Research Fellows Directory
Jo Shien Ng
Dr Jo Shien Ng
University of Sheffield
My research focuses on developing photodiodes for a wide range of applications. A photodiode senses light (optical power) and convert it into an electrical current, which can be easily detected and processed by electronic circuits. A photodiode is usually sensitive to a range of wavelengths, which depends on the semiconductor material used to make the photodiode and the photodiode design. For example silicon photodiode usually cover 450 to 1000nm wavelength light. Choosing the semiconductor material appropriately is critical to matching the required detection wavelength range. The photodiode can also be designed to provide internal signal amplification through a process called avalanche multiplication. The resultant device is thus termed avalanche photodiodes (APDs).
Light detections at 1.3 micron are essential to optical fibre communication systems. Existing APDs for this application used InP substrates because the suitable material for sensing 1.3micron light must be grown on InP substrates. However it is highly desirable to use GaAs substrates because they are available in much larger sizes, giving significant cost savings. I study the material GaInNAs, which has several attractive attributes. My work has shown that it can be grown on GaAs substrate without sacrificing device quality and it detects light at 1.3 micron (and possibly beyond). I am working with collaborators at UK and Europe to develop low-cost high-performance GaAs-based APDs using this material.
I also work with an x-ray detector group based in University of Leicester. We are trying to improve semiconductor x-ray detectors, with emphasis on detecting “soft” x-rays, which are used in medical imaging and security scanning systems. We would like to use semiconductor diodes that can be operated at room temperature, thus minimising cooling requirements (which add cost and power consumption). X-ray APDs (to boost the incoming signal) are also a topic that I am working on.