Porous Silicon p-type with Different Current Density

permeable ti p-type with Different Current DensityPhotoluminescence and Band Energy Gap For Porous Silicon p-type with Different Current Densityand Different Etching Time1Mohammed Jabbar Hussein, *1W. Mahmood Mat Yunus, 2Halimah Mohamed Kamari3Josephine Liew Ying Chyl,AbstractPhotoluminescence (PL) for holey silicon lead to studied by many interrogationer .this phenomenon which has application in many devices. Porous silicon can be used in the optoelectronic devices and sensor. Therefore, the study to development holey silicon is very necessary,. In this study, porous silicon was active by chemical etch used silicon , the based electrolyte was ued HF acid with ethanol 11 . The porous silicon was characterized by Photoluminescence Spectrometer (PLS) and (SEM) Microscope. The range of the porosity (20.33 78.2) % and it is dependent on true denseness and print time. The has Band quip cypher which is from 1.81 ev to 2.o7 ev , the mob cattle farm energy is increased wit h change magnitude certain tautness and increasing etch timeIntroductionSince the discovery of visible luminescence in the room temperature 15, porous silicon (PS) has become a subject of considerable interest, optoelectronic device 6,7. many several methods 810 for fabricating PS from crystalline silicon wafers. The electrochemical etching 1,8. Both method is the difference between them the chemical etching without utilise the external bias, therefore, considered this method the localized electrochemical process chemically 11. Porous silicon was discovered in 1956 by Uhlir ( Uhlir 1956) while performing electro polishing experiments ,hydrofluoric acid (HF) was prepared in to silicon wafer by electrolyte containing . He found that beneath the fascinate conditions applied ongoing and solution composition , the silicon did not dissolve uniformly but instead fine holes were produced, porous silicon formation was obtained using electrochemical dissolution of silicon wafer in a queous or ethanoic HF solution The surface dependency of the PL energy , which explains the efficient luminescence , causes the peaks to sift towards the high energy or lower wavelength , as already reported 12,13 ,the red shift in PL peaks with decreasing average size of Si structure size in psi is considered to be strong evidence that the visible PL is caused by the quantum confinement effect 14 . The degree of the blue shift for psi usually depends forwardness condition , Si resistivity , substrate ,type and dopant concentration , which can cause different modification of psi microstructure during anodisation 15 The values of the band gap energy of the porous silicon are the same range of the reported ( 1.5ev to 2.5 ev) 16.17,18 In this work , porous silicon p-type was prepared by electrochemical etching technique and photoluminescence PL spectrometry was used to determine the wavelength the emitted light .Preparation porous siliconAll experiments were prepared on (100) n- type silicon (Si) single crystal wafers of 537 thickness. Silicon substrates were cleaned by sonification for 5min in ethanol, and acetone. A Si substrate was placed at the bottom of a cylindrical Teflon cell and fixed by an aluminium eggshell as a backing material. A platinum (Pt) rod serves as a cathode perpendicular to the Si surface at a distance of (1cm). The samples were prepared with constant current, density, and etching time at a concentration of ethanol ( in the volume ratio of 11. Theaside is an essential ingredient for the anodical etching of . fermentation alcohol was added into electrolyte to enhance the homogeneity and uniformity of the () surface because it acts as a promoting agent to increase the wettability of () surface and to remove the extraneous H2 bubbles that appear during the anodical etching process. In fact, ethanic solutions pass through the pores, while purely aqueous HF solution does not. This is very important for the lateral homogeneity and the u niformity in depth of the () layer. A digital current source () was used to supply constant current. Figure (1) visual aspects the schematic diagram of all the elements used for the preparation of (). To generate the electron hole pairs, the surface of sample was illuminated with halogen lamp () during iodisation. For all samples, a voltage of was applied to the halogen lamp for illumination. The current densities used for samples are 10 mA/cm2, 20 mA/cm2, and 30 mA/cm2 with