Optical Science and Engineering ETDs

Publication Date

Fall 11-15-2023

Abstract

Solid-state lighting has achieved significant success over the past two decades, but the low quantum efficiency of green LEDs (i.e., the “green gap”) remains a barrier to full red-green-blue (RGB) displays in numerous applications. Combating efficiency reduction in longer-wavelength LEDs requires understanding the relative roles of intrinsic effects (e.g., wave-function overlap, carrier-current density relationship, phase-space filling (PSF)) vs. extrinsic effects (e.g., material degradation due to increased defect density, compositional inhomogeneities, etc.). A systematic study of the carrier dynamics in InGaN/GaN LEDs is very important for understanding the origin of the green gap and for providing solutions to improve the efficiency of the LEDs.

In this dissertation, several techniques, such as small-signal electroluminescence (SSEL), deep-level optical spectroscopy (DLOS) and lighted capacitance-voltage (LCV), were applied to LEDs grown under state-of-the-art growth conditions using metal-organic chemical vapor deposition (MOCVD). The effect of indium composition was examined to study the origin of the lower quantum efficiency in green LEDs compared with blue and cyan LEDs. The impact of the deep-level defect density on various non-radiative recombination mechanisms was also investigated, and the role of each recombination mechanism was analyzed separately. Furthermore, the effect of quantum well (QW) thickness was studied to determine the optimized value and tradeoffs between various design parameters. Finally, a novel multiple carrier lifetime model was developed to study carrier dynamics in InGaN/GaN multiple-quantum-well (MQW) LEDs with non-uniform carrier distribution. This model can also be applied to micro-LEDs and other LEDs with similar carrier dynamics behavior. The studies mentioned above will contribute to a better understanding of carrier dynamics in green InGaN/GaN LEDs and inform approaches for improving quantum efficiency in LEDs that already possess state-of-the-art growth quality.

Degree Name

Optical Science and Engineering

Level of Degree

Doctoral

Department Name

Optical Science and Engineering

First Committee Member (Chair)

Daniel Feezell

Second Committee Member

Ganesh Balakrishnan

Third Committee Member

Payman Zarkesh-Ha

Fourth Committee Member

Tara Drake

Fifth Committee Member

Andrew Armstrong

Keywords

Light-emitting diodes, Gallium nitride, Electroluminescence, Quantum efficiency, Carrier dynamics

Sponsors

Department of Energy

Document Type

Dissertation

Language

English

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