Three-Dimensional Carrier Confinement in Strain-Induced Self-Assembled Quantum Dots
- PDF / 2,089,900 Bytes
- 5 Pages / 576 x 777.6 pts Page_size
- 80 Downloads / 142 Views
Carrier Confinement in Strain-Induced Self-Assembled Quantum Dots P.M. Petroff and G. Medeiros-Ribeiro
Introduction Recent technological and materials advances in semiconductors have brought about the possibility of producing heterostructures within which carriers are confined to an ultrasmall region of space (a few thousand atoms) by a potential barrier. When the dimensions of the confining potential are smaller than the electron wavelength (a few tens of nanometers), the semiconductor electronic and optical properties are drastically altered. In these so-called quantum structures, carrier energy levels are quantized and their energy depends on the confiningpotential dimensions and magnitude. Some of these quantum structures have already found technological applications. For example the quantum-well (QW) semiconductor laser is part of every CD player. It is also widely used as the light source for intercontinental optical communications. The carrier confining potential in this case is provided by two wider bandgap semiconductor layers sandwiching a thin (3-20 nm) smaller bandgap semiconductor film. The carriers have two degrees of freedom within the QW. The QWs are grown by epitaxial deposition on a crystalline substrate. The substrate may or may not be latticematched with the epitaxial film. In some instances, a small lattice mismatch may be required to obtain the desired bandgap value for the QW material. These are the so-called pseudomorphically strained QW structures and devices. One can also use lithography and etching techniques to fabricate quantum
50
wires (QWIs) or quantum dots (QDs) in which carriers are additionally confined to have only one or zero degrees of freedom, respectively. A large increase of the oscillator strength and localization of the exciton are expected with higher degrees of confinement. Novel physical properties and device applications are predicted, and considerable efforts have been spent in producing QWI and QD structures. Success with the lithographyand-etching approach has been limited
because of the technological requirements of producing ultrasmall structures that are defect-free and that exhibit an abrupt carrier confining potential. An alternative approach that uses direct epitaxy for the fabrication of QWIs and QDs has recently been introduced. In the self-assembling method, we use both the growth thermodynamics and kinetics to direct the atoms to a specific region (e.g., steps or high strain regions on the substrate) on the surface. The method also relies on choosing the proper growth mode—that is, layer or island growth regime for the epitaxy of the QWIs and QDs, respectively. The lateral superlattice and serpentine superlattice' were the first attempt at demonstrating the self-assembled growth of QWI superlattices and QWI laser devices.2 These QWI structures showed characteristics that were associated with two-dimensional carrier confinement. Here we discuss the direct growth of self-assembled QDs, which recently has been the subject of much interest. The method for p
Data Loading...
