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51.  
Ga<sub>2</sub>O<sub>3</sub> Metal-oxide-semiconductor Field Effect Transistors on Sapphire Substrate by MOCVD
Ga2O3 Metal-oxide-semiconductor Field Effect Transistors on Sapphire Substrate by MOCVD
Ji-Hyeon Park, Ryan McClintock and Manijeh Razeghi
Semiconductor Science and Technology, Volume 34, Number 8-- June 26, 2019
Si-doped gallium oxide (Ga2O3) thin films were grown on a c-plane sapphire substrate by metalorganic chemical vapor deposition (MOCVD) and fabricated into metal oxide semiconductor field effect transistors (MOSFETs). The Ga2O3 MOSFETs exhibited effective gate modulation of the drain current with a complete channel pinch-off for VG < −25 V, and the three-terminal off-state breakdown voltage was 390 V. The device shows a very low gate leakage current (~50 pA/mm), which led to a high on/off ratio of ~108. These transistor characteristics were stable from room temperature to 250 °C reprint
 
52.  
AlGaN/AlN MOVPE heteroepitaxy: pulsed co-doping SiH4 and TMIn
AlGaN/AlN MOVPE heteroepitaxy: pulsed co-doping SiH4 and TMIn
Ilkay Demir, Yusuf Koçak, A. Emre Kasapoğlu, Manijeh Razeghi, Emre Gür and Sezai Elagoz
Semicond. Sci. Technol. 34 075028-- June 24, 2019
We report a new growth approach pulsed co-doping growth of AlxGa1−xN (x > 0.5) epilayers on AlN/Al2O3 templates by metal organic vapor phase epitaxy (MOVPE). Using this approach SiH4 (silane) and TMIn (trimethylindium) supplied to the growth chamber alternately and pulsed during the growth of AlGaN epilayers. Structural and morphological quality of AlGaN epilayers were investigated by high resolution x-ray diffraction (HR-XRD), atomic force microscopy (AFM), Raman spectroscopy, and scanning electron microscopy (SEM) techniques. It has shown that higher crystalline quality with low full width at half maximum (FWHM) and smoother surface morphology with reduced hexagonal hillock density has been obtained by the pulsed co-doping growth approach. Volcano like hillock structures has been confirmed by Raman mapping. reprint
 
53.  
Room temperature terahertz semiconductor frequency comb
Room temperature terahertz semiconductor frequency comb
Quanyong Lu, Feihu Wang, Donghai Wu, Steven Slivken & Manijeh Razeghi
Nature Communications 10, 2403-- June 3, 2019
A terahertz (THz) frequency comb capable of high-resolution measurement will significantly advance THz technology application in spectroscopy, metrology and sensing. The recently developed cryogenic-cooled THz quantum cascade laser (QCL) comb has exhibited great potentials with high power and broadband spectrum. Here, we report a room temperature THz harmonic frequency comb in 2.2 to 3.3 THz based on difference-frequency generation from a mid-IR QCL. The THz comb is intracavity generated via down-converting a mid-IR comb with an integrated mid-IR single mode based on distributed-feedback grating without using external optical elements. The grating Bragg wavelength is largely detuned from the gain peak to suppress the grating dispersion and support the comb operation in the high gain spectral range. Multiheterodyne spectroscopy with multiple equally spaced lines by beating it with a reference Fabry-Pérot comb confirms the THz comb operation. This type of THz comb will find applications to room temperature chip-based THz spectroscopy. reprint
 
54.  
Investigation of surface leakage reduction for small pitch shortwave infrared photodetectors
Investigation of surface leakage reduction for small pitch shortwave infrared photodetectors
Arash Dehzangi, Quentin Durlin, Donghai Wu, Ryan McClintock, Manijeh Razeghi
Semiconductor Science and Technology, 34(6), 06LT01-- May 25, 2019
Different passivation techniques are investigated for reducing leakage current in small pixel (down to 9 μm) heterostructure photodetectors designed for the short-wavelength infrared range. Process evaluation test chips were fabricated using the same process as for focal plane arrays. Arrays of small photodetectors were electrically characterized under dark conditions from 150 K to room temperature. In order to evaluate the leakage current, we studied the relation between the inverse of dynamic resistance at −20 mV and zero bias and perimeter over area P/A ratio as the pixel size is scaled down. At 150 K, leakage current arising from the perimeter dominates while bulk leakage dominates at room temperature. We find that in shortwave devices directly underfilling hybridized devices with a thermoset epoxy resin without first doing any additional passivation/protection after etching gives the lowest leakage with a surface resistance of 4.2 × 109 and 8.9 × 103 Ω· cm−1 at 150 and 300 K, for −20 mV of bias voltage, respectively. reprint
 
