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 nitride semiconductor light-emitting device has an active layer of a single-quantum well structure or multi-quantum well made of a nitride semiconductor containing indium and gallium. A first p-type clad layer made of a p-type nitride semiconductor containing aluminum and gallium is provided in contact with one surface of the active layer. A second p-type clad layer made of a p-type nitride semiconductor containing aluminum and gallium is provided on the first p-type clad layer. The second p-type clad layer has a larger band gap than that of the first p-type clad layer. An n-type semiconductor layer is provided in contact with the other surface of the active layer.

Nitride semiconductor light emitting device

By alloying GaN with AlN the emission of AlGaN light-emitting diodes can be tuned to cover almost the entire ultraviolet spectral range (210–400 nm), making ultraviolet light-emitting diodes perfectly suited to applications across a wide number of fields, whether biological, environmental, industrial or medical. However, technical developments notwithstanding, deep-ultraviolet light-emitting diodes still exhibit relatively low external quantum efficiencies because of properties intrinsic to aluminium-rich group III nitride materials. Here, we review recent progress in the development of AlGaN-based deep-ultraviolet light-emitting devices. We also describe the key obstacles to enhancing their efficiency and how to improve their performance in terms of defect density, carrier-injection efficiency, light extraction efficiency and heat dissipation. This Review covers recent progress in AlGaN-based deep-ultraviolet light-emitting devices. The key technologies of how to improve their performance, carrier-injection efficiency, light extraction efficiency and heat dissipation are discussed.

The emergence and prospects of deep-ultraviolet light-emitting diode technologies

The invention provides methods and devices for fabricating printable semiconductor elements and assembling printable semiconductor elements onto substrate surfaces. Methods, devices and device components of the present invention are capable of generating a wide range of flexible electronic and optoelectronic devices and arrays of devices on substrates comprising polymeric materials. The present invention also provides stretchable semiconductor structures and stretchable electronic devices capable of good performance in stretched configurations.

Methods and devices for fabricating and assembling printable semiconductor elements

Provided are optical devices and systems fabricated, at least in part, via printing-based assembly and integration of device components. In specific embodiments the present invention provides light emitting systems, light collecting systems, light sensing systems and photovoltaic systems comprising printable semiconductor elements, including large area, high performance macroelectronic devices. Optical systems of the present invention comprise semiconductor elements assembled, organized and/or integrated with other device components via printing techniques that exhibit performance characteristics and functionality comparable to single crystalline semiconductor based devices fabricated using conventional high temperature processing methods. Optical systems of the present invention have device geometries and configurations, such as form factors, component densities, and component positions, accessed by printing that provide a range of useful device functionalities. Optical systems of the present invention include devices and device arrays exhibiting a range of useful physical and mechanical properties including flexibility, shapeability, conformability and stretchablity.

Optical systems fabricated by printing-based assembly

In this letter, the achievement of over 60 mW output power from pseudomorphic ultraviolet light-emitting diodes in continuous wave operation is reported. Die thinning and encapsulation improved the photon extraction efficiency to over 15%. Improved thermal management and a high characteristic temperature resulted in a low thermal rolloff up to 300 mA injection current with an output power of 67 mW, an external quantum efficiency (EQE) of 4.9%, and a wall plug efficiency (WPE) of 2.5% for a single-chip device emitting at 271 nm in continuous wave operation.

https://iopscience.iop.org/article/10.7567/APEX.6.032101/pdf

270 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Over 60 mW Continuous Wave Output Power

This letter reports on the improved performance of a pseudomorphic ultraviolet light-emitting diode (LED) At 100 mA input current, 92 mW of quasi-CW output power was measured in a calibrated integrating sphere The addition of a heat sink, required for CW and higher power operation, introduced a numerical aperture of 086, and 72 mW was measured in pulsed mode at 17 A, indicating that the total output power exceeds 100 mW when corrected by the coupling factor The high characteristic temperature of 983 K was instrumental in achieving these record output powers for an LED with wavelength shorter than 265 nm

https://iopscience.iop.org/article/10.1143/APEX.4.082101/pdf

High Output Power from 260 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Improved Thermal Performance

A light-emitting element ( 24 ) is disclosed. A light emitting diode (LED) includes a sapphire substrate ( 26 ) having front and back sides ( 33, 35 ), and a plurality of semiconductor layers ( 28, 30, 32 ) deposited on the front side ( 33 ) of the sapphire substrate ( 26 ). The semiconductor layers ( 28, 30, 32 ) define a light-emitting structure that emits light responsive to an electrical input. A metallization stack ( 40 ) includes an adhesion layer ( 34 ) deposited on the back side ( 35 ) of the sapphire substrate ( 26 ), and a solderable layer ( 38 ) connected to the adhesion layer ( 34 ) such that the solderable layer ( 38 ) is secured to the sapphire substrate ( 26 ) by the adhesion layer ( 34 ). A support structure ( 42 ) is provided on which the LED is disposed. A solder bond ( 44 ) is arranged between the LED and the support structure ( 42 ). The solder bond ( 44 ) secures the LED to the support structure ( 42 ).

GaN LED with solderable backside metal

High quality bulk aluminum nitride substrates were used to obtain pseudomorphic AlxGa1-xN layers with low dislocation density, smooth surfaces, and high conductivity. These layers were fabricated into mid-ultraviolet light emitting diodes with peak wavelengths in the range of 240–260 nm. The low dislocation density of the pseudomorphic quantum wells resulted in improved performance over previously published data. The output powers of the on-wafer measurements were greater than 5 mW in continuous wave operation, and 16 mW in pulsed operation. This was achieved utilizing single die (with an active area of 1×10-3 cm2).

https://iopscience.iop.org/article/10.1143/APEX.3.072103/pdf

Properties of Mid-Ultraviolet Light Emitting Diodes Fabricated from Pseudomorphic Layers on Bulk Aluminum Nitride Substrates

Semiconductor structures are fabricated to include strained epitaxial layers exceeding a predicted critical thickness thereof.

Shawn R. Gibb

Papers

270 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Over 60 mW Continuous Wave Output Power

High Output Power from 260 nm Pseudomorphic Ultraviolet Light-Emitting Diodes with Improved Thermal Performance

GaN LED with solderable backside metal

Properties of Mid-Ultraviolet Light Emitting Diodes Fabricated from Pseudomorphic Layers on Bulk Aluminum Nitride Substrates

Thick pseudomorphic nitride epitaxial layers