We investigated the carrier-injection effects in the emission spectrum of strained GaN/InGaN/AlGaN quantum well (QW) blue emitters using a pulsed current excitation technique. Spectral blueshift as large as 80 meV in the emission peak energy was observed as the injection current increases from 1 mA to 1 A. Based on a self-consistent calculation that couples the Poisson equation with a wurtzite-type Rashba–Sheka–Pikus Hamiltonian, four important interactions are evaluated in order to determine the optical properties of InGaN QW. It is shown that the spectral redshifting caused by a piezoelectricity induced quantum confined Stark effect and carrier-induced band gap renormalization is counteracted by a blueshift due to the band filling and charge screening effects. The increase of InGaN QW emission peak energy and intensity with injected carriers suggests a dominant contribution from the latter in a band-to-band recombination process.

Specially designed intermediate carrier blocking layers (ICBLs) in multi-active regions of III-nitride LEDs were shown to be effective in controlling the carrier injection distribution across the active regions. In principle, the majority of carriers, both holes and electrons, can be guided into targeted quantum wells and recombine to generate light of specific wavelengths at controlled current-densities. Accordingly we proposed and demonstrated a novel monolithic InGaN-based LED to achieve three primary colors of light from one device at selected current densities. This LED structure, which has three different sets of quantum wells separated with ICBLs for three primary red-green-blue (RGB) colors, was grown by metal-organic chemical vapor deposition (MOCVD). Results show that this LED can emit light ranging from 460 to 650 nm to cover the entire visible spectrum. The emission wavelength starts at 650 nm and then decreases to 460 nm or lower as the injection current increases. In addition to three primary colors, many other colors can be obtained by color mixing techniques. To the best of our knowledge, this is the first demonstration of monolithic full-color LED grown by a simple growth technique without using re-growth process.

QPI is a new generation of spatial light modulator (SLM) that combines light source and light modulation at the pixel level, thus eliminating the waste in most existing SLMs where light is separately generated and modulated. This paper explains the QPI architecture and its 3D application and beyond.

A color-temperature tunable white light-emitting diode (LED) based on a newly developed monolithic color-tunable LED structure was demonstrated. The color-tunable LED structure consists of three different sets of quantum wells separated by intermediate carrier blocking layers that can independently emit visible lights from 460 to 650 nm under different injection currents. To generate white light, the color-tunable LED is operated under pulsed conditions with each pulse consisting of multiple steps of different current amplitudes and widths emitting different colors. The combined spectrum of different colors is aimed to mimic that of the blackbody radiation light source. The pulse rate is designed to be higher than the human eye response rate, so the human eye will not discern the emission of successive colors but a singular emission of white light. Results of a two-step pulse design show this method is able to generate white light from 2700 K – 6500 K. Moreover, their color coordinates fall within the 4-step MacAdam ellipses about the Planckian locus while achieving the Color Rendering Index (CRI) in the 80-90 range. Finally, simulations show improvement of CRI into the 90-100 range is possible with further optimization to the color-tunable LED spectral emission and use of three-step pulses.

We investigate the effects of structural asymmetry on the electronic and optical properties of indium gallium nitride (InGaN) quantum wells (QW's). Using a pulsed current excitation technique, spectral blue shift as large as 80 meV is observed in a strained 3.0-nm In 0:2 Ga 0:8 N QW as the pulsed current increases from 1 mA to 1A. Based on a self-consistent calculation, we are able to quantify a gain competition process among the interactions of piezoelectricity, many-body, charge screening, and band filling effects. Such interactions are shown to provide a mechanism for shaping the QW confined potential such that superior carrier confinement and charge screening of the piezoelectric field can be obtained in the asymmetric InGaN QW. At high carrier injection of Ninj > 2 2 10 19 cm 03 , a tenfold increase in the TE-polarized optical gain can be achieved by using the asymmetric GaN-InGaN-AlGaN QW instead of the symmetric InGaN-AlGaN QW. Due to the diminishing of piezoelectricityinduced quantum-confined Stark effect, the calculated optical gain spectra of the asymmetric InGaN QW exhibit a spectral blue shift with respect to those of the symmetric InGaN QW.