Electrical characterization of InGaN/GaN multiple-quantum-well structures by thermal admittance spectroscopy

Experimental results of electrical characterization of InGaN/GaN multiple-quantum-well electrolu- minescence test structures obtained by thermal admittance spectroscopy are presented. The stu- died GaN : Mg/5 × (InGaN/GaN)/GaN:Si structures were grown on c-plane sapphire substrate by metal-organic vapor phase epitaxy. Admittance measurements were conducted from room tem- perature down to 125 K for a wide frequency range and for different applied bias voltages. Analy- sis of the capacitance versus frequency curves shows the presence of several cutoff frequencies which originate from the response of equivalent RC series circuits and give peaks in the conduc- tance divided by angular frequency. The dependence of the position and the amplitude of these peaks on temperature is discussed.