 W/mm associated with a power-added efficiency of 20.1% and a linear power gain of 10.6 dB is obtained.

RF Performance of AlGaN/GaN High-Electron-Mobility Transistors Grown on Silicon (110)

We report the first microwave performance for AlGaN/GaN HEMT structures grown by molecular beam epitaxy on Si(110) high-resistivity substrates. Transistors were fabricated with gate lengths of 50, 75, and 100 nm, achieving short-circuit current cutoff frequencies as high as fT = 70 GHz and maximum oscillation frequencies of fMAX(U) = 93 GHz. Because complementary metal–oxide–semiconductor (CMOS) technology is compatible with (110) substrates, this demonstration establishes a foundation for the future integration of GaN devices into mainstream CMOS on a common Si(110) platform.

Assessment of transistors based on GaN on silicon substrate in view of integration with silicon technology

In this work, AlGaN/GaN high electron mobility transistors on (1u20090u20090) and (1u20091u20090) oriented silicon substrates are investigated in view of monolithic integration with silicon MOSFETs for making more compact microwave power electronics. Epilayers are grown by molecular beam epitaxy on highly resistive substrates. It was shown that a better crystal quality as well as higher low-field electron mobility are obtained on the (1u20091u20090) orientation. Sub-micron gate length devices are then processed to estimate the millimeter-wave and microwave power performances of this new generation of devices. Load-pull measurements are performed from 4xa0GHz up to 40xa0GHz. Optimizations for the best power-added efficiency or for maximum output power density show the great potential of the Si(1u20091u20090) substrate for GaN-based power devices. At 18xa0GHz, these two different optimizations lead to a saturated output power density and an associated power-added efficiency of 2.4xa0W mm−1–40% and 3.76xa0W mm−1–33%, respectively. At 40xa0GHz, a record saturated output power density of 3.3xa0W mm−1xa0is achieved with an associated power-added efficiency of 20.1% and a linear power gain of 10.6xa0dB. In comparison, devices on Si(1u20090u20090) show less attractive performance due to a lower material quality with an output power density of 2.9xa0W mm−1, an associated power-added efficiency of 20.4% and a linear power gain of 7.5xa0dB at 10xa0GHz.

Optimization of

In this paper, we propose to optimize Al0.29Ga0.71N/GaN heterostructures on silicon substrate to obtain high electron mobility transistors featuring high-power/frequency performances. The polarization electric fields are engineered by varying the layer thicknesses of the cap and the barrier, and by changing the type of buffer (GaN or AlGaN). The aim of this paper is to find the best tradeoff between the active layer thickness reduction and the achievement of a reasonable drain current to satisfy the requirements for high performances. The optimum heterostructure device presents an output power density of 1.5 W/mm at 40 GHz, among the best reported on silicon substrate.

{\rm Al}_{0.29}{\rm Ga}_{0.71}{\rm N}/{\rm GaN}

We report on measurements of radiation transmission in the 0.220–0.325 THz frequency range through GaN quantum wells grown on sapphire substrates at nitrogen and room temperatures. Significant enhancement of the transmitted beam intensity with applied voltage is found at nitrogen temperature. This effect is explained by changes in the mobility of two-dimensional electrons under electric bias. We have clarified which physical mechanism modifies the electron mobility and we suggest that the effect of voltage-controlled sub-terahertz transmission can be used for the development of electro-optic modulators operating in the sub-THz frequency range.

High Electron Mobility Heterostructures for High-Power/Frequency Performances

The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Idsxa0>xa01 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

Voltage-controlled sub-terahertz radiation transmission through GaN quantum well structure

The aim of this paper is to optimize the epitaxial layer structure of an AlGaN/GaN high electron mobility transistor (HEMT) for high power density at high frequency. The idea is to play on the polarization engineering with the different layers of the epitaxial stack. The influence of the cap and barrier layer thicknesses, the aluminum content in the barrier and the insertion of an AlGaN buffer layer are studied through the electron gas density, electron mobility and sheet resistance. This permits to find out the best trade-off in order to satisfy the requirements for high performances.

Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor

Emission of terahertz (THz) radiations from interdigitated GaN quantum-wells structures under DC-bias has been measured at room temperature. This measurements has been performed by a 4K Si-Bolometer associated with a Fourier Transform Spectrometer. Using an analytical model, we have shown that the observed peak at approximately 3 THz due to 2D ungated plasma-waves oscillations in the quantum well, is emitted by the metallic contacts of our device acting as antennas.

Polarization Engineering of Al(Ga)N/GaN HEMT Structures for Microwave High Power Applications

We report on measurements of radiation transmission in the 0.220-0.325 THz and 0.75-1.1 THz frequency ranges through GaN quantum wells grown on sapphire substrates at nitrogen and room temperatures. Significant enhancement of the transmitted beam intensity with applied voltage is found at nitrogen temperature. This effect is explained by changes in the mobility of two-dimensional electrons under electric bias. We have clarified which physical mechanism modifies the electron mobility and we suggest that the effect of voltage-controlled sub-terahertz transmission can be used for the development of electro-optic modulators operating in the sub-THz frequency range.