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Purpose Porous silicon (PS) was successfully fabricated using an alternating current photo-assisted electrochemical etching (ACPEC) technique. This study aims to compare the effect of different crystal orientation of Si n(100) and n(111) on the structural and optical characteristics of the PS. Design/methodology/approach PS was fabricated using ACPEC etching with a current density of J = 10 mA/cm2 and etching time of 30 min. The PS samples denoted by PS100 and PS111 were etched using HF-based solution under the illumination of an incandescent white light. Findings FESEM images showed that the porous structure of PS100 was a uniform circular shape with higher density and porosity than PS111. In addition, the AFM indicated that the surface roughness of porous n(100) was less than porous n(111). Raman spectra of the PS samples showed a stronger peak with FWHM of 4.211 cm−1 and redshift of 1.093 cm−1. High resolution X-ray diffraction revealed cubic Si phases in the PS samples with tensile strain for porous n(100) and compressive strain for porous n(111). Photoluminescence observation of porous n(100) and porous n(111) displayed significant visible emissions at 651.97 nm (Eg = 190eV) and 640.89 nm (Eg = 1.93 eV) which was because of the nano-structure size of silicon through the quantum confinement effect. The size of Si nanostructures was approximately 8 nm from a quantized state effective mass theory. Originality/value The work presented crystal orientation dependence of Si n(100) and n(111) for the formation of uniform and denser PS using new ACPEC technique for potential visible optoelectronic application. The ACPEC technique has effectively formed good structural and optical characteristics of PS.

Porous silicon (PS) was successfully synthesized via novel integrated pulsed electrochemical etching of an n-type (100) silicon (Si) substrate under various condition. The PS was etched using hydrofluoric acid (HF) based solution and the porosity was optimized by introducing electroless chemical etching process prior to photo electrochemical (PEC) anodization. In the electroless etching, a delay time (TD) of 2 min was applied. After that a cycle time (T) and pause time () of pulsed current were supplied throughout the 30 min PEC etching process. As grown Si and PS through conventional direct current (DC) anodization were also included for comparison. The result obtained showed that applying delay time helps to improve the uniformity and density of the porous structures. AFM indicated that the roughness of the Si increases as the dissolution of the Si occurred. Raman spectroscopy showed that an improvement in the crystalline quality of PS under pulse etching method compared to DC method indicated by the reduction of full width at half maximum (FWHM). A broad visible photoluminescence (PL) was observed from green to red with blue shift as nanocrystallite size decreases which constituted quantum confinement effect from the PS structures. Nickel (Ni) finger contact was deposited onto the PS to form metal semiconductor metal (MSM) photodetector. Ni/PS MSM photodetector by pulse method exhibited higher gain (2 times) compared to conventional Si device at 5 V bias.

general purpose processor

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PurposeThe purpose of this paper is to describe a very low‐cost way to prepare Ge nano/microstructures by means of filling the material inside porous silicon (PS) using a conventional and cost effective technique in which thermal evaporator with PS acts as patterned substrate. Also, the potential metal‐semiconductor‐metal (MSM) photodetector IV characteristics of the structure are demonstrated.Design/methodology/approachPS was prepared by anodization of Si wafer in ethanoic hydrofluoric acid. The Ge layer was then deposited onto the PS by thermal evaporation. The process was completed by Ni metal deposition using thermal evaporator followed by metal annealing of 400°C for 10 min. Structural analysis of the samples was performed using energy dispersive X‐ray analysis (EDX), scanning electron microscope (SEM), X‐ray diffraction (XRD) and Raman spectroscopy.FindingsA uniform circular network distribution of pores is observed with sizes estimation of 100 nm to 2.5 μm by SEM. Also observed are clusters with near spherical shape clinging around the pores believed to be Ge or GeO2. The EDX spectrum suggests the presence of Ge or GeO2 on and inside the pore structure. Raman spectrum showed that good crystalline structure of the Ge can be produced inside the silicon pores. XRD showed the presence of a Ge phase with the diamond structure by (111), (220), and (400) reflections. Finally, current‐voltage (I‐V) measurement of the Si/Ge/PS MSM photodetector was carried out. It showed lower dark currents compared to control device of Si. The device showed enhanced current gain compared to conventional Si device which can be associated with the presence of Ge nanostructures in the PS.Originality/valueThis paper shows that it is possible to grow Ge nano/microstructure on PS by using a simple and low‐cost method of thermal evaporation and thermal annealing and demonstrates potential MSM photodetector IV characteristics from the device.

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