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

A high-performance novel photodetector is demonstrated, which consists of graphene and CH3 NH3 PbI3 perovskite layers. The resulting hybrid photodetector exhibits a dramatically enhanced photo responsivity (180 A/W) and effective quantum efficiency (5× 10(4) %) over a broad bandwidth within the UV and visible ranges.

High-Performance Perovskite–Graphene Hybrid Photodetector

This timely second edition has been substantially expanded to keep students and practicing power conversion engineers ahead of the learning curve in GaN technology advancements. Acknowledging that GaN transistors are not one-to-one replacements for the current MOSFET technology, this book serves as a practical guide for understanding basic GaN transistor construction, characteristics, and applications. Included are discussions on the fundamental physics of these power semiconductors, layout and other circuit design considerations, as well as specific application examples demonstrating design techniques when employing GaN devices.

/pdf/gan-transistors-for-efficient-power-conversion-1vxm76211t.pdf

GaN Transistors for Efficient Power Conversion

Recent advances in ultraviolet photodetectors

Advances in power electronics enable efficient and flexible processing of electric power in the application of renewable energy sources, electric vehicles, adjustable-speed drives, etc. More and more efforts are devoted to better power electronic systems in terms of reliability to ensure high availability, long lifetime, sufficient robustness, low maintenance cost and low cost of energy. However, the reliability predictions are still dominantly according to outdated models and terms, such as MIL-HDBK-217H handbook models, Mean-Time-To-Failure (MTTF), and Mean-Time-Between-Failures (MTBF). A collection of methodologies based on Physics-of-Failure (PoF) approach and mission profile analysis are presented in this paper to perform reliability-oriented design of power electronic systems. The corresponding design procedures and reliability prediction models are provided. Further on, a case study on a 2.3 MW wind power converter is discussed with emphasis on the reliability critical components IGBTs. Different aspects of improving the reliability of the power converter are mapped. Finally, the challenges and opportunities to achieve more reliable power electronic systems are addressed.

Design for reliability of power electronic systems

We report on the optoelectronic properties of Al0.25Ga0.75N/GaN-based ultraviolet (UV) photodetectors for the application as a high current, high gain optical switch. Due to an internal gain mechanism combined with the high conductivity of the two-dimensional electron gas at the heterostructure interface, photocurrents in the milliampere-range were obtained with UV illumination. By employing a mesa structure design with meander geometry very low dark currents below 50 nA up to a bias voltage of 100 V were achieved. Optical switching with an on/off-current-ratio of five orders of magnitude was demonstrated. The response time was determined to be 6 ms and persistent photoconductivity was observed. The photodetector is visible-blind with a cut-off wavelength of 365 nm according to the band gap energy of the GaN absorption layer. A high responsivity with a maximum of 70 A/mW at 312 nm and 100 V bias voltage was demonstrated.

High gain ultraviolet photodetectors based on AlGaN/GaN heterostructures for optical switching

Reliability issues of GaN based high voltage power devices

Operation of AlGaN/GaN HFETs in space was simulated by irradiation with protons and heavy ions at 68 MeV and 2MeV and fluences up to 1013 cm-2. Before and after irradiation dc and pulsed I-V characteristics of the AlGaN HFET devices were measured. A thick GaN reference layer was characterized by photoluminescence, X-ray diffraction and Hall measurements before and after irradiation. The results of the material characterization correlate with the device results. High energy (68 MeV) irradiation has no impact on device performance while high fluences at lower energy (2 MeV) result in degradation

Proton and Heavy Ion Irradiation Effects on AlGaN/GaN HFET Devices

Comparative study of AlGaN/GaN HEMTs robustness versus buffer design variations by applying Electroluminescence and electrical measurements

DC-Step-Stress-Tests of GaN HEMTs have been performed on wafers with and without GaN-cap. The tests consist of a step ramping of drain-source voltage V DS by 5V every two hours at off-state. The irreversible evolution of leakage current starting at a certain drain voltage has been taken as a criterion for the onset of device degradation. It has been stated that there is a stability limit for V DS depending on the epitaxial design. It has been found that wafers with GaN cap show much higher critical voltages as compared to non-capped epitaxial designs. Electroluminescence measurements have been performed to localize defects after DC-Step-Stress-Tests up to 80V for wafer without GaN cap and 120V for wafer with GaN cap.

Richard Lossy

Papers

High gain ultraviolet photodetectors based on AlGaN/GaN heterostructures for optical switching

Reliability issues of GaN based high voltage power devices

Proton and Heavy Ion Irradiation Effects on AlGaN/GaN HFET Devices

Comparative study of AlGaN/GaN HEMTs robustness versus buffer design variations by applying Electroluminescence and electrical measurements

Influence of GaN cap on robustness of AlGaN/GaN HEMTs