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2015 | 19 | 32-49
Article title

Improved photoresponse of porous silicon photodetectors by embedding CdS nanoparticles

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In this research, the nanocrystalline porous silicon (PSi) films are prepared by electrochemical etching of p types silicon wafers with 15 mA/cm2 etching current densities and 15 min etching time on the formation nanosized pore array. PSi was characterized by the measurement of XRD, FTIR spectroscopy and atomic force microscopy properties (AFM). We have estimated crystallites size from X-Ray diffraction about nanoscale for PSi and Atomic Force microscopy confirms the nanometric size Chemical fictionalization during the electrochemical etching show on the surface chemical composition of PSi. The atomic force microscopy investigation shows the rough silicon surface. Also, it is reported the preparation of colloidal CdS nanoparticles NPs prepared by laser ablation in liquid (LAL) technique by irradiating with a Nd:YAG laser pulses CdS target immersed in methanol and varying the laser fluence 1.32 J/cm2. The structural, morphological and optical of CdS NPs has been studied. XRD measurement disclosed that the CdS NPs were of wurtzite hexagonal crystal structure. Transmission electron microscopy (TEM) investigation revealed that the synthesized CdS particles are spherical and have an average particle size in the range of (25 nm). AFM investigations showed that the produced CdS particles have ball-shape with good disposability. The energy band gap of CdS NPs prepared with 1.32 J/cm2 laser fluence has been determined from optical properties and found to be in the range (2.9 eV). Optical constants of CdS NPs were determined from transmittance and reflectance spectra.The effect of CdS NPs diffusion on properties of PSi Photodetector have reported which reveals that improving in (Al/PSi/Si/Al). The results show that a linear relationship between 1/C2 and reverse bias voltage was obtained. The built-in potential have values depending on the etching time current density and laser flunce. Al/CdSe/PSi/Si/Al photodetector hetrojunction have two peaks of response located at 415 nm and (700 -800nm) with max sensitivity  0.6 A/W. The maximum specific detectivity is 6.8×〖10〗^12 cm•〖Hz〗^(1/2) 〖•W〗^(-1) at  770 nm wavelength.
Physical description
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