Stark Effects on Band Gap and Surface Phonons of Semiconductor Quantum Dots in Dielectric Hosts
- PDF / 452,037 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 77 Downloads / 181 Views
ABSTRACT We have investigated quantum-confined Stark effect (QCSE) on GaAs and CdSe nanocrystals and the electric field effect on surface phonons of GaAs nanocrystals isolated in sapphire substrates. For a strongly quantum-confined system, GaAs quantum dots illustrated no exciton energy shift. When the excitons are weakly confined in CdSe, a - 2 meV red-shift was observed. On the other hand, the results of the electric field effect on surface phonon are dramatic both phonon oscilator strength and freqnency. As the strength of the electric field increases, the total intensity of the surface phonon decreases. At the same time, an additional peak was also observed at 277 cm-1, which is about 3 cm 1 above the center frequency of the surface phonon mode of GaAs nanocrystals embedded in a sapphire host. INTRODUCTION The study of semiconductor quantum dots (QDs) has attracted much attention in recent years due to the unique optical properties considerably differing from the parent (bulk) materials. To understand the physical and optical properties of the QDs and to fabricate more controllable quantum dots in terms of size and shape in various host materials are both the intriguing and challenging fundamental problems and the crucial steps towards the true realization of the new device applications. There have been number of ways' developed to fabricate quantum dots in different solid host materials and in solutions, such as inorganic synthesis, sol-gel synthesis, impregnation into porous hosts, vapor deposition, and ion implantation. Recently, it has been demonstrated that the sequential ion implantation of lI-VI and III-V elements into dielectric hosts followed by thermal annealing can lead to semiconductor quantum dots formation. The combination of linear optical and far-infrared reflectance (FIR) spectroscopy has been proved to be an effective characterization technique to identify the formation of quantum dots in dielectric hosts. The linear spectroscopy can be used to study excitonic absorption energy of the QDs due to the quantum confinements, while FIR technique can be used to study the surface phonon mode of the QDs falling between TO and LO modes of the bulk. In order to increase the versitility of the optical and vibrational techniques into the size- and shape-sensitive tools in characterizing QDs in various dielectric hosts, efforts have been made to study electric field effects on exciton energy and the surface phonon modes of the QDs embedded in the matrix. THEORETICAL CONSIDERATION Ouantum-Confined Stark Effect (OCSE) on Ouantum Dots QCSE on quantum well studied extensively in the past in a series of investigation by Miller at
al.9 New devices , such as optical modulators and self-electrooptical devices (SEED) have been
developed based on this effect. When the quantum dots are placed in an static electric field F, both 127 Mat. Res. Soc. Symp. Proc. Vol. 405 @1996 Materials Research Society
the exciton energy and their oscillator strength are modified. A model calculation by Jaziri4 showed that the total
Data Loading...
