Characteristics of GaN-based light emitting diodes with different thicknesses of buffer layer grown by HVPE and MOCVD

Pengfei Tian, Paul R. Edwards, Michael J. Wallace, Robert W. Martin, Jonathan J.D. McKendry, Erdan Gu, Martin D. Dawson, Zhi-Jun Qiu, Chuanyu Jia, Zhizhong Chen, Guoyi Zhang, Lirong Zheng, Ran Liu

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GaN-based light emitting diodes (LEDs) have been fabricated on sapphire
substrates with different thicknesses of GaN buffer layer grown by a combination of hydride vapor phase epitaxy and metalorganic chemical vapor deposition. We analyzed the LED efficiency and modulation characteristics with buffer thicknesses of 12 µm and 30 µm. With the buffer thickness increase, cathodoluminescence hyperspectral imaging shows that the dislocation density in the buffer layer decreases from ∼1.3X10 8 cm-2 to∼1.0 X 10 8 cm-2, and Raman spectra suggest that the compressive stress in the quantum wells is partly relaxed, which leads to a large blue shift in the peak emission
wavelength of the photoluminescence and electroluminescent spectra. The combined effects of the low dislocation density and stress relaxation lead to improvements in the efficiency of LEDs with the 30 µm GaN buffer, but the electrical-to-optical modulation bandwidth is higher for the LEDs with the 12 µm GaN buffer. A rate equation analysis suggests that defect-related nonradiative recombination can help increase the modulation bandwidth but reduce the LED efficiency at low currents, suggesting that a compromise should be made in the choice of defect density.
Original languageEnglish
Article number075101
Number of pages12
JournalJournal of Physics D: Applied Physics
Issue number7
Publication statusPublished - 23 Jan 2017


  • light emitting diode
  • GaN
  • buffer
  • modulation bandwidth
  • solid state lighting


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