55.  
High-power, continuous-wave, phase-locked quantum cascade laser arrays emitting at 8 μm
High-power, continuous-wave, phase-locked quantum cascade laser arrays emitting at 8 μm
WENJIA ZHOU,QUAN-YONG LU,DONG-HAI WU, STEVEN SLIVKEN, AND MANIJEH RAZEGHI
OPTICS EXPRESS 27, 15776-15785-- May 20, 2019
We report a room-temperature eight-element phase-locked quantum cascade laser array emitting at 8 μm with a high continuous-wave power of 8.2 W and wall plug efficiency of 9.5%. The laser array operates primarily via the in-phase supermode and has single-mode emission with a side-mode suppression ratio of ~20 dB. The quantum cascade laser active region is based on a high differential gain (8.7 cm/kA) and low voltage defect (90 meV) design. A record high wall plug efficiency of 20.4% is achieved from a low loss buried ridge type single-element Fabry-Perot laser operating in pulsed mode at 20 °C. reprint
 
56.  
Extended short wavelength infrared heterojunction phototransistors based on type II superlattices
Extended short wavelength infrared heterojunction phototransistors based on type II superlattices
Arash Dehzangi , Ryan McClintock, Donghai Wu , Abbas Haddadi, Romain Chevallier , and Manijeh Razeghi
Applied Physics Letters 114, 191109-- May 17, 2019
A two terminal extended short wavelength infrared heterojunction phototransistor based on type-II InAs/AlSb/GaSb on a GaSb substrate is designed, fabricated, and investigated. With the base thickness of 40 nm, the device exhibited a 100% cut-off wavelength of 2.3 λ at 300 K. The saturated peak responsivity value is 320.5 A/W at 300 K, under front-side illumination without any antireflection coating. A saturated optical gain of 245 at 300K was measured. At the same temperature, the device exhibited a collector dark current density (at unity optical gain) and a DC current gain of 7.8 X 103 A/cm² and 1100, respectively. The device exhibited a saturated dark current shot noise limited specific detectivity of 4.9 X 1011 cm·Hz½/W at 300 K which remains constant over a broad range of wavelengths and applied biases. reprint
 
57.  
Antimonite-based gap-engineered type-II superlattice materials grown by MBE and MOCVD for the third generation of infrared imagers
Antimonite-based gap-engineered type-II superlattice materials grown by MBE and MOCVD for the third generation of infrared imagers
Manijeh Razeghi, Arash Dehzangi, Donghai Wu, Ryan McClintock, Yiyun Zhang, Quentin Durlin, Jiakai Li, Fanfei Meng
Proc. SPIE Defense + Commercial Sensing,Infrared Technology and Applications XLV, 110020G -- May 7, 2019
Third generation of infrared imagers demand performances for higher detectivity, higher operating temperature, higher resolution, and multi-color detection all accomplished with better yield and lower manufacturing costs. Antimonidebased gap-engineered Type-II superlattices (T2SLs) material system is considered as a potential alternative for MercuryCadmium-Telluride (HgCdTe) technology in all different infrared detection regimes from short to very long wavelengths for the third generation of infrared imagers. This is due to the incredible growth in the understanding of its material properties and improvement of device processing which leads to design and fabrication of better devices. We will present the most recent research results on Antimonide-based gap-engineered Type-II superlattices, such as highperformance dual-band SWIR/MWIR photo-detectors and focal plane arrays for different infrared regimes, toward the third generation of infrared imaging systems at the Center for Zuantum Devices. Comparing metal-organic chemical vapor deposition (MOCVD), vs molecular beam epitaxy (MBE). reprint
 
