Increase In Nonradiative Recombination Rate Research Articles

Analysis of carrier recombination dynamics in InGaN-based light-emitting diodes by differential carrier lifetime measurement

In this work, we investigate the carrier recombination dynamics in InGaN-based blue LED devices by analyzing the radiative and nonradiative carrier lifetimes as functions of driving current. To separate the radiative and nonradiative carrier lifetimes, we utilize the information on the internal quantum efficiency (IQE) and differential carrier lifetime. For comparative analysis, the characteristics of the IQE and electroluminescence spectrum are also used. Through measurements and analyses, we demonstrate that the saturation of the radiative recombination rate induced by the phase-space filling in the active volume triggers the increase in nonradiative recombination rate, thus leading to the efficiency droop.

Carrier dynamics in blue and green emitting InGaN MQWs

Spectrally and spatially‐resolved nonlinear optical techniques were combined with the photoluminescence spectroscopy to study carrier dynamics and photoluminescence efficiency in highly excited blue‐ and green‐emitting InGaN/GaN quantum wells. The differential transmission and transient grating techniques provided carrier lifetimes and diffusivity in the extended states with energies above the photoluminescence emission band and revealed their dependences on excess carrier density. At high excitation conditions, an increase of diffusivity led to the increase of nonradiative recombination rate, being more pronounced in the green QW structures with respect to the blue ones. Enhancement of these processes in the extended states has a strong impact on diminishing the photoluminescence efficiency in the localized states.

Observation of photo darkening in self assembled InGaAs/GaAs quantum dots

Photo darkening was observed in epitaxial InGaAs/GaAs quantum dots (QDs). The photoluminescence (PL) intensity of the QDs showed a non-reversible decrease under continuous laser irradiation. The time constants varied from tens of minutes to several hours, depending on the applied laser power. Based on the spectral evolution, it was concluded that the observed phenomenon should originate from laser induced structural damage and a sustained increase of non-radiative recombination rate in the wetting layer. Additionally, according to the PL decay dynamics at different laser powers, it is argued that there should exist other processes that hinder PL degradation at a high laser power.

Nonlinear optical properties and phase-relaxation processes in single-walled carbon nanotubes

We have investigated third-order nonlinear optical properties of bundled and isolated semiconducting single-walled carbon nanotubes (SWNTs) by means of Z-scan method, pump–probe method, and two-beam time-resolved degenerate four-wave mixing (DFWM) method. The figures of merit Im χ (3)/ α in both bundled and isolated SWNTs samples were found to be enhanced with increasing tube diameter. The measured Im χ (3)/ α value in the bundled SWNTs was an order of magnitude smaller than that in the isolated SWNTs. Both population relaxation time T 1 and phase-relaxation time T 2 for bundled samples were smaller than those in the isolated samples. These experimental results can be explained by an increase in nonradiative recombination rate and phase-relaxation rate in the bundled sample. The phase-relaxation time T 2 is considered to have a significant role in the enhancement of Im χ (3)/ α.