Showing papers by "Stacia Keller published in 2023"

Record RF Power Performance at 94 GHz From Millimeter-Wave N-Polar GaN-on-Sapphire Deep-Recess HEMTs

Abstract: In this article, N-polar GaN-on-sapphire deep-recess metal–insulator–semiconductor (MIS)-high-electron-mobility transistors (HEMTs) with a breakthrough performance at ${W}$ -band are presented. Compared with prior N-polar GaN MIS-HEMTs, a thin GaN cap layer and atomic layer deposition (ALD) ruthenium (Ru) gate metallization were used along with high-quality GaN-on-sapphire epitaxy from Transphorm Inc. Before SiN passivation, 94 GHz large signal load–pull shows that the transistor obtains a record-high 9.65 dB linear transducer gain and demonstrated 42% power-added efficiency (PAE) with associated 4.4 W/mm of output power density at 12 V drain bias. By biasing the drain at 8 V, the device shows an even higher PAE of 44% with an associated 2.6 W/mm of output power density. After SiN passivation, the fabricated N-polar GaN-on-sapphire HEMTs show a high PAE of 40.2% with an associated 4.85 W/mm of output power density. Furthermore, a very high output power density of 5.83 W/mm with 38.5% PAE is demonstrated at a 14 V drain bias. This power performance shows significant efficiency improvement over previous N-polar GaN-on-SiC and demonstrates a combined efficiency and power density beyond what has been reported for Ga-polar devices, in spite of the low-thermal-conductivity sapphire substrate. This shows that N-polar GaN-on-sapphire technology is an attractive candidate for millimeter-wave power amplifier applications with simultaneous high efficiency and power density.

First Demonstration of Four-Finger N-polar GaN HEMT Exhibiting Record 712-mW Output Power With 31.7% PAE at 94 GHz

Abstract: In this letter, the first four-finger (4 $\times25\,\,\mu \text{m}$ ) N-polar GaN high-electron-mobility transistor (HEMT) with an outstanding large signal performance of 712-mW (7.1 W/mm) with 31.7% power-added efficiency (PAE) is demonstrated at 94 GHz. To the best of our knowledge, this is a record output power from a single device cell in any semiconductor technology at $W$ -band. An equivalent two-finger device (2 $\times37.5\,\,\mu \text{m}$ ) exhibits 6.9 W/mm with 30.6% PAE, demonstrating no degradation of either power density or efficiency with increased number of fingers and gate width. Additionally, the design considerations for multifinger devices are presented with the simulations of airbridge parasitics using COMSOL Multiphysics and Ansys high-frequency structure simulator (HFSS), along with the exploration of the design space in number and width of fingers for the best gain performance for >1 W. Simultaneous high-output power with high efficiency (>30%) shows the great potential of multifinger N-polar GaN HEMT technology for the state-of-the-art $W$ -band power amplifiers.

GaN/AlGaN Superlattice Based E-Mode Hole Channel FinFET With Schottky Gate

Abstract: In this work, we report on a GaN/AlGaN superlattice based normally-off hole channel FinFET devices. A combination of Schottky gate and 60 nm wide fins led to enhancement mode operation. The device had an on-current of 13 mA/mm and an on-resistance of $300~\Omega $ .mm. simultaneously, a large Ion/Ioff > 107 and a current modulation of more than two orders of magnitude in the enhancement mode regime was also achieved.

N-Polar Indium Nitride Quantum Dashes and Quantum Wire-like Structures: MOCVD Growth and Characterization

Abstract: The electrical properties of InN give it potential for applications in III-nitride electronic devices, and the use of lower-dimensional epitaxial structures could mitigate issues with the high lattice mismatch of InN to GaN (10%). N-polar MOCVD growth of InN was performed to explore the growth parameter space of the horizontal one-dimensional InN quantum wire-like structures on miscut substrates. The InN growth temperature, InN thickness, and NH3 flow during growth were varied to determine optimal quantum wire segment growth conditions. Quantum wire segment formation was observed through AFM images for N-polar InN samples with a low growth temperature of 540 °C and 1–2 nm of InN. Below 1 nm of InN, quantum dashes formed, and 2-D layers were formed above 2 nm of InN. One-dimensional anisotropy of the electrical conduction of N-polar InN wire-like samples was observed through TLM measurements. The sheet resistances of wire-like samples varied from 10–26 kΩ/□ in the longitudinal direction of the wire segments. The high sheet resistances were attributed to the close proximity of the treading dislocations at the InN/GaN interface and might be lowered by reducing the lattice mismatch of InN wire-like structures with the substrate using high lattice constant base layers such as relaxed InGaN.

Properties of high to ultrahigh Si-doped GaN grown at 550 °C by flow modulated metalorganic chemical vapor deposition

Abstract: The heterogeneous integration of III-nitride materials with other semiconductor systems for electronic devices is attractive because it combines the excellent electrical properties of the III-nitrides with other device platforms. Pursuing integration through metalorganic chemical vapor deposition (MOCVD) is desirable because of the scalability of the technique, but the high temperatures required for the MOCVD growth of III-nitrides (>1000 °C) are incompatible with direct heteroepitaxy on some semiconductor systems and fabricated wafers. Thus, the MOCVD growth temperature of III-nitride films must be lowered to combine them with other systems. In this work, 16 nm-thick Si:GaN films were grown by MOCVD at 550 °C using a flow modulation epitaxy scheme. By optimizing the disilane flow conditions, electron concentrations up to 5.9 × 1019 cm−3 were achieved, resulting in sheet resistances as low as 1070 Ω/□. Film mobilities ranged from 34 to 119 cm2 V−1 s−1. These results are promising for III-nitride integration and expand device design and process options for III-nitride-based electronic devices.