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 dc operation at 30 °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 ${\text{1.1×10}}^{\text{−3}},$ ${\text{1.9×10}}^{\text{−3}},$ and ${\text{3.9×10}}^{\text{−3}}\hspace{0.17em}{\mathrm{h}}^{\mathrm{-1}}$ under the injected current density of $\text{100\hspace{0.17em}}{\mathrm{A/cm}}^{\mathrm{2}},$ and ${\text{1.6×10}}^{\text{−2}},$ ${\text{3.6×10}}^{\text{−2}},$ and ${\text{8×10}}^{\text{−2}}\hspace{0.17em}{\mathrm{h}}^{\mathrm{-1}}$ under $\text{200\hspace{0.17em}}{\mathrm{A/cm}}^{\mathrm{2}}$ at ambient temperatures of 30, 50, and 80 °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 InGaAsP LEDs.