58.  
Type–II superlattices base visible/extended short–wavelength infrared photodetectors with a bandstructure–engineered photo–generated carrier extractor
Type–II superlattices base visible/extended short–wavelength infrared photodetectors with a bandstructure–engineered photo–generated carrier extractor
Arash Dehzangi, Ryan McClintock, Abbas Haddadi, Donghai Wu, Romain Chevallier, Manijeh Razeghi
Scientific Reports volume 9, Article number: 5003 -- March 21, 2019
Visible/extended short–wavelength infrared photodetectors with a bandstructure–engineered photo–generated carrier extractor based on type–II InAs/AlSb/GaSb superlattices have been demonstrated. The photodetectors are designed to have a 100% cut-off wavelength of ~2.4 μm at 300K, with sensitivity down to visible wavelengths. The photodetectors exhibit room–temperature (300K) peak responsivity of 0.6 A/W at ~1.7 μm, corresponding to a quantum efficiency of 43% at zero bias under front–side illumination, without any anti–reflection coating where the visible cut−on wavelength of the devices is <0.5 µm. With a dark current density of 5.3 × 10−4 A/cm² under −20 mV applied bias at 300K, the photodetectors exhibit a specific detectivity of 4.72 × 1010 cm·Hz½W-1. At 150K, the photodetectors exhibit a dark current density of 1.8 × 10−10 A/cm² and a quantum efficiency of 40%, resulting in a detectivity of 5.56 × 1013 cm·Hz½/W reprint
 
59.  
p-Type thin film field effect transistors based on lithium-doped nickel oxide channels grown by pulsed laser deposition
p-Type thin film field effect transistors based on lithium-doped nickel oxide channels grown by pulsed laser deposition
V. E. Sandana; D. J. Rogers; F. H. Teherani; P. Bove; R. McClintock; M. Razeghi
SPIE Proceedings Volume 10919, Oxide-based Materials and Devices X; 109191H -- March 12, 2019
Staggered back-gated Field Effect Transistor (FET) structures were made by growing Li-doped NiO on Si3N4/SiO2/Si (111) using room temperature pulsed laser deposition. Optical studies showed over 80% transmission for the NiO:Li channel at wavelengths > 500nm. The MISFET revealed rectifying transfer characteristics, with a VON close to zero, a channel mobility of ~ 1 cm²/V·s, a gate leakage current (at +5V) of 0.8 mA and an ION/IOFF ratio (at a Vgs of −15V) of ~ 103. The transistors showed enhancement-mode output characteristics indicative of a p-type channel with sharp pinchoff, hard saturation, a comparatively high (milliampere range) Id and a relatively low on-resistance of ~11 kΩ. Hence the adoption of Li doping in NiO channels would appear to be a promising approach to obtain p-type TFTs with superior transparency, speed and energy efficiency. reprint
 
60.  
Fabrication of 12 µm pixel-pitch 1280 × 1024 extended short wavelength infrared focal plane array using heterojunction type-II superlattice-based photodetector
Fabrication of 12 µm pixel-pitch 1280 × 1024 extended short wavelength infrared focal plane array using heterojunction type-II superlattice-based photodetector
Arash Dehzangi , Abbas Haddadi, Romain Chevallier, Yiyun Zhang and Manijeh Razegh
Semicond. Sci. Technol. 34, 03LT01-- February 4, 2019
We present an initial demonstration of a 1280 × 1024 extended short-wavelength infrared focal plane array (FPA) imager with 12μm pixel-pitch based on type–II InAs/AlSb/GaSb superlattice heterojunction photodetectors, with a novel bandstructure-engineered photo-generated carrier extractor as the window layer in the hetero structure to efficiently extract the photo-generated carriers. This heterostructure with a larger bandgap top window/contact layer leads to the device having lower dark current density compared to conventional pn junction devices. The large format FPA was fabricated with 12 μm pixel-pitch using a developed fabrication process. Test pixels fabricated separately exhibit 100% cut–off wavelengths of ∼2.22, ∼2.34μm, and ∼2.45μm at 150, 200K, and 300K. The test devices achieve saturated quantum efficiency values under zero bias of 54.3% and 68.4% at 150 and 300K, under back-side illumination and without any anti-reflection coating. At 150K, these photodetectors exhibit dark current density of 1.63 × 10−7 A·cm−2 under −20mV applied bias providing a specific detectivity of 1.01 × 1011 cm ·Hz½/W at 1.9μm. reprint
 
