Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Improved infrared photoluminescence characteristics from circularly ordered self-assembled Ge islands | Das et al. Nanoscale Research Letters 2011 6 416 http content 6 1 416 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Improved infrared photoluminescence characteristics from circularly ordered self-assembled Ge islands 12 1 1 1 1 Samaresh Das Kaustuv Das Raj Kumar Singha Santanu Manna Achintya Dhar Samit Kumar Ray and Arup Kumar Raychaudhuri2 Abstract The formation of circularly ordered Ge-islands on Si 001 has been achieved because of nonuniform strain field around the periphery of the holes patterned by focused ion beam in combination with a self-assembled growth using molecular beam epitaxy. The photoluminescence PL spectra obtained from patterned areas . ordered islands show a significant signal enhancement which sustained till 200 K without any vertical stacking of islands. The origin of two activation energies in temperature-dependent PL spectra of the ordered islands has been explained in detail. Introduction The confinement of charge carriers in low-dimensional Ge Si heterostructures allows one to increase the efficiency of the radiative recombination making the indirect gap group-IV semiconductors attractive for optical devices. Owing to the type-II band alignment 1 Ge dots form a potential well only for holes whereas the electrons are weakly confined in the vicinity of the Ge dots . by the tensile strain field in the Si cap induced by Ge quantum dots QDs 2 3 . The resulting recombination energy depends strongly on size shape strain and composition of the QDs leading to a wide emission energy spectrum. Therefore intensive effort is currently undertaken to prepare arrays of identical QDs which emit in a resonant mode 4 . Infrared IR photoluminescence PL at room temperature has been reported by vertical ordering of Ge islands in three-dimensional stack of 10-20 periods 5 6 . To improve the lateral ordering of QDs one of the strategies is to convert the stochastic nucleation process into a .
