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  • APPLIED PHYSICS LETTERS
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2013 2016

We report the crack-free growth of a 45-pair Al[subscript 0.30]Ga[subscript 0.70]N/Al[subscript 0.04]Ga[subscript 0.96]N distributed Bragg reflector (DBR) on 2 in. diameter AlN/sapphire template by metalorganic chemical vapor deposition. To mitigate the cracking issue originating from the tensile strain of Al[subscript 0.30]Ga[subscript 0.70]N on GaN, an AlN template was employed in this work. On the other hand, strong compressive strain experienced by Al[subscript 0.04]Ga[subscript 0.96]N favors 3D island growth, which is undesired. We found that inserting an 11 nm thick GaN interlayer upon the completion of AlN template layer properly managed the strain such that the Al[subscript 0.30]Ga[subscript 0.70]N/Al[subscript 0.04]Ga[subscript 0.96]N ...

Contributors
Liu, Yuh-Shiuan, Wang, Shuo, Xie, Hongen, et al.
Created Date
2016-08-25

The dehydrogenation of intrinsic hydrogenated amorphous silicon (a-Si:H) at temperatures above approximately 300 °C degrades its ability to passivate silicon wafer surfaces. This limits the temperature of post-passivation processing steps during the fabrication of advanced silicon heterojunction or silicon-based tandem solar cells. We demonstrate that a hydrogen plasma can rehydrogenate intrinsic a-Si:H passivation layers that have been dehydrogenated by annealing. The hydrogen plasma treatment fully restores the effective carrier lifetime to several milliseconds in textured crystalline silicon wafers coated with 8-nm-thick intrinsic a-Si:H layers after annealing at temperatures of up to 450 °C. Plasma-initiated rehydrogenation also translates to complete solar ...

Contributors
Shi, Jianwei, Boccard, Mathieu, Holman, Zachary, et al.
Created Date
2016-07-19

We report photon-noise limited performance of horn-coupled, aluminum lumped-element kinetic inductance detectors at millimeter wavelengths. The detectors are illuminated by a millimeter-wave source that uses an active multiplier chain to produce radiation between 140 and 160 GHz. We feed the multiplier with either amplified broadband noise or a continuous-wave tone from a microwave signal generator. We demonstrate that the detector response over a 40 dB range of source power is well-described by a simple model that considers the number of quasiparticles. The detector noise-equivalent power (NEP) is dominated by photon noise when the absorbed power is greater than approximately 1 ...

Contributors
Flanigan, D., McCarrick, H., Jones, G., et al.
Created Date
2016-02-25

The giant magnetoresistance (GMR) of a point contact between a Co/Cu multilayer and a superconductor tip varies for different bias voltage. Direct measurement of spin polarization by Andreev reflection spectroscopy reveals that the GMR change is due to a change in spin polarization. This work demonstrates that the GMR structure can be utilized as a spin source and that the spin polarization can be continuously controlled by using an external magnetic field.

Contributors
Gifford, Jessica, Zhao, Gejian, Li, Bochao, et al.
Created Date
2016-05-23

We numerically demonstrate a switchable metamaterial absorber/emitter by thermally turning on or off the excitation of magnetic resonance upon the phase transition of vanadium dioxide (VO2). Perfect absorption peak exists around the wavelength of 5 lm when the excitation of magnetic resonance is supported with the insulating VO2 spacer layer. The wavelength-selective absorption is switched off when the magnetic resonance is disabled with metallic VO2 that shorts the top and bottom metallic structures. The resonance wavelength can be tuned with different geometry, and the switchable metamaterial exhibits diffuse behaviors at oblique angles. The results would facilitate the design of switchable ...

Contributors
Wang, Hao, Wang, Yue, Wang, Liping, et al.
Created Date
2014-08-19

We demonstrate transverse-magnetic (TM) dominant deep-ultraviolet (DUV) stimulated emission from photo-pumped AlGaN multiple-quantum-well lasers grown pseudomorphically on an AlN/sapphire template by means of photoluminescence at room temperature. The TM-dominant stimulated emission was observed at wavelengths of 239, 242, and 243 nm with low thresholds of 280, 250, and 290 kW/cm[superscript 2], respectively. In particular, the lasing wavelength of 239 nm is shorter compared to other reports for AlGaN lasers grown on foreign substrates including sapphire and SiC. The peak wavelength difference between the transverse-electric (TE)-polarized emission and TM-polarized emission was approximately zero for the lasers in this study, indicating the ...

Contributors
Li, Xiao-Hang, Kao, Tsung-Ting, Satter, Md. Mahbub, et al.
Created Date
2015-01-26

The emission properties of GeSn heterostructure pin diodes have been investigated. The devices contain thick (400–600 nm) Ge [subscript 1− y] Sn [subscript y] i-layers spanning a broad compositional range below and above the crossover Sn concentration y [subscript c] where the Ge [subscript 1− y] Sn [subscript y] alloy becomes a direct-gap material. These results are made possible by an optimized device architecture containing a single defected interface thereby mitigating the deleterious effects of mismatch-induced defects. The observed emission intensities as a function of composition show the contributions from two separate trends: an increase in direct gap emission as ...

Contributors
Gallagher, J. D., Senaratne, Charutha Lasitha, Sims, Patrick, et al.
Created Date
2015-03-02

In this letter, we study the near-field radiative heat transfer between two metamaterial substrates coated with silicon carbide (SiC) thin films. It is known that metamaterials can enhance the near-field heat transfer over ordinary materials due to excitation of magnetic plasmons associated with s polarization, while strong surface phonon polariton exists for SiC. By careful tuning of the optical properties of metamaterial, it is possible to excite electrical and magnetic resonances for the metamaterial and surface phonon polaritons for SiC at different spectral regions, resulting in the enhanced heat transfer. The effect of the SiC film thickness at different vacuum ...

Contributors
Basu, Soumyadipta, Yang, Yue, Wang, Liping, et al.
Created Date
2015-01-19

Photoluminescence spectroscopy has been used to determine the direct gap E [subscript 0] of Ge [subscript 1− y] Sn [subscript y] alloys over a broad compositional range from pure Ge to Sn concentrations exceeding 10%. A fit of the compositional dependence of E [subscript 0] using a standard quadratic expression is not fully satisfactory, revealing that the bowing parameter (quadratic coefficient) b [subscript 0] is compositionally dependent. Excellent agreement with the data is obtained with b [subscript 0](y) = (2.66 ± 0.09) eV − (5.4 ± 1.1)y eV. A theoretical model of the bowing is presented, which explains the strong ...

Contributors
Gallagher, J. D., Senaratne, Charutha Lasitha, Kouvetakis, John, et al.
Created Date
2014-10-06

Optically pumped deep-ultraviolet (DUV) lasing with low threshold was demonstrated from AlGaN-based multiple-quantum-well (MQW) heterostructures grown on sapphire substrates. The epitaxial layers were grown pseudomorphically by metalorganic chemical vapor deposition on (0001) sapphire substrates. Stimulated emission was observed at wavelengths of 256 nm and 249 nm with thresholds of 61 kW/cm[superscript 2] and 95 kW/cm[superscript 2] at room temperature, respectively. The thresholds are comparable to the reported state-of-the-art AlGaN-based MQW DUV lasers grown on bulk AlN substrates emitting at 266 nm. These low thresholds are attributed to the optimization of active region and waveguide layer as well as the use ...

Contributors
Li, Xiao-Hang, Detchprohm, Theeradetch, Kao, Tsung-Ting, et al.
Created Date
2014-10-06