61.  
New design strategies for multifunctional and inexpensive quantum cascade lasers
New design strategies for multifunctional and inexpensive quantum cascade lasers
Steven Slivken; Manijeh Razeghi
Proc. SPIE 10926, Quantum Sensing and Nano Electronics and Photonics XVI, 1092611-- February 1, 2019
This manuscript describes some of the new advances in active mid-infrared photonic integrated circuits enabled by new quantum cascade laser technologies. This includes monolithic beam steering which was achieved via the integration of a widely tunable QCL and a tapered grating outcoupler. A record 17.9 degrees of steering with a low divergence beam (0.5 degrees) was achieved. In addition, the use of surface emitting architectures is proposed as a means to reduce the manufacturing cost of next-generation QCLs. A reflective outcoupler is demonstrated which can allow for stable surface emission from a quantum cascade laser and has potential for cost-effective wafer-scale manufacturing. This outcoupler is integrated with an amplified, electrically tunable laser architecture to demonstrate high power surface emission at a wavelength near 4.9 μm. Single mode peak power up to 6.7 W is demonstrated with >6 W available over a 90 cm−1 (215 nm) spectral range. All of this is achieved while maintaining a high quality output beam, similar to a standard edge emitter. reprint
 
62.  
Surface Emitting, Tunable, Mid-Infrared Laser with High Output Power and Stable Output Beam
Surface Emitting, Tunable, Mid-Infrared Laser with High Output Power and Stable Output Beam
Steven Slivken, Donghai Wu & Manijeh Razeghi
Scientific Reports volume 9, Article number: 549-- January 24, 2019
A reflective outcoupler is demonstrated which can allow for stable surface emission from a quantum cascade laser and has potential for cost-effective wafer-scale manufacturing. This outcoupler is integrated with an amplified, electrically tunable laser architecture to demonstrate high power surface emission at a wavelength near 4.9 μm. Single mode peak power up to 6.7 W is demonstrated with >6 W available over a 90 cm−1 (215 nm) spectral range. A high quality output beam is realized with a simple, single-layer, anti-reflective coating. The beam shape and profile are shown to be independent of wavelength. reprint
 
63.  
Photoluminescence linewidth narrowing in Yb-doped GaN and InGaN thin films
Photoluminescence linewidth narrowing in Yb-doped GaN and InGaN thin films
K. Dasari, J. Wang, W.M. Jadwisienczak, V. Dierolf, M. Razeghi, R. Palai
Journal of Luminescence Volume 209, May 2019, Pages 237-243-- January 14, 2019
We report on photoluminescence (PL) properties of GaN, GaN:Yb, InGaN, and InGaN:Yb thin films grown on (0001) sapphire substrates by plasma assisted molecular beam epitaxy (MBE). X-ray diffraction pattern of the films confirms c-axis oriented growth. The concentration of Yb and In was obtained by X-ray photoelectron spectroscopy (XPS) and was found to be 5 (+/- 0.5) at.% and 30 (+/- 1.5) at.%, respectively. The GaN:Yb and InGaN:Yb thin films show a significant linewidth narrowing in PL spectra compared to GaN and InGaN thin films. This could be attributed to the reduction of the defect related non-radiative recombination paths and suppression of the structural defects and dislocations because of the in situ rare earth (Yb)-doping during the growth. The temperature dependent photoluminescence of GaN:Yb thin film follows the Varshni model, whereas InGaN:Yb film shows a complex S-shaped like behavior, which can be explained by the localization effect using the Band-Tail model. reprint
 
