Silicon detectors currently completely dominate the ultra violet, visible and very near-infrared (IR) regions - but do not work above 1.2 um. Following the spin-off discovery of band edge modified rare earth (RE) optical transitions, specific to europium, ytterbium and cerium in silicon, we have shown that, remarkably, silicon photodetector responsivity can be extended from 1.2 um, at the silicon band gap, out to the important mid-IR region and beyond. Experimentally the absolute responsivities and detectivities of these devices now offer a real challenge to existing materials and devices in the 2 to 15 um range currently dominated by exotic and expensive materials such as mercury cadmium telluride (MCT). Replacing these with silicon detectors would offer enormous benefits in cost, reliability, performance, and integration with silicon microelectronics for detection and imaging, as well as using much less toxic materials and production processes. Low leakage currents achievable in silicon based photodiodes mean that further development of this new silicon based technology may lead to room temperature or thermoelectrically cooled detectors, replacing current detectors that have to be cooled to liquid nitrogen temperatures (77 K) to achieve the required high detectivity values.
Photonics has been identified as a key enabling technology with a substantial leverage effect on the global economy. More generally, silicon and its associated technologies underpin microelectronics, information technology and the digital world as we currently know it. Silicon photonics, and major breakthroughs in it such as mid-IR detection, would widen its application areas into a range of high value, important societal, environmental, security and health applications. Green photonics that generate or conserve energy, cut greenhouse emissions, reduce pollution, yield environmentally sustainable outputs or improve public health is expected to have a growth rate value of near to 20% p.a. A major market is the use of mid-IR sensors in smart buildings and cities to give more efficient use of resources. The low cost intrinsic to silicon technology could be paramount.
This price reduction and market expansion would be enabled by mid-IR silicon based detectors as the fabrication process steps are well known and entirely compatible with low cost CMOS production, as opposed to the current high cost of MCT and other detectors, whether they are cryogenically or thermoelectrically cooled or operating at room temperature.
Silicon mid-IR photodetectors as well as being significantly cheaper to manufacture and more reliable than current detection devices, would enable the elimination of processes using highly toxic materials such as MCT, lead sulphide, lead selenide and arsenic containing alloys.
