Stoichiometry of GaAs nanodots on GaAs(001)
- PDF / 770,058 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 84 Downloads / 195 Views
Stoichiometry of GaAs nanodots on GaAs(001) Anahita Haghizadeh1 and Haeyeon Yang1 * 1
Department of Nanoscience and Nanoengineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, U.S.A. ABSTRACT We present a strain-free, self-assembled GaAs nanodots on GaAs(001) surfaces. Nanodots are studied by atomic force microscopy and field emission scanning electron microscopy. Nanodots self-assemble on the GaAs surface when two laser pulses overlap on the surface interferentially. Their stoichiometry is characterized by energy dispersive X-ray spectroscopy in the electron microscope. For the stoichiometry study, electrons with voltages less than 5 kilovolts were used to produce the characteristic X-rays from dots in order to enhance the surface sensitivity. The stoichiometric analysis indicates that the nanodots’ relative composition ratio of Ga over As reaches to that of GaAs substrate when the dot size becomes smaller than 100 nm. The chemical analysis suggests a novel route of strain-free semiconductor nanodots. INTRODUCTION The self-assembly of epitaxial nanocrystals typically requires a lattice mismatch larger than 2% between the substrate and the heteroepilayers that are deposited on top of the substrate. The lattice mismatch is the basis of the so-called Stranski-Krastanov (S-K) growth mode. Three dimensional nanocrystals, or quantum dots (QDs) smaller than the thermal de Broglie wavelength[1] for GaAs have been successfully fabricated using the strain-driven S-K growth technique that utilizes the energy minimization processes for nanocrystals to form. However, it has been difficult to fabricate epitaxial nanocrystals without strain, which limits the number of available material systems because the quantum dot should have a larger lattice constant as well as a smaller bandgap than the surrounding matrix. Recently lasing from strain-free GaAs QDs embedded in AlGaAs barrier material have been reported,[2] which suggests that the GaAs QDs grown from Ga rich droplets can be used to fabricate novel optoelectronic devices. The QDs are fabricated via the droplet epitaxy technique, where Ga rich droplets are formed by depositing Ga on GaAs or by heating GaAs substrates at temperature higher than 500 °C under no or low enough arsenic overpressure. Due to preferential evaporation of arsenic at the elevated temperature or by the deposition of Ga, the surface becomes gallium rich, resulting in Ga congregation and forming a gallium rich regions or the so-called “Ga droplets”. In this paper we report GaAs nano dots formed on the GaAs(001) surface, when it is irradiated interferentially by laser pulses (IILP). The temporal width of pulse is 7 nanoseconds. Absorption of laser energy induces heating of the exposed region, raises the temperature, which induces melting and evaporation at high pulse energy while annealing at low laser intensity. For example, direct laser heating has been used to create and align self-assembled metallic nano dots on glass substrates.[3, 4] The dots are aligned along interference lines
Data Loading...