64.  
Strain-Induced Metastable Phase Stabilization in Ga<sub>2</sub>O<sub>3</sub> Thin Films
Strain-Induced Metastable Phase Stabilization in Ga2O3 Thin Films
Yaobin Xu, Ji-hyeon Park, Zhenpeng Yao, Christopher Wolverton, Manijeh Razeghi, Jinsong Wu, and Vinayak P. Dravid
ACS Appl. Mater. Interfaces-- January 10, 2019
It is well known that metastable and transient structures in bulk can be stabilized in thin films via epitaxial strain (heteroepitaxy) and appropriate growth conditions that are often far from equilibrium. However, the mechanism of heteroepitaxy, particularly how the nominally unstable or metastable phase gets stabilized, remains largely unclear. This is especially intriguing for thin film Ga2O3, where multiple crystal phases may exist under varied growth conditions with spatial and dimensional constraints. Herein, the development and distribution of epitaxial strain at the Ga2O3/Al2O3 film-substrate interfaces is revealed down to the atomic resolution along different orientations, with an aberration-corrected scanning transmission electron microscope (STEM). Just a few layers of metastable α-Ga2O3 structure were found to accommodate the misfit strain in direct contact with the substrate. Following an epitaxial α-Ga2O3 structure of about couple unit cells, several layers (4~5) of transient phase appear as the intermediate structure to release the misfit strain. Subsequent to this transient crystal phase, the nominally unstable κ-Ga2O3 phase is stabilized as the major thin film phase form. We show that the epitaxial strain is gracefully accommodated by rearrangement of the oxygen polyhedra. When the structure is under large compressive strain, Ga3+ ions occupy only the oxygen octahedral sites to form a dense structure. With gradual release of the compressive strain, more and more Ga3+ ions occupy the oxygen tetrahedral sites, leading to volumetric expansion and the phase transformation. The structure of the transition phase is identified by high resolution electron microscopy (HREM) observation, complemented by the density functional theory (DFT) calculations. This study provides insights from the atomic scale and their implications for the design of functional thin film materials using epitaxial engineering.
 
65.  
High quantum efficiency mid-wavelength infrared type-II InAs/InAs<sub>1-x</sub>Sb<sub>x</sub> superlattice photodiodes grown by metal-organic chemical vapor deposition
High quantum efficiency mid-wavelength infrared type-II InAs/InAs1-xSbx superlattice photodiodes grown by metal-organic chemical vapor deposition
Donghai Wu , Quentin Durlin, Arash Dehzangi , Yiyun Zhang , and Manijeh Razeghi
Appl. Phys. Lett. 114, 011104-- January 8, 2019
We report the growth and characterization of mid-wavelength infrared type-II InAs/InAs1-xSbx superlattice photodiodes on GaSb substrates grown by metal-organic chemical vapor deposition. At 150 K, the 50% cut-off wavelength is 5.0 um, the dark current density is 3.3x10−4 A/cm2 under −20mV bias, and the peak responsivity is 1.76A/W corresponding to a quantum efficiency of 55% without anti-reflection coating. A specific detectivity of 1.2x1011cmHz1/2/W is achieved at 4.0 um under −20mV bias at 150 K. reprint
 
66.  
High Frequency Extended Short-Wavelength Infrared Heterojunction Photodetectors Based on InAs/GaSb/AlSb Type-II Superlattices
High Frequency Extended Short-Wavelength Infrared Heterojunction Photodetectors Based on InAs/GaSb/AlSb Type-II Superlattices
Romain Chevallier, Abbas Haddadi, Ryan McClintock, Arash Dehzangi , Victor Lopez-Dominguez, Pedram Khalili Amiri, Manijeh Razeghi
IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 54, NO. 6-- December 1, 2018
InAs/GaSb/AlSb type-II superlattice-based photodetectors, with 50% cut-off wavelength of 2.1 µm and a −3 dB cut-off frequency of 4.8 GHz, are demonstrated, for 10 µm diameter circular mesas under 15 V applied reverse bias. A study of the cut-off frequency with applied bias and mesa size was performed to evaluate some of the limiting factors of photodetectors high frequency performance. reprint
 
67.  
Suppressing Spectral Crosstalk in Dual-Band LongWavelength Infrared Photodetectors With Monolithically Integrated Air-Gapped Distributed Bragg Reflectors
Suppressing Spectral Crosstalk in Dual-Band LongWavelength Infrared Photodetectors With Monolithically Integrated Air-Gapped Distributed Bragg Reflectors
Yiyun Zhang, Abbas Haddadi, Arash Dehzangi , Romain Chevallier, Manijeh Razeghi
IEEE Journal of Quantum Electronics Volume: 55, Issue:1-- November 22, 2018
Antimonide-based type-II superlattices (T2SLs) have made possible the development of high-performance infrared cameras for use in a wide variety of thermal imaging applications, many of which could benefit from dual-band imaging. The performance of this material system has not reached its limits. One of the key issues in dual-band infrared photodetection is spectral crosstalk. In this paper, air-gapped distributed Bragg reflectors (DBRs) have been monolithically integrated between the two channels in long-/very long-wavelength dualband InAs/InAs1−xSbx/AlAs1−xSbx-based T2SLs photodetectors to suppress the spectral crosstalk. This air-gapped DBR has achieved a significant spectral suppression in the 4.5–7.5-µm photonic stopband while transmitting the optical wavelengths beyond 7.5 µm, which is confirmed by theoretical calculations, numerical simulation, and experimental results. reprint
 
