Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

/pdf/the-2018-gan-power-electronics-roadmap-2iunv619fh.pdf

The 2018 GaN power electronics roadmap

J. Y. Tsao,* S. Chowdhury, M. A. Hollis,* D. Jena, N. M. Johnson, K. A. Jones, R. J. Kaplar,* S. Rajan, C. G. Van de Walle, E. Bellotti, C. L. Chua, R. Collazo, M. E. Coltrin, J. A. Cooper, K. R. Evans, S. Graham, T. A. Grotjohn, E. R. Heller, M. Higashiwaki, M. S. Islam, P. W. Juodawlkis, M. A. Khan, A. D. Koehler, J. H. Leach, U. K. Mishra, R. J. Nemanich, R. C. N. Pilawa-Podgurski, J. B. Shealy, Z. Sitar, M. J. Tadjer, A. F. Witulski, M. Wraback, and J. A. Simmons

/pdf/ultrawide-bandgap-semiconductors-research-opportunities-and-49ev1zu2ym.pdf

Ultrawide-Bandgap Semiconductors: Research Opportunities and Challenges

This letter reports high-voltage GaN field-effect transistors fabricated on Si substrates. A halide-based plasma treatment was performed to enable normally off operation. Atomic layer deposition of Al2O3 gate insulator was adopted to reduce the gate leakage current. Incorporation of multiple field plates, with one field plate connected to the gate electrode and two field plates connected to the source electrode successfully enabled a high breakdown voltage of 1200 V and low dynamic on-resistance at high-voltage operation.

1200-V Normally Off GaN-on-Si Field-Effect Transistors With Low Dynamic on -Resistance

We performed hybrid functional calculations of native point defects and dangling bonds (DBs) in α-Al2O3 to aid in the identification of charge-trap and fixed-charge centers in Al2O3/III-V metal-oxide-semiconductor structures. We find that Al vacancies (VAl) are deep acceptors with transition levels less than 2.6 eV above the valence band, whereas Al interstitials (Ali) are deep donors with transition levels within ∼2 eV of the conduction band. Oxygen vacancies (VO) introduce donor levels near midgap and an acceptor level at ∼1 eV below the conduction band, while oxygen interstitials (Oi) are deep acceptors, with a transition level near the mid gap. Taking into account the band offset between α-Al2O3 and III-V semiconductors, our results indicate that VO and Al DBs act as charge traps (possibly causing carrier leakage), while VAl, Ali, Oi, and O DBs act as fixed-charge centers in α-Al2O3/III-V metal-oxide-semiconductor structures.

https://www.mrl.ucsb.edu/~vandewalle/publications/JAP113,044501(2013)-Choi-Al2O3-dielectric.pdf

Native point defects and dangling bonds in α-Al2O3

Structural and XPS characterization of ALD Al2O3 coated porous silicon

Solid-state devices including a layer of a superconductor material epitaxially grown on a crystalline high thermal conductivity substrate, the superconductor material being one of TiNx, ZrNx, HfNx, VNx, NbNx, TaNx, MoNx, WNx, or alloys thereof, and one or more layers of a semiconducting or insulating or metallic material epitaxially grown on the layer of superconductor material, the semiconducting or insulating material being one of a Group III N material or alloys thereof or a Group 4b N material or SiC or ScN or alloys thereof.

Expitaxial semiconductor/superconductor heterostructures

Solid-state quantum acoustodynamic (QAD) systems provide a compact platform for quantum information storage and processing by coupling acoustic phonon sources with superconducting or spin qubits. The multi-mode composite high-overtone bulk acoustic wave resonator (HBAR) is a popular phonon source well suited for QAD. However, scattering from defects, grain boundaries, and interfacial/surface roughness in the composite transducer severely limits the phonon relaxation time in sputter-deposited devices. Here, we grow an epitaxial-HBAR, consisting of a metallic NbN bottom electrode and a piezoelectric GaN film on a SiC substrate. The acoustic impedance-matched epi-HBAR has a power injection efficiency > 99% from transducer to phonon cavity. The smooth interfaces and low defect density reduce phonon losses, yielding fxQ products and phonon lifetimes up to 1.36 x 10^17 Hz and 500 microseconds respectively. The GaN/NbN/SiC epi-HBAR is an electrically actuated, multi-mode phonon source that can be directly interfaced with NbN-based superconducting qubits or SiC-based spin qubits.

/pdf/epitaxial-bulk-acoustic-wave-resonators-as-highly-coherent-5aw2tz5kmw.pdf

Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamics

The ultra-thin barrier AlN/GaN high electron mobility transistor (HEMT) has recently demonstrated over 2 A/mm dc drain current and an appreciable 480 mS/mm transconductance [1] owing to the high mobility and enhanced polarization effects of the binary AlN/GaN heterointerface [2] Due to a large lattice mismatch the strained AlN barrier is limited in thickness to less than 7 nm Therefore, in order to mitigate high gate currents in an AlN/GaN HEMT a gate insulator is essential Atomic Layer Deposited (ALD) oxides offer a means to accurately control oxide thickness down to the angstrom scale while simultaneously achieving a dense, high dielectric constant oxide In this work we have grown, fabricated, and analyzed dc and RF characteristics of an ALD Al 2 O 3 gate-insulated, 35 nm thick barrier AlN/GaN HEMT In particular, small signal modeling was performed using standard ColdFET and on-state techniques which allow the extraction of bonding pad and parasitic element influences on RF operation The extraction of these elements becomes even more necessary for either of two conditions: 1) the electron-beam defined sub-micron gate length reduces gate capacitance and causes the bonding pad capacitance to dominate RF operation or 2) the presence of high-k Al 2 O 3 in the access and inter-pad regions of the device further increases parasitic and pad-to-pad capacitance Both conditions occur for our devices

Modeling the small signal characteristics of an ALD Al 2 O 3 insulated-gate AlN/GaN high electron mobility transistor

This work presents detailed characterization and analysis of recently reported magnetoelastic high overtone bulk acoustic resonators (ME-HBARs), which are multi-mode RF-acoustic (phononic) resonators operating in the S-Band. These unique devices are fabricated by micro-transfer printing (MTP) piezoelectric GaN transducers onto a ferrimagnetic yttrium iron garnet (YIG) substrate. The YIG substrate also supports spin waves (magnons) when biased with an external magnetic field. The resulting phonon-magnon hybridization can be used to suppress or tune the acoustic modes of the ME-HBAR. The experiment spans 66 distinct acoustic resonance modes from 2.4 GHz to 3 GHz, each of which can be suppressed or tuned as much as ± 6 MHz, with a bias magnetic field ≤ 0.21 T. The experimental ME-HBAR data show good agreement with analytical modeling of the magnetoelastic hybridization in YIG. Such ME-HBARs can be used as dynamically tunable or switchable resonators, oscillators, comb filters, or frequency selective limiters in RF signal processing sub-components. By integrating incompatible materials (YIG, epitaxial GaN), and disparate functionalities (spin waves, acoustic waves), into one hybrid multi-domain system, this work also demonstrates the power and broad scope of the MTP technique.

Dynamic mode suppression and frequency tuning in S-band GaN/YIG magnetoelastic HBARs.

https://apps.dtic.mil/sti/pdfs/AD1075623.pdf

David J. Meyer

Papers

Expitaxial semiconductor/superconductor heterostructures

Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamics

Modeling the small signal characteristics of an ALD Al 2 O 3 insulated-gate AlN/GaN high electron mobility transistor

Dynamic mode suppression and frequency tuning in S-band GaN/YIG magnetoelastic HBARs.

Epitaxial Transition Metal Nitride/111 N Alloys for RF Devices