High-electron-mobility transistors (HEMTs) based on gallium nitride (GaN) grown on silicon substrates are emerging as a promising solution for high-performance and cost-effective power electronics. However, their widespread adoption is hindered by a critical limitation: the vertical breakdown voltage, typically capped at around 900 V, due to leakage current and destructive breakdown occurring beneath the drain contact. In this work, we introduce a novel device architecture that integrates a thin p-type GaN layer inserted below the buffer layer. This additional layer enables a more favorable redistribution of the electric field, effectively suppressing undesirable vertical destructive breakdown of the device. This innovative idea is validated through both TCAD simulations and experimental device fabrication. A vertical breakdown voltage of 530 V was achieved for a GaN buffer layer thickness reduced to 1.5 mu m, representing state-of-the-art performance for GaN-on-silicon devices within this thickness range. Furthermore, the occurrence of an avalanche is of critical importance, as it ensures that the observed breakdown remains nondestructive, preventing catastrophic failure and enhancing the overall robustness of the device. This new idea marks a significant step forward in the development of reliable and economically viable GaN-on-silicon power devices, with substantial potential for impact on electric mobility, renewable energy conversion, and data center power infrastructure.

Proton therapy offers highly localized dose delivery for cancer treatment, but its clinical precision critically depends on accurate beam monitoring and patient imaging. Conventional detector technologies remain constrained by limited spatial resolution, dynamic range, and radiation tolerance. Here we demonstrate gallium nitride (GaN) diode arrays as a new platform for proton imaging. Using a one-dimensional GaN array, we image a 65 MeV clinical proton beam with linear response across three orders of magnitude, high sensitivity down to 10 pA, and robustness under irradiation up to 100 kGy. 2D profiles are reconstructed through transverse mechanical scanning with uncertainties in the beam position and linewidth as low as ± 0.07 mm and ± 0.14 mm, respectively. The intrinsic radiation hardness of GaN was experimentally confirmed, while key requirements for 65 MeV proton beam quality assurance and patient radiography were addressed. This proof of concept establishes the foundations for extending the approach to 2D detector matrices, combining high-resolution and real-time imaging.

This study reports significant progress in the field of high temperature wireless surface acoustic wave (SAW) sensors in the 2.45 GHz ISM band, using AlN/Sapphire based resonators. AlN thin films with a thickness of 0.6 & micro;m, synthesized on (0001) sapphire substrates by Metal Organic Chemical Vapor Deposition (MOCVD), demonstrated high crystalline quality and nanometric surface roughness, essential properties for SAW applications. Initially, SAW devices operating in the 2.45 GHz ISM band were tested up to 500 degrees C in both wired and wireless configurations using aluminium electrodes. Wireless interrogation was carried out successfully at a distance of 3 m up to 500 degrees C, with a temperature coefficient of frequency (TCF) measured at -58 ppm/degrees C. Critically, when the NiAl alloy was used for the thin film electrodes, the operating temperature was extended to 600 degrees C while maintaining a TCF of -43 ppm/degrees C and stable wireless performance at 3 m, with potential up to 10 m. These results exceed the state-of-the-art for high temperature SAW sensors in the wide 2.45 GHz ISM band. A long-duration annealing test has confirmed the self-passivation properties of the NiAl electrodes and the robustness of the NiAl/AlN/Sapphire structure, with a minimal degradation after 176 h at 500 degrees C, thus demonstrating its potential for long term use in extreme environments.

This work presents a temperature-dependent micro-Raman spectroscopy study (300-573 K) of homoepitaxial n-type GaN layers with different Si doping levels ranging from 1015 to a few 1018 cm-3, where the analysis of different vibrational modes enables simultaneous extraction of structural and electronic properties. The evolution of the E2(high) mode and the associated phonon correlation length with doping and temperature reveal progressive lattice disorder, allowing static disorder related to dopant incorporation to be distinguished from dynamic disorder arising from phonon interactions. In parallel, the A1(LO) mode highlights the Fano interaction between the discrete phonon and the electron continuum, where the asymmetry parameter provides access to the Fermi level EF position. At 300 K, the energy separation between the conduction band and EF decreases from ∼0.19 eV for the lightly doped sample to ∼0.03 eV for the heavily doped sample. At 573 K, this distance increases to ∼0.43 eV and ∼0.08 eV, respectively, reflecting the temperature-dependent shift of the chemical potential. These results confirm both efficient dopant activation and the transition toward quasi-degenerate behavior at high carrier concentrations. Finally, analysis of A1(LO) phonon-plasmon coupling within the LPP model allows the determination of carrier mobility as a function of doping and temperature: at 300 K, the mobility decreases from 916 cm2/V·s in lightly doped samples to 355 cm2/V·s in heavily doped layers, with further reductions at elevated temperatures due to thermally activated scattering and carrier redistribution. These results demonstrate that Raman spectroscopy is a powerful nondestructive tool to simultaneously assess electronic transport properties and crystalline disorder in vertical GaN-based power electronics.

