A journey of growth: β-Ga2O3 on GaN and sapphire via Pulsed Laser Deposition

Abstract

The exceptional breakdown field and ultra-wide bandgap of beta-gallium oxide (β-Ga2O3) position it as a promising material for next-generation high-power electronics. This thesis systematically investigates the growth behaviour, structural quality, and surface morphology of β-Ga2O3 thin films deposited via Pulsed Laser Deposition (PLD) on both c-plane sapphire (Al2O3) and MOCVD-grown GaN-on-sapphire templates under identical conditions. Deposition parameters were mapped across a broad experimental matrix, varying substrate temperatures from 500°C to 800°C and oxygen background pressures from 10^-6 mbar (vacuum) to 10^-1 mbar. Characterization was performed using spectroscopic ellipsometry, X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Three main parameters were used to assess the overall quality of the films: growth rate, crystal quality, and surface roughness. First, the growth rate evolution is evaluated for all grown layers to delineate the material tendencies with respect to the growth conditions. Next, a comparative structural analysis of the (-201) crystal orientation is presented for both substrates to isolate how growth parameters influence overall crystalline quality. To overcome severe interfacial degradation caused by premature GaN substrate oxidation under oxygen-rich environments, a two-step deposition process utilizing an inert Argon (Ar) sacrificial buffer layer is introduced. Finally, the surface topography is analyzed to establish a correlation between substrate temperature and surface roughness (RMS). Together, these structured analyses provide a comprehensive framework for understanding β-Ga2O3 thin films deposited via PLD.

Popular Abstract

It is a freezing winter day in Lund. The snow is slowly falling, and as it touches the ground, you notice a snowflake form. It is symmetric and beautifully ordered: it crystallized. This is a rare sight in a city where slask (slush) reigns. You snap a picture to send to your mum and quickly check the weather app: -5°C. The next day you wake up, and it's even colder, darker, a bit more humid even. Charming Lund. On your way to university, you spot it again: a snowflake. This time, though, something is different. Its shape and symmetry have completely changed. You snap a new picture and, comparing both, you notice that while both are flawlessly ordered, their shape, size, and structural perfection are entirely different. That must be it! The atmospheric conditions must have changed it all.

In physics, any solid material whose atoms are arranged in a highly ordered, three-dimensional pattern is called a crystal. You interact with them every day: your diamond engagement ring, cooking salt, or the tip of your pencil (though some of them are more expensive than others).

This thesis explores the formation of a very specific crystal: β-Ga2O3 (beta-gallium oxide). While it might not be as beautiful as snowflakes at plain sight, this material possesses great technological powers. It is capable of controlling electricity under extreme conditions. The ultimate advantage of beta-Ga2O3 lies in its ability to sustain very high voltage while reducing energy losses when an electronic device is running.

Just like snowflakes, the formation of this crystal is highly sensitive to its environment. Therefore, to achieve its full potential, specific techniques are needed to fine-tune and customize its growth conditions. To grow these gallium oxide crystals, a simple but effective method is used: Pulsed Laser Deposition (PLD). To picture how it works, let's step back out into the slaskigt streets of Lund. Think about stomping through heavy slask. With every step you take, the energy from your foot sends the *slask* flying through the air, unfortunately landing on the bottom of your pants, leaving a distinct wet stain. In the lab, this process is recreated on an atomic scale:

* The foot: a high-power pulsing laser.
* The slask: a block of (not crystalline) gallium oxide material.
* The pants: a specialized base material called a substrate.

When the laser strikes the target material, it acts just like your foot hitting the slask, blasting a cloud of atoms into the air. These flying particles travel across an enclosed chamber and land on the substrate. By carefully tuning the temperature and pressure of this environment, it is possible to form highly ordered and crystalline β-Ga2O3.

Hence, this work aims to pave the way for next-generation electronics by identifying the optimal atomic "weather conditions" for high-quality β-gallium oxide growth.

• author: de la Fuente Esteban, Laura
• supervisor: Vanya Darakchieva; Andri Dhora
• organization: Solid State Physics; Department of Physics
• course: PHYM03 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: semiconductors, epitaxy, crystal growth, ultra-wide bandgap, nanoscience, deposition, pulsed laser deposition
• language: English
• id: 9244193
• date added to LUP: 2026-06-28 11:34:17
• date last changed: 2026-06-28 11:34:17