Prospects of Laser Operation in Erbium Doped Silicon
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Prospects of Laser Operation in Erbium Doped Silicon M. Q. Huda, S. I. Ali Dept. of EEE, Bangladesh University of Engineering and Technology, Dhaka 1000, Bangladesh Email: [email protected] ABSTRACT Prospects of laser operation in erbium doped silicon has been analyzed by a ShockleyRead-Hall (SRH) model. Erbium atoms have been considered to be introducing strong recombination centers in the silicon lattice. Electron-hole recombination at these sites were considered to be the source of erbium excitation. A two level system was considered for calculation of optical gain and the laser threshold. For a laser cavity of 300 µm with mirror reflectivities of 90%, and an optimistic absorption coefficient of 5 cm-1, a population inversion of 1.4x1018/cm3 was estimated as the threshold value. Achievement of the lasing condition was found feasible, but only for certain conditions of erbium activation. Effects of nonradiative deexcitation routes have been analyzed. On the assumption of 1019/cm3 of active erbium sites, linear increase of optical power in the laser cavity has been estimated for injected carrier densities above 1018/cm3. INTRODUCTION The indirect nature of its bandgap prevents silicon from being used as an optical emitter. Efforts have long been taken for achieving a viable silicon based light source in order to achieve complete optoelectronic functionality in silicon. Erbium, due to its sharp intra 4f shell transition at 1.54 µm in silicon, has been considered to be the most promising option for on-chip light emitters [1]. Electroluminescence from erbium doped silicon have been reported several years ago [2,3]. The problem of limited solid solubility of erbium in silicon has been overcome by the process of solid phase epitaxial recrystallization [4]. It has also been found that, presence of codopants can enhance erbium activity in silicon [5]. There has been recent work on the mechanism of erbium luminescence in silicon [6-8]. However, most of the work on erbium in silicon is focused on the spontaneous emission from erbium. Radiative lifetime of the decay of an erbium atom from its 4I13/2 state to the ground state is of the order of 1 ms. The process however is in strong competition with other nonradiative processes in silicon [7]. For optimized conditions of pumping action and minimized nonradiative competition, it may be possible to achieve a population inversion and lasing action in erbium doped silicon. Xie et al. [9] evaluated erbium doped silicon for light emitting diode (LED), amplifier, and laser operations. In this paper, we present a detailed study on spontaneous and stimulated emission from erbium in silicon. Using a Shockley-Read-Hall (SRH) model for erbium excitation, we analyze the feasibility of laser operation in erbium incorporated silicon. ELECTRONIC EXCITATION Erbium luminescence in silicon originates from the 4I13/2 - 4I15/2 transition of erbium atoms. The mechanism of excitation of erbium atoms from the ground state to the 4I13/2 state is
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