Sub‐microscopic transient lens spectroscopy of InGaN/GaN quantum wells

Abstract

Transient lens (TL) spectroscopy was developed with sub-micrometer spatial resolution to observe the temporal and special behavior of the nonradiative processes of carrier dynamics in InGaN/GaN quantum wells (QW). We have observed the carrier density dynamics and the thermal dynamics in the TL signals with a nanosecond pulsed laser. We have also observed TL and photoluminescence (PL) signals by using near-field scanning optical microscopy (NSOM), and find that both PL and TL images are correlated and exhibit submicron scale spatial inhomogeneity. . We have also succeeded in the direct observation of the nonradiative processes (thermalization, heat conduction [3] and carrier diffusion [4]) by using transient grating (TG) spectroscopy. Although nonradiative processes of carriers are very important in determining optical emission properties, only few investigations have so far been conducted to experimentally elucidate the nonradiative processes, primarily due to the difficult nature of such measurements. We expect that transient lens (TL) spectroscopy, which has been developed for the photochemistry research field [5,6], is also applicable for the direct observation of nonradiative carrier processes. The principle of TL spectroscopy, which is based on the third order nonlinear optical effect, is similar to TG spectroscopy, but the experimental configuration is much simpler and the spatial resolution is significantly improved. Recently, we have reported for the first time an investigation of the TL spectroscopy to experimentally observe nonradiative processes in GaN and InGaN/GaN materials [7]. In this work, we show results from TL spectroscopy measurements with micro or sub-micro spatial resolution, and observe the temporal and special behavior of nonradiative processes of carries in InGaN/GaN quantum wells.

Pump–Probe Microscopy: Spatially Resolved Carrier Dynamics in ZnO Rods and the Influence of Optical Cavity Resonator Modes

“…Scans obtained at intermediate locations show that the negative lobe increases in magnitude as the pair is moved toward the center, becoming entirely negative at the midpoint (Figure ). These results suggest that the pump–probe signals include contributions from both an induced absorption, arising from near-infrared excitation of free-carriers, and a lensing component originating from a spatial variation in the index of refraction due to the localized excitation. ,− …”

Carrier Decay and Diffusion Dynamics in Single-Crystalline CdTe as Seen via Microphotoluminescence

“…Crystalline defects in bulk and quantum-confined semiconductors often act as regions of strong nonradiative carrier recombination [1,2] and can detrimentally alter the spatially averaged carrier densities that are photogenerated in solar cells [3] or electrically injected in light-emitting devices [4]. It is, therefore, essential to be able to experimentally probe the extent to which defects locally influence carrier lifetimes and diffusion lengths in order to understand their overall effect on device performance.…”

Near-field scanning optical microscopic transient lens for carrier dynamics study in InGaN∕GaN

“…17,18 Also we reported the spatial resolved measurements of carrier and thermal dynamics by the transient lens ͑TL͒ technique. 19,20 The TG and TL techniques measure the third-order nonlinear response induced in the materials by the excitation laser. In this letter, the TL technique is developed to the time-resolved measurement ͑TR-M-TL͒ and near-field scanning optical microscopic measurement ͑NSOM-TL͒, and applied to the carrier dynamics study in InGaN/ GaN QWs.…”