This study reports significant progress in the field of high temperature wireless surface acoustic wave (SAW) sensors in the 2.45 GHz ISM band, using AlN/Sapphire based resonators. AlN thin films with a thickness of 0.6 µm, synthesized on (0001) sapphire substrates by Metal Organic Chemical Vapor Deposition (MOCVD), demonstrated high crystalline quality and nanometric surface roughness, essential properties for SAW applications. Initially, SAW devices operating in the 2.45 GHz ISM band were tested up to 500°C in both wired and wireless configurations using aluminium electrodes. Wireless interrogation was carried out successfully at a distance of 3 m up to 500°C, with a temperature coefficient of frequency (TCF) measured at −58 ppm/°C. Critically, when the NiAl alloy was used for the thin film electrodes, the operating temperature was extended to 600°C while maintaining a TCF of −43 ppm/°C and stable wireless performance at 3 m, with potential up to 10 m. These results exceed the state-of-the-art for high temperature SAW sensors in the wide 2.45 GHz ISM band. A long-duration annealing test has confirmed the self-passivation properties of the NiAl electrodes and the robustness of the NiAl/AlN/Sapphire structure, with a minimal degradation after 176 h at 500°C, thus demonstrating its potential for long term use in extreme environments.

Exciton-polariton lasers are coherent light sources which do not require the population inversion (transparency) condition to be fulfilled. They have been conceptualized at the end of the XXth century but until now they operate almost exclusively under optical injection, which severely limits the widespread integration of the polariton-based devices implemented so far. Here we tackle this issue by reporting an electrically-pumped exciton-polariton laser based on GaN and operating at room temperature in a mode-locked regime. The laser architecture is close to the geometry of commercial ridge-waveguide GaN lasers, but based on a bulk GaN active region instead of quantum wells. Unique features of polariton lasers are demonstrated, in particular the breakdown of the transparency condition, which enables our polariton lasers to operate even when only a small fraction (20%) of the cavity length is injected. Moreover, the large polaritonic gain allows for the operation of a short cavity length (60μm) compared to commercial lasers. From the very same sample, we also achieve polariton lasing under optical injection, confirming that the doped layers necessary for electrical injection do not prevent strong-coupling nor polariton lasing. Our results open a new perspective for polariton-based devices.

In this article, we study the effect of the doping level in the intermediate layer of a pseudo-vertical GaN-based p-i-n diode. By decreasing the doping level, from 1.1 × 1016 to 1.6 × 1014 cm−3, we show that the OFF-state capacitance can be reduced by a factor 2.2, without affecting the ON-state resistance too much, which is increased by only 16%. The main consequence is an increase in the cutoff frequency by a factor 1.8, from 137 ± 5 to 250 ± 16 GHz. The DC characteristics of the diode are preserved since no significant variation of the turn on voltage has been found and no breakdown occurs for up to −200 V biasing.

In this work, using micro-Raman spectroscopy mapping, we propose a methodology to separate the stress effect from the n-doping effect on A(1) (LO) and E-2(H) GaN phonon modes frequency for low n-doped (<1017 cm-3) GaN layers grown on various substrates (GaN, sapphire, and silicon). This methodology shows a linear relation between the two phonon modes, in which the slope corresponds to GaN biaxial stress coefficients ratio K-A1(B) ((LO))/K-E(B)H 2 and is 0.76 6 0.01. Our value may act as a useful guideline for selecting or refining K-E(B)H 2 and K-A1(B)(LO) values. Samples that are mainly biaxially stressed show good agreement with the linear relation independently of the substrate. As for GaN/GaN samples, the change of slope indicates that layers are predominantly under dislocation-induced stress. However, independently of the substrate, the y-intercept increases with the n-carrier concentration, which provides a qualitive estimation of the net doping.

We are developing a compact gas sensor for 10 ppb–10 ppm detection of formaldehyde and acetaldehyde using electroluminescence, multi-dielectric microcavities, chemical functionalization, and microfluidic integration for enhanced sensitivity and molecular specificity in confined environments.

This work presents physical and electrical characterizations of low n-doped MOCVD GaN-on-sapphire layers and associated quasi-vertical Schottky Barrier Diodes (SBDs). Samples’ GaN drift layers have globally a similar quality as examined by XRD, AFM Raman spectroscopy, C-V measurements and I-V characteristics. Some crystal defects in the GaN layer are identified by Raman spectroscopy and SEM, and their effect on the electrical characteristics of the diodes is assessed. Most of the SBDs have reverse current densities at −100 V that are comparable to that of some of the best vertical GaN-on-GaN SBDs, which can be correlated to drift layers’ doping homogeneity and dislocation density.

