Quantum Dots
Semiconductor Quantum Dots (QDs) are crystalline nano-particles ranging from 2-50nm in size, that exhibit unique optical properties derived from quantum confinement effects. The optical emission wavelength of QDs can be tuned with great precision, depending on their composition, size, and surrounding matrix. Also, their emission wavelength and intensity is less sensitive to temperature. Such properties make this class of materials highly attractive to use in a variety of optoelectronic applications and devices.
The most studied semiconductor QD materials are made from InGaAs, SiGe or CdSe; however the III-Nitride family (InGaAlN) potentially offers devices that will emit light efficiently across all of the visible wavelength range and also into the UV and IR spectral regions. III-nitrides also experience an internal piezoelectric field that can affect its emission properties and possibly be exploited in device applications.
Research at Sharp laboratories of europe (SLE)
At SLE we have an MBE (click here for further information on MBE) system dedicated to the growth of quantum dots and we are investigating the formation of quantum dots by Stranski-Krastanov and seeding methods. Stranski-Krastanov growth occurs during strained layer epitaxy, when a semiconductor material is grown on an underlying substrate layer with a lattice constant several percent smaller. Initially the growing layer (the wetting layer) is fully strained to the lattice constant of the underlying layer. Strain energy increases with increasing layer thickness until a critical thickness is reached; at this point clusters form and the strain energy is reduced by elastic relaxation. Under the correct growth conditions these clusters can be high crystalline quality quantum dots. Creating QDs by seeding involves patterning the surface lithographically to determine where the QDs will be formed and can result in a highly uniform array of QDs.
Researchers at SLE will investigate the growth and properties of these quantum
dots and develop new devices based on this technology.
