Characterization of SiGe Alloy Nanocrystallites Prepared by Pulsed Laser Ablation in Inert Gas Ambient
- PDF / 433,101 Bytes
- 6 Pages / 412.92 x 646.2 pts Page_size
- 69 Downloads / 192 Views
"**Institute
of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
ABSTRACT We report nanometer-sized silicon germanium (SiGe) alloy crystallites prepared by excimer laser ablation in constant-pressure inert gas. Size distribution of the SixGei-x ultrafine particles decreases with decreasing x under fixed conditions of deposition such as ambient gas pressure. Raman scattering spectra of the deposited SiGe ultrafine particles show three peaks intrinsic to crystalline SiGe alloys, and the linewidths of these peaks broaden due to the reduced size of the
crystallites. Furthermore, a visible photoluminescence (PL) band with a peak at around 2.2 eV is obtained at room temperature after an annealing process. INTRODUCTION In the past several years, extensive studies have been carried out on nanometer-sized silicon (Si) and germanium (Ge) structures since visible photoluminescence (PL) spectra were observed [ 1-4]. In particular, the strong PL from porous Si has attracted much attention and much research has been undertaken to clarify its origin [5]. Furthermore, SiGe alloys have the possibility of band structure engineering by controlling the composition [6], and there have been several reports on optical properties of porous SiGe [7,8]. When we discuss the optical properties of nanoscale group IV materials as one of the quantum confinement effects, it is significant to adopt another approach using the nanoscale "spherical" structures which have well-controlled size and surface chemical structure. For this purpose, pulsed laser ablation into a gas ambient has been applied to the preparation of Si ultrafine particles [9-12]. Werwa et al.[9] reported that the minimum diameter of Si ultrafme particles was about 2 nm in laser ablation into a pulsed inert gas. Yoshida et al.[1 1] reported that the size distribution of Si nanocrystallites was effectively controlled by varying the ambient gas pressure. Furthermore, pulsed laser ablation has the potential for use in the deposition of complex materials with congruent transfer of the target composition [13), and SiGe thin films have been prepared using this method [14]. However, there have been few studies where alloy nanocrystallites are obtained using laser ablation in a gas ambient. In this work, we adopt the laser ablation method combined with the constant-pressure inert gas evaporation system. A sintered mixture of Si and Ge powders is used as a target. We characterize structures and optical properties of SiGe alloy nanocrystallites prepared by laser ablation in an inert gas. EXPERIMENT In order to deposit Si and Ge, which have different melting points and vapor pressures, at the same time by laser ablation, an appropriate target should be a mixture of Si and Ge with high purity. Thus, sintered SiGe targets were fabricated as follows. Si and Ge powders with the size of pm order and high purity of 6N were mixed without binder and sintered using a hot press system 123 Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Materials Research Society
in an inert gas. Then,
Data Loading...
