Vibrational and Electronic Transition in InAs Quantum Dots Formed by Sequential Implantation of in and as in a-SiO 2
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ABSTRACT The optical, structural, and thermodynamic properties of materials can be changed by reducing their dimensions. We sequentially implanted In and As into fused silica windows in order to investigate the formation and properties of InAs nano-particles. The UV/VIS/NIR, FTIR in mid-IR, and far-IR spectroscopy were mainly used to study the change in electronic transitions and in vibrational modes (phonons) of the nanoparticle InAs. The phonons can be confined to the surface of nanoparticles and have frequencies falling between the transverse and longitudinal optical modes of the bulk material. Thermal annealing developed the formation of InAs quantum dots from as-implanted In+As system. At a certain annealing temperature, we observed a change in UV/VIS transmission spectra and IR reflectance spectra indicating the formation of InAs quantum dots. This is particularly evident from the absorption in the IR, and surface phonon bands are observed confirming the presence of quantum confined InAs.
INTRODUCTION Reducing the dimension of materials causes a change in their optical, structural and thermodynamic properties. The study of nanometer-size semiconductor particles (quantum dots:
QDs) has drawn great attention both in fundamental physics and in applied science area. Recently, for example, it was proposed that an array of QDs can be parts of a new type of computer by controlling of the number of electrons in QDs,'' One of the most remarkable characteristics of these QDs is the quantum confinement effect. When the photo-induced electron-hole pairs are spatially confined within the QDs, this quantum confinement effect will modify the bulk electronic band structure which leads to the alteration of the exciton properties in the QDs. There have been number of ways developed to fabricate QDs in various substrate materials and in solution phases, such as inorganic synthesis 2'2, sol-gel synthesis,', impregnation into porous substrate 41,vapor deposition'', and ion implantation(6). Although ion implantation can be considered as one of the most clean and flexible techniques to obtain the QDs in substrate, the fabrication of the QDs has been limited to single element systems, such as Ge, Si, and P. Recently we have shown that sequential ion implantation(7) followed by thermal annealing is a promising and effective technique to fabricate III-V and 1I-VI QDs in dielectric substrates. In this paper, we report our experimental procedure and results for InAs QDs fabricated in SiO. by sequential ion implantation of As and In ions into a silica substrate followed by thermal annealing. Optical (UV-VIS range) and vibrational (IR) spectra have provided unambiguous identification of InAs QD formation.
S............................................................................................................................... t Author to whom correspondence should be addressed. 441 Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
EXPERIMENT As-ions (150 keV) and In-ions (160 keV) were sequentially implanted
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