The superconducting transition width and illumination wavelength dependence of the response of MgO substrate YBCO transition edge bolometers B. Oktem a,b, * , A. Bozbey c , I. Avci b , M. Tepe d , D. Abukay b , M. Fardmanesh c a Material Science and Nanotechnology, Bilkent University, TR-06800 Ankara, Turkey b Department of Physics, Izmir Institute of Technology, TR-35430 Izmir, Turkey c Department of Electrical and Electronics Engineering, Bilkent University, TR-06800 Ankara, Turkey d Department of Physics, Ege University, TR-35100 Izmir, Turkey Received 9 November 2006; received in revised form 31 January 2007; accepted 28 February 2007 Available online 7 March 2007 Abstract Dependence of the phase and magnitude of the response of MgO substrate YBa 2 Cu 3 O 7d (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 depen- dence 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 depen- dence 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. Ó 2007 Elsevier B.V. All rights reserved. PACS: 85.25.j; 74.72.Bk; 74.78.w; 74.10.+v; 74.62.c; 68.35.Bs; 95.55.Rg; 07.57.Kp; 81.10.Aj Keywords: High temperature superconductor devices; High-T c superconducting transition temperature; YBCO transition edge bolometers; Surface morphology; Optical response 1. Introduction Since the discovery of high-T c superconductors (HTS), much attention has been focused on the application of these materials in different types of bolometers for the near and far infrared wavelength regime [1–8]. High tempera- ture superconductor transition edge bolometers are one of the prominent devices that can be used to detect electro- magnetic radiation over the whole spectrum from X-ray to the far infrared wavelength range. There have been several studies investigating the optical and thermal performance of YBa 2 Cu 3 O 7d (YBCO) transition edge superconductive bolometers with respect to the bias temperature and the radiation modulation frequency [9–16]. There have been many reports on the parameters that affect the response of the bolometers. Fardmanesh et al. have already analyzed effects of the bias current and variation of thermal conduc- tance on the magnitude and phase of the response of the HTS transition edge bolometers [12]. Chou et al. have 0921-4534/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2007.02.016 * Corresponding author. Address: Department of Physics, Bilkent University, TR-06800 Ankara, Turkey. Tel.: +90 555 456 5315; fax: +90 312 266 4579. E-mail address: oktembulent@gmail.com (B. Oktem). www.elsevier.com/locate/physc Physica C 458 (2007) 6–11