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

Properties of a photovoltaic detector based on an n-type GaN Schottky barrier

International audienceIn this article, we report on the characterization of a photovoltaic detector based on an n-type GaN Schottky barrier. We first present the photovoltaic responsivity above the gap. Its spectrum is explained by the combined effects of absorption and diffusion. The hole diffusion length is estimated to be in the 0.1 mu m range with a numerical model. The photoresponse below the gap is also investigated and it is shown that the current generated by the internal photoemission is the major contribution to the photocurrent at reverse biases at 80 K. At room temperature, an additional component to the photocurrent is clearly demonstrated and identified. This extra current stems from the existence of traps. Several spectroscopy techniques are used to characterize those traps. The supplementary current emitted from the traps in the depletion region accounts for the spectral and the temporal behavior of the Schottky photodetector at room temperature. (C) 1997 American Institute of Physics

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

Characterization of ALN buffer layers on (0001)-sapphire substrates

International audienceIt is now established that low-temperature grown buffer layers are needed to improve the structural and electronic properties of GaN layers grown on sapphire. We studied the recrystallization of AIN buffer layers grown by low-pressure MOVPE as a function of annealing time. The Warren-Averbach method was applied to the analysis of broadening and line shape of the (0 0 0 2) and (0 0 0 4) X-ray diffraction peaks. This method yielded a separation of the grain size distribution from microstrain effects. The evolution of the relative frequency distribution of the grain size with annealing is correlated with atomic force microscopy experiments. The distribution of the reflecting-planes orientation was determined by X-ray rocking-curve experiments, (C) 1998 Elsevier Science B.V. All rights reserved

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

NRC publication: Ye