L. E. Rodak
United States Army Research Laboratory
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Featured researches published by L. E. Rodak.
Applied Physics Express | 2013
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
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
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
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
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
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
Paul H. Shen; L. E. Rodak; Chad S. Gallinat; Anand V. Sampath; Michael Wraback
Physica Status Solidi (c) | 2014
Craig Moe; Gregory A. Garrett; James R. Grandusky; Jianfeng Chen; L. E. Rodak; Paul Rotella; Michael Wraback; Leo J. Schowalter
Electronics Letters | 2013
Anand V. Sampath; L. E. Rodak; Yaojia Chen; Q. Zhou; Joe C. Campbell; H. Shen; Michael Wraback
Archive | 2016
Paul H. Shen; L. E. Rodak; Chad S. Gallinat; Anand V. Sampath; Michael Wraback