Nitride-based semiconductors, such as GaN, InGaN and AlGaN, are materials that are used in ubiquitous white, blue and green LEDs, and laser diodes (for Blu-ray players) which is a huge industry with a multi-billion dollar market. The technologies of these semiconductors have progressed and matured enormously over the last two decades and has resulted in very low cost production for these devices.
Nanowires are quasi-1-D structures having diameters of a few tens to hundreds on nm but with lengths of um’s. These structures have many unique and desirable properties such as large surface area-to-volume ratio, which has great potential for applications such as high efficiency solar cells and the next generation of ultrasensitive sensors for the detection of biological and chemical species on an unprecedented atomic scale level. The synthesis of nanowires also result in the spontaneous formation of energetically preferred facets, such as the non-polar m-plane. These facets can be utilised to circumvent the effect of internal piezoelectric polarisation field, which causes the electron and hole wavefunctions to separate spatially and hence reduce quantum efficiency.
There are many applications that utilise the UV region of the electromagnetic spectrum such as water sterilisation, air purification, surface disinfection, free-space non-line-of-sight covert communication, epoxy curing, counterfeit detection, light therapy and fluorescence identification of biological/chemical agents. Currently nearly all UV lamps generate radiation by means of a gas discharge. They are fragile, bulky, expensive, and contain toxic substances such as mercury or deuterium. Hence there are lots of interests in realizing small, robust and highly portable UV sources. AlGaN is a good candidate as it has a large bandgap that corresponds to the UV range and also the maturity of LED technology.
This project can be divided into two main modules in which students choose both or either modules or any aspects of each module depending on interests of the students and duration of the program:
- The first is to synthesise the AlGaN nanowires using our new MOCVD system and understand, through various structural, electrical, and optical characterisation techniques, how to (i) improve the material quality, (ii) efficiently dope this semiconductor layer, (iii) control the composition and material, and (iv) to engineer the bandstructure of multilayer structures
- The second part of the project involves (i) the design of the LED structures, (ii) the use of state-of-the-art device fabrication facilities to transform these nanostructures into LEDs with electrical contacts and (iii) characterising the performance and properties of these LEDs to understand the underlying physics of the devices.