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West, JM, 2023. Laser induced nitrogen doping of zinc oxide. PhD, Nottingham Trent University.
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Abstract
The p-n junction is the fundamental building block of many electronic and optoelectronic devices, including diodes, transistors, light emitting diodes (LEDs), solar cells, integrated circuits and many more. Of the many devices, UV LEDs based on wide bandgap semiconductor p-n homojunctions promise a plethora of widescale functionalities for use in a variety of important medical, environmental, and industrial applications. However, the development of low-cost, highly efficient materials for use in UV LEDs with emissions spanning across the UV spectrum is essential if such widescale applications are to be realised. Zinc oxide (ZnO) is a promising candidate for a low cost, non-toxic alternative material to Gallium Nitride (GaN) for use in UV LEDs. Yet, the desirable ZnO p-n homojunction remains elusive due to the current research bottleneck in achieving stable, reproducible, and high-quality p-type ZnO. Various research groups have investigated routes to achieving p-type doping in ZnO, but most of the materials developed exhibit poor crystalline quality with unstable and unreproducible p-type conductivity with high native point defect densities and in-active dopants. As such, several major research challenges must be addressed if the full potential and advantages of ZnO as a UV LED material are to be harnessed in real devices. These challenges include improving dopant solubility, minimising hole compensation by native defects or background impurities, and the production of shallow acceptor states with low ionisation energies for the realisation of high quality and stable p-type ZnO. To address these challenges, this work is devoted to the development of a robust and repeatable doping strategy to achieve high quality, stable, and controllable p-type ZnO material. A disruptive progression towards the realisation of such p-type conductivity in ZnO is demonstrated through the development of a Controlled Environment Excimer Laser Doping (CEELD) process conducted in a pressurised nitrogen (N) containing environment to induce high-level, stable and reproducible N acceptor doping in Atomic Layer Deposition (ALD) ZnO. It is revealed that CEELD can incorporate and promote N into preferential lattice sites in the film through co-doping with the high level of background impurity hydrogen (H) present in the as grown ALD films. Once the N is incorporated, the high laser energy density simultaneously breaks the N − H bond and provides enough thermal energy for the out-diffusion of the otherwise passivating H from the film, in turn activating N as an acceptor type dopant. Extensive characterisation of the electrical, optical, and compositional properties of the films is performed to further verify the achievement of CEELD induced p-type ZnO. The development of Ohmic contacts to the seed n- and p-type materials are investigated, and the seed materials implemented into simple p-n junction and thin film transistor (TFT) devices to further demonstrate the achievement of p-type ZnO. The CEELD process is then presented as a one-step, ultra-fast, low thermal budget, and highly selective doping strategy for the achievement of ultra-shallow p-n junctions for both lateral and laterally printed vertical p-n homojunction devices in ZnO.
| Item Type: | Thesis |
|---|---|
| Creators: | West, J.M. |
| Contributors: | Name Role NTU ID ORCID |
| Date: | May 2023 |
| Rights: | The copyright in this work is held by the author. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed to the author. |
| Divisions: | Schools > School of Science and Technology |
| Record created by: | Laura Ward |
| Date Added: | 29 Jul 2024 15:42 |
| Last Modified: | 29 Jul 2024 15:42 |
| URI: | https://irep.ntu.ac.uk/id/eprint/51838 |
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