Vertically aligned InGaN/GaN nanorod light emitting diode (LED) arrays were created from planar LED structures using a new top-down fabrication technique consisting of a plasma etch followed by an anisotropic wet etch. The wet etch results in straight, smooth, well-faceted nanorods with controllable diameters and removes the plasma etch damage. 94% of the nanorod LEDs are dislocation-free and a reduced quantum confined Stark effect is observed due to reduced piezoelectric fields. Despite these advantages, the IQE of the nanorod LEDs measured by photoluminescence is comparable to the planar LED, perhaps due to inefficient thermal transport and enhanced nonradiative surface recombination.

The influence of threading dislocation (TD) density on electroluminescence and deep level defect incorporation in the multi-quantum well regions of InGaN/GaN light emitting diodes (LEDs) was investigated. LED efficiency increased with decreasing TD density. To elucidate the impact of TD density on deep level defect incorporation and resulting radiative efficiency, deep level optical spectroscopy and lighted capacitance voltage measurements were applied to the LEDs. Interestingly, the concentration of all observed deep levels decreased with TD density reduction, but their concentration also varied strongly with depth in the multi-quantum well region. These trends indicate that (1) TDs strongly influence point defect incorporation in InGaN/GaN LEDs and (2) TDs, possibly in conjunction with point defects, are detrimental to LED efficiency.

We report a method to determine the radiative efficiency (RE) of a semiconductor by using room-temperature excitation-dependent photoluminescence measurements. Using the ABC model for describing the recombination of carriers, we show that the theoretical width of the RE-versus-carrierconcentration (n) curve is related to the peak RE. Since the normalized external quantum efficiency, EQE normalized , is proportional to the RE, and the square root of the light-output power, ffiffiffiffiffiffiffiffiffi LOP p , is proportional to n, the experimentally determined width of the EQE normalized-versus-n curve can be used to determine the RE. We demonstrate a peak RE of 91% for a Ga 0.85 In 0.15 N quantum well.

A computationally efficient radiative transport model is presented that predicts a camera measurement and accounts for the light reflected and blocked by an object in a scattering medium. The model is in good agreement with experimental data acquired at the Sandia National Laboratory Fog Chamber Facility (SNLFC). The model is applicable in computational imaging to detect, localize, and image objects hidden in scattering media. Here, a statistical approach was implemented to study object detection limits in fog.

The scattering of light in fog is a complex problem that affects imaging in many ways. Typically, imaging device performance in fog is attributed solely to reduced visibility measured as light extinction from scattering events. We present a quantitative analysis of resolution degradation in the long-wave infrared regime. Our analysis is based on the calculation of the modulation transfer function from the edge response of a slant edge blackbody target in known fog conditions. We show higher spatial frequencies attenuate more than low spatial frequencies with increasing fog thickness. These results demonstrate that image blurring, in addition to extinction, contributes to degraded performance of imaging devices in fog environments.