Metal lenses allow photodetectors to see better

Submitted by Stuart Watson on Sun, 05/04/2009 - 18:01

Researchers in the US have come up with a way of improving the sensitivity of metal-semiconductor-metal (MSM) photodetectors without compromising their performance in terms of speed. They accomplished this by modifying the area around the detector to produce a plasmonic lens, which enables it to detect more of the incoming light1,2.

The plasmonic lens is comprised of 10 parallel, linear corrugations, fabricated using electron beam lithography, in each of the two gold terminal pads that form the anode and the cathode of the MSM photodetector. These pads are positioned symmetrically on either side of the aperture which exposes the photo-sensitive region of the device.

Photons incident on the surface of the device are coupled with the free electrons in this metallic lens, producing surface plasmons which propagate along the surface and are guided into the aperture. This effectively increases the cross-sectional area of the detector, thereby enhancing its sensitivity.

A working device was demonstrated and reported to achieve a 90% increase in sensitivity to a laser source of near infra-red light. Computer simulations suggest that further optimisation of the device could yield a 10 fold increase in sensitivity. The plasmonic lens can also be designed to work across the visible wavelength range, as well as the infra-red wavelengths typically used for telecommunications.

The integrated plasmonic lens is a relatively simple modification to the existing MSM device and has no adverse affects on the speed with which it responds. It has obvious benefits for imaging applications where photon-generated current needs to be maximised. It could also bring improvements in fibre optic communication by allowing a signal to be transmitted further and yet still be detected after its intensity has been diminished by the deleterious effects of absorption and scattering.

 

 

  1. Integrated plasmonic lens photodetector. James A. Shackleford, Richard Grote, Marc Currie, Jonathan E. Spanier, and Bahram Nabet, Appl. Phys. Lett. 94, 083501 (2009), DOI:10.1063/1.3086898
  2. Plasmonic lens improves photodetector
 
 

 
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