Document Type

Dissertation

Date of Award

12-31-2021

Degree Name

Doctor of Philosophy in Electrical Engineering - (Ph.D.)

Department

Electrical and Computer Engineering

First Advisor

Hieu Pham Trung Nguyen

Second Advisor

Marek Sosnowski

Third Advisor

Dong Kyun Ko

Fourth Advisor

Xuan Liu

Abstract

III-nitride materials are extensively studied for various applications. Particularly, III-nitride-based light-emitting diodes (LEDs) have become the major component of the current solid-state lighting (SSL) technology. Current III-nitride-based phosphor-free white color LEDs (White LEDs) require an electron blocking layer (EBL) between the device active region and p-GaN to control the electron overflow from the active region, which has been identified as one of the primary reasons to adversely affect the hole injection process. In this dissertation, the effect of electronically coupled quantum well (QW) is investigated to reduce electron overflow in the InGaN/GaN dot-in-a-wire phosphor-free white LEDs and to improve the device performance. With the incorporation of electronically coupled quantum well, it is demonstrated that light output power and external quantum efficiency (EQE) are increased, and efficiency droop is reduced. It is attributed to the significant reduction of electron overflow primarily responsible for efficiency degradation through the near-surface GaN region. In addition, a blue-emitting InGaN QW is incorporated between the quantum dot (QD) active region and p-GaN, wherein electrons escaping from the device active region can recombine with holes to contribute to white-light emission.

Moreover, different device design approaches are presented in this dissertation to mitigate the electron overflow in AlGaN deep ultraviolet (DUV) LEDs. A novel EBL-based LED structure is demonstrated instead of conventional EBL-based LED which shows enhancement in the output power by ~3.5 times at 254 nm wavelength. Additionally, another novel approach is presented to mitigate the electron overflow problem in AlGaN DUV LEDs using concave quantum barriers (QBs) instead of conventional QBs. These concave QB structures are favorable for cooling down the hot electrons before entering into the QWs thus achieving lower velocity and mean free path, and resulting in remarkably reduced electron leakage. Further, an EBL-free approach is demonstrated to improve the performance of the AlGaN DUV LEDs at ~284 nm wavelength. The proposed LED design provides the solution for the electron leakage problem and opens a new path for the realization of high-power UV light emitters. Next, another III-nitride material-based UV LED has been studied which is relatively unexplored though it holds the potentiality and optical tuning capability from UV to infrared region. In particular, a detailed study of the light extraction efficiency (LEE) of AlInN nanowires in the UV wavelength range is performed using the three-dimensional finite-difference time-domain (FDTD) simulation method. Here the improvement in the EQE of AlInN based UV nanowire LEDs is demonstrated by enhancing the LEE using a periodic array of nanowires and different photonic crystal structures.

Consequently, resistive switching capabilities of AlN-based resistive random-access memory (RRAM) devices are investigated and demonstrated in this dissertation. The results suggest that AlN-based RRAM devices can be utilized for low power applications due to the switching capabilities at a very low compliance current (CC) of 10 nA.

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