Bulk silicon (Si) and germanium (Ge) have an indirect band gap transitions; howeverrnwhen they are miniaturized to nanometeric scale, the energy gap between the highestrnoccupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO)rnincreases, and hence the transition changes to direct due to confinement. The HOMOLUMOrngap determines the excitation of electrons so that the nanostructures will emitrnlight.rnIn this thesis, quantum confinement effects for Si and Ge, some methods of calculatingrnband structures, comparative analysis of photoluminescence (PL) and electroluminescencern(EL) are presented. The thesis focuses on EL and for comparison purpose, some studiesrnon PL is touched. Both are the emission of energy in the form of light spectrum of differentrnwavelength by optical radiation, and current or strong electric field.rnThe dependence of EL on different parameters like size of the nanocluster, appliedrnvoltage, band gap energy, wavelength, temperature, and time for Si are briefly examined.rnThe dielectric matrix silicon dioxide has unique optical and electrical properties, as arnresult the dependence of EL intensity on the above parameters for Si-terminated withrnoxygen and hydrogen is included in the thesis; in fact passivation enhances EL and highlyrnefficient EL is obtained at low operating voltages (< 6V ), it is also observed that ELrndegrades with time. The EL and PL intensities occur at the same energy, however thernEL intensity has sharp Gaussian peak and red shifted compared to the PL intensity. Tornget our result, we used the idea of quantum confinement model (QCM) and surface staternmodel (SSM), that can explain PL and EL on pure Si nanostructures, and Si-terminatedrnwith impurities. Our results are consistent with experimental reports.rnixrnAcknowledgementsrnI am grateful to my advisor, Dr. S. K. Ghoshal for his critical and constructive suggestion,rnwell planned follow up, constant support, and friendly approach during this research, hernwas tireless, programmed, and ready to encourage me at any time when I consult himrnnot only in my thesis work but also in my entire graduate study. As an advisor he put arnlot of impression on me that I never forget whenever and wherever in my academic life;rnI want to forward my gratitude to Mr. Anteneh Getachew and Mr. Billilign Tsigie forrntheir unreserved academical and technical support; with out the help of these persons thernwork could not be completed duly.rnI am indebted to express my heart felt gratitude to the following individuals, who havernbeen electronic communications with me for providing journals and other materials relatedrnto my thesis; Mr. Ayesheshim Kebie from Alberta University, Canada, Dr. AsdesachrnZenamarkos from Germany, Mr.Getasew Admasu from Antwerp University, Belgium andrnMr. Semere Ayalew from Jimma University.rnI want to express my due appreciation to Addis Ababa University, physics department,rnfor providing this chance, rendering good office service during my stay, and I want tornextend my acknowledgement to the staff members of the department, who devote theirrntime for academic matters that made my stay very happy in the graduate program.rnFinally, with no words for me to express my heart feeling for his patience, I wouldrndeeply like to thank Mr. Solomon H/M, for his great cooperation on conducting manyrnof my affairs directly or indirectly related to Jimma University on behalf of me and Irnwant to extend my gratitude to Jimma University, providing sponsorship, for faculty ofrneducation, and Physics department for creating conducive situations to get sponsorshiprnfrom the University to my study