Wide-bandgap semiconductors such as zinc selenide (ZnSe) have become popular for ultraviolet (UV) photodetectors due to their broad UV spectral response. Schottky barrier detectors made of ZnSe in particular have been shown to have both low dark current and high responsivity. This paper presents the results of electrical and optical characterization of UV sensors based on ZnSe/Ni Schottky diodes fabricated using single-crystal ZnSe substrate with integrated UV-A (320–400？nm) and UV-B (280–320？nm) filters. For comparison, characteristics characterization of an unfiltered detector is also included. The measured photoresponse showed good discrimination between the two spectral bands. The measured responsivities of the UV-A and UV-B detectors were 50？mA/W and 10？mA/W, respectively. A detector without a UV filter showed a maximum responsivity of about 110？mA/W at 375？nm wavelength. The speed of the unfiltered detector was found to be about 300？kHz primarily limited by the RC time constant determined largely by the detector area. 1. Introduction Schottky barrier photodetectors using wide-bandgap semiconductors have been fabricated for detection of ultraviolet radiation [1–19]. The materials used include SiC [7], III–V nitrides [8, 9], and II–VI compounds such as ZnSe [10–19]. Previous studies by Bouhdada et al. showed that the wide-bandgap ZnSe has a promising spectral response on detection of short wavelengths [15]. Though other wide-bandgap semiconductor materials are readily available, ZnSe has advantages due to its broader wavelength response in the UV spectral range compared to the nitrides [15]. The responsivity of ZnSe detectors was measured to be in the 0.1 A/W range while detectivity as high as ？cm (Hz)1/2/W was reported [13, 15]. In addition, most wide-bandgap III–V compounds suffer from the lack of lattice-matched substrates on which to grow them while ZnSe is closely lattice matched to GaAs substrates, and high crystalline quality can thus be obtained [20]. ZnSe Schottky diodes have been shown to have a relatively low leakage current which translates into a higher signal-to-noise ratio [17]. The response of ZnSe Shottky detectors was also analyzed to determine various decay mechanisms after light excitation [14]. In this paper, fabrication and characterization of ZnSe/Ni Schottky barrier photodetectors operating in the UV-A and UV-B spectral ranges are described. The detectors were fabricated on 1？mm thick n-type (aluminum doped) single crystal ZnSe substrate. 2. Device Fabrication The structure of the ZnSe/Ni Schottky diode sensor is shown
References
[1]
E. Monroy, F. Omnès, and F. Calle, “Wide-bandgap semiconductor ultraviolet photodetectors,” Semiconductor Science and Technology, vol. 18, no. 4, pp. R33–R51, 2003.
[2]
A. BenMoussa, A. Soltani, and A. Soltani, “Recent developments of wide-bandgap semiconductor based UV sensors,” Diamond and Related Materials, vol. 18, no. 5–8, pp. 860–864, 2009.
[3]
S. N. Mohammed, A. A. Salvazdor, and H. Markoc, “Emerging GaN based devices,” Proceeding of IEEE, vol. 83, pp. 1306–1355, 1995.
[4]
D. Walker, X. Zhang, A. Saxler, P. Kung, J. Xu, and M. Razeghi, “ ultraviolet photodetectors grown on sapphire by metal-organic chemical-vapor deposition,” Applied Physics Letters, vol. 70, no. 8, pp. 949–951, 1997.
[5]
A. Bouhdada, M. Hanzaz, P. Gibart, F. Omnès, E. Monroy, and E. Mu？oz, “Modeling of the spectral response of schottky ultraviolet photodetectors,” Journal of Applied Physics, vol. 87, no. 12, pp. 8286–8290, 2000.
[6]
M. Y. Chen and C. C. Chang, “Integrated a ZnSe MSM photodiode and an InGaP/GaAs hbt on a GaAs substrate for high sensitivity short wavelength photodetector,” IEEE Sensors Journal, vol. 9, no. 8, pp. 902–907, 2009.
