Porous Silicon p-type with Different Current Density

Porous Silicon p-type with Different Current Density Photoluminescence and Band Energy Gap For Porous Silicon p-type with Different Current Density  and Different Etching Time 1Mohammed Jabbar Hussein, *1W. Mahmood Mat Yunus, 2Halimah Mohamed Kamari 3Josephine Liew Ying Chyl, Abstract Photoluminescence (PL) for porous silicon lead to studied by many researcher .this phenomenon which has application in many devices. Porous silicon can be used in the optoelectronic devices and sensor. Therefore, the study to development porous silicon is very necessary,. In this study, porous silicon was prepared by chemical etching used silicon , the based electrolyte was ued HF acid with ethanol 1:1 . 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 current density and etching time. The has Band gap energy which is from 1.81 ev to 2.o7 ev , the band gap energy is increased with increasing current density and increasing etching time Introduction Since the discovery of visible luminescence in the room temperature [1–5], porous silicon (PS) has become a subject of considerable interest, optoelectronic device [6,7]. many several methods [8–10] for fabricating PS from crystalline silicon wafers. The electrochemical etching [1,8]. Both method is the difference between them the chemical etching without using 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 under the appropriate conditions applied current 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 aqueous or ethanoic HF solution The size dependency of the PL energy , which explains the efficient luminescence , causes the peaks to sift towards the higher 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 preparation 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 spectroscopy was used to determine the wavelength the emitted light . Preparation porous silicon All samples 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 plate 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 1:1. Theaside is an essential ingredient for the anodical etching of . Ethanol 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 infiltrate the pores, while purely aqueous HF solution does not. This is very important for the lateral hom ogeneity and the uniformity in depth of the () layer. A digital current source () was used to supply constant current. Figure (1) shows 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 plate Figure 1: Schematic of electrochemical etching cell for iodisation of () samples Figure (2):porous silicon (). a without light .b)with light .c) after remove the porous . Figure(3) : SEM images of PSi a) silicon wafer as scale 1m, b)-porous silicon (). as scale. c) porous silicon as scale 500 nm .d) porous silicon as scale . Results and discussion The optical properties of psi samples electrochemically etched at three different current density and by varying etching time. Figures (4- a,b,and c) shows the variation 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. respectively The 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 (ÃŽ ») 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 function of etching time and current density , respectively Figures (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 . Respectively Figure (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 [16] Figure (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 time Table (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 another 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 energy 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 . Acknowledgment The authors would like to thank Physics Department in the University Putra Malaysia for providing the research fealties. References [1]Canham, L.. (1990). Silicon quantum wire †¦Ã¢â‚¬ ¦Applied Physics Letters,57(10), 1046-1048. [2]Lehmann, V., Gà ¶sele, 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). Pore morphology and the mechanism †¦Journal of applied physics,72(1), 253-258. [4] Hummel, R. E., Morrone, A., Ludwig, M., Chang, S. S. (1993). On the origin of photoluminescence †¦Applied physics letters,63(20), 2771-2773. [5] Calderà ³n, A., Alvarado-Gil, J. J., Gurevich, Y. ., Cruz-Orea, A., Delgadillo, Vargas, ., Miranda, L. (1997). Photo-thermal characterization †¦.Physical Review Letters,79(25), 5022. [6] Joubert, P., Abouliatim, A., Guyader, P., Briand, D., Lambert, B., Guendouz, M. (1995). Growth and luminescence of n-†¦. Films,255(1), 96-98. [7Lockwood, D. J. (1994). Optical properties of porous silicon.Solid State Communications,92(1), 101-112. [8] Beale, M. I. J., Benjamin, J. D., Uren, M. J., Chew, N. G., Cullis, A. G. (1985). An experimental and †¦Ã¢â‚¬ ¦ porous silicon.Journal of Crystal Growth,73(3), 622-636. [9] Hummel, R. E., Chang, S. S. (1992). Novel technique †¦Applied physics letters,61(16), 1965-1967. [10]Maeda, Y., Tsukamoto, N., Yazawa, Y., Kanemitsu, Y., Masumoto, Y. (1991). Visible photoluminescence †¦ matrices.Applied physics letters,59(24), 3168-3170.). [11]Lemus, R.G., Rodriguez, C.H., Hander, F.B. and Duart, J.M.M. 2002. Anodic and optical characterisation †¦Ã¢â‚¬ ¦. Solar Energy Materials Solar Cell 72:495-501 [12] Bisi, O., Ossicini, S., Pavesi, L. (2000). Porous silicon: a quantum †¦Ã¢â‚¬ ¦Surface science reports,38(1), 1-126. [13] Nguyen, T. P., Le Rendu, P., Tran, V. H., Parkhutik, V., Esteve, R. F. (2000). Electrical and optical †¦Ã¢â‚¬ ¦. silicon structures.Journal of Porous Materials,7(1-3), 393-396. [14] Hirschman, K. D., Tsybeskov, L., Duttagupta, S. P., Fauchet, P. M. (1996). Silicon-based visible light†¦..microelectronic circuits. [15] Bernini, U., Lettieri, Maddalena, P., Vitiello., Francia. (2001). Evaluation of the thermal conductivity of porous †¦Journal of Physics: Condensed Matter,13(5), 1141. [16] Rajabi, M., Dariani, R. S. (2009). â€Å"Current improvement †¦Ã¢â‚¬ ¦Ã¢â‚¬ Journal of Porous Materials,16(5), 513-519. [17] Sheng, C. K., Mahmood Mat Yunus, W., Yunus, W. M. Z. W., Abidin Talib, Z., Kassim, A. (2008). Characterization of thermal†¦Ã¢â‚¬ ¦. B: Condensed Matter,403(17), 2634-2638. [18] Srinivasan, R., Jayachandran, M., Ramachandran, K. (2007). Photoacoustic studies †¦Ã¢â‚¬ ¦..Crystal Research and Technology,42(3), 266-274. [19]Ee, D. T. J., Sheng, C. K., Isa, M. I. N. (2011). Photoluminescence of porous †¦Ã¢â‚¬ ¦..Malaysian Journal of Analytical Sciences,15(2), 227-231.

