Characteristics of InGaN/AlGaN light-emitting diodes on sapphire substrates

We report characteristics and degradation of an InGaN/AlGaN double-heterostructure light-emitting diode (LED) grown by metalorganic chemical vapor deposition on a sapphire substrate. The InGaN/AlGaN LED exhibited an optical output power of 0.17 mW, an external quantum efficiency of 0.2%, a peak emission wavelength at 440 nm with a full width at half-maximum of 63 nm, and a stable operation up to 3000 h under 30 mA de operation at 30 degrees C. However, the InGaN/AlGaN LED showed electrical and optical degradations under high injected current density and high ambient temperature. Electroluminescence, electron-beam-induced current and cathodoluminescence observations showed that the degraded InGaN/AlGaN LED exhibited formation and propagation of dark regions, which act as nonradiative recombination centers. The values of the degradation rate were determined to be 1.1x10(-3), 1.9x10(-3), and 3.9x10(-3) h(-1) under the injected current density of 100 A/cm(2), and 1.6x10(-2), 3.6x10(-2), and 8x10(-2) h(-1) under 200 A/cm(2) at ambient temperatures of 30, 50, and 80 degrees C, respectively. The activation energy of degradation was also determined to be 0.23-0.25 eV. The degradation of electrical and optical characteristics was caused by the growth of dark regions. It was also observed that GaN-based LEDs on sapphire substrates have longer lifetime than the ZnSe-based LED, but shorter than the AlGaAs and InCaAsP LEDs. (C) 1997 American Institute of Physics.