tailieunhanh - Báo cáo hóa học: " Electromodulated reflectance study of self-assembled Ge/Si quantum dots"

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: Electromodulated reflectance study of self-assembled Ge/Si quantum dots | Yakimov et al. Nanoscale Research Letters 2011 6 208 http content 6 1 208 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Electromodulated reflectance study of self-assembled Ge Si quantum dots Andrew Yakimov Aleksandr Nikiforov Aleksei Bloshkin Anatolii Dvurechenskii Abstract We perform an electroreflectance spectroscopy of Ge Si self-assembled quantum dots in the near-infrared and in the mid-infrared spectral range. Up to three optical transitions are observed. The low-energy resonance is proposed to correspond to a band-to-continuum hole transition in the Ge valence band. The other two modulation signals are attributed to the spatially direct transitions between the electrons confined in the L and A 4 valleys of the Ge conduction band and the localized hole states at the r point. Introduction In order to realize Si-based optoelectronics Ge quantum dots QDs in Si matrices have attracted a large interest during the past years. Detailed knowledge on the electronic band structure and related optical transitions is very important when using self-assembled Ge Si QDs in Si-based photonic devices. To date most work on the optical properties of Ge Si QDs is based on the photoluminescence PL spectroscopy 1-4 . However as a rule PL measurements provide information on the groundstate transitions only. To study high-energy excited states it is more useful to perform absorption 5 or reflectance 6 7 experiments. In this study the optical transitions in layers of Ge Si QDs are investigated by electroreflectance ER spectroscopy as a function of applied electric field. Experimental details For controlled tuning of the electric field the Ge QDs are embedded in the intrinsic region of a Si pin diode allowing fields to be applied parallel the growth direction. To rule out spurious effects and to correctly assign the spectral features due to the presence of the dots three sets of samples were grown by means of molecular beam .