MOCVD GaN sensorių su chemiškai modifikuotu paviršiumi tyrimai /

Final thesis was prepared in Vilnius University, Faculty of Physics, Institute of Photonics and Nanotechnology (FNI), photoelectric phenomena research group. The main research topics of the group include the analysis of charge carrier processes in modern materials and devices, the search for radiation-resistant materials, and the creation of radiation sensors. Additionally, the creation of new spectroscopy methods that are based on photoelectric phenomena. In the thesis MOCVD grown GaN was chosed as the main analysis subject, since it has a lot of research potential in the subjects of space physics, medicine and particle physics, due its ability to detect both electrical and optical signals. The main goal of this thesis was to modify GaN surface with wet etching method while using acidic (H3PO4) and basic (KOH-ethylene glycol) solutions, then use various analysis techniques to understand the defects present in the material and how they affect the electrooptical properties. The analysis methods were primarily divided into two categories: contactless and contact-based. Contactless methods included optical microcopy, photoluminscence (PL) measurements and microwave probed photosconductivity spectrocopy (MW-PC). Contact-based methods comprised I-V characteristics, charge transient analysis and pulsed photo-ionisation spectroscopy (PPIS). The results of PL proved that inhomogenous dislocation distribution in MOCVD grown GaN plays and important role in the effects of wet surface etching, because dislocation concentration is the main factor which affected the PL results. Additionally, PL results together with PPIS analysis proved ability to detect various groups of defects present in the material. One of the key observations in the thesis was the formation of an oxide layer on the GaN surface during the etching process. It was concluded that gallium oxide significantly enhances the blue spectrum photoluminescence band (~2.6 – 2.9 eV). The MW-PC method demonstrated that etching reduces the lifetimes of charge carriers on the surface. Additionally, when comparing crystals grown by MOCVD and ammonothermal methods, the MW-PC method revealed differences in dislocation concentration. This was evidenced by significantly lower bulk and SER lifetime components in the ammonothermal material. Finally, contact-based transient measurements showed a significant increase in photovoltaic effectiveness after the etching process successfully texturized the material's surface. To sum up, a variety of methodologies were employed to examine the impact of chemical wet etching on the surface of MOCVD GaN. The findings effectively demonstrated the capability of these approaches to enhance the electrooptic characteristics. In addition, these advancements hold promise for future applications in improving sensor technologies across various fields, including medicine, space physics, and particle physics.

Grantor dc:publisher

Institutional Repository of Vilnius University

Year dc:date

2024

Author dc:creator

• Juškevičius, Giedrius,

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

lit

Repository record dc:identifier

https://repository.vu.lt/VU:ELABAETD210577921&prefLang=en_US

OAI identifier oai:identifier

oai:vu.lt:elaba:210577921