Semiconductor Materials and Photonics

Semiconductor materials and photonics

Research is focused on the epitaxial growth of new semiconductor materials and the investigation of the underlying physics which determine the efficiency limiting processes in infrared light sources, thermo-photovoltaics and solar cells.

Key research areas

  • Mid-infrared LEDs and laser for gas sensing and environmental monitoring
  • Thermophotovoltaic cells for industrial waste heat recovery
  • Infrared photodetectors for thermal imaging
  • Quantum dot lasers for telecommunications
  • Solar cells for renewable energy generation.

Research themes

Solar cells

The Intermediate Band Solar Cell (IBSC) is a concept that has the potential to increase the efficiency to 63%. The intermediate band acts as a ‘stepping stone’ allowing absorption of photons (energy particles from the sun) from three distinct levels compared to a single level in conventional SCs. We are developing nanostructured IBSCs using GaSb Quantum Rings.

The band alignment in this system is type-II, such that holes are localized within the GaSb QDs but there is no electron confinement. Compared to InAs QDs this produces a red-shift of the photoresponse and could increase the short-circuit current and improve carrier extraction. GaSb nanostructures grown by molecular beam epitaxy (MBE) tend to preferentially form quantum rings (QRs) which are less strained and contain fewer defects than the GaSb QDs, which implies that they are more suitable for dense stacking in the active region of a solar cell to reduce the accumulation of internal strain and enhance the light absorption. GaAs based p-i-n solar cells containing between 5 and 10 layers of GaSb QRs were fabricated. They show extended long wavelength photoresponse into the near-IR up to 1500 nm compared to the GaAs control cell due to absorption of low energy photons.

Key publications

Funding

  • EPSRC: Dilute Nitride Type II Quantum Dot Materials for Solar Cells based on GaAs - Collaborative Research in Energy with South Africa (EP/G070334/1)
  • Joy Welch Educational Charitable Trust: Using Advanced Photovoltaic Materials to increase the commercial viability of Renewable Energy
Solar cells

Mid-infrared photonics

III-V semiconductors based on the family of 6.1 Ȧ semiconductors which includes InAs, GaSb, AlSb and related alloys have a wide range of band gaps that corresponds to the mid-infrared spectral range (MIR) (2-5 µm), where many molecules such as hydrocarbons and greenhouse gases have their absorption lines.

The MIR spectral range is thus well suited for implementing a variety of devices such as photonic, biological and chemical sensors. Specifically, the research involves the growth of new semiconductor nanostructures including quantum dots, nanowires and 2D materials and studies of the fundamental quantum phenomena at the nano-scale. The devices are fabricated using the state-of-art nanofabrication facilities of the Quantum Technology Centre including e-beam lithography, photolithography and thin-film deposition techniques. A range of scanning probe microscopy and cross-sectional imaging techniques are used to image and characterise the materials at the nano-scale. Our research is carried out in collaboration with industrial partners including IQE, CST, GSS, Amethyst, Oclaro, Pilkington, SELEX as well as worldwide academic groups.

Key publications

Funding

  • EPSRC: Novel InSb quantum dots monolithically grown on Silicon for low-cost mid-infrared light emitting diodes
  • Royal Academy of Engineering: High-Efficiency Mid-Infrared Semiconductor Materials Grown on Silicon
Mid-infrared photonics for gas sensing

Key information

People

Facilities

  • Veeco Xplor System
    Ultra-high vacuum system designed to grow a wide range of III-V materials. The system is designed with a specially designed substrate heater for III-V/Silicon integration.
  • Quantum Technology Centre
    Our devices are processed in the state-of-the-art QTC clean room.