Miracles of Life Essay

IÂ’m standing on the pavement outside my house, a coffee mug warming my hand, my hair dishevelled and my bare feet cold. ItÂ’s dawn. I love the way the purple of the sky stretches across to the fringes of the trees, seeping into the vivid orange of the sun. IÂ’m remembering mornings like this when we stood out here together, a frayed, woollen blanket draped across our shoulders, coffee mugs in our hands, shivering from the cold and gazing awe-struck at the sun as its fiery head slowly rose out from between the trees. The cars on Springvale Rd would buzz past us, whipping wind into out faces. Sometimes we shared opinions on these cars Ââ€" each car contained a person, you told me, and each person had a story to tell. We agreed with wonderment how it was quite amazing, this choreography of life. The cars themselves were moving capsules containing stories. Maybe in that polished Honda, there would be a joyful father and mother, and a new-born cuddled in soft blankets. Or maybe, that sleek, black Holden would contain an ASIS agent, investigating a terrorist attack. You laughed at the latter example, saying that my imagination must have gone wild from reading too much Alex Rider. I protested that possibilities were open and everything was possible. Once, we sat on the street curb, and I told you that I wanted to go to somewhere as exciting as medieval Paris, so that I could hunt on horseback all day and flirt with the lovely ladies. Eyebrows raised, you retorted that I should shut my perverted mouth, before primly reminding me that the medieval French had never heard of McDonaldÂ’s and often went for days without baths.

