Professor Ming-Hua Mao’s Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Carrier transport was studied both numerically and experimentally using scanning photocurrent microscopy (SPCM) in two-dimensional (2D) transport structures, where the structure size in the third dimension is much smaller than the diffusion length and electrodes cover the whole terminal on both sides. The scanning photocurrent simulation results surprisingly showed almost identical profiles from structures with different widths. The simulation results indicate that the integrated carrier distribution in the 2D transport structures with finite width can be well described by a simple-exponential-decay function with the carrier decay length as the fitting parameter, just like in the 1D transport structures. Furthermore, our simulation results demonstrate that the scanning photocurrent profiles in the ohmic- or Schottky-contact three-dimensional (3D) transport structures with electrodes covering the whole terminal on both sides will reduce to those described by the corresponding 1D fitting formulae. Finally, experimental SPCM on a p-type InGaAs air-bridge two-terminal thin-film device was carried out. This study allows us to extract the minority carrier decay length and to obtain the mobility-lifetime product which can be used to evaluate the performance of 2D carrier transport devices. This work has been published in Scientific Reports:

Yu‑Chien Wei, Cheng‑Hao Chu, and Ming‑Hua Mao*, “Minority Carrier Decay Length Extraction from Scanning Photocurrent Profiles in Two-Dimensional Carrier Transport Structures,” Scientific Reports, 11, 21863, (2021).

Figure 1. (a) Schematic of the SPCM setup in an InGaAs air-bridge two-terminal thin-film device. (b) SEM images for one side of the measured InGaAs air-bridge two-terminal thin-film device. (c) Scanning photocurrent profile of the 0.2 μm wide case compared with that of the 1D transport structure. (d) Scanning photocurrent profiles with different widths.

Professor Chung-Chih Wu

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Although active-matrix light-emitting diode displays (AM-LEDs) have been widely applied, effective optical out-coupling techniques possessing both integration compatibility and image quality remain highly desired for further improving their efficiency and power consumption performances . In our studies, a 3-dimensional (3D) reflective pixel structure filled with a patterned high-index material was proposed for boosting light extraction efficiency of common top-emitting AM-LED pixel devices. Using the OLEDs, we conducted experimental studies on the proposed 3D pixel configuration to validate the simulation and design. 3D OLED pixel devices with varied pixel dimensions were implemented and their structures, electrical properties, efficiencies, and EL characteristics were characterized. Significant efficiency gains were obtained with the mm-scale reflective 3D pixel devices and experiment results well corroborated multiscale optical simulation results, confirming effectiveness of the 3D LED pixel for enhancing light extraction of emissive displays.

Figure 1. (A) 3D reflective concave OLED pixel structure having the reflective bank slope surface and the patterned high-index filler. (B) Characteristics of of pixel devices 2-7 (2/4/6 patterned filler pixels and 3/5/7 non-filler conventional pixels) observed by optical microscopy and cross-sectional SEM (2/4/6). (C) EQEs and EQE gain (filler vs. non-filler device) of pixel array devices (devices 2-7) as a function of the PDL opening size W1, for both filler and non-filler reference devices.

 

PSTD Simulation Analysis of the Transparency and Opacity of Biological Tissues