[7]
L. A. Kosyachenko, V. M. Sklyarchuk, and Y. F. Sklyarchuk, “Electrical and photoelectric properties of Au-SiC schottky barrier diodes,” Solid-State Electronics, vol. 42, no. 1, pp. 145–151, 1998.
[8]
L. S. Yu, D. J. Qiao, Q. J. Xing, S. S. Lau, K. S. Boutros, and J. M. Redwing, “Ni and Ti Schottky barriers on n-AlGaN grown on SiC substrates,” Applied Physics Letters, vol. 73, no. 2, pp. 238–240, 1998.
[9]
E. Monroy, F. Calle, and F. Calle, “Analysis and modeling of -based Schottky barrier photodiodes,” Journal of Applied Physics, vol. 88, no. 4, pp. 2081–2091, 2000.
[10]
V. P. Makhnii and V. V. Melnik, “Photoelectric properties of Ni-ZnSe contacts,” Semiconductors, vol. 29, pp. 764–766, 1995.
[11]
A. Gerhard, J. Nürnberger, K. Schüll, V. Hock, C. Schumacher, M. Ehinger, and W. Faschinger, “ZnSe-based MBE-grown photodiodes,” Journal of Crystal Growth, vol. 184-185, pp. 1319–1323, 1998.
[12]
V. P. Makhnii, “Schottky barrier UV photodetectors based on zinc selenide,” Technical Physics, vol. 43, no. 9, pp. 1119–1120, 1998.
[13]
F. Vigué, P. de Mierry, J. P. Faurie, E. Monroy, F. Calle, and E. Mu？oz, “High detectivity ZnSe-based Schottky barrier photodetectors for blue and near-ultraviolet spectral range,” Electronics Letters, vol. 36, no. 9, pp. 826–827, 2000.
[14]
E. Monroy, F. Vigué, F. Calle, J. I. Izpura, E. Mu？oz, and J. P. Faurie, “Time response analysis of ZnSe-based Schottky barrier photodetectors,” Applied Physics Letters, vol. 77, no. 17, pp. 2761–2763, 2000.
[15]
A. Bouhdada, M. Hanzaz, F. Vigué, and J. P. Faurie, “Electrical and optical proprieties of photodiodes based on ZnSe material,” Applied Physics Letters, vol. 83, no. 1, pp. 171–173, 2003.
[16]
S. J. Chang, T. K. Lin, and T. K. Lin, “Homoepitaxial ZnSe MSM photodetectors with various transparent electrodes,” Materials Science and Engineering B: Solid-State Materials for Advanced Technology, vol. 127, no. 2-3, pp. 164–168, 2006.
[17]
M. Hanzaz, A. Bouhdada, F. Vigue, and J. P. Faurie, “ZnSe-and GaN-based schottky barrier photodetectors for blue and ultraviolet detection,” Journal of Active and Passive Electronic Devices, vol. 2, pp. 165–169, 2007.
[18]
T. K. Lin, S. J. Chang, and S. J. Chang, “Homoepitaxial ZnSe MIS photodetectors with SiO2 and BST insulator layers,” Solid-State Electronics, vol. 50, no. 5, pp. 750–753, 2006.
[19]
V. P. Makhnii and V. V. Melnik, “Surface barrier diode based on zinc selenide with a passivating zinc oxide film,” Technical Physics Letters, vol. 29, no. 9, pp. 712–713, 2003.
[20]
V. Bousquet, E. Tournié, and J. P. Faurie, “Defect density in ZnSe pseudomorphic layers grown by molecular beam epitaxy on to various GaAs buffer layers,” Journal of Crystal Growth, vol. 192, no. 1-2, pp. 102–108, 1998.
[21]
V. S. Fomenko, Handbook of Thermionic Properties, Plenum, New York, NY, USA, 1996.
[22]
M. Vos, F. Xu, J. H. Weaver, and H. Cheng, “Influence of metal interlayers on Schottky barrier formation for Au/ZnSe (100) and Al/ZnSe (100),” Applied Physics Letters, vol. 53, no. 16, pp. 1530–1532, 1988.
