Influences of the p-GaN Growth Temperature on the Optoelectronic Performances of GaN-Based Blue Light-Emitting Diodes

We investigate the influence of p-(Al)GaN growth temperature (Tg) on the optoelectronic performances of InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs). We systematically combine various characterization techniques, such as current-voltage, current-light output power, capacitance-voltage (C-V) under forward and reverse biases, photocurrent and electroreflectance (ER) spectroscopies, temperature-dependent electroluminescence, and the internal quantum efficiency (IQE). From the experimental analyses, it is shown that increasing Tginduces: 1) the reduced optical loss by the improved crystal quality of the p-GaN layer (improved light extraction efficiency) and 2) the decreased IQE due to the Mg diffusion from the p-(Al)GaN layer to the MQW region. This paper demonstrates that the fine control of the Mg diffusion from the p-GaN layer to the InGaN/GaN MQW region is the key factor for achieving highly efficient blue LEDs. Moreover, a method of estimating the Mg diffusion length is proposed for the first time by analyzing both the C-V curves and the ER spectra under reverse biases.