| Summary: | Observation of visible luminescence in porous silicon(PS) by Canham in 1990[1] seemed to solve the physical inability of silicon to act as light emitter. PS has unique properties such as direct and wide modulated energy bandgap, high resistivity, vast surface area-to-volume ratio and the same single-crystal structure as bulk Si. These characteristics make it a suitable material for use in photodetectors. Embedding other semiconductor materials inside PS is interesting where one can tailor the wavelength of the emitted light. In addition, the PS substrate can act as a sink for threading dislocations and accommodate the strain[2]. ZnO as being wide bandgap semiconductor material has attracted numerous attentions for its prospective application in many fields. Combining Ge with ZnO inside PS, one can expect the wider absorption of the light in the visible spectrum while increasing the probability of the Ge ion to replace the Zn ion vacancy. Modification of the electronic structure around the band edge from this device is expected to enhance its optical properties. A metal-semiconductor-metal (MSM) photodetector offers attractive applications in optoelectronic integration circuits, primarily due to its planar structure, easy processes and fast response. In this paper we reported a very low cost technique to prepare the PS-based photodetectors. PS was prepared by anodization of Si wafer in ethanoic hydrofluoric acid (HF). The Ge and ZnO layers were deposited onto the PS by conventional thermal evaporation. Three samples were prepared, sample A was PS, sample B was Ge/PS and sample C was ZnO/Ge/PS. Structural and optical analyses of the samples were conducted using energy dispersive x-ray analysis (EDX), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL). The synthesis process was completed by inter-digitated Paladium(Pd) metal deposition to form the MSM photodetector. SEM revealed that the structures contained 500-700nm circular-pores and EDX suggested the presence of Ge and ZnO inside the pores for samples B and C respectively (Figure 1). Generally, PL spectrum showed that the A, B and C PS-based structures exhibited emissions at 380 nm, 520 nm and 639 nm respectively(Figure 2). Specifically, sample C displays high UV emission peak with a low and broad blue-green emission peaks. Sample B shows emission peaks from blue to red and sample A reveals broad peak in the red region. These characteristics demonstrate the potential of the PS-based structures to emit light at broader spectrum, opening up a route to prospective applications in future optoelectronic devices. Finally current-voltage (I-V) measurement of the Pd/PS-based MSM photodetectors will be conducted to illustrate their potential application in photonics. © 2012 IEEE.
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