interview
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2017-08-01 |
| Journal | Electronics Letters |
| Authors | Anonymous |
Abstract
Section titled āAbstractāJoshua D John Dr Joshua D John from the International Christian University, Japan, talks to us about the work behind the paper āElectronic Properties and Potential Applications of the Heterojunction between Silicon and Multi-nanolayer Amorphous Seleniumā, page 1270. During my undergraduate studies, my thesis was an attempt at visible light communication. I concluded that such an application requires unique photodetectors, beyond those available off-the-shelf. Afterwards, confronted with the intense energy crisis in my home country Zimbabwe, and in many other parts of the world, I realised that the solution was in renewable energy. There was need for low-cost, low-tech fabrication of wide-area and high-efficiency solar cells. Research in this area led me to joining the Photoelectronics Research Group at the International Christian University, led by Professor Ken Okano. One of the greatest challenges in our field is achieving ultrasensitive detection of X-ray photons for medical applications; X-ray detection having changed very little since its invention. The goal is a direct-detection, high-resolution, real-time, digital, flat-panel detector. The main challenge is finding the best material and the best driving mechanisms that can be used reliably and in very low doses. In our work, we investigate amorphous selenium (a-Se) as an X-ray direct-detection material, which has led us to also consider multilayer, multi-material, tandem solar cells. We investigated electronic properties of the junction formed between multi-nanolayer a-Se and silicon. The large built-in potential of the a-Se/n-type (n-Si) structure and UV sensitivity means that there is potential in applying the a-Se/n-Si structure in a tandem solar cell. The main challenge has been lattice mismatches. As a work-around to this problem, we have adopted an amorphous material, a-Se, which cannot be described in terms of a lattice constant due to its random arrangement. This means we need only focus on optimising other aspects of the interface such as current matching by using nanometre thicknesses of a-Se. For the solar cell device, we are developing the electrochemical method of doping a-Se selectively to produce regions of n-a-Se and p-type (p-Se) and form a p-n junction. We are now working on doping a-Se that is already deposited on n-Si. Ultimately, we could obtain a n-a-Se/p-a-Se/n-Si/p-Si multi-structure which could extend the silicon solar cell to capture the UV part of the solar spectrum. Towards X-ray detector applications, we are considering extending the a-Se/n-Si heterostructure to include N-doped diamond, which, in theory, promises some interesting real-time detection and display possibilities. We are currently working on a-Se-based X-ray detectors driven by carbon-based field emitters. We have done some work on a diode structure detector with a-Se as anode and N-doped diamond as cathode. We are also working on using graphene as the cold-field emitter cathode and are considering a-Se/n-Si/diamond heterostructures. We are also extending our work on the electrochemical doping of a-Se. We are investigating the electrolysis process further to establish methods of controlling the resulting p-n junction characteristics. I think in the next ten years a-Se will be one of the main semiconductor materials used in photovoltaics and photodetectors. I also believe as researchers we are quite close to achieving ultrasensitive X-ray detectors. We should be seeing the use of real-time direct-detection X-ray imagers as common practice within ten years. Going further, I see a trend towards portable X-ray imaging systems. Personally, in keeping with my original motivation, I would like to see mainstream adoption of visible light communication. I hope one of our photodetectors will be the mainstay of such applications.