NSF Award
1012256
This Small Business Innovative Research (SBIR) Phase I project will conduct feasibility studies for development of light emitting diodes (LEDs) that emit in the green spectral region. A need exists for efficient green emitting LEDs for use as a green source used singly and also for use in LED lamps that utilize direct color-mixing of three or more colors, e.g., red, green and blue, to achieve white. Green LED sources are typically made from indium gallium nitride (InGaN) semiconductor material; however, such LEDs suffer from a decrease in efficiency as operating current is increased. The research objective is to develop a green LED with high quantum efficiency at high current values by reducing the observed efficiency droop at operating current values. This research objective will be achieved by forming a hybrid LED comprised of a p-type zinc oxide (ZnO) semiconductor layer deposited on the quantum well region of an InGaN wafer during the wafer fabrication process. The p-type ZnO layer will provide additional hole carriers and thereby increase quantum efficiency. The anticipated technical results will be an increased efficiency of at least 20% for the hybrid LED device. <br/><br/>The broader impact/commercial potential of this project will enhance technical and scientific understanding of the mechanisms by which a layer of p-type ZnO semiconductor material with high hole concentration and deposited during wafer growth in close proximity to the active layer region comprised of InGaN quantum wells can increase significantly the quantum efficiency of the hybrid LED device fabricated from such wafers. A potential societal impact is energy savings for the U.S. by employing higher efficiency electrical lighting and thereby decreasing electrical power demand and bright color displays. The potential commercial impact of the project is availability of a green LED with sufficiently high efficiency to be utilized in combination with blue and red LEDs to achieve a commercially viable white LED lamp by direct color-mixing, without use of phosphors to achieve green light from blue. A direct color mixing approach will eliminate inefficiencies associated with use of down-converting phosphors. These direct color-mixed LED lamps will be cost effective and possess spectral qualities desirable to consumers that will help speed market entry. The market sector impacted includes semiconductor chip manufacturing, white light lamps for residential and commercial use, and color displays.
