Plonasluoksnių galio nitrido dangų modifikavimas lazerine femtosekundine UV spinduliuote /

Gallium nitride has recently emerged as a material with numerous beneficial properties for electronic and optoelectronic applications. These properties include a wide band-gap (3.4 eV), high heat capacity, thermal conductivity, breakdown voltage, electron mobility, and high quantum efficiencies. These characteristics make gallium nitride invaluable in the development of light-emitting diodes (LEDs), field-effect transistors (FETs), high-temperature devices, and many other applications. High-quality processing of gallium nitride is essential to manufacture these devices effectively. Advancements in ultrashort pulse laser technology have enabled high-precision micro-processing of materials. Ultrashort laser pulses, compared to longer pulses, offer better control in the ablation process and enhance the resolution of micro-processing due to reduced heat-affected zones (HAZ), as the pulse duration is shorter than the thermal diffusion time. Most approaches employ femtosecond lasers with wavelengths longer than ultraviolet. However, shorter UV wavelengths could further reduce heat-affected zones due to linear (single-photon) absorption and a smaller focal point, which is directly proportional to the wavelength. While this technique has been tested with longer nanosecond pulses of excimer UV lasers, the use of UV femtosecond laser pulses for laser processing remains underexplored. In this study, we directly ablated thin-film undoped gallium nitride using femtosecond ultraviolet laser pulses (257 nm, 100 kHz, 240 fs) with varying pulse energy and pulse overlap to explore the effect of these parameters on ablation and on the formation of periodic surface structures. The topographies of the ablated regions were measured with a profilometer (repeatability σ_n-1 = 12 nm). The ablated structures were characterized using three variables: ablation depth, ablation efficiency, and average modified surface roughness S_a, calculated according to ISO 25178-3:2012. Our results indicate that femtosecond UV laser pulses enable high-resolution, high-quality ablation with minimal heat-affected zones (HAZ) when processing wide band-gap materials like gallium nitride. We demonstrate efficient ablation with average surface roughness S_a values ranging from 16 nm to 86 nm without any post-processing and show that it is possible to form and control periodic surface structures with a period 15-20% shorter than the incident wavelength.

Grantor dc:publisher

Institutional Repository of Vilnius University

Year dc:date

2024

Author dc:creator

• Zakarauskas, Paulius,

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

lit

Repository record dc:identifier

https://repository.vu.lt/VU:ELABAETD210578653&prefLang=en_US

OAI identifier oai:identifier

oai:vu.lt:elaba:210578653