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Dive into the research topics where L. E. Rodak is active.

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Featured researches published by L. E. Rodak.


Applied Physics Express | 2013

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

James R. Grandusky; Jianfeng Chen; Shawn R. Gibb; Mark C. Mendrick; Craig Moe; L. E. Rodak; Gregory A. Garrett; Michael Wraback; Leo J. Schowalter

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.


Semiconductor Science and Technology | 2014

High power AlGaN ultraviolet light emitters

Max Shatalov; Wenhong Sun; Rakesh Jain; A. Lunev; X. Hu; Alex Dobrinsky; Yuri Bilenko; Jinwei Yang; Gregory A. Garrett; L. E. Rodak; Michael Wraback; M. S. Shur; Remis Gaska

We present the analysis of the external quantum efficiency in AlGaN deep ultraviolet (DUV) light-emitting diodes (LEDs) on sapphire substrates and discuss factors affecting the output power of DUV LEDs. Performance of the LED is related to optimization of the device structure design and improvements of the epitaxial material quality.


Applied Physics Letters | 2013

Solar-blind AlxGa1−xN/AlN/SiC photodiodes with a polarization-induced electron filter

L. E. Rodak; Anand V. Sampath; Chad S. Gallinat; Yaojia Chen; Qiugui Zhou; Joe C. Campbell; H. Shen; Michael Wraback

Heterogeneous n-III-nitride/i-p silicon carbide (SiC) photodetectors have been demonstrated that enable the tailoring of the spectral response in the solar blind region below 280 nm. The negative polarization induced charge at the aluminum gallium nitride (AlxGa1−xN)/aluminum nitride (AlN) interface in conjunction with the positive polarization charge at the AlN/SiC interface creates a large barrier to carrier transport across the interface that results in the selective collection of electrons photoexcited to the Γ and L valleys of SiC while blocking the transport of electrons generated in the M valley. In addition, the AlxGa1−xN alloys act as transparent windows that enhance the collection of carriers generated by high energy photons in the fully depleted SiC absorption regions. These two factors combine to create a peak external quantum efficiency of 76% at 242 nm, along with a strong suppression of the long-wavelength response from 260 nm to 380 nm.Heterogeneous n-III-nitride/i-p silicon carbide (SiC) photodetectors have been demonstrated that enable the tailoring of the spectral response in the solar blind region below 280 nm. The negative polarization induced charge at the aluminum gallium nitride (AlxGa1−xN)/aluminum nitride (AlN) interface in conjunction with the positive polarization charge at the AlN/SiC interface creates a large barrier to carrier transport across the interface that results in the selective collection of electrons photoexcited to the Γ and L valleys of SiC while blocking the transport of electrons generated in the M valley. In addition, the AlxGa1−xN alloys act as transparent windows that enhance the collection of carriers generated by high energy photons in the fully depleted SiC absorption regions. These two factors combine to create a peak external quantum efficiency of 76% at 242 nm, along with a strong suppression of the long-wavelength response from 260 nm to 380 nm.


Applied Physics Letters | 2012

Enhanced THz emission from c-plane InxGa1−xN due to piezoelectric field-induced electron transport

Nathaniel Woodward; Chad S. Gallinat; L. E. Rodak; Grace D. Metcalfe; Hongen Shen; Michael Wraback

Enhanced terahertz emission from coherently strained InxGa1−xN epilayers on GaN is observed, which exceeds or is comparable to bulk InAs emission at pump wavelengths of 400 nm or 800 nm, respectively. The inverted terahertz waveform from the InxGa1−xN/GaN heterostructure indicates that the dominant terahertz generation mechanism is electron acceleration toward the InxGa1−xN surface in an internal electric field primarily associated with piezoelectric polarization charge at the heterointerface, rather than diffusive transport away from the surface typically observed in bulk semiconductors. The persistence of the inverted waveform for 266 nm excitation provides evidence of ultrafast electron relaxation via LO phonon emission.


device research conference | 2014

Enhancing the deep ultraviolet response of 4H-silicon carbide-based photodiodes between 210 nm and 255 nm

L. E. Rodak; Anand V. Sampath; Yaojia Chen; Q. Zhou; Joe C. Campbell; H. Shen; Michael Wraback

This work demonstrates two novel 4H-SiC-based photodiode structures that enhance the response from ~200 nm to 260 nm by increasing the absorption of DUV photons within the high-electric-field depletion region and more efficiently collecting photo-generated carriers through drift as opposed to diffusion, despite the presence of surface recombination. In particular, the two devices discussed in this work have replaced the heavily doped, top-illuminated, n+-layer of conventional p-n--n+ diodes by a semi-transparent metal contact to create a p-n--metal based device and by an n-type, wider bandgap AlGaN layer to create a heterojunction 4H-SiC/AlGaN p-n--n+ based device.


conference on lasers and electro optics | 2013

Pseudomorphic Mid-ultraviolet light-emitting diodes for water purification

Craig Moe; Jianfeng Jeff Chen; James R. Grandusky; Mark C. Mendrick; Rajul V. Randive; L. E. Rodak; Anand V. Sampath; Michael Wraback; Leo J. Schowalter

UVC light output of 66 mW at 300 mA CW has been achieved from LEDs on AlN substrates with extensive photon extraction. Proper vessel design allows for efficient irradiation of a water sample for purification.


Archive | 2014

Variable range photodetector and method thereof

Paul H. Shen; L. E. Rodak; Chad S. Gallinat; Anand V. Sampath; Michael Wraback


Physica Status Solidi (c) | 2014

Correlation between optical and electrical performance of mid‐ultraviolet light‐emitting diodes on AlN substrates

Craig Moe; Gregory A. Garrett; James R. Grandusky; Jianfeng Chen; L. E. Rodak; Paul Rotella; Michael Wraback; Leo J. Schowalter


Electronics Letters | 2013

High quantum efficiency deep ultraviolet 4HSiC photodetectors

Anand V. Sampath; L. E. Rodak; Yaojia Chen; Q. Zhou; Joe C. Campbell; H. Shen; Michael Wraback


Archive | 2016

VARIABLE RANGE PHOTODETECTOR WITH ENHANCED HIGH PHOTON ENERGY RESPONSE AND METHOD THEREOF

Paul H. Shen; L. E. Rodak; Chad S. Gallinat; Anand V. Sampath; Michael Wraback

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Yaojia Chen

University of Virginia

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Q. Zhou

University of Virginia

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James R. Grandusky

State University of New York System

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Leo J. Schowalter

Rensselaer Polytechnic Institute

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James S. Speck

University of California

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A. Lunev

University of South Carolina

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Jinwei Yang

University of South Carolina

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Jordan R. Lang

University of California

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