Observation of the population inversion of erbium ion states in Si/Si 1x Ge x :Er/Si structures under optical excitation M.V. Stepikhova a, * , L.V. KrasilÕnikova a , Z.F. KrasilÕnik a , V.G. Shengurov b , V.Yu. Chalkov b , D.M. Zhigunov c , O.A. Shalygina c , V.Yu. Timoshenko c a Institute for Physics of Microstructures, Russian Academy of Sciences, GSP-105, 603950 Nizhny Novgorod, Russia b Physico-Technical Research Institute, Nizhny Novgorod State University, Gagarin Ave. 23, 603950 Nizhny Novgorod, Russia c Moscow State University, Physics Faculty, 119992 Moscow, Russia Available online 23 November 2005 Abstract In this work we present the results of theoretical analysis and experimental studies carried out for Si/Si 1x Ge x :Er/Si structures con- sidered as the candidates for a laser realization. Analysis of the electromagnetic modes distribution and parameters of Si/Si 1x Ge x :Er/Si waveguides enabling strong localization of the optical modes in the active Si 1x Ge x :Er layers is given. The Si/Si 1x Ge x :Er/Si structures in question were grown by the method of sublimation MBE in germane gas atmosphere. The capability of such a method for producing effectively emitting Si/Si 1x Ge x :Er/Si structures has been demonstrated. The photoluminescence intensity of the structures produced is comparable with that determined for the uniformly doped Si:Er layers with the external quantum efficiency 0.4%. We show the pos- sibility to achieve the population inversion of Er 3+ ion states in Si/Si 1x Ge x :Er/Si structures under optical excitation. The population inversion of Er 3+ states in these structures sets in at the pump density of 0.2 W/cm 2 and reaches its maximal value at 4 W/cm 2 , where the concentration of Er 3+ ions being inversely populated amounts to 80% of the total concentration of optically active Er ions. Ó 2005 Published by Elsevier B.V. Keywords: Er-ions; Si/SiGe/Si waveguide structures; Population inversion 1. Introduction Considerable interest expressed recently in the erbium- doped silicon structures stems mainly from the possibility to create optoelectronic devices on silicon basis operating at the wavelength of 1.54 lm [1]. The radiative transitions of Er 3+ ions at this wavelength coincide with the spectral window of the quartz fibers, which opens wide perspectives for using Si:Er structures in modern fiber-optic communi- cation systems. The search for conditions to create laser- type structures, and development of the technology for their production are of particular importance in this field. An essential condition for the laser realization on Si:Er basis is the development of effective waveguide structures capable of providing strong localization of the optical modes in the active layer. Such kind of structures can be developed on the basis of Si/Si 1x Ge x :Er/Si heterostruc- tures with the active Si 1x Ge x :Er layers. In this case, the waveguiding effect is realized through introduction of Si 1x Ge x layers, the refractive index of which strongly depends on Ge content. Here we present the results of theoretical simulations and experimental studies carried out for Si/Si 1x Ge x :Er/ Si heterostructures produced by a specific method of subli- mation MBE (SMBE) in the germane gas atmosphere. The- oretical estimations of the optimal parameters for Si/ Si 1x Ge x :Er/Si waveguides will be given. By analyzing the kinetic behavior of Er-related photoluminescence (PL), we demonstrate a possibility to achieve the popula- tion inversion of Er 3+ ion states in such kind of structures under optical pumping. 0925-3467/$ - see front matter Ó 2005 Published by Elsevier B.V. doi:10.1016/j.optmat.2005.09.041 * Corresponding author. Tel.: +007 8312 385555; fax: +007 8312 385553. E-mail address: mst@ipm.sci-nnov.ru (M.V. Stepikhova). www.elsevier.com/locate/optmat Optical Materials 28 (2006) 893–896