Interactive Study of Electroreflectance and Photocurrent Spectra in InGaN/GaN-Based Blue LEDs

We experimentally and theoretically investigate the relationship between the electroreflectance (ER) and photocurrent (PC) spectra, and how they can be utilized to estimate the flat-band voltage and the bandgap energy of the InGaN/GaN-based quantum-well (QW) structure in blue light-emitting diodes. With theoretical modeling of ER and PC spectra, we calculate the changes in both the refractive index (<inline-formula> <tex-math notation="LaTeX">$\Delta \text{n}$ </tex-math></inline-formula>) and optical absorption (<inline-formula> <tex-math notation="LaTeX">$\Delta \alpha )$ </tex-math></inline-formula> spectra from experimental ER and PC data by using the Kramers–Kronig relation. Then, we compare <inline-formula> <tex-math notation="LaTeX">$\Delta \text{n}$ </tex-math></inline-formula> (or <inline-formula> <tex-math notation="LaTeX">$\Delta \alpha )$ </tex-math></inline-formula> spectra obtained differently from the ER and PC data and try to comprehend their physical meanings interactively. From these combined studies, we propose an exact method of determining the flat-band voltage, the piezoelectric field, the emission energy, the effective bandgap energy, and the Stokes shift of a QW structure under the quantum-confined Stark effect (QCSE).