Heterogeneous Reactions of GaAs Quantum Dots with Organometallic Precursors
- PDF / 3,438,028 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 7 Downloads / 208 Views
HETEROGENEOUS REACTIONS OF GaAs QUANTUM DOTS WITH ORGANOMETALLIC PRECURSORS WINSTON A. SAUNDERS*, ROBERT B. LEE*, HARRY A. ATWATER-, KERRY J. VAHALA*, RICHARD C. FLAGAN t , AND PETER C. SERCEL*1 *Applied Physics, M. S. 128-95 t Chemical Engineering, M. S. 210-41 California Institute of Technology, Pasadena, CA 91125 ABSTRACT We report recent results on the homogeneous nucleation of GaAs quantum dots from organometallic precursors and subsequent heterogeneous nucleation of epitaxial regrowth of GaAs on the clusters. We find that clusters onto which we have regrown GaAs exhibit a much higher degree of faceting, whereas particles subject to the same thermal cycles but onto which no new GaAs has been grown, though crystalline, have highly irregular shapes. These results suggest that epitaxial regrowth exhibits selectivity in the growth rates on the various crystal facets akin to that found in bulk samples. INTRODUCTION Recently we have demonstrated the formation of nanometer-scale GaAs clusters from the homogeneous nucleation of organometallic precursors.' The resulting clusters were shown to be faceted, stoichiometric and crystalline in the 10 to 20 nm size regime, making them excellent candidates for 0-D 2 confined semiconductors (quantum dots). However, the clusters are not optically active, i.e. they show no photoluminescence, owing to the high density of surface states derived from the dangling bonds at the cluster surface. The nonradiative decay of excitons caused by these states is much faster than radiative decay. Thus, as in the case of bulk semiconductors, it is necessary to passivate the surface states. Indeed, because of the high surface to volume ratio of the clusters, passivation becomes rather more critical. The regrowth of a passivation layer onto a nanometer scale quantum dot presents many challenges not present in the growth of epitaxial layers on planar GaAs substrates. For example, a quantum dot in the gas phase presents many surfaces of different crystalline orientation, thus anisotropy of the growth rates, known for planar samples, 3 can be expected to modify strongly the morphology of the clusters. Regrowth of like materials onto existing particles has 5 already been demonstrated for silicon particles 4 and also dissimilar materials. In this paper we report studies of the heterogeneous nucleation of GaAs onto pre-synthesized GaAs clusters. We find evidence that heterogeneous growth of GaAs on GaAs clusters results in highly faceted particles. Clusters which go through the same thermal cycles but are not exposed to additional metalorganic precursors in the second growth step, on the other hand, have highly irregular shapes. This data suggests that heterogeneous growth on the clusters results in faceting via mechanisms akin to those which play a role in selective epitaxy of planar devices. 1.Present address: Physics Dept., University of Oregon, Eugene, OR 97403 Mat. Res. Soc. Symp. Proc. Vol. 283. 01993 Materials Research Society
772
EXPERIMENTAL METHOD As reported previously, 1 the clusters are
Data Loading...
