Change the world

Physics

Semiconductor Materials and Nanostructures

Prospective Students

The group has opportunities for research students (MSc and PhD) and postdoctoral researchers. Successful applicants will work together with an international team of students on all steps of proto-type device fabrication, including device simulation, substrate preparation, growth and sample characterization. We are always looking for suitable and highly motivated MSc students to participate in this programme, which is currently funded by the NRF and the National Laser Center. For further information, contact Prof Reinhardt Botha. (If you are a graduate student and would like to explore your own ideas in a stimulating environment do not hesitate to contact us.)

Research Projects

  • Infrared technology

    Here we study the growth of GaSb, InAs and the related III-V compound InAsSb for infrared applications such as emitters and sensors. Of specific interest is the ternary semiconductor InAsSb, which has a band gap that can be changed between ~ 3.5 μm and 11 μm, thus making it ideally suited for applications like trace gas detection and even optical communication. This compound can be combined with GaInSb to form superlattices with improved electro-optical properties and additional degrees of freedom in terms of band gap engineering and device design. Although these materials have been successfully incorporated in a variety of device structures, there is a lack of fundamental knowledge in terms of defects, impurities, band alignment, etc. which our work aims to address.

  • ZnO thin films

    Zinc-oxide is an important group II-VI wide-bandgap semiconductor material. Recent progress has led to its use as a light emitter in the blue-to-UV range. Other applications for ZnO include antireflection (AR) coatings for photovoltaic (solar cell) structures. When Mg is incorporated into the lattice of ZnO, a ternary compound MgZnO is formed, with band gap larger than that of ZnO. The combination of ZnO and MgZnO in the form of a quantum well structure provides additional degrees of freedom in terms of device design and perfomance. One PhD student is currently focusing on this promising material combination.

  • InAsSb-based diode structures

    This project is aimed at the development of InAsSb/GaSb structures for photodiode applications. InAsSb, when lattice matched to a GaSb substrate, has a band gap of 3.8 um at 77K, and is therefore an attractive material compound for backside-illuminated detector structures. X-ray diffraction is used to establish the Sb content of the grown epilayers. In this project InAsSb is grown on GaAs and GaSb substrates and characterized using Zeebeck coefficient, Hall, I-V, C-V and photocurrent measurements. In addition, optical microscopy is used to study the surface morphologies of the epilayers. Special considerations are also necessary in terms of doping and contacting to the grown semiconductor system.

  • MOVPE-grown InAs/GaInSb superlattices

    This study focuses on the development of strained InAs/GaInSb superlattice systems. The design flexibility in terms of bandedge alignment in the superlattice structure allows the tuning of the band gap of the material system to range from 3 – 12 um. The superlattices are grown on GaSb substrate, which is transparent in the desired wavelength range. We use TEM and double crystal X-ray diffraction to study the structure and interface properties of the superlattice.

  • ZnO nanorods

    ZnO can be produced in a variety of architectures, such as nanowires, nanorods, nanobelts, etc. This project aims to combine ZnO nanorods, produced by chemical bath deposition, with a silicon substrate for white light emitting diodes. Chemical bath deposition is a cheap, environmentally friendly way of producing ZnO nanostructures. The challenge is to control the size, shape, density, orientation and alignment in a reproducible way. Our approach involves the control of the properties of a ZnO seed layer produced prior to the growth of the nanorods, as well as the use of diblock copolymers to produce nano-sized patterns on the substrate.

Nanoflower ZnO