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InGaN/GaN multiple quantum well (MQW) light emitting diode (LED) structures with blue and green light emissions have been grown on sapphire substrates by metalorganic chemical vapor deposition. They are investigated by high-resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HR-TEM), photoluminescence (PL) and photoluminescence excitation (PLE). HR-XRD showed multiple satellite peaks up to 10th order due to the quantum well superlattice confinement effects. HR-TEM determined the MQW structures and parameters, indicating the high quality of layer interfaces of these LED samples. Excitation power-dependent PL predicates that both piezoelectric field-induced quantum-confined Stark effect and band filling effect influence the luminescent properties. Temperature-dependent PL shows that the QW PL emission peak exhibits a monotonic red-shift and that the full width at half maximum of the PL band shows a W-shaped temperature-dependent behavior with increasing temperature. From the PLE results, a large energy difference, so-called quantum confined Stokes shift, between the band-edge absorption and emission was observed. Penetrating TEM revealed the V-shape defects, and quantum dot-like structures within the InGaN well region, which leads to intense light emissions from these MQW LEDs.

An optical-field-ionization soft x-ray laser with prepulse-controlled nanoplasma expansion in a cluster gas jet was demonstrated. Pd-like xenon lasing at 41.8-nm with 95 nJ pulse energy and 5-mrad divergence was achieved, indicating near-saturation amplification. In addition, by using deflectometry of a longitudinal probe pulse to resolve the spatiotemporal distribution of the preformed plasma, we characterize and control the plasma density distribution near the target surface for the development of solid-target x-ray lasers. We show that the use of prepulses in an ignitor-heater scheme can increase the scale length of the preformed plasma and how the effect varies with target materials.

InGaN/GaN Multiple Quantum Well (MQW) structures have been grown on sapphire substrates by low pressure metalorganic chemical vapor deposition (MOCVD), for wide range of blue, blue-green and green light emission device application. The compositions and sizes within QWs were designed according to the requirements on the LED performance. Samples were investigated by a variety of characterization techniques. Optimization of the growth parameters and process was realized and evidenced by high resolution X-ray diffraction (XRD) measurements. High quality of MQW wafers have been achieved with excellent characteristics, showing XRD multiple satellite peaks up to 10 th order due to the quantum well superlattice confinements and fine fringe structures among satellite peaks. Transmission electron microscopy confirmed the sharp MQW structures and dimensional parameters, and revealed the V-shape defects. Optical properties were further studied and Quantum confined Stokes effect was observed from photoluminescence and photoluminescence excitation measurements.