Effect of Polarity on the Electrical Properties and Low-Frequency Noise Characteristics of LEDs Grown on Sapphire Substrates

Abstract

Abstract In this study, the electrical properties, photoluminescence spectra and the low-frequency noise behaviors of the polar, semipolar, and nonpolar AlGaN-based UV LEDs grown on the sapphire substrate have been measured and investigated at room temperature. The electrical parameters (such as threshold voltage Vth, reverse saturate current Is, series resistor Rs and ideality factor n), photoluminescence spectra (peak wavelength, FWHM) and the low-frequency noise parameters (white noise amplitude A, 1/f noise amplitude B, the frequency exponent of 1/f noise γ, the amplitude of g-r noise C, the corner frequency of g-r noise f0 and the frequency exponent factor α) of the examined UV LEDs have been fitted and extracted using the classical LED current-voltage equation and low-frequency noise equation. In addition, we studied the relationships between the parameters of low-frequency noise, γ, f0, α and the current during the LED turn-on process. The conclusion shows that the electrical properties, peak wavelength of photoluminescence and low-frequency noise parameters of the three studied AlGaN-based UV LEDs show a strong polarity-dependence under the operation process. The quantum-confined Stark effect induced by the built-in electric field, strength of the polarization field and the defect density in the active region play the major factors affecting the electrical properties, luminescence properties and low-frequency noise behaviors of AlGaN-based UV LEDs.