Unintentionally degenerately doped n-type hexagonal wurtzite InN samples were studied by using Fouriertransform photoluminescence spectroscopy and reflectivity measurements. We found in luminescence overlapping band acceptor ͑e , A 0 ͒ transitions related to two different acceptors with a strong enhancement of their intensities close to the Fermi energy of the electrons recombining with the localized holes. Our explanation is in terms of a Fermi-edge singularity of the electrons due to strongly increased electron-hole scattering. Electron-hole pairs with such resonantly enhanced oscillator strengths have been referred to as Mahan excitons. Temperature-dependent reflectivity measurements confirm this interpretation.

Metamorphic (i.e., linear composition graded) GaInN buffer layers with an increased in-plane lattice parameter, grown by plasma-assisted molecular beam epitaxy, were used as templates for metal organic vapor phase epitaxy (MOVPE) grown GaInN/GaInN quantum wells (QWs), emitting in the green to red spectral region. A composition pulling effect was observed allowing considerable higher growth temperatures for the QWs for a given In composition. The internal quantum efficiency (IQE) of the QWs was determined by temperature and excitation power density dependent photoluminescence (PL) spectroscopy. An increase in IQE by a factor of two was found for green emitting QWs grown on metamorphic GaInN buffer compared to reference samples grown on standard GaN buffer layers. The ratio of room temperature to low temperature intensity PL of the red emitting QWs were found to be comparable to the PL efficiency of green emitting QWs, both grown on metamorphic GaInN buffers. The excitation density and well width dependence of the IQE indicate a reduction of the quantum confined Stark effect upon growth on GaInN buffer layers with increased in-plane lattice parameter

In order to deposit semipolar GaN layers on foreign substrates while still starting the growth along the c-direction, we have etched trenches into r-plane and n-plane sapphire wafers. The GaN MOVPE growth then starts from c-plane-like sidewalls of these trenches, eventually leading to semipolar {1122} and {1011} surfaces with very good properties. GaInN quantum wells grown on such surfaces show very uniform properties on {1011} surfaces, but still reflect the stripe geometry on {1122} surfaces by a slightly larger In uptake at the stripe coalescence regions

An efficient enantioselective synthesis of the chiral polycyclic cholesteryl ester transfer protein (CETP) inhibitor 1 has been developed. The synthesis was rendered practical for large scale via the development of a modified Hantzsch-type reaction to prepare the sterically hindered pyridine ring, enantioselective hydrogenation of hindered ketone 6 utilizing novel BIBOP-amino-pyridine derived Ru complex, efficient ICl promoted lactone formation, and a BF3 mediated hydrogenation process for diastereoselective lactol reduction. This efficient route was successfully scaled to produce multikilogram quantities of challenging CETP drug candidate 1.

The luminescence spectrum of degenerately n‐type doped hexagonal InN extends to energies significantly higher than the renormalized band edge of the material. The line shape cannot be explained by simple band‐filling. Reflectivity spectra reveal at low temperatures a strongly enhanced intensity at the Fermi energy which we ascribe to a Fermi edge singularity of the electrons interacting with holes to form so‐called Mahan excitons. High k ‐values of the holes recombining with Fermi edge electrons are provided by localization at acceptors. A weak binding energy for a Mahan exciton is expected due to screening of the electron liquid in the conduction band. The concept of Mahan excitons allows us to understand the observed near band gap photoluminescence spectra (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)