Despite the high density of threading dislocations generally found in (AlGaIn)N heterostructures, the light emission efficiency of such structures is exceptionally high. It has become common to attribute the high efficiency to compositional fluctuations or even phase separation in the active GaInN quantum well region. The resulting localization of charge carriers is thought to keep them from recombining nonradiatively at the defects. Here, we show that random disorder is not the key but that under suitable growth conditions hexagonal V-shaped pits decorating the defects exhibit narrow sidewall quantum wells with an effective band gap significantly larger than that of the regular c-plane quantum wells. Thereby nature provides a unique, hitherto unrecognized mechanism generating a potential landscape which effectively screens the defects themselves by providing an energy barrier around every defect.

The high quantum efficiency of light emission from GaInN/GaN quantum wells despite the typically large defect density still lacks a quantitative explanation. From a detailed analysis of the efficiency of highly efficient samples we find that a reduction of the radiative probability due to free exciton dissociation is the dominant mechanism limiting the quantum efficiency. Random exciton localization is shown to be only a minor contribution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We report an experimental determination of the internal polarization field in GaInN/GaN quantum wells, due to piezoelectric and spontaneous polarization, utilizing the quantum confined Stark effect, with fields as large as 3.1 MV/cm at 22% In. From its dependence on quantum well composition and strain, we find that the total field in GaInN is a linear combination of polarization charges from GaN and InN. The piezoelectric constants d31 for GaN and InN derived from our data are 1.05±0.05 pm/V and 3.7±0.5 pm/V, in fair agreement with theoretical data.

Using a high-resolution low-temperature spectroscopic scanning near-field optical microscope we observe highly localized high-energy emissions from highly efficient Ga x In 1−x N / GaN quantum wells. These sharp emissions about 300-400 meV above the main quantum well luminescence are characteristic for highefficiency structures and originate from the immediate vicinity of threading dislocations. Thus, areas of increased bandgap surrounding the defects appear to exist only in high-efficiency structures, which act as barriers prohibiting carriers from recombining nonradiatively at the defects.

Two-dimensional laser-induced periodic surface structures with a deep-subwavelength periodicity (80 nm ≈ λ/ 10) are obtained for the first time on diamond surfaces. The distinctive surface nanotexturing is achieved by employing a single step technique that relies on irradiation with two temporally delayed and cross-polarized femtosecond-laser pulses (100 fs duration, 800 nm wavelength, 1 kHz repetition rate) generated with a Michelson-like interferometer configuration, followed by chemical etching of surface debris. In this Letter, we demonstrate that, if the delay between two consecutive pulses is ≤2 ps, the 2D periodicity of nanostructures can be tuned by controlling the number of pulses irradiating the surface. Under scanning mode, the method is effective in treating uniformly large areas of diamond, so to induce remarkable antireflection properties able to enhance the absorptance in the visible up to 50 times and to pave the route toward the creation of metasurfaces for future diamond-based optoelectronic devices.