Preparation, structure and optical properties of SiO1.5 alloys doped with boron
Résumé
Silicon nanocrystals (Si NCs) are the subject of an intense research activity, due to their optical and electronic properties. As in the case of bulk semiconductors, the fine tuning of their optical and electronic properties is related to the effective capability to control doping, i.e. incorporation of atoms such as phosphorous or boron within these nanostructures. We present in this study the preparation method, the structure and the optical properties of SiO1.5 thin films doped with boron. The alloys were prepared by co-evaporation of SiO and SiO2 from two electron-beam guns in an ultrahigh vacuum chamber. Boron was introduced from a Knudsen cell for the low contents and from an electron beam gun for the high contents. The films were annealed at different temperatures until 1100°C in order to obtain the dismutation of SiO which results in Si NCs embedded in a SiO2 matrix. The structure and the optical properties were studied by transmission electron microscopy (TEM), infrared absorption spectrometry and by photoluminescence (PL) experiments. Si NCs are observed by TEM in the annealed samples. Infrared absorption spectrometry allows us to follow the dismutation process and to observe an absorption band at 1380 cm-1 attributed to the O-B bonds. For low annealing temperatures, the PL spectra show bands attributed to defects. For annealing temperatures greater than 700°C, a band attributed to the Si NCs appears near 800 cm-1. This band disappears for high boron contents.