68.  
High brightness ultraviolet light-emitting diodes grown on patterned silicon substrate
High brightness ultraviolet light-emitting diodes grown on patterned silicon substrate
Yoann Robin, Kai Ding, Ilkay Demir, Ryan McClintock, Sezai Elagoz, Manijeh Razeghi
Materials Science in Semiconductor Processing 90, pp. 87–91-- November 5, 2018
We report on the fabrication of high brightness AlGaN-based ultraviolet light emitting diodes (UV-LED) on patterned silicon. Using the lateral epitaxial overgrowth approach, we demonstrate the growth of a 6 μm thick AlN layer of high crystalline quality. X-ray diffraction characterization showed a rocking curve with a full width at half maximum of 553 and 768″ for the (00.2) and (10.2) planes, respectively. The low dislocation density of the AlN template enabled the growth of bright AlGaN/ GaN quantum wells emitting at 336 nm. By appropriate flip-chip bonding and silicon substrate removal processing steps, the patterned AlN surface was exposed and efficient bottom-emission UV-LEDs were realized. Improvement of the AlN quality and the structure design allowed the optical output power to reach the milliwatt range under pulsed current, exceeding the previously reported maximum efficiency. Further investigations of the optical power at different pulsed currents and duty cycles show that thermal management in this device structure is still challenging, especially in continuous wave mode operation. The strategy presented here is of interest, since AlN crystalline quality improvement and optimization of the light extraction are the main issues inhibiting efficient UV emitter on silicon fabrication. reprint
 
69.  
Single-mode, high-power, midinfrared, quantum cascade laser phased arrays
Single-mode, high-power, midinfrared, quantum cascade laser phased arrays
Wenjia Zhou , Donghai Wu , Quan-Yong Lu, Steven Slivken & Manijeh Razeghi
Scientific Reports 8:14866-- October 5, 2018
We demonstrate single-mode, 16-channel, optical phased arrays based on quantum cascade laser technology, with emission wavelengths around 4.8 μm. The integrated device consists of a distributed feedback seed section, a highly-efficient tree array multi-mode interferometer power splitter, and a 16-channel amplifier array with a 4° angled facet termination. With a single layer Y2O3 coating, the angled facet reflectivity is estimated to be less than 0.1% for suppressing amplifier self-lasing. A peak output power of 30 W is achieved with an emission spectrum narrower than 11 nm and a side mode suppression ratio over 25 dB. Far field distribution measurement result indicates a uniform phase distribution across the array output. Using the same phased array architecture, we also demonstrate single-mode 3.8 μm QCL amplifier arrays with up to 20 W output power. reprint
 
70.  
Multiple-band, Single-mode, High-power, Phase-locked, Mid-infrared Quantum Cascade Laser Arrays
Multiple-band, Single-mode, High-power, Phase-locked, Mid-infrared Quantum Cascade Laser Arrays
Manijeh Razeghi, Wenjia Zhou, Quanyong Lu, Donghai Wu, and Steven Slivken
Imaging and Applied Optics 2018, JTh1A.2-- September 15, 2018
Single-mode, 16-channel, phase-locked laser arrays based on quantum cascade laser technology are demonstrated at multiple spectral bands across the mid-infrared spectrum region. High peak output power of 50W is achieved around the long-wavelength band of 7.7µm, while a side mode suppression ratio over 25dB is obtained. Far field distribution measurement result indicates a uniform phase distribution across the array output. reprint
 
71.  
Review of high power frequency comb sources based on InP From MIR to THZ at CQD
Review of high power frequency comb sources based on InP From MIR to THZ at CQD
Manijeh Razeghi, Quanyong Lu, Donghai Wu, Steven Slivken
Event: SPIE Optical Engineering + Applications, 2018, San Diego, California, United States-- September 14, 2018
We present the recent development of high performance compact frequency comb sources based on mid-infrared quantum cascade lasers. Significant performance improvements of our frequency combs with respect to the continuous wave power output, spectral bandwidth, and beatnote linewidth are achieved by systematic optimization of the device's active region, group velocity dispersion, and waveguide design. To date, we have demonstrated the most efficient, high power frequency comb operation from a free-running room temperature continuous wave (RT CW) dispersion engineered QCL at λ~5-9 μm. In terms of bandwidth, the comb covered a broad spectral range of 120 cm−1 with a radio-frequency intermode beatnote spectral linewidth of 40 Hz and a total power output of 880 mW at 8 μm and 1 W at ~5.0 μm. The developing characteristics show the potential for fast detection of various gas molecules. Furthermore, THz comb sources based on difference frequency generation in a mid-IR QCL combs could be potentially developed. reprint
 
