We present a programmable array microscope that uses a ferroelectric liquid-crystal spatial light modulator (SLM) for dynamic generation of scanning apertures. A single SLM serves as both the source and the detector aperture array in a double-pass confocal system. Successive aperture frames scan the array across the viewing area for complete imaging of a sample while preserving depth discrimination. Integration of the microscope output across all aperture frames produces a confocal image.

Abstract-The optical designs of resonant GaN light-emitting diodes (LEDs) have been determined for maximum extraction efficiency into typical plastic optical fiber of numerical aperture 0.5. An optimum extraction efficiency of 3.9% can be achieved for a practical resonant cavity LED (RCLED), taking account of current growth and processing considerations. The optimized device is a metal-active layer distributed Bragg reflector construction. Constructive interference effects from the top metal mirror are found to play the dominant role in efficiency enhancement. The extraction efficiency of an optimized resonant single-mirror LED is found to be 3.3%, indicating a small compromise in performance compared with the more complex RCLED structure.Index Terms-High-temperature applications, light-emitting diode (LED), plastic optical fiber (POF), resonant cavity enhancement.

The lasing properties of quantum well structures, where the cavity is defined in the plane of the wells by circular Bragg reflectors are investigated. Diffraction of the in-plane lasing modes into the vertical direction by the circular distributed Bragg reflector (DBR) allows the simultaneous measurement of near-field emission patterns and emission spectra, allowing unambiguous assignment of azimuthal quantum numbers to the lasing modes. The radial quantum number is determined by fitting the lasing spectrum to theory. Lasing is shown to occur in modes whose wave vector is mainly radial, confined by the circular DBR structure, rather than in whispering gallery type modes which are mainly azimuthal.

Resonant-cavity light-emitting diodes (RCLEDs) with multiple InGaN/GaN quantum wells have been grown on sapphire substrates. The emission was through the substrate, and the top contact consisted of a highly reflecting Pd/Ag metallization. The peak emission wavelength was measured to be 490 nm. Under constant current biasing, the intensity was observed to fluctuate irregularly accompanied by correlated variations in the voltage. To investigate this further, emission from the RCLED was focused through a GaAs wafer onto a Vidicon camera. This gave a series of infrared, near-field images, spectrally integrated over a wavelength range from 870 nm to 1.9 microm. Flashes from point sources on the RCLED surface were observed, indicating that short-lived, highly localized "hot spots" were being formed that generated pulses of thermal radiation. It is proposed that this phenomenon results from the migration of metal into nanopipes present in this material. The filled pipes form short circuits that subsequently fuse and are detected by bursts of infrared radiation that are recorded in real time.

We have studied carrier diffusion in self-assembled InAs/GaAs quantum dots (QDs) and light emission from deeply etched microstructures containing QDs using a novel micro-photoluminescence technique based on scanning the laser excitation spot across an etched feature. Complete suppression of carrier diffusion is observed in these QDs at temperatures less than 150 K. At temperatures above 150 K the carrier diffusion length in the QD layer increases with increasing temperature but remains less than the carrier diffusion length in an InGaAs/GaAs quantum well (QW). Carrier diffusion lengths of 6.5 and 9.5 µm were measured for the QD and QW layers at room temperature, respectively. Photoluminescence spectra measured on the same QD sample over the 77–297 K temperature range indicate carrier redistribution occurring between different sized dots in the layer at temperatures above 70 K, suggesting carrier trapping in only the larger dots in the layer is sufficient to prevent carrier diffusion. The expected increase in non-radiative edge recombination in deeply etched microstructures with increasing carrier diffusion length is observed for etched photonic bandgap structures containing both QD and QW active layers. Despite the reduced carrier diffusion length in QD active layers, edge effects dominate carrier recombination processes in a 3.2 µm diameter etched microstructure containing InAs/GaAs QDs at room temperature.