T. Yamaguchi

Formation and morphology of InGaN nanoislands on GaN(0001)

The morphology and density of InGaN nanoislands can be controlled by the choice of proper growth conditions for metal organic vapor phase epitaxy. Scanning tunneling microscopy has been used to investigate the dependence of InGaN island morphology on the growth parameters. A heterogeneous nucleation of large InGaN islands with a complex structure is observed after growth at 650°C in conjunction with a high In partial pressure. For 600°C and low In partial pressure, however, the homogeneous nucleation of small islands of sizes suitable for three-dimensional quantum confinement is found, with very high densities of 1012cm−2. The influence of the growth temperature and the In partial pressure is discussed in terms of thermally activated diffusion and surface mobility.

Concentration Evaluation in Nanometre-Sized In x Ga 1- x N Islands Using Transmission Electron Microscopy

In this work the indium concentration of uncapped InGaN samples is measured by three different transmission electron microscopy approaches which are based on measurement of local lattice plane distances. In the case of three dimensional, nanometre-sized, uncapped InGaN islands, an increase of the indium concentration from the base of the islands toward their tip is observed. Additionally, an indication is presented that the local indium concentration in the islands is influenced by the vicinity of other islands.

Wide-Bandgap Quantum Dot Based Microcavity VCSEL Structures

In this contribution we report on the optical properties of planar and pillar structured GaN- and ZnSe-based monolithic microcavities. These structures reveal three-dimensional confined optical modes with high quality factors and potentially small mode volumes especially for the ZnSe-based samples. The measurements are completed with theoretical calculations. Furthermore, the optical emission properties of CdSe quantum dots embedded into microcavities have been studied. The Purcell effect demonstrated by means of the pronounced enhancement of the spontaneous emission rate of quantum dots coupled to the discrete optical modes of the cavities. This enhancement depends systematically on the pillar diameter and thus on the Purcell factor of the individual pillars.

InGaN Selfassembled Quantum Dots Investigated By X‐Ray Diffraction‐Anomalous‐Fine Structure Technique

Local chemical composition of InGaN quantum dots grown by molecular‐beam epitaxy on GaN virtual substrates was investigated by x‐ray diffraction anomalous fine‐structure method. Using this approach, we found that the In content increases from 20% at the dot base to 40–50% at the top. From the detailed numerical analysis of the data we were able to reconstruct the local neighborhood of Ga atoms in different positions in the dots, as well as the local elastic relaxation state.

Local structure of uncapped and capped InGaN/GaN quantum dots

The local structure around the indium atoms in uncapped and capped In(x)Ga(1-x)N quantum dots has been studied by In K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The samples were grown by metal organic vapour phase epitaxy. The EXAFS was successfully applied to study the structural properties of buried quantum dots which are not optically active. The analysis revealed that capping the quantum dots with GaN does not affect the bond distances of the In-N and In-Ga, but makes the In-In distance shorter by 0.04 A.

Investigation of InxGa1−xN islands with electron microscopy

InxGa1−x N islands grown by molecular beam epitaxy are analysed by transmission electron microscopy. Samples are compared which were of different nominal In concentrations and with or without GaN capping. The optimum imaging conditions for evaluation are described with special focus on polarity determination during analysis.