72.  
Terahertz emitters at Center for Quantum Devices: recent advances and future trends
Terahertz emitters at Center for Quantum Devices: recent advances and future trends
Manijeh Razeghi
Proc. SPIE 10177, Infrared Technology and Applications XLIII, 1017705-- August 23, 2018
This paper reviews the recent advances and future trends of terahertz (THz) emitters at CQD/NU, highlights the high-performance THz sources based on intracavity nonlinear frequency generation in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the power, wall plug efficiency are achieved by systematic optimizing the device's active region, waveguide, and chip bonding strategy. High THz power up to 1.9 mW and 0.014 mW for pulsed mode and continuous wave operations at room temperature are demonstrated, respectively. Even higher power and efficiency are envisioned based on enhancements in outcoupling efficiency and mid-IR performance. Our compact THz device with high power and wide tuning range is highly suitable for the imaging, sensing, spectroscopy, medical diagnosis, and many other applications. reprint
 
73.  
Demonstration of long wavelength infrared Type-II InAs/InAs<sub>1-x</sub>Sb<sub>x</sub> superlattices photodiodes on GaSb substrate grown by metalorganic chemical vapor deposition
Demonstration of long wavelength infrared Type-II InAs/InAs1-xSbx superlattices photodiodes on GaSb substrate grown by metalorganic chemical vapor deposition
D. H. Wu, A. Dehzangi, Y. Y. Zhang, M. Razeghi
Applied Physics Letters 112, 241103-- June 12, 2018
We report the growth and characterization of long wavelength infrared type-II InAs/InAs1−xSbx superlattices photodiodes with a 50% cut-off wavelength at 8.0 μm on GaSb substrate grown by metalorganic chemical vapor deposition. At 77 K, the photodiodes exhibited a differential resistance at zero bias (R0A) 8.0 Ω·cm2, peak responsivity of 1.26 A/W corresponding to a quantum efficiency of 21%. A specific detectivity of 5.4×1010 cm·Hz1/2/W was achieved at 7.5 μm. reprint
 
74.  
Monolithic, steerable, mid-infrared laser realized with no moving parts
Monolithic, steerable, mid-infrared laser realized with no moving parts
Slivken S, Wu D, Razeghi M
Scientific Reports 7, 8472 -- May 24, 2018
The mid-infrared (2.5 < λ < 25 μm) spectral region is utilized for many purposes, such as chemical/biological sensing, free space communications, and illuminators/countermeasures. Compared to near-infrared optical systems, however, mid-infrared component technology is still rather crude, with isolated components exhibiting limited functionality. In this manuscript, we make a significant leap forward in mid-infrared technology by developing a platform which can combine functions of multiple mid-infrared optical elements, including an integrated light source. In a single device, we demonstrate wide wavelength tuning (240 nm) and beam steering (17.9 degrees) in the mid-infrared with a significantly reduced beam divergence (down to 0.5 degrees). The architecture is also set up to be manufacturable and testable on a wafer scale, requiring no cleaved facets or special mirror coating to function. reprint
 
75.  
Phase-locked, high power, mid-infrared quantum cascade laser array
Phase-locked, high power, mid-infrared quantum cascade laser array
W. Zhou, S. Slivken, and M. Razeghi
Applied Physics Letters 112, 181106-- May 4, 2018
We demonstrate phase-locked, high power quantum cascade laser arrays, which are combined using a monolithic, tree array multimode interferometer, with emission wavelengths around 4.8 μm. A maximum output power of 15 W was achieved from an eight-element laser array, which has only a slightly higher threshold current density and a similar slope efficiency compared to a Fabry-Perot laser of the same length. Calculated multimode interferometer splitting loss is on the order of 0.27 dB for the in-phase supermode. In-phase supermode operation with nearly ideal behavior is demonstrated over the working current range of the array. reprint
 

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