Research Overview
The Laboratory of Semiconductor Materials carries out research and education in the area of materials, structures and devices needed for advanced photonic and electronic applications. With a focus on semiconductor hetero- and nanostructure fabrication, including crystal growth, wafer processing and characterization, we develop novel devices and applications. We continue our strong tradition of research and innovation with a focus on devices in III-V materials for fiber-optic communications, and in addition we have adapted or developed technologies for new application areas such as sensing and photovoltaics. We investigate nanophotonics concepts and disruptive technologies such as photonic crystals and nanowires for energy efficient solutions in optoelectronic components. The division has been a partner in several large scale national programs and EU projects on photonics. Major current research programs/centers in which the division is a partner include the “Linné center in advanced optics and photonics (ADOPT)”, EU-Network of excellence “Nanophotonics for energy efficiency – N4E” and the Nordic project “Semiconductor Nanowire solar cells – NANORDSUN”. The division also conducts research projects in collaborations with industries in the field of photonics.
The major current research activities of the division are:
- Epitaxy for integrated photonics
- Photonic crystals
- Nanopillars/Nanowires
- Nanoscale characterization
The rapidly maturing crystal growth technology for III-V heterostructures has moved our research focus from conventional, nearly lattice matches structures in gallium arsenide (GaAs) and indium phosphide (InP) towards strongly lattice mismatched material combinations. One reason for this is that increased photonic integration is becoming imperative to improve functionality and decrease cost of photonic subsystems. We are exploring novel techniques for growing III-V structures on silicon to facilitate integration with silicon waveguide technology as well as electronics. This work is based on our worldwide unique Hydride Vapor Phase Epitaxy (HVPE) facilitiy which combines large growth rate and substrate selectivity and possibility for epitaxial lateral overgrowth.
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Photonic crystals is one of the hottest scientific topics today. A photonic crystal could make it possible to manipulate light in much the same way as we handle electrons in a semiconductor crystal. Realization of photonic crystals in semiconductors would open the way towards photonic integration with ensuing increases in functionality and compactness. Our primary fabrication technology for two-dimensional photonic crystal devices is by dry etching nanometer sized holes in a semiconductor slab, developed both for deeply etched photonic crystals and for membranes. The group is a pioneer in deep-etching of photonic crystals in InP-based structures and has demonstrated several devices or device-concepts such as lasers, filters, negative-refraction etc. The group has also made significant contributions on the understanding of the physical mechanisms in nanofabrication of photonic crystals and its implication on electrical conduction and carrier-lifetimes.
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Nanophotonics for energy is an emerging field. The need for efficient light generation and light harvesting devices will continue to be a major driving force both for research and for business. Our research focuses on the investigations of new concepts in light-matter interaction together with disruptive technologies for efficient photovoltaic and light emitters. This includes research on nano-wire/nano-pillar solar cells in III-Vs and Si, low-cost nanostructuring methods and plasmonic solar cells.
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With increasing complexity and decreasing dimensions of structures the need for advanced characterization is obvious. Methods to spatially map with nanoscale lateral resolution a whole range of electrical and optical properties of devices have to be developed. We have focused on scanning probe techniques, in particular scanning capacitance microscopy (SCM), scanning spreading resistance microscopy (SSRM) and Kelvin force probe microscopy techniques for nanoscale characterization of the electrical properties of materials and devices. In addition, the a whole range of structural, optical, and electrical characterization tools such as high resolution x-ray diffraction, electron microcopies, micro-PL, micro-Raman etc are continuously refined and applied to all of the project areas mentioned above.
