Research

Optoelectronic Materials and Devices Laboratory

The research laboratory comprises three sections:
(i) Clean room and Micro-fabrication facility
The clean room has the essential equipment needed to create semiconductor devices like light emitters and receivers from novel wafer structures. Electrical connections are made with gold wires thinner than a human hair using wire bonders and other bonding techniques used by worldwide semiconductor manufacturers. The devices made in the facility may have etched features with dimensions smaller than a micrometre. Thin film contacts and waveguides for the devices are deposited by a vacuum coating system. The contact metals (gold and dopants like germanium, tin, magnesium and zinc) are annealed to make the ohmic and Schottky contacts needed for devices like HEMTs and MESFETs.
(ii) The laser/photonics laboratory
We have a range of high power solid state lasers as well as tunable and fixed wavelength semiconductor lasers, detectors and analytical equipment such as optical and frequency spectrum analysers. Spectral measurements can be carried out in the wavelength range between 0.35 μm (UV) and 1.7 µm (NIR) at temperatures between 4.2 K and 320K.  Novel lasers, Vertical cavity optical amplifiers, photodetectors and high efficiency multi junction and nipi structured novel solar cells are investigated in this laboratory
(iii) Optical and Electrical characterisation laboratory
Most of the research activities in the optoelectronic materials and devices laboratory are carried out in this laboratory where experimental facilities exists to investigate electrical, optical and magnetic properties of semiconductors between 1.3K and 300K. The experimental sets include magneto transport, electrical transport, and hot electron devices, electrical instabilities in 2D semiconductors, quantum dots and wires. We also have transient and CW photoconductivity, photoluminescence and electroluminescence spectra experiments for optical characterisation. The lab has an international reputation for work on hot electrons and instabilities in semiconductors. This work has led to a series of unique, light emitting and lasing devices (HELLISH) utilising hot electron transport parallel to heterojunctions and Gunn Lasers.
Recently, an off-shoot of the HELLISH work has led to novel devices, combining wavelength conversion with optical amplification, achieved with a wide range of tunability. The group has also continued its national and international collaborations and published widely on novel materials for photonic devices; including the first UK based experimental work on GaInAsN/GaAs quantum well structures for applications in 1.3 µm uncooled lasers.  The laboratory's activities also include work on transport and optoelectronic properties of GaN and related compounds, such as the study of hot electron energy and momentum relaxation, the effects of spontaneous polarisation; the phenomenon of squeezed electrons, Bloch oscillations, spin transport and the possibility of a nitride-based cascade laser.

current research projects

For descriptions of these projects please use the links.

experimental research projects

• Very high Efficiency novel Solar Cells
• Light emission and lasing from travelling space charge domains (Gunn Laser)
• Hot Electron transport devices in wide band gap materials (GaN/GaInN)
• Hot Electron assisted lasing and wavelength conversion devices (HELLISH)
• Electronic and optoelectronic properties of and devices based on dilute nitrides (VCSEL, VCSOA, Negative Mass NDR)
• Hot electron energy and momentum relaxation in InN and indium rich GaInN

theoretical research projects

The general research area is semiconductor physics and semiconductor device modelling.

• Hot Electron transport in GaN-based FETs: what transport processes affect the performance of a FET?
• The Effect of Electron-Electron Scattering on Transport: GaN based devices typically have very large electron concentrations. How does the rapid interaction between electrons affect devices performance?
• Dynamic Screening and Coupled Mode Effects: static fields are efficiently screened by mobile carriers, but non-static fields such as the polar field produced by an optical phonon fluctuate rapidly. How do the mobile carriers respond?
• Phonons in 2D structures: the spectrum of phonons in layered structures is different from that in bulk material. How does that affect scattering rates and phonon lifetime?
• Capture into Wells: the rate at which electrons and holes get captured by the wells in a quantum well laser or amplifier contribute to the speed of the device. What determines the rate and how can speed be optimised?

research students

There are places available for MSc and PhD studies in the research group for students with backgrounds in physics, electronics or optoelectronic engineering and applied mathematics. Minimum requirement for the MSc is a lower second class ( >50%) BSc degree. Minimum requirement for the PhD is an upper second class (>60%) BSc degree or an MSc degree.

If you are interested in working in the research group, in any of the research fields listed above, please contact Dr Nick Zakhleniuk (naz@essex.ac.uk). Colleagues from both UK and overseas that wish to join the group for a short-period, as visiting, or research fellows are also welcome to apply.

group members and contact e-mail addresses