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

A method for patterned deposition of an arbitrary thin film on an arbitrary substrate. A GaAs substrate having a bi-layer structure deposited thereon, the bi-layer structure consisting of a bottom layer of Ge and a top layer of SiN. A photoresist deposited on the top SiN surface of the sample is patterned to form one or more desired patterned features on the sample. The Ge—SiN bi-layer structure on the patterned sample is aniostropically etched so that an undercut is formed in the Ge layer, the SiN forming an overhang over a portion of the GaAs substrate. The remaining photoresist is removed from the sample and the film is deposited on the sample to form a feature on the substrate. The remaining Ge layer is etched away and the SiN layer and film deposited on the SiN layer are lifted from the sample, leaving only the patterned features on the substrate.

Patterned lift-off of thin films deposited at high temperatures

Heterogeneous integration of complementary materials and device technologies is a demonstrated pathway for meeting the demand for next generation RF and mixed-signal circuits and has historically been accomplished via chip or circuit level wafer bonding and through-substrate vias [1] . A more intimate approach is integration at the device level via a micro-assembly technique such as micro-transfer printing [2] , which uses a polymer stamp to pick-and-place individual devices released from a source substrate to a multi-technology target substrate with micron-level alignment accuracy. This approach decouples the device technology from the growth substrate and enables technology agnostic circuit design and application-specific substrate choice. Here we demonstrate micro-transfer printing of GaN high-electron-mobility transistors (HEMTs) released from SiC growth substrates to other technologically relevant substrates such as Si and diamond. We show that there is no significant degradation in DC electrical characteristics after transfer printing, improved thermal performance can be achieved when the devices are transferred to single crystal diamond, and that post-transfer processing, such as interconnect metallization is possible with standard 2D lithographic techniques.

Micro-transfer Printing of GaN HEMTs for Heterogeneous Integration and Flexible RF Circuit Design

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Microstructure of TiAlNiAu ohmic contacts for N-polar GaN/AlGaN HEMTs

Methods for integrating transition metal oxide (TMO) layers into a compound semiconductor device structure via selective oxidation of transition metal nitride (TMN) layers within the structure.

Selective oxidation of transition metal nitride layers within compound semiconductor device structures

Nitride semiconductors offer many unique and beneficial properties for new generation electronic devices [1]. GaN-based HEMTs are contenders for replace existing Si and GaAs devices in high-power RF applications. AlGaN/GaN High Election Mobility Transistors (HEMTs) are devices designed for applications where high-power and high-frequency devices are needed. AlGaN/GaN HEMTs take advantage of a two-dimensional electron gas (2DEG) that forms at the AlGaN/GaN interface to create a layer of highly mobile electrons that are easily modulated by an applied bias. Unfortunately, high-power operating conditions often result in unpredictable and catastrophic device degradation [2]. In our previous ex-situ work, we observed the formation of defects under the drain side edge of the gate during bias. The amount of defects present increased with bias duration and this was related to changes in ID and strain near the AlGaN/GaN interface [3]. However, the formation mechanism of these defects has not been fully investigated as a function of operating time. As such, quantitative analysis on the evolution of defects is needed to further understand device failure mechanisms.

/pdf/in-situ-characterization-of-the-evolution-of-defects-in-418cy6uqxp.pdf

David J. Meyer

Papers

Patterned lift-off of thin films deposited at high temperatures

Micro-transfer Printing of GaN HEMTs for Heterogeneous Integration and Flexible RF Circuit Design

Microstructure of TiAlNiAu ohmic contacts for N-polar GaN/AlGaN HEMTs

Selective oxidation of transition metal nitride layers within compound semiconductor device structures

In-Situ Characterization of the Evolution of Defects in AlGaN\GaN HEMTs in the On-state and Off-state condition