Hag Fishes

My name is Khari Spencer, and I am running for treasurer. I know all of you are probably tired and bored of hearing all these speeches of people telling you to vote for them, so I hope my speech stands out to you. I think the quote â€Å"Life is not measured by the number of breaths we take, but by the moments that take our breath away,† is something we should all keep in our minds. If I am elected for treasurer, I will try to make school something that you wish you could go back to. Money moves the wheels of history, and this year I will move those wheels like never before n the history of this school. Friends, desks and chairs will tremble and shake with the triumphent roar of coins and cash flowing into the hands of our excellent student council. Things will get done and we shall acquire great things for all people of all ages and classses within this family that is Paradise. Things will be done, and they will be done for -you-. As Franklin Roosevelt once said, â€Å"Happi ness is not in the mere possession of money; it lies in the joy of achievement, in the thrill of creative effort. I feel that we can all embrace the joy of achieving something great this year, and I know that all of our efforts will bring a financial blessing upon the school if you elect me for student council treasurer. What would make me a good treasurer? What qualities could I possibly possess that could accord me the rights to be in any position of relative power? Behind this outer shell of awesomeness and an incredible personality lies someone who is more than capable of being meticulous.I've yet to overdraw my checking account (I'm saving that for college), and I actually do work out a personal budget (granted, that's something I'm made to do, but hey. It still counts. ). This ridiculous amount of person greed and over the top focus on personal finance would make me an excellent treasurer. As for the non-financial element of the position, while it's true I've never held an off ice, I'm a creative person, with many different ideas (even if a lot of them are ridiculous. I'm easy to talk to and I love working around and with people, so the suggestions of others would be more than welcomed. It would probably make my life a heck of a lot easier. I look forward to coming up with creative fundraising methods. I may not have a coin collection that could rival that of the US Federal Mint, nor do I have any skills at basketball. At all. Whatsoever. I do not have one thing that many of the greatest political candidates of our time all have in common: empty promises.I do not make promises that if elected, Led Zeppelin will play in the cafeteria . I do not make promises that if you vote for me, a poor African boy will be given food. I also do not make promises to embezzle only a small portion of our school funds for dubious personal use. Ultimately, one could say, this would not be something I could do alone. Whether I'm elected or not, it isn't just the responsibilit y of the student government to make a fantastic school day.It comes down to all of you, even the people sitting in this room, bored out of your minds, to make this a possibility. While I'm sure that I could deal with the funds for a field trip, I certainly don't want to pay $100 for two tickets. That's insane. And four people can't keep costs down while still maintaining all of the fun that is our learning time. While I'm looking to get involved in running our class's finances and helping to organize class related events, I certainly don't want to make all about me (only a little bit).If elected, I would ask for and regularly enlist the help of all of you. While I could attempt to commandeer this position in a bloody coop, I have chosen to take the legal route into student office. In order to win, succeed, and actually do a good job, I'll need all of your help. I'm asking you to vote for me, and when/if I'm elected, I'm asking for you to help me and give me your input. This is, afte r all, about you, and not me. I'm running to work for you to make your 7th grade year as good as it can possibly

French Does Il Est Nécessaire Need the Subjunctive

The French phrase il est nà ©cessaire means it is necessary, and its used quite often. The question many French students have is whether or not it requires the subjunctive. The quick answer is yes, it does need the subjunctive. Well explain why. Why Does  Il Est Nà ©cessaire  Require the Subjunctive? There are many rules that tell us when the French subjunctive is required,  and its all about the underlying meaning of the phrase in question. The subjunctive is used when expressing an order, need, desire, or offering advice. In the case of  il est nà ©cessaire, it is required because the phrase expresses a need. The fact that something is necessary automatically qualifies it for the subjunctive. Also, it doesnt matter if you use il est  or cest, in either case, the subjunctive is mandatory. That means this rule also applies to  cest nà ©cessaire. Examples Il est nà ©cessaire quil le fasse. / Cest nà ©cessaire quil le fasse. -  Its necessary for him to do it.Il est nà ©cessaire quelle à ©tudie.  - It is necessary that she studies.Il est nà ©cessaire que tu à ©crives une lettre  - It is necessary that you write a letter. You can even use this phrase to remember that the subjunctive is necessary: Il est nà ©cessaire que vous utilisiez le subjonctif.  - It is necessary that you use the subjunctive.