Surface morphology effect on the photoresponse of high temperature superconducting microbridges

Chou, Hsiung; Chen, H. Z.; Chen, Y. C.; Lin, Ting‐Hui; Chow, T. C.; Wang, T. P.

doi:10.1063/1.117400

Cited by 3 publications

(2 citation statements)

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“…Fardmanesh et al have already analyzed effects of the bias current and variation of thermal conductance on the magnitude and phase of the response of the HTS transition edge bolometers [12]. Chou focused on dependence of the photoresponse of high temperature superconducting microbridges on surface morphology [17], where in their study there is no strong evidence to support this relation. Dwir et al have reported the wavelength independent performance of the HTS bolometers from k $ 0.6-450 lm [18].…”

Section: Introductionmentioning

confidence: 99%

The superconducting transition width and illumination wavelength dependence of the response of MgO substrate YBCO transition edge bolometers

Öktem¹,

Bozbey²,

Avci³

et al. 2007

Physica C: Superconductivity

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Dependence of the phase and magnitude of the response of MgO substrate YBa 2 Cu 3 O 7Àd (YBCO) transition edge bolometers to the near infrared radiation on the superconducting transition width is presented in this work. The bolometers were made of YBCO thin films of 200 nm thickness that were grown on single crystal MgO (1 0 0) substrates by DC inverted cylindrical magnetron sputtering. We have measured the responses of both large and small area devices with respect to the bias temperature and radiation modulation frequency. We have observed that the superconducting transition width has major effects on the response of the bolometers such as; on a dip of the phase of the response versus modulation frequency curve around 1 Hz, the rate of decrease of the magnitude of the response, and dependence of the phase of the response on temperature at mid-range modulation frequency. We have investigated a correlation between the superconducting transition width and the YBCO film surface morphology of the devices. In addition, the illumination wavelength dependence of the optical response of both wide and narrow transition width devices has been investigated. Here we present the analysis and the possible mechanisms that can affect the response of the bolometers at the superconducting transition region.

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Section: Introductionmentioning

confidence: 99%

The superconducting transition width and illumination wavelength dependence of the response of MgO substrate YBCO transition edge bolometers

Öktem¹,

Bozbey²,

Avci³

et al. 2007

Physica C: Superconductivity

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“…Several techniques have been developed to achieve single-mode emission in VCSELs, e.g. using an extended cavity [1], anti-resonance reflecting optical waveguide [2], and locally etched surface relief [3], and similar for polarization control, including sub-wavelength gratings in amorphous silicon [4], external feed-back [5], growth on non-(100) substrates [6]. However, only a few methods have been developed for combined mode and polarization selection.…”

mentioning

confidence: 99%

Experimental study of the combined mode and polarization control in VCSELs with a sub-wavelength surface grating

Haglund

Gustavsson

Jedrasik

et al. 2005

2005 IEEE LEOS Annual Meeting Conference Proceedings

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Vertical-cavity surface-emitting lasers (VCSELs) are inherently multimode with unpredictable polarization due to their relative large transverse dimensions and lack of structural asymmetry. In a number of applications, such as spectroscopy, optical data storage, and demanding fiber-optic communication, a single-frequency light source with low polarization drift is desirable. Several techniques have been developed to achieve single-mode emission in VCSELs, e.g. using an extended cavity [1], anti-resonance reflecting optical waveguide [2], and locally etched surface relief [3], and similar for polarization control, including sub-wavelength gratings in amorphous silicon [4], external feed-back [5], growth on non-(100) substrates [6]. However, only a few methods have been developed for combined mode and polarization selection. These include photonic crystal pattern [7], asymmetric air-post structure [8], and locally etched surface grating. In the latter method, a grating with a period larger than the optical wavelength in the material has been presented [9], and recently we have demonstrated VCSELs with a sub-wavelength grating [10]. A locally etched surface grating allows for the use of a relatively large oxide aperture, which reduces device resistance and thereby self-heating, enabling higher output powers. The advantage of using a sub-wavelength grating compared to a larger grating period is that the diffraction related losses and beam degradation are minimized. The fabrication of a sub-wavelength grating is however challenging since it requires high-resolution definition. In this work we have performed a parametric study to investigate the maximum achievable single-mode and polarization stable output power of 850-nm oxide-confined VCSELs with a locally etched sub-wavelength surface grating, and also how this performance depends on the grating geometry, which gives information on fabrication tolerances.The investigated 850-nm (1-cavity) oxide-confined VCSELs have an epitaxial structure consisting of an active region with three GaAs quantum wells and a top and bottom DBR with 22 and 34 layer pairs of Al 0.9 Ga 0.1 As/Al 0.12 Ga 0.88 As, respectively. Graded interfaces and modulation doping is used in the mirror layers to reduce the differential resistance while maintaining a low free-carrier absorption loss. A 30-nm-thick Al 0.98 Ga 0.02 As layer is positioned just above the active region. This layer is selectively oxidized to form the oxide aperture. For selecting the fundamental mode with a fixed polarization state an "inverted" sub-wavelength surface grating is used: a /4-thick topmost GaAs layer is added to the epitaxial structure to introduce anti-phase reflections, which significantly increases the top mirror loss; a surface grating with a period of 120 nm is etched in a circular region into the top mirror, see Fig. 1, to locally restore the low mirror loss for the fundamental mode with a polarization perpendicular to the grating grooves. The grating etch depth is 60 nm (~ /4). The principle is that the spati...

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Polishing effect of the plasma on the growth of YBa2Cu3O7−δ films by radio frequency sputtering

Chou

Lin

Hsu

et al. 2002

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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The surface morphology of YBa2Cu3O7−δ (YBCO) films is crucial for applications such as multilayering and optical detection. In this article, we showed that the resputtering effect due to the rf plasma can planarize the surface morphology of YBCO films under specific conditions. By setting the relative position and angle of the heater to the gun, the plasma density over the substrate can be altered from an asymmetric to a symmetric distribution. When the substrate was near the plasma, the negative oxygen ions resputtered part of the mobile atoms from the surface of the film back into the plasma, which caused compositional distortion, delaying the merge of grains and leaving uncovered holes. With a longer distance, the resputtering effect was suppressed, and precipitates appeared on the surface of films, resulting in a rougher surface. At an optimum heater-to-gun configuration, the function of the resputtering effect produced a polishing effect on the surface of films, which made a smooth and precipitate-free YBCO film possible. We also found that this film with smooth and precipitate-free morphology exhibited suppressed superconductivity, Tc0 and Ton.

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Surface morphology effect on the photoresponse of high temperature superconducting microbridges

Cited by 3 publications

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The superconducting transition width and illumination wavelength dependence of the response of MgO substrate YBCO transition edge bolometers

The superconducting transition width and illumination wavelength dependence of the response of MgO substrate YBCO transition edge bolometers

Experimental study of the combined mode and polarization control in VCSELs with a sub-wavelength surface grating

Polishing effect of the plasma on the growth of YBa2Cu3O7−δ films by radio frequency sputtering

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