Colloidal Quantum Dot Active Layers for Light Emitting Diodes

Nanotechnology is proliferating at a rapid rate in many areas including semiconductor lasers, biotechnology, and optoelectronics, as researchers create applications which capitalize on the unique advantages operating on the nanoscale afford them. In the case of semiconductor lasers it was found that by creating active layers on order of the de Broglie wavelength in all spatial directions, the movement of the free electrons would be restricted. This electron confinement inhibits the spreading of carriers thereby reducing the thermal sensitivity of a device. In fact thermal effects should be zero when electrons are three dimensionally confined. In such a system the density of states is defined as a delta function resulting in a larger and narrower gain profile for the laser (Arakawa and Sakaki, 1982; Asada et al., 1986). Quantum dots are the closest representation of a semiconductor system where there is three dimensional electron confinement. The emission spectrum of a quantum dot can be tuned across a wide range of wavelengths due to the quantum size effect, making the technology ideal for use in light emitting diode (LED) active layers (Alivisatos, 1996). Semiconductor materials from the III-V group are used in high-efficiency LEDs at both ends of the visible spectrum, III-arsenide-phosphide (III-AsP) materials provide emission from yellow to infrared, and III-nitride (III-N) materials emit from blue-green into the ultraviolet. However only III-nitride LEDs are fabricated with InGaN quantum dots which are epitaxially grown, and there is no material in either the III-AsP or III-N regime that provides efficient deep green (555-585nm) emission. Highly efficient deep green colloidal CdSe quantum dot emitters are available however, and it has been recently suggested to use these colloidal quantum dots as the active layer in a GaN heterostructure to create a LED (Stokes et al.,2005). Presented are efforts to integrate colloidal quantum dots into GaN heterostructures to a- - ct as luminescent centers forming the active layer of a LED