Technology Opportunities

Surface treatment and constant UV illumination produces photoresistors with enhanced spectral response, recovery time and repeatability

Highlights

• Gallium nitride (GaN), an important semiconductor can be used to emit brilliant light in the form of light emitting diodes (LEDs) and laser diodes. Mass production has made it low-cost and readily available.
• While GaN light detectors are sensitive to ultra-violate (UV) radiation below 365 nm wavelength due to their wide band-gap (– 3.4 eV), the presence of impurities, especially surface traps, leads to slow relaxation rates resulting in photoresistors with slow response.
• Currently, in order to improve GaN fabrication processes and diode performance, use is made of GaN/AlGaN layers or highly doped GaN which require high precision, costly processes and special wafer growing techniques.
• This innovative method for surface modification of GaN photoresistors leads to a broadband photoresistor that can detect visible (VIS) to near infrared (NIR) wavelengths in addition to UV without the need for epitaxial GaN/AlGaN layers or a photo-diode structure.

Our Innovation

The use of a variety of surface treatments, such as plasma asher and organic molecule adsorption, to produce photoresistors with enhanced response, recovery time and repeatability. When the detector is illuminated by constant UV light it becomes sensitive to visible and NIR radiation and when it is not illuminated, it functions as a regular GaN detector that can detect UV light.

Left – The detector spectral response when illuminated by constant UV light

Right – schematic diagram of the measurement setup that was used

Features

• Simple, repeatable process
• Can operate from the UV to the NIR band without the need for the growth of epitaxial GaN/AlGaN layers or a photo-diode structure
• The detector can be electronically switched between the UV mode, which operates as a regular surface photoresistor, and VIS/NIR mode.
• The detector is sensitive to changes at the surface that make it ideal for biological and chemical uses as well as for broadband light detectors.

Development Milestones

• The spectral response will be measured over a wider range.
• Many variables need to be optimized, such as UV illumination intensity, applied voltage, detector size and shape.
• Time response will be improved.
• A prototype will be built for field tests.
• CCD will be built based on this technology.

The Opportunity

• Increasing demand in military and space research sensors for a broad band of wavelengths from the UV through VIS up to NIR
• Surface sensitive detectors important for biological and chemical use
• Improved GaN fabrication processes
• Broad band detection is important in missile detection

Researcher Information http://nanoscience.huji.ac.il/researchers/paltiel.html, http://qnelab.weebly.com/group.html