We present results from a combined experimental and numerical investigation of trap-assisted tunneling contributions to subthreshold forward current in InGaN/GaN light-emitting diodes. We show that the excess forward leakage current in single-quantum-well InGaN/GaN light-emitting diodes can be explained by non-local tunneling-into-traps processes and subsequent non-radiative recombination with free carriers.
KEYWORDS: Eye, Light emitting diodes, Colorimetry, Control systems, Cameras, Head, Picture Archiving and Communication System, RGB color model, LabVIEW, Visualization
A portable pupillometer has been developed which is capable of performing accurate measurements of the pupil diameter
during chromatic flicker stimulations. The handheld measuring system records the near-infrared image of the pupil at the
rate of 25 fps and simultaneously stimulates the eye using a diffused flicker light generated by light emitting diodes
(LEDs). Intensity, frequency and chromatic coordinates of the stimulus can be easily adjusted using a user-friendly
graphical interface. Thanks to a chromatic monitoring of the stimulus close to the plane of the eye, photopically matched
conditions can be easily achieved. The pupil diameter/area can be measured during flickering stimuli that are generated
with frequency in a range of 0.1-20 Hz. The electronic unit, properly connected to the personal computer through a USB
port, drives the optical unit, which can be easily held in a hand. The software interface controlling the system was
developed in LabVIEW. This paper describes the instrument optical setup, front-end electronics and data processing.
Moreover preliminary results obtained on a voluntary are reported.
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