D.J. Denninghoff

Bio: D.J. Denninghoff is an academic researcher from Wright-Patterson Air Force Base. The author has contributed to research in topics: High-electron-mobility transistor & Short-channel effect. The author has an hindex of 2, co-authored 2 publications receiving 249 citations.

Short-Channel Effect Limitations on High-Frequency Operation of AlGaN/GaN HEMTs for T-Gate Devices

Abstract: AlGaN/GaN high-electron mobility transistors (HEMTs) were fabricated on SiC substrates with epitaxial layers grown by multiple suppliers and methods. Devices with gate lengths varying from 0.50 to 0.09 mum were fabricated on each sample. We demonstrate the impact of varying the gate lengths and show that the unity current gain frequency response (fT) is limited by short-channel effects for all samples measured. We present an empirically based physical model that can predict the expected extrinsic fT for many combinations of gate length and commonly used barrier layer thickness (tbar) on silicon nitride passivated T-gated AlGaN/GaN HEMTs. The result is that even typical high-aspect-ratio (gate length to barrier thickness) devices show device performance limitations due to short-channel effects. We present the design tradeoffs and show the parameter space required to achieve optimal frequency performance for GaN technology. These design rules differ from the traditional GaAs technology by requiring a significantly higher aspect ratio to mitigate the short-channel effects.

Surmounting W-band Scalar Load-Pull Limitations Using the ASM-HEMT Model for Millimeter-Wave GaN HEMT Technology Large-Signal Assessment

Abstract: This paper presents for the first time an accurate ASM-HEMT model for millimeter-wave GaN HEMT technology validated with W-band scalar load-pull and power sweep measurements. The accurate model is used to predict the optimal performance of a GaN HEMT with operating conditions beyond the limitations of the scalar W-band load-pull system. The GaN HEMT measurements exhibits a peak PAE of 35% and the ASMHEMT model predicts a peak PAE of 42%.

Materials Characterization and Device Performance Survey of InAlN/GaN HEMT Layers from Commercial Sources

Abstract: In this work, we compare the most recent efforts to develop device-quality InAlN/GaN HEMT structures from three commercial sources. These structures were grown by MOCVD on SiC substrates and all had the same nominal thickness and mole fraction. Device data from two- and fourfinger HEMTs will be presented for each material source. We will show the trends observed in the dc, small-signal, and load-pull data as a function of the material stoichiometry, and an estimate of the barrier layer bandgap

Scaling of GaN HEMTs and Schottky Diodes for Submillimeter-Wave MMIC Applications

Abstract: In this paper, we report state-of-the-art high frequency performance of GaN-based high electron mobility transistors (HEMTs) and Schottky diodes achieved through innovative device scaling technologies such as vertically scaled enhancement and depletion mode (E/D mode) AlN/GaN/AlGaN double-heterojunction HEMT epitaxial structures, a low-resistance n+-GaN/2DEG ohmic contact regrown by MBE, a manufacturable 20-nm symmetric and asymmetric self-aligned-gate process, and a lateral metal/2DEG Schottky contact. As a result of proportional scaling of intrinsic and parasitic delays, an ultrahigh fT exceeding 450 GHz (with a simultaneous fmax of 440 GHz) and a fmax close to 600 GHz (with a simultaneous fT of 310 GHz) are obtained in deeply scaled GaN HEMTs while maintaining superior Johnson figure of merit. Because of their extremely low on-resistance and high gain at low drain voltages, the devices exhibited excellent noise performance at low power. 501-stage direct-coupled field-effect transistor logic ring oscillator circuits are successfully fabricated with high yield and high uniformity, demonstrating the feasibility of GaN-based E/D-mode integrated circuits with transistors. Furthermore, self-aligned GaN Schottky diodes with a lateral metal/2DEG Schottky contact and a 2DEG/ n+-GaN ohmic contact exhibited RC-limited cutoff frequencies of up to 2.0 THz.

N-polar GaN epitaxy and high electron mobility transistors

Abstract: This paper reviews the progress of N-polar () GaN high frequency electronics that aims at addressing the device scaling challenges faced by GaN high electron mobility transistors (HEMTs) for radio-frequency and mixed-signal applications. Device quality (Al, In, Ga)N materials for N-polar heterostructures are developed using molecular beam epitaxy and metalorganic chemical vapor deposition. The principles of polarization engineering for designing N-polar HEMT structures will be outlined. The performance, scaling behavior and challenges of microwave power devices as well as highly-scaled depletion- and enhancement-mode devices employing advanced technologies including self-aligned processes, n+ (In,Ga)N ohmic contact regrowth and high aspect ratio T-gates will be discussed. Recent research results on integrating N-polar GaN with Si for prospective novel applications will also be summarized.

Barrier-Layer Scaling of InAlN/GaN HEMTs

Abstract: We discuss the characteristics of high-electron mobility transistors with barrier thicknesses between 33 and 3 nm, which are grown on sapphire substrates by metal-organic chemical vapor deposition. The maximum drain current (at VG = 2.0 V) decreased with decreasing barrier thickness due to the gate forward drive limitation and residual surface-depletion effect. Full pinchoff and low leakage are observed. Even with 3-nm ultrathin barrier, the heterostructure and contacts are thermally highly stable (up to 1000degC).

Very high channel conductivity in low-defect AlN/GaN high electron mobility transistor structures

Abstract: Low defect AlN/GaN high electron mobility transistor (HEMT) structures, with very high values of electron mobility (>1800 cm2/V s) and sheet charge density (>3×1013 cm−2), were grown by rf plasma-assisted molecular beam epitaxy (MBE) on sapphire and SiC, resulting in sheet resistivity values down to ∼100 Ω/◻ at room temperature Fabricated 12 μm gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of ∼13 A/mm and a peak transconductance of ∼260 mS/mm Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results of thin-film characterizations and device measurements are presented

Effect of Optical Phonon Scattering on the Performance of GaN Transistors

Abstract: A model based on optical phonon scattering is developed to explain peculiarities in the current drive, transconductance, and high-speed behavior of short-gate-length GaN transistors. The model is able to resolve these peculiarities and provides a simple way to explain transistor behavior in any semiconductor material system in which electron-optical-phonon scattering is strong.