We report on a gate-recessed AlGaN/GaN highelectron mobility transistor (HEMT) on a SiC substrate with a record power-gain cutoff frequency (f max). To achieve this high f max , we combined a low-damage gate-recess technology, scaled device geometry, and recessed source/drain ohmic contacts to simultaneously enable minimum short-channel effects (i.e., high output resistance R ds) and very low parasitic resistances. A 60-nm-gate-length HEMT with recessed AlGaN barrier exhibited excellent R ds of 95.7 Ω • mm, R on of 1.1 ∼ 1.2 Ω • mm, and f max of 300 GHz, with a breakdown voltage of ∼20 V. To the authors' knowledge, the obtained f max is the highest reported to date for any nitride transistor. The accuracy of the f max value is verified by small signal modeling based on carefully extracted S-parameters.

Strained transition layers, which are common for heteroepitaxial growth of functional semiconductors on foreign substrates, include high defect densities that impair heat conduction. Here, we measure the thermal resistances of AlN transition layers for GaN on Si and SiC substrates in the temperature range 300 < T < 550 K using time-domain thermoreflectance. We propose a model for the effective resistance of such transition films, which accounts for the coupled effects of phonon scattering on defects and the two interfaces. The data are consistent with this model using point defects at concentrations near 10 20 cm −3 and transmission coefficients based on the diffuse mismatch model. The data can be also described using lower transmission coefficients and eliminating the defects in the AlN. The data and modeling support the hypothesis that point defect scattering in the AlN film dominates the resistance, but may also be consistent with a high presence of near-interfacial defects in the bounding films.

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GaN high electron mobility transistors (HEMTs) were monolithically integrated with silicon CMOS to create a functional current mirror circuit. The integrated circuit was fabricated on 100 mm diameter modified silicon-on-insulator (SOI) wafers incorporating a resistive (111) silicon handle substrate and a lightly doped (100) silicon device layer. In a CMOS-first process, the CMOS was fabricated using the (100) device layer. Subsequently GaN was grown by plasma molecular beam epitaxy in windows on the (111) handle substrate surface without wire growth despite using gallium-rich growth conditions. Transmission lines fabricated on the GaN buffer/SOI wafer exhibited a microwave loss of less than 0.2 dB/mm up to 35 GHz. Direct current measurements on GaN HEMTs yielded a current density of 1.0 A/mm and transconductance of 270 mS/mm. At 10 GHz and a drain bias of 28 V, 1.25 mm long transistors demonstrated a small signal gain of 10.7 dB and a maximum power added efficiency of 53% with a concomitant power of 5.6 W. The silicon and GaN transistors were interconnected to form high yield test interconnect daisy chains and a monolithic current mirror circuit. The CMOS output drain current controlled the GaN transistor quiescent current and consequently the microwave gain.

A direct growth approach using composite metamorphic buffers was employed for monolithic integration of InP-based high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs) on Ge and Ge-on-insulator (GeOI)/Si substrates using molecular beam epitaxy. GaAs layers nucleated on these substrates and grown to a thickness of 0.5μm were optimized to minimize the nucleation and propagation of antiphase boundaries and threading dislocations, and exhibited an atomic force microscopy rms roughness of ∼9Å and x-ray full width at half maximum of ∼36arcsec. A 1.1μm thick graded InAlAs buffer was used to transition from the GaAs to InP lattice parameters. The density of threading dislocations at the upper interface of this InAlAs buffer was ∼107cm−2 based on cross-sectional transmission electron microscopy analyses. HEMT structures grown metamorphically on GeOI/Si substrates using these buffer layers demonstrated transport properties equivalent to base line structures grown on InP substrates, with room temperature mobility greater than 10000cm2∕Vs. Similarly, double heterojunction bipolar transistors (D-HBTs) grown metamorphically on GeOI/Si substrates and fabricated into large area devices exhibited dc parameters close to reference D-HBTs grown on InP substrates.

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GaN high electron mobility transistor (HEMT) structures have been grown by plasma molecular beam epitaxy on 100 mm diameter ⟨111⟩ silicon substrates. Crack-free films with thicknesses of up to 1.7 μm were deposited without the use of strain-relaxing buffer layers. X-ray measurements indicate high structural uniformity and the Pendellosung oscillations are observed due to the abruptness of the AlGaN/GaN interface. Capacitance-voltage measurements display a sharp pinch-off with a depleted GaN buffer layer and no measurable charge accumulation at the substrate-epi interface. Transmission line measurements on the GaN HEMT buffer and substrate indicate a loss of less than 0.2 dB/mm up to 20 GHz. An average sheet resistance of 443 Ω/sq with a standard deviation of 0.8% and a mobility of 1600 cm2/V s were obtained for an Al0.25Ga0.75N/GaN HEMT. Transistors were fabricated with a current density of 1.2 A/mm and a transconductance of 290 mS/mm which is quite comparable to GaN HEMTs on SiC.