Papers by Keyword: InGaN

Abstract: GaN-based nanopillar crystals are directly grown on multicrystalline Si and amorphous-carbon-coated graphite substrates whose surfaces are not mirror-polished. Light-emitting diodes (LEDs) of a double-hetero structure are prepared from the nanopillar crystals, and their optical–emission properties are investigated. Despite the substrate type and surface conditions, moderate light emissions are obtained from nanopillar LEDs though the light emissions are not always homogeneous, especially in the LEDs prepared on the graphite-based substrate. Nevertheless, these results will lead to realizations of novel large-area light-emitting devices.

Abstract: Indium gallium nitride / gallium nitride (InGaN/GaN) heterostructures were grown by using metal organic vapor deposition technique with four different growth temperatures (740 °C, 760 °C, 780 °C, and 800 °C). The structural properties and crystalline quality were investigated using high resolution X-ray diffraction (HRXRD) technique. XRD ω-2θ scan mode at GaN (002) diffraction plane was performed to assess the film’s quality. Through the simulation fitting, the indium composition and the thickness of the thin films were obtained. From the observation, an increase in the growth temperature resulted in higher intensity and smaller full-width at half maximum value of the InGaN (002) diffraction peak, which indicated improvement to the crystalline quality of the InGaN/GaN heterostructure. Moreover, the indium composition of the InGaN epilayer was found to decrease with an increase of the growth temperature due to the thermal decomposition of In-N bond and its re-evaporation from the growing surfaces.

Abstract: Thermal distribution in solar cells has been rarely investigated despite it significant impact on the performance. The current contribution presents a COMSOL Multiphysics 3-D analysis of the electrical and optical photogeneration properties in relation with the heat distribution in InGaN solar cell. For this simulation, we have coupled the “Semiconductor Module”, the “Heat Transfer Module for Solids,” and the “Wave Optics Module” allowing us to calculate the Shockley–Read–Hall heating, the total heat flux, the Joule heating the carrier’s concentration, the electric field, and the temperature dissipation in the InGaN solar cell structure. Despite the fact that the achievements of InGaN solar cells are still mostly at the state of laboratory studies, the current contribution presenting original results on coupled phenomena occurring in the cells makes it possible to highlight new possible guidelines for an improve of their efficiency.

Abstract: The performance of the InGaN single-junction thin film solar cells has been analyzed numerically employing the Solar Cell Capacitance Simulator (SCAPS-1D). The electrical properties and the photovoltaic performance of the InGaN solar cells were studied by changing the doping concentrations and the bandgap energy along with each layer, i.e. n-and p-InGaN layers. The results reveal an optimum efficiency of the InGaN solar cell of ~ 15.32 % at a band gap value of 1.32 eV. It has been observed that lowering the doping concentration N_A leads to an improvement of the short circuit current density (J_sc) (34 mA/cm² at N_A of 10¹⁶ cm⁻³). This might be attributed to the increase of the carrier mobility and hence an enhancement in the minority carrier diffusion length leading to a better collection efficiency. Additionally, the results show that increasing the front layer thickness of the InGaN leads to an increase in the J_sc and to the conversion efficiency (η). This has been referred to the increase in the photogenerated current, as well as to the less surface recombination rate.

Abstract: Gallium nitride (GaN)-based thin films consist of its nanocrystals are grown on some metal-foils and a multi-crystalline silicon (Si) substrates. Their morphologies are compared with each other and the differences are discussed. Pillar-shaped nanocrystals are observed in the film grown on the multi-crystalline Si substrate while such structures are not observed in the films grown on the metal-foils when they are grown at higher growth temperatures. On the other hand, the morphologies of the films grown on the metal-foils approach to pillar-like structures by reducing the growth temperature. Band-edge emission is clearly observed in a cathodoluminescence spectrum of the film grown on the metal-foil at the reduced growth temperature.

Abstract: The simulation of multicomponent nanoheterostructures (MNH) InGaN for light-emitting diodes (LEDs) was made. The results are presented in graphs, for example, the current-voltage characteristics, the dependence of the internal quantum efficiency (IQE) on the number of quantum wells (QW) and spectral characteristics. The optimal structure of the MNH and the influence of the inhomogeneous distribution of In atoms in the quantum-well region is investigated.

Abstract: The photoluminescence from III-V wide band-gap semiconductors as InGaN is characterized by localized large intensity fluctuations, known as blinking, that, despite decades of research, is not yet completely understood. In structures where there is a three-dimensional confinement, as for example semiconductors nanocrystals, the phenomena is supposed to be related to temporary quenching due to highly efficient non-radiative recombination processes (for example, Auger). Nevertheless, in typical InGaN devices, the band structure is an infinitely wide quantum well, so the understanding of the blinking phenomenon remains elusive. We present experimental data and a model that suggests that the discussed optical fluctuations are a general phenomena caused by the slow beating between THz thermal vibrations of the Quantum Well. These minuscule displacements are occurring naturally all over the device, the displacements along the growth direction induce a modulation of the matrix elements that drives the optical emission process; this have measurable effect on the device photo-luminescence. In presence of impurities or gradient of concentration, the vibrations have locally slight frequency differences on adjacent domains, this give rise to a band of beats, and we observe the lower frequency tail of this band.

Abstract: Recent developments in the growth of InGaN layers made it possible to grow a heavily doped p-type layer with Indium concentration up to 40%. In this work, a tunnel junction based on these developments has been designed with the use of Silvaco TCAD. This diode introduces a low resistive path to the current carriers, effectively adds voltages and encounters the parasitic effects of the stacked sub-cells. A double-junction solar cell is designed based on our interfacing tunnel diode and simulated results are presented in this paper. Remarkable results are achieved comparing to the existing InGaN based multijunction solar cells. A high V_oc of ~3.1V and conversion efficiency greater than 17.5% has been achieved under AM 1.5. This paper also highlights and discusses the challenges in fabrication of such a highly efficient solar cell.

Abstract: It is imperative to determine the dependence of the quality and characteristics of the epitaxial film on different growth parameters. A mathematical model has been developed showing the effect of different growth parameters e.g. temperature, TMI and TEG flow rate, molar ratio on epitaxial film. This model is considered for InGaN film on GaN template with an Indium mole fraction up to 0.4 by Metal Organic Vapor Phase Epitaxy (MOVPE). The results obtained from this model has been compared and fitted with experimentally obtained data through XRD, RSM, PL, SEM etc. Finally, a phase diagram has been proposed to interpret the phase separation and Indium content evolution under the influence of growth temperature and precursor gas flow.

Abstract: Retracted paper: InGaN with high InN molar fraction is a promising material for next generation optoelectronic devices and electronic devices such as solar cells, laser diodes for communications, and high mobility transistors and so on. However, the growth of InGaN with high InN molar fraction is still a tough challenge for metal organic chemical vapor deposition (MOCVD). This paper provides experimental clues for the key factors, including the influences of the growth temperature, the V/III ratio, the group III supply ratio, and the reactor pressure. In addition, the effectiveness of the pressurized MOCVD growth of the InGaN with high InN molar fraction will be testified.