SBIR Phase I: Realization of Transparent Gallium Nitride Wafers by Ammonothermal Growth

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This Small Business Innovation Research Phase I project will address the coloration problem of gallium nitride (GaN) grown by the ammonothermal method. Despite its promise to reduce the cost of GaN wafers by 90%, the ammonothermal growth technique has a coloration problem which impedes the use of the resulting substrates for high-brightness light emitting diodes (HB-LEDs). The current major application of GaN wafers is for growing laser diodes (LDs), for which performance is not seriously affected by the coloration issue. However, optical loss in the substrate is a serious issue for HB-LEDs. This project aims to further develop the ammonothermal growth technology to realize low-cost, transparent GaN wafers usable for HB-LEDs. Removing oxygen, which is the primary impurity in ammonothermal bulk GaN, is one of the most challenging aspects of this effort because of the presence of oxygen-sensitive mineralizers. In the Phase I project, we will first conduct controlled sets of experiments to reveal the correlation between impurities and coloration. We will also develop an improved process to minimize the oxygen contamination. The goal of the Phase I project is to prove the feasibility of these new approaches in obtaining transparent GaN.The broader impact/commercial potential of this project is the realization of low-cost, transparent GaN wafers via ammonothermal growth, which will improve the performance and reduce the cost of HB-LEDs. The current high price of GaN wafers does not permit cost competitiveness of HB-LEDs with competing products. The high wafer cost is attributed to the current labor-intensive, low-yield production method of hydride vapor phase epitaxy (HVPE). Since the ammonothermal growth process is a scalable liquid-phase method, it is expected to reduce GaN wafer cost by 90%. The availability of low-cost, transparent GaN wafers will permit substrates grown via this method to address a market which is ten times the size of the current niche (~$1 billion in 2015). Currently, several domestic and international competitors are pursuing this goal; however, none has achieved colorless GaN wafers suitable for the HB-LED application. Our novel processes will directly address the oxidation problem of mineralizers which, we expect, will solve the coloration problem. This project will contribute to realization of low-cost HB-LEDs not only for energy-efficient solid-state lighting products, but also for automobile headlamps and display backlights.