The influence of vicinal sapphire substrate on GaN epilayers and LED structures grown by metalorganic chemical vapor deposition

The effects of the GaN epilayers and LED structures grown by metalorganic chemical vapor deposition on 1° off c-plane sapphire substrate were studied. Although the 1° off-axis GaN sample has slightly rough surface morphology, it has narrower full-width at half-maximum (FWHM) of X-ray asymmetrical reflection (10–12), higher mobility, lower compensating acceptor concentration and lower etching pits densities (EPD) than the on-axis GaN sample. And it also has lower etching pits densities (EPD). To reduce the threading dislocations in GaN films grown on vicinal substrates is attributed. A very weak yellow luminescence is observed in photoluminescence (PL) spectra of 1° off-axis GaN sample. Finally, comparing to LED structures grown on on-axis c-plane sapphire substrates, the LED structures grown on 1° off substrate show a blue shift of PL wavelength and 2.6 times stronger in PL intensity. The electroluminescence (EL) intensity of 1° LED sample rises faster in small amount of driving current region.

Source:Materials Science and Engineering: B

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