An ultra-sensitive photodetector based on phase change materials

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Optical sensors are widely used throughout many different industries, from medical instrumentation to consumer electronics, yet there is still a need for inexpensive, smaller optical sensors with high photo-sensitivity.

Currently, most commercially available optical sensors that operate at room temperature in the visible to near infrared spectral range are typically based on semiconductor materials, such as silicon and indium gallium arsenide. Silicon is also used in image sensors used in phone and webcameras, where active pixel sensor arrays are manufactured using CMOS technology. These sensors offer high photo-sensitivity but are expensive to manufacture, have a limited dynamic range and may be difficult to scale down in size.

In most conventional semiconductor-based optical sensors responsive to visible light near-IR light, the photo-response originates from the separation and drift of photo-excited charge carriers (photocarriers) in an electric field present between the terminals of the device. This means that the photo-response is largely determined by fixed material specific properties that govern photocarrier generation and drift, such as optical absorption and charge carrier mobility. The material specific properties also limit the dynamic range of the device, which means that typical optical devices saturate at fixed and relatively low light levels. Due to these limitations, alternative optoelectronic devices and methods of photodetection are desirable, preferably with increased adaptability to light levels.

Oxford academics have invented a new optoelectronic device that is based on phase change materials. The device is operated in a mixed mode optoelectronic configuration, which uses electrical and optical energies. The device works with an inherent negative feedback loop, where the electrical conductance of the device is modulated by the optical input flux. This essentially replicates the functioning of a human eye.

There are multiple benefits of Oxford technology:

  • fast
  • robust
  • sensitive
  • wavelength selective
  • energy inexpensive
  • carries high signal to noise ratio
  • easily scaled down

Combining these benefits allows very high device densities, which results in high spatial image resolution, an incredibly useful property for medical applications.

This technology is subject to a patent application and is now available to licence.

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