etching times of 20mins, 40mins, 60mins, and 80mins. HF based electrolyte Pt electrode Teflon cell Si wafer Current source AL plateFigure 1 Schematic of electrochemical etching cell for iodisation of () samplesFigure (2)porous silicon (). a without light .b)with light .c) after remove the porous . Figure(3) SEM images of PSi a) silicon wafer as carapace 1m, b)-porous silicon (). as scale. c) porous silicon as scale 500 nm .d) porous silicon as scale .Results and discussionThe optical properties of psi s amples electrochemically etched at three different current density and by varying etching time. Figures (4- a,b,and c) shows the variant of PL spectra with etching time for the psi samples obtained at the current density 10 mA /cm2 , 20 mA/cm 2, and 30 mA/cm2. The intense luminescence spectra emitted from porous silicon structures formed on the samples. The pl peaks show a steady red color shift from 500 nm to 800 nm with increasing the etching time .,Figures (4-a,b,c) PL peaks for porous silicon samples prepared under differnet etching time with the current density a) 10 ma/cm2 ,b)20 mA/cm2 ,c)30 mA/cm2. respectivelyThe Figure (5) show the PL spectra of samples prepared by current density of 10, 20 and 30 , respectively ..The band gap energy () was inferred from (PL) wavelength () using (. the relationship between band energy gap with the current density and etching time is increased the band energy gap when the current density and etching time increasing 19 . Figure (5-a,b) show the energy gap () variation of psi samples as a share of etching time and current density , respectivelyFigures (5-a,b) Band energy gap as a function to a) etching time with different current density ,b) currents density with the different etching time . RespectivelyFigure (6) show the band energy gap versus the porosity for three different current density of the samples and deferent etching time. The band gap energy value is not linearly increased with increasing porosity because the change in the structure size of the silicon. The results show the dependency of the band gab energy value to the current density especially in high porosity 16Figure (6) .band gap energy as a function to porosity with different current density.Table (1) .the values of porosity, band gap energy, and PL peaks intensity for porous silicon with different current density and different etching timeTable (1) shows that the band gap energy increases from ( 1.82 ,1.90,194,and 1.97 ) ev to (1.86,1.91,196,and 2,01) in etching time (20,40,60,and 80 )min respectively when the current density increasing from 10 to 20 ,also the increases the band energy gap from ( 1.86,1.93,196,and 2,01) ev to ( 1.93,1.97,2.01 ,and 2.07 ) in the etching time20,40,60,and 80 )min respectively when the current density increasing from 20 to 30. The results show an increase the band energy gap when the etching time increasing. That mean the band energy gap depended of the current density and etching time . the results shown the band gap energy is increased with etching time , it is increase from (1.82,1.86,and 1.93 ) ev to (1.90 , 1.93 , and 1.97 ) ev in the current density (10,20,and 30) mA/cm2 respectively when the etching time increasing from 20 min to 40 min . as well to some other etching time from 40 min to 60 min and from 60 min to 80min .Conclusion.In summary. The results show for the effects the etching time and current density to the band energy gap and the porosity. In this experimental the band ener gy gap is increased with increasing the current density the band gap energy increases from ( 1.81 ,1.88,194,and 1.99 ) ev to (1.86,1.91,196,and 2,01) in etching time (20,40,60,and 80 )min respectively when the current density increasing from 10 to 20 , . as well to another current density ,also the band energy gab is increased from (1.81,1.86,and 1.93 )ev to (1.88 , 1.91 , and 1.97 ) ev in the current density (10,20,and 30) mA/cm2 respectively when the etching time increasing from 20 min to 40 min . as well to another etching time .AcknowledgmentThe authors would like to thank Physics Department in the University Putra Malaysia for providing the research fealties.References1Canham, L.. (1990). Silicon quantum wire Applied Physics Letters,57(10), 1046-1048.2Lehmann, V., Gsele, U. (1991). Porous silicon formation A quantum wire effect.Applied Physics Letters,58(8), 856-858.3 Searson, P. C., Macaulay, J. M., Ross, F. M. (1992). 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