Search

Theory concerning the high ideality factor of gallium nitride (GaN) based lightemitting diode (LED) has been reviewed. The presence of a high ideality factor indicates a large forward voltage that results in efficiency reduction. The paper suggests that tunneling is the main reason defining the exponential behaviour of current-voltage measurements, which leads to a high ideality factor. However, there is also a paper that suggests that the design of current geometry in the LED chip defines the value of ideality factor. An effective current spreading geometry in the LED chip will minimize the ideality factor and make it fall between the ideal range of 1 to 2. Besides, how the ideality factor is calculated will also play a major role in defining its value. By calculating the ideality factor based solely on the radiative recombination current formula, the value of ideality factor can result in an ideal ideality factor of 1.08. [ABSTRACT FROM AUTHOR]

Current-voltage measurements have been performed on InAs/InGaAs/GaAs quantum dot structures with varying growth and design parameters. These measurements show that the forward and reverse bias dark currents decrease with increasing spacer growth temperature, however, they are relatively insensitive to the number of periods of the quantum dot layers. Temperature dependent current-voltage measurements show that the mechanism that governs the reverse bias leakage current is due to generation-recombination via mid-band traps assisted by the Frenkel-Poole emission of carriers from these traps. [ABSTRACT FROM AUTHOR]

We present a study of InAs/GaAs quantum dot-in-well (DWELL) material using transmission electron microscopy and leakage current-voltage measurements. The spacer layers between the DWELL layers have a variety of annealing and growth temperatures. We show that there is a strong correlation between spacer layer, annealing temperature, defect density, and these leakage currents, with the most defective sample having 30 times more defects and a leakage current several orders of magnitude above that of the least defective. Cross section transmission electron microscope (TEM) shows that surface roughness above defective dots is responsible for the high defect densities. However, even in the best sample the reverse bias leakage current is several orders of magnitude above that typically seen in quantum well materials and a measurable density of defective dots are observed in planar view TEM. [ABSTRACT FROM AUTHOR]

The main scope of this paper is to present in a simple and concise way a mathematical model of composite materials able to describe the propagation of shear horizontal waves in the case where composite is rotating and subjected to an initial stress. This work is aimed at the relevant possibility to apply the obtained results for the establishment of high-achievement applications of piezoelectric and semiconductor composites and surface acoustic waves devices. We conclude by analyzing numerical computations in which the influence of the rotation, initial stress and electromagnetic boundary conditions are graphically observed. [ABSTRACT FROM AUTHOR]