Developments in AlGaN and UV-C LEDs grown on SiC

AlGaN-based UV-C LEDs (260-300 nm) remain inefficient compared to InGaN visible LEDs due to optically absorptive layers limiting light extraction, optical polarization, and poor material quality. Sapphire, the most popular substrate material, is transparent and inexpensive but has many disadvantages in material quality and device performance. In contrast, SiC has small lattice mismatch with AlN (~1%), similar crystal structure, more chemically stable and contains no oxygen, which degrades the IQE and compensates holes. We report low threading dislocations density (TDD) AlN on SiC (TDD < 7x108cm-2) by metalorganic chemical vapor deposition (MOCVD). We demonstrate innovative thin-film flipchip (TFFC) LEDs with 7.8 mW at 95 mA at 278.5 nm grown on AlN/SiC with TDD~1x109 cm-2. (Respectively, EQE and WPE are 1.8% and 0.6%.) We also demonstrate that KOH roughening does not impact the IV voltage of TFFC LED. KOH roughening enhanced the light extraction efficiency (LEE) by 100% and ~180% for UV LEDs with 10 nm p-GaN and 5 nm p-GaN, respectively.

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