Radiative emission mechanism analysis of green InGaN/GaN light-emitting diodes with the Si-doped graded short-period superlattice

Abstract

The optical features of green InGaN/GaN light-emitting diodes (LEDs) with a graded Si-doped short-period InGaN/GaN superlattice (GSL) were examined by photoluminescence spectroscopy (PL). The power dependency of the PL peak energy and the linewidth (FWHM) at low temperatures showed that the Coulomb screening effects of Quantum confined stark effect and localized state filling are dominant processes for low and high excitation power, respectively. An increase in temperature activated the non-radiative centers at low excitation power. The abnormal temperature dependence of the peak energy indicated that the carrier dynamic is changed by the temperature owing to the spatial fluctuations of the In content and subsequent change in the state of carrier localization in InGaN/GaN MQWs. The localization effects were analyzed in the structure by fitting the temperature-dependent emission energy and utilizing a band-tailed model. The emission wavelength of the green InGaN/GaN LED with the GSL was 555 nm at 25 K and was red-shifted with increasing temperature up to 115 K. Then, it becomes blue-shift with further increases in the ambient temperature up to 260 K at low excitation power. The internal quantum efficiency was associated with the conversion from non-radiative to the radiative mechanism and is related to the carriers escaping from the localized state. The measured strain using the high-resolution x-ray rocking curve indicates that the strain of the structure is reduced because of the GSL layer. The strained structure shows a strong localization, and high efficiency. In addition, low power and high thermal energy are needed to enhance the localization effect and efficacy.