A study of nitrogen incorporation in pyramidal site-controlled quantum dots

We present the results of a study of nitrogen incorporation in metalorganic-vapour-phase epitaxy-grown site-controlled quantum dots (QDs). We report for the first time on a significant incorporation (approximately 0.3%), producing a noteworthy red shift (at least 50 meV) in some of our samples. Depending on the level of nitrogen incorporation/exposure, strong modifications of the optical features are found (variable distribution of the emission homogeneity, fine-structure splitting, few-particle effects). We discuss our results, especially in relation to a specific reproducible sample which has noticeable features: the usual pattern of the excitonic transitions is altered and the fine-structure splitting is suppressed to vanishing values. Distinctively, nitrogen incorporation can be achieved without detriment to the optical quality, as confirmed by narrow linewidths and photon correlation spectroscopy

Multilayer (Al,Ga)N Structures for Solar-Blind Detection

We report on solar-blind metal-semiconductor-metal (MSM) detectors fabricated on stacks of (Al,Ga)N layers with different AI mole fraction. These structures were grown by molecular beam epitaxy on sapphire substrates to allow backside illumination and a low-temperature GaN buffer layer. They consist of a 9-3-0.4-μm active layer grown on a thick (Al,Ga)N window layer (≈ 1 μm) that is transparent at the wavelength of interest. Different Al contents were used in the window layer. We observed that, in general, samples with a high Al content were cracked, which is explained in terms of mechanical strain. MSM photodetectors fabricated on these samples showed large leakage currents that were correlated with the crack density. In order to reduce the strain and eliminate the cracks, we inserted an AIN layer between the buffer and window layer. A crack-free sample was obtained and the solar-blind photodetector fabricated on this structure showed record performance

Effects of the Buffer Layers on the Performances of (Al,Ga)N Ultraviolet Photodetectors

The fabrication of (Al,Ga)N-based metal–semiconductor–metal (MSM) photovoltaic detectors requires the growth of high-quality (Al,Ga)N films. Inserting a low-temperature deposited buffer layer enables the growth of an epitaxial layer with a reduced density of defects. Two structures using GaN and AlN buffer layers have been deposited by low-pressure metalorganic chemical vapor deposition and used to fabricate MSM interdigitated detectors. The devices have been characterized to investigate the effects of the buffer layers on the detector performance

UV Metal Semiconductor Metal Detectors. A Robust Choice for (Al,Ga)N Based Detectors

UV detection is interesting for combustion optimization, air contamination control, fire and solar blind rocket launching detection. Most of these applications require that UV detectors have a huge dynamic response between UV and the visible, and a very low dark current in the range of the UV flux measured. (Al,Ga)N alloys present a large direct bandgap in this range and therefore can be used as an active region in such detectors. To take advantage of the large Schottky barrier, the good alloy quality, and to avoid any doping problems, we have developed MSM photodetectors. High quality material has been grown with MOCVD and MBE on sapphire substrates. Stress management is employed for aluminum contents up to 65% to reduce crack density. This is correlated with non-ideal features like dark current, sub-bandgap response and non-linearity between photocurrent and optical flux. The spectral selectivity between UV and visible reaches five orders of magnitude. A geometry of inter-digitized fingers is optimized in regards to the peak response. The Schottky barrier and a dielectric passivation result in dark currents lower than 1 fA up to 30 V for a 100 x 100 mum(2) pixel. Consequently, detectivity is mainly limited by shot noise and corresponds to a noise of 500 photons per second and per pixel

Microcavity light emitting diodes based on GaN membranes grown by molecular beam epitaxy on silicon

NRC publication: Ye