Environment-adaptabilities are always critical for optical and electrical components while Ga2O3 thin films have been attractive in UV photodetectors, flexible optoelectronics and multifunctional integrations. Here, we present the atomic-layer deposited amorphous Ga2O3 thin films and the solar-blind UV photodetectors with temperature-adaptabilities across a wide temperature range of 100–450 K. The devices exhibit an excellent responsivity (∼3.99 mA/W) and detectivity (∼1.19 × 1011 Jones) at 120 K, and remain operational during temperature changes between 100 and 450 K. The distinct non-monotonic variations that were observed in the UV photoresponses may originate from the thermal-driven evolution of oxygen-vacancy-related trap states. We believe that these investigations will provide an alternative approach to understanding amorphous Ga2O3 thin films and temperature-tolerant devices, and exploring reliable integration used for sensing and observation under extreme environment changes.
Gallium oxide (Ga2O3) is an ultra-wide bandgap semiconductor with several polymorphs, among which the orthorhombic κ-phase is particularly attractive for high-power electronics, non-volatile memory, and charge-tunable devices due to its large spontaneous polarization and potential ferroelectric behavior. However, commonly grown κ-Ga2O3 thin films contain nanoscale rotational domains, hindering the characterization of intrinsic properties and complicating device integration. In this work, we present the first combined experimental and theoretical Raman spectroscopy study of single-domain κ-Ga2O3 thin films grown on orthorhombic ε-GaFeO3 substrates. Using polarization- and angle-resolved Raman spectroscopy, we identify over 100 phonon modes, which correlate with 117 modes calculated via density functional perturbation theory. A systematic nomenclature is introduced based on mode symmetry and frequency to aid identification and comparison across future studies. Direct comparison with rotational-domain samples shows that single-domain films exhibit pronounced angle-dependent Raman intensities consistent with theoretical selection rules, features that are obscured in multi-domain films due to domain averaging. These findings establish polarization angle-resolved Raman spectroscopy as an effective alternative to XRD and TEM for domain structure analysis and provide a robust framework for further studies of κ-Ga2O3 in electronic applications.
Research on monolayer materials remains at the forefront of materials research. Here, we present a systematic study of graphenic carbon layers focusing on their structural evolution and electrical properties as film thickness approaches the atomic limit. The ultrathin carbon films are obtained from the pyrolysis of photoresist films (PPF) directly on the target substrate, also allowing structuring by lithographic means. Thus, pre-defined graphenic structures can be realized with controlled thickness, down to the sub-nanometer scale as determined by atomic force microscopy. X-ray photoelectron spectroscopy confirms the predominant sp2 hybridization of our films, transmission electron microscopy reveals domains with hexagonal atomic structure, and Raman spectroscopy shows signatures of evolving nanocrystallinity with decreasing film thickness until dimensional confinement imposes a lower limit. We further demonstrate the functionality of the sub-nanometric pyrolyzed polymer film as a chemiresistive NO2 sensor. The films' scalability and patternability across multiple length scales, together with their chemical inertness and biocompatibility, make them promising candidates for future applications.
This study presents a comprehensive investigation into the noise behavior of piezoelectric MEMS devices using a combined experimental and modeling-based approach. A detailed analysis is performed to decompose the total noise into its constituent sources, including thermal noise in the piezoelectric layer, input voltage noise of the amplifier, input current noise of the amplifier, and the thermal noise of the bias resistor within the amplifier. Noise spectral density measurements are carried out from a few Hz to 1 MHz. They exhibit a pronounced 1/f characteristic at lower frequencies, where amplifier-related noise sources are significant. The proposed electrical noise modeling framework accurately reproduces the experimental data, validating its effectiveness in capturing noise contributions across the operating bandwidth. Additionally, temperature-dependent measurements reveal reductions in both capacitance (3%) and loss tangent (75%) of the aluminum nitride piezoelectric layer when cooled from 300 to 80 K, correlating with a corresponding decrease in the device's thermal noise. These results provide valuable insights into the optimization of piezoelectric MEMS devices for low-noise applications, particularly in cryogenic environments, and contribute to advancing the design of next-generation high-sensitivity MEMS/NEMS sensors and actuators.
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