Investigating Semiconductor Nanostructures Functionalized by Emerging Materials for Optoelectronic Devices

Abstract

Wide and direct bandgap semiconductors (WBSs) are promising materials for many deep UV (DUV) applications. However, several challenges presently hinder the enhancement of DUV optoelectronics, such as low crystal quality, as well as complex and costly fabrication and growth processes that prevent production of high-performance devices, especially for large-scale applications. As a part of the study reported in this dissertation, I demonstrate several novel WBS-based devices with improved or novel functionalities, for the first time.

The first part of work reported in this dissertation is designated for the novel, highly ordered and well-defined hexagonal ZnO nanotube (NT) arrays that were obtained without a catalyst. These arrays were grown on a p-GaN template using pulsed laser deposition (PLD), resulting in a highly bright and cost-effective UV light emitting diode (LED). In the second part, Gd-doped ZnO NRs grown on cost-effective metal substrate by PLD are presented and it is demonstrated that these can be functionalized by CH3NH3PbI3 perovskite to extend the functionality of ZnO photodetector from the ultraviolet to the infrared region (λ > 1000 nm), for the first time.

The work reported in the third part demonstrates that the PLD method adopted in the present study can be extended to other high-quality metal oxide nanostructures. For this purpose, uniform p-type CuO pyramids were grown by PLD on Si substrate without a metal catalyst. Moreover, laser ablation method was advanced from vacuum based (PLD) to liquid based (femtosecond-laser ablation in liquid − FLAL) method to synthesize high-quality ZnO quantum dots (QDs). Adoption of this novel strategy allows producing high-performance self-powered DUV photodetectors based on p-CuO pyramids/n-ZnO QDs heterojunction device. In the last part, this research field is further advanced by exploring the functionality of other metal oxides synthesized by FLAL to fabricate a high-performance self-powered DUV photodetector. Such photodetector was fabricated using p-MnO QDs that were synthesized by FLAL and functionalized by high-quality mechanically exfoliated n-β-Ga2O3 nanoflakes as an active heterojunction layer grown on SiO2, confirming its superior response. All fabrication strategies, including use of heterojunction structures (mainly p−n junction), adopted in this work overcome the aforementioned issues related to the currently available WBS devices.