AVS 72 Session EM-WeA: Wide Bandgap Materials and Devices

β-Ga₂O₃ is among the most promising candidates to replace Si in power electronics as it features an ultrawide band gap, shallow n-type dopants, and a large Baliga’s figure of merit. It has the potential to surpass both SiC and GaN as a material for high power electronics due to the above considerations and presents the potential for scaling up manufacturing due to its ability to be grown in large areas from the melt. Wide and ultra-wide band gap semiconductors, like β-Ga₂O₃, offer the ability to operate at high voltages, high power, and high temperatures (> 300 °C). However, these aspects of β-Ga₂O₃ can be limited due to the metal/semiconductor interface when high operating temperatures are required. The work examines the metallurgical stability of contact metallizations at elevated temperatures up to 700 °C.

Aluminum gallium nitride (AlGaN) has become a major focus in the area of ultra-wide bandgap (UWBG) semiconductor technology due to its ability to modulate its electronic and optical properties by changing the Al-content. A wide range of devices can be developed by the community including but not limited to solar-blind photodetectors, small wavelength LEDs, and vertical power devices. When a semiconductor device is applied under high voltages (resulting in high internal electric fields) the absorption edge of the material shifts such that sub-bandgap photons can be absorbed in the material and lead to the production of electron-hole pairs. This phenomenon, known as the Franz-Keldysh effect (FKE), has been studied more recently in wide bandgap semiconductors such as SiC and GaN. Understanding this effect can not only be used to predict the device performance under illumination but also give insight into the fundamental material properties of AlGaN which is currently not well established. In this study, the FKE in Al_0.7Ga_0.3N was observed and a similar approach reported in literature was used to develop a model with high accuracy. The model considers the optical transitions from each valence subband (heavy-hole band (HHB), light-hole band (LHB), and split-off (SO) band) towards the conduction band. Two different models were calculated. The first model, the 1-hole band model, assumes that the dominating optical transition is between the LHB and CB (this assumes that the incoming light is not normally incident on the c-axis of the crystal). The second model, the 2-hole band model, assumes that the dominating optical transitions are between the HHB and CB and the SO and CB (this assumes that the incoming light is normally incident on the c-axis of the crystal). 252 nm light (sub-bandgap energy) and 244 nm light (above bandgap energy) was illuminated on a quasi-vertical Al_0.7Ga_0.3N PiN diode and the measured photocurrents were investigated. The presented model gives insights into various material properties including the electron effective mass, the hole effective mass, and the optical momentum matrix element. According to the measured I-V characteristics and the calculated absorption coefficients due to the proposed model, the diode exhibited absorption of photons with sub-bandgap energy, therefore showing FKE. This work was supported in part by the US Army Research Office under grant W911NF-22-2-0158 (Program Manager: T. Oder) and the National Science Foundation under grant ECCS-2145340.

Lead-halide perovskites have gained importance because of strong light-matter interactions, including room-temperature excitonic effects and bandgap tunability, and have been explored in applications such as light-emitting devices, photodetectors, photovoltaics, and optical sensing. Layered and low-dimensional lead-halide perovskite materials offer additional degrees of freedom to control these properties through morphology and thickness, which prompts the need for efficient thickness-determination techniques. In our work, we demonstrated a controlled hydrothermal procedure for synthesizing cesium lead bromide (CsPb₂Br₅) single crystals with thicknesses below 100 nm, along with a non-destructive approach for thickness estimation based on reflection measurements. We developed an automated thickness-estimation model by comparing experimental reflectance spectra with calculated spectra obtained from Frensel equation and further calibrating it with atomic force microscopy (AFM) measurements. The reliability of the estimated thickness was evaluated through a quantitative error analysis using root mean square (RMSE) and the coefficient of determination (R²) with matching of spectral features. The combination of controlled synthesis and reflection measurements provides a practical framework for thickness-dependent characterization of CsPb₂Br₅ flakes, enabling rapid thickness screening for subsequent development of perovskite-based nanophotonic and optoelectronic devices.

Silicon carbide (SiC) has emerged as a testbed for designing defect-based qubits for quantum technologies. In particular, the negatively-charged silicon vacancy in SiC is being explored as a solid-state spin qubit due to its long spin coherence time at room temperature and near-telecom range emission energies. To ensure that the bright negative charge state of this defect remains stable, SiC is often doped with nitrogen [1], although it can form unwanted complexes [1,2]. In our first-principles based study, we investigate the effect of phosphorus doping on the quantum emission properties of the silicon vacancyin SiC. We show that phosphorus is an efficient donor and stabilizes the bright charge state of the monovacancy, resulting in the desirable spin-3/2 bright ground state. We further establish its influence on the excited-state properties, paving way for experimental development of defects with desired properties.

[1] Carter et al. “Influence of nitrogen doping and annealing on the silicon vacancy in 4𝐻-SiC” Phys. Rev. B 112, 085209 (2025)

[2] Rauls et al. “The different behavior of nitrogen and phosphorus as n-type dopants in SiC” Physica B 340–342, 184–189 (2003)

A novel fabrication process for hexagonal aluminum nitride (AlN) thin films on diamond (001) substrates was fabricated using RF magnetron sputtering at elevated temperatures. Highly crystalline c-axis-oriented AlN films were successfully grown, exhibiting a diffraction full width at half maximum (FWHM) of 928.8 arcsec, which is significantly lower than the previously reported value for sputtered AlN films on diamond, indicating a substantial improvement in crystalline quality and c-axis alignment. The nucleation and initial growth stages of AlN at the interface were found to play a crucial role in determining the final film quality, where a transition zone from randomly oriented AlN grains to highly c-axis-oriented grains was observed. The microstructure and surface morphology of the films were investigated using field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), respectively. X-ray photoelectron spectroscopy (XPS) was employed to analyze the chemical composition and bonding states of the films. Furthermore, the film thickness and optical constants were determined using spectroscopic ellipsometry.

Keywords: Magnetron sputtering, hexagonal aluminium nitrite, Surface roughness, thin film.