Analysis of Carrier Dynamics in InGaN/GaN Multiple-Quantum-Shell Nanorod Light-Emitting Diodes by Impedance Spectroscopy

Abstract

Optoelectronic characteristics of the InGaN/GaN nanorod light-emitting diode (NR-LED) are reported. The fabricated NR-LED device has InGaN/GaN multiple-quantum-shells on c-, r-, and m-planes, which have been grown on the GaN nanorod template. The electroluminescence spectra measured as a function of current reveal that carrier injection occurs from the lowest-energy c-plane to the r-plane, and eventually to the m-plane on the side of the rod. The peak wavelength shows a shift >150 nm (600 to 435 nm) as the injection current increases. The impedance spectroscopies are performed at low current levels to assess the carrier injection mechanism of the device. It is demonstrated that the impedance data cannot be fitted with the conventional small-signal equivalent circuit consisting of a resistor and a capacitor connected in parallel as well as a series resistor. Another circuit of parallel resistor-capacitor needs to be added to the conventional equivalent circuit to fit the experimental impedance data more accurately. Differential carrier lifetimes and the separated parallel capacitance and resistance values indicate that one of the parallel resistor-capacitor circuits reflects not the recombination process, but a transport to the active region, hindering the radiative recombination in the low-current regime. This additional charge-storage element is considered to reflect the unique current injection mechanism of the NR-LED.