Ultra-small Pixels for Photodetection: Design and simulation of narrowband, tunable plasmonic absorbers for hot electron photodetectors



Research areas


The detection of photons has a hugely important role to play in modern society. Photodetection spans a wide range of imaging and sensing technologies with a vast array of applications in bio-medicine, environmental monitoring, entertainment, astronomy and aerospace, and communications.

In standard photodetectors, the bandwidth of operation is determined by the band gap of the semiconductor. If further wavelength selectivity is required - for example to isolate the red-green-blue components of the visible spectrum for imaging purposes - additional filters are necessary. State-of-the-art on-chip sensors use checkerboard patterns of organic dyes to provide colour sensitivity. This represents a significant complication of the fabrication process, requiring multiple aligned nano-lithography steps, and ultimately places a lower limit on the pixel size. This is driving research into plasmonic filters, and solutions for filter-less photodetectors. However, there is a more fundamental limit: pixel size is also limited by cross talk between pixels, and ultimately, by the diffraction limit of light. Cross-talk occurs optically due to large absorption lengths, and electrically due to large carrier diffusion lengths in the semiconductor. To achieve subwavelength pixels, both absorption and carrier collection needs to occur on the nanoscale.

Plasmonically enhanced hot-electron devices exploit strongly absorbing “plasmonic” resonances supported by metal nanoparticles to generate highly energetic electrons. Under the right conditions, these ‘hot’ electrons can be emitted from the metal and used to drive a variety of physical or chemical processes. This has generated significant interest for applications photo-detection applications, as absorption of light and emission of electrons occurs on the nano-scale, offering the possibility of truly subwavelength pixels. Additionally, metal nanostructures can be engineered to selectively absorb light with very high efficiency.  

This project aims to advance plasmonically enhanced hot-electron technologies to develop the next generation of low-cost, spectrally tuneable photodetectors with sub-wavelength pixels. We will exploit the tuneable absorption of metal nanoparticles to design and simulate hot electron devices with narrowband and wavelength selective absorption spectra. In particular, we will exploit interference effects between different types of optical resonances to precisely control the wavelength and bandwidth of the absorbed light.


  1. Use COMSOL Multiphysics software to simulate optical absorption in plasmonically enhanced hot-electron photodiode geometries.  
  2. Systematically investigate the effect of changing the size and shape of metal nanostructures on the absorption spectra.
  3. Study the interaction of plasmonic resonances with cavity resonances to produce narrowband absorption spectra
  4. Ultimate you will attempt to design and demonstrate ultra-small RGB pixels for Photodetection  



This is a computer based modelling project, suitable for students with an interest in solar cells, optical devices and optoelectronics.  It would be particularly good experience for anyone interested in a research career, or in R&D in the area of optoelectronics.  This project will require you to learn to use COMSOL Multiphysics software to build and run optical simulations. A basic understanding of the principles of numerical modelling and optical physics is desirable

Prerequisite: ENGN2218 (Electronic systems and design) or ENGN3334 (Semiconductors). ENGN3512 (Optical Physics) would be useful, a basic understanding of optical optics is essential.

Suitable for: 12-18 unit courses for R&D students (ENGN 3712, 4712, 4718), or as an honours project for a good student (ENGN 4200)

Background Literature

Brongersma, M. L., Halas, N. J. & Nordlander, P. Plasmon-induced hot carrier science and technology. Nat. Nanotechnol. 10, 25–34 (2015).

Maier, S. A. et al. Plasmonics - A route to nanoscale optical devices. Adv. Mater. 13, 1501 (2001).

Yokogawa, S., Burgos, S. P. & Atwater, H. A. Plasmonic color filters for CMOS image sensor applications. Nano Lett. 12, 4349–54 (2012).


Over the course of the project you will:

  • Engage with a novel research problem in the up-and-coming research field of hot electron science
  • Develop a deeper understanding of optical and semiconductor physics and how photodetectors operate
  • Gain real experience in the design and simulation of optoelectronic devices using commercial modelling software
  • Get a chance to independently and creatively solve problems
  • Undertake independent research and build up your analytical skills

Updated:  8 September 2015/Responsible Officer:  Head of School/Page Contact:  CECS Marketing