Organic Semiconductors are an interesting sub-class of organic materials that exhibit a bandgap. Because of this bandgap they are interesting for a variety of optical applications. One of these applications is Organic Light Emitting Diodes or OLED's which is the organic equivalent of normal inorganic LEDs and are readily found in modern smartphones, tablets and high-end television sets and displays. Another optical application that requires the existence of a bandgap is Light Amplification by Stimulated Emission of Radiation or LASERs. A LASER requires a gain medium that can be forced into a state of population inversion. This state is most commonly reached through either optical or electrical pumping of the medium. Even though optical pumping is considered the simplest of the two it does require a wavelength specific mirror to be used to form the lasing cavity.
A Distributed Brag Reflector or DBR can be used as a wavelength specific reflector and could be fabricated from organic layers. A pair of DBRs can be designed around an organic active medium that can support population inversion to create an all-organic LASER.
Figure1: Example of an optically pumped organic laser realised at
the University of St Andrews.
In this thesis a large component will be design and fabrication of the device. A DBR has to be designed and fabricated. The student will have to determine the optimal materials and layer thicknesses as well as the optimal number of pairs to be used. Fabrication will be done with our dedicated organic evaporator in the cleanroom in Zwijnaarde. Simulations and measurements are done in our labs in Technicum. The student will be encouraged to find new ways of introducing refractive index variations by, for example, altering deposition conditions. Once the optical design of the DBR mirrors is complete, they can be incorporated into an all-organic laser which can then be characterised in our labs.
This thesis strikes a good balance between simulations, during the initial design, and experimental work in both lab and cleanroom environment. In addition to this, organic light emitting devices are a field of study that has many practical applications and would be a nice addition to your CV should you consider working in the display industry.