Study of metal/ZnO based thin film ultraviolet photodetectors: The effect of induced charges on the dynamics of photoconductivity relaxation

Ultraviolet photoconductivity relaxation in ZnO thin films deposited by rf magnetron sputtering are investigated. Effect of oxygen partial pressure in the reactive gas mixture and film thickness on the photoconductivity transients is studied. A different photodetector configuration comprising ZnO thin film with an ultrathin overlayer of metals like Cu, Al, Sn, Au, Cr, and Te was designed and tested. Photoresponse signal were found to be stronger (four to seven times) in these configurations than the pure ZnO thin films. Sn(30 nm)/ZnO sample exhibits highest responsivity of ∼8.57 kV/W whereas Te(20 nm)/ZnO structure presents highest sensitivity of ∼31.3×103 compared to unloaded ZnO thin film. Enhancement in the photoresponse of ZnO thin films is attributed to the change in surface conductivity due to induced charge carriers at the interface because of the difference in work function and oxygen affinity values of metal overlayer with the underlying semiconducting layer. Charge carrier transfer from the meta...

[1]  G. Heiland,et al.  Electronic Processes in Zinc Oxide , 1959 .

[2]  G. Heiland.  Photoconductivity of zinc oxide as a surface phenomenon , 1961 .

[3]  三橋 広二,et al.  S.M. Ryvkin: Photoelectric Effects in Semiconductors. Consultants Bureau, New York 1964, 402頁, 16.5×26cm, 9,000円. , 1965 .

[4]  D. Kohl,et al.  Interpretation of surface phenomena on ZnO by the compensation model , 1978 .

[5]  T. Skettrup,et al.  Ultraviolet detectors in thin sputtered ZnO films. , 1986, Applied optics.

[6]  Y. Takahashi,et al.  Photoconductivity of Ultrathin Zinc Oxide Films , 1994 .

[7]  D. E. Brodie,et al.  Crystallite orientation and the related photoresponse of hexagonal ZnO films deposited by r.f. sputtering , 1994 .

[8]  Dongdong Zhang.  Fast photoresponse and the related change of crystallite barriers for ZnO films deposited by RF sputtering , 1995 .

[9]  T. Miyata,et al.  Work function of transparent conducting multicomponent oxide thin films prepared by magnetron sputtering , 1998 .

[10]  S. Studenikin,et al.  Carrier mobility and density contributions to photoconductivity transients in polycrystalline ZnO films , 2000 .

[11]  Michael Wraback,et al.  Ultraviolet detectors based on epitaxial ZnO films grown by MOCVD , 2000 .

[12]  F. D. Auret,et al.  Electrical Characterization of 1.8 MeV Proton-Bombarded ZnO , 2001 .

[13]  Hongen Shen,et al.  Ultraviolet photoconductive detector based on epitaxial Mg0.34Zn0.66O thin films , 2001 .

[14]  Parmanand Sharma,et al.  Ultraviolet photoresponse of porous ZnO thin films prepared by unbalanced magnetron sputtering , 2002 .

[15]  Pu-Xian Gao,et al.  Measuring the Work Function at a Nanobelt Tip and at a Nanoparticle Surface , 2003 .

[16]  Parmanand Sharma,et al.  Analysis of ultraviolet photoconductivity in ZnO films prepared by unbalanced magnetron sputtering , 2003 .

[17]  P. Bhattacharya,et al.  Fabrication of stable wide-band-gap ZnO/MgO multilayer thin films , 2003 .

[18]  Ichiro Takeuchi,et al.  Monolithic multichannel ultraviolet detector arrays and continuous phase evolution in MgxZn1−xO composition spreads , 2003 .

[19]  E. Monroy,et al.  Wide-bandgap semiconductor ultraviolet photodetectors , 2003 .

[20]  Hong Koo Kim,et al.  Ultraviolet detection with ultrathin ZnO epitaxial films treated with oxygen plasma , 2004 .

[21]  J. Muth,et al.  Enhanced photoconductivity of ZnO films Co-doped with nitrogen and tellurium , 2005 .

[22]  J. Park,et al.  Synthesis, electrical and photoresponse properties of vertically well-aligned and epitaxial ZnO nanorods on GaN-buffered sapphire substrates , 2005 .

[23]  K. Sreenivas,et al.  Synthesis of photoconducting ZnO nano-needles using an unbalanced magnetron sputtered ZnO/Zn/ZnO multilayer structure , 2005 .

[24]  S. Pearton,et al.  Zinc oxide bulk, thin films and nanostructures : processing, properties and applications , 2006 .

[25]  Photoresponsivity of ZnO Schottky barrier diodes , 2006 .

[26]  L. J. Mandalapu,et al.  p-type behavior from Sb-doped ZnO heterojunction photodiodes , 2006 .

[27]  T. Murphy,et al.  Sub-bandgap photoconductivity in ZnO epilayers and extraction of trap density spectra , 2006 .