Investigations about the epitaxy of AlBGaN hetero structures for applications in UV-LEDs

点击翻译按钮获取中文摘要

After having optimized successfully GaN-based LEDs for visible light emission, other spectral ranges move more and more into the scientific focus. In this project, we intend to concentrate on LEDs for the short wavelength ultraviolet (UV-C) spectral range, as many applications like sterilisation and disinfection of air and water become more and more interesting. Such LEDs require AlGaN hetero-structures grown on AlN (quasi) substrates. A major problem in such hetero-structures still is the fairly high defect density, partly caused by the large lattice mismatch between the different single layers and the resulting strain. Therefore, we intend to study how these problems can be managed by using boron (B) as a further component. Already quite small B fractions of a few percent can help reducing the lattice mismatch considerably. However, the incorporation of B into AlGaN is known to be limited because of a fairly small solubility. We will apply high-temperature epitaxial growth with temperatures up to 1400°C to get best solubility. Our investigations will clarify whether this indeed helps to reduce the strain in Al-containing hetero-structures - particularly in those with large Al content - without deteriorating the crystalline quality and defect density. Moreover, only scarce or even contradictory information about many fundamental properties of this quaternary material system such as band gap as function of composition, band offsets, donor and acceptor ionisation energies is currently available. By performing measurements with well-correlated methodology of various characterisation tools on our samples, we will find answers to such questions. Motivated by the very promising properties of hexagonal BN concerning p-doping with Mg, we will additionally investigate, whether this also can lead to better p-doping of AlBGaN layers.