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Institute of Electronic Structure & Laser (IESL)
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  Title Solid-state transparent materials and devices for transparent opto-electronic applications
  Group Microelectronics Research Group, IESL
  Researcher Dr. Elias Aperathitis
  Abstract Transparent devices and circuits, i.e., devices for transparent applications, is an emerging technology which is based on transparent (non-polymer) materials. Transparent materials not necessarily oxides, with tuned, controlled and reproducible optical and electrical properties (transparency at specific wavelength range and doping, carrier concentration and conductivity) can lead to transparent devices like diodes, PVs, TTFT, LEDs, detectors, etc, with applications to telecommunications, automobile industry, architecture, energy, and more.
  Description Transparent materials and particularly transparent conductive oxides (TCOs) have been widely used as coatings for heat reflective windows, anti-static instrument windows, as well as vehicle window heaters, electrochromic devices, solar cells, Liquid Crystal Displays and electrochemical cells. Transparent conductive materials continue to be in high demand because of the immediate applications they can find in a variety of new technologies, ranging from thin film coatings and sensor devices to light-detecting and emitting devices in telecommunications.

The main feature of an active device in optoelectronics, either for light detecting or light emitting applications, is the p-n junction. One of the main factors that can affect the output performance of the devices is the electrical characteristics of the diode in the dark. Other factors are the absorption of photons and the collection of photogenerated carriers, the recombination mechanisms (radiative or non-radiative) and a damage-free processing procedure of the diode structure (ohmic contact formation and etching steps) which will lead to the device. However, the development of transparent p/n junctions is still an open technological challenge:
  • new transparent In-free materials are needed because: (a) indium suffers, for the time being, of an increased price level related to an increase demand and a reduced availability of indium metal used in the manufacturing of ITO sputtering targets and (b) the continuous growth in demand of ITO coatings for LCD displays. It is important to note that ITO coatings account for about 75 % of the consumption of indium. As a result of the increasing demand of indium and shortage of indium supply on the market, at the end of March 2004, the price of indium had risen above an eight year maximum ($600/kg) and a six-time increase compared with the price in January 2003. This trend of the indium price will continue due to soaring demand for flat-panel screens and shortage of indium supply.
  • p-type transparent materials are not yet available in a controllable and reproducible manner. The market of telecommunications, including the consumer electronics market (DVDs, digital cameras and feature-enhanced mobile phones) which is based on light emitting and detecting devices is showing high prospect of growth for the next years. For example, according to "Strategies Unlimited", high brightness emitters (LEDs and some lasers) are estimated to show an annual growth rate of about 20% for at least the next five years, with sales value reaching almost $6bn in 2008. Furthermore, the wide band-gap of transparent materials will enable the development of UV optoelectronic devices for a large number of new applications (data storage, flame detection, sensors, etc). New organic emitting devices (OLEDs) will be made if p-type transparent materials with tailored work function will be discovered.
In the photonics dominated market era, the exploitation of these foreseen emerging technologies will lead to capture of new market in the next decade.
  Current development phase The technology for both n- and p-type transparent materials and devices is at the development phase.
  Type of collaboration sought Research Institutes and Academic partners for joint R&D activities in existing and new applications, to contribute to further investigation on transparent materials and devices, to the commercialization of the technology, to facilitate market penetration.