In this study, the impact of surface treatment by TMAH and HF on the electrical characteristics of GaN-on-GaN Schottky diodes is examined through I–V and C–V characterizations. A TMAH surface treatment leads to an improvement in the reverse characteristics of the devices and improvement in breakdown voltage (BV) by almost 200 V compared to HF treatment. Additional XPS characterizations reveal a reduction in both O and C concentration from the surface due to TMAH treatment. When combined with proper edge termination techniques, this approach can help achieve breakdown voltages that are closer to the theoretical limits.

GaN diodes for high energy(64.8 MeV)proton detection were fabricated and investigated.A comparison of the perfor-mance of GaN diodes with different structures is presented,with a focus on sapphire and on GaN substrates,Schottky and pin diodes,and different active layer thicknesses.Pin diodes fabricated on a sapphire substrate are the best choice for a GaN pro-ton detector working at 0 V bias.They are sensitive(minimum detectable proton beam<1 pA/cm2),linear as a function of pro-ton current and fast(<1 s).High proton current sensitivity and high spatial resolution of GaN diodes can be exploited in the future for proton imaging of patients in proton therapy.

This article compares the impact of different freestanding GaN substrates on the material and electrical properties of Schottky diodes. Material characterization using cathodoluminescence and Raman spectroscopy was performed to analyze defects in the wafers. Randomly distributed clusters of dislocations were observed in one sample, whereas the other sample was free of such clusters. Schottky diodes were subsequently fabricated on these wafers and electrically characterized to investigate the influence of material characteristics on key device parameters, including barrier height, ideality factor, on-resistance, leakage current, and breakdown voltage. A lower barrier height, higher ideality factor, and lower breakdown voltage were observed in the sample with clusters.

In this article, we propose a high-frequency model taking into account the series resistance of pseudo-vertical gallium nitride (GaN)-based p-i-n diodes. This model relies on the specific contact resistance on p-type GaN and the sheet resistance of the bottom n-type GaN. Those two quantities are obtained while fitting the RF experimental data and are slightly different from the dc values. The interest of this model is that the effective values, at the working frequency instead of “only” the dc values, are extracted using only a few devices. The novelty of the work resides in the consideration of the geometrical dimensions of the diode (anode radius and distance between anode and cathode) in the model. Furthermore, the model allows the determination of the most limiting geometrical parameters and can predict the series resistance of other topologies. In the present case, we show the most limiting factor is the radius of the anode due to the difficulties of achieving low specific contact resistance on p-type GaN. The parasitic capacitance is also extracted using the measured devices, allowing the modeling of the effective capacitance as a function of the frequency.

Semiconductors form the basis of high-performance optoelectronic devices, enabling efficient light emission and detection. While crystalline perfection is generally sought to optimize device performance, specific lattice defects can endow materials with unexpected and useful functionalities. Here, we show that engineered defect states in gallium nitride (GaN) diodes markedly enhance their response to high-energy protons. Through a combination of device simulations and experimental measurements, we demonstrate that forward biasing the diode just below its turn-on voltage activates a defect-mediated photoconductive regime. This operating mode induces substantial carrier trapping and photoconductive gain while simultaneously suppressing the dark current-a behaviour in stark contrast to conventional photoconductors. The exploitation of this previously underexplored detection mechanism yields a three-orders-of-magnitude enhancement in sensitivity over standard photovoltaic operation, enabling reliable quantification of proton fluxes down to a few particles per second. This novel mode of operation is not limited to protons but also extends to X-rays and other high-energy particles, and may be generalized to a broader class of semiconductors exhibiting high levels of doping compensation. These findings open new avenues for very low-flux particle detection across diverse application spaces, including medical, astronomy, and industrial imaging.

So far, exciton-polariton (polariton) lasers were mostly single-mode lasers based on microcavities. Despite the large repulsive polariton-polariton interaction, a pulsed mode-locked polariton laser was never, to our knowledge, reported. Here, we use a 60-µm-long GaN-based waveguide surrounded by distributed Bragg reflectors forming a multi-mode horizontal cavity. We demonstrate experimentally and theoretically a polariton mode-locked micro-laser operating in the blue-UV, at room temperature, with a 300 GHz repetition rate and 100-fs-long pulses. The mode-locking is demonstrated by the compensation (linearization) of the mode dispersion by the self-phase modulation induced by the polariton-polariton interaction. It is also supported by the observation in experiment and theory of the typical envelope frequency profile of a bright soliton.

The forward and reverse current transport mechanisms, temperature dependence of Schottky barrier height (SBH) and ideality factor, barrier inhomogeneity analysis, and trap parameters for Schottky barrier diodes (SBDs) fabricated on 4H-SiC, GaN-on-GaN and AlGaN/GaN epitaxial substrates are reported. High SBH is identified for Ni/4H-SiC (1.31 eV) and Ti/4H-SiC (1.18 eV) SBDs with a low leakage current density of <10(-8) A cm(-2) at -200 V. Thermally stimulated capacitance detects the well-known Z(1/2) electron trap at E-C-0.65 eV in both 4H-SiC SBDs, while an additional deep-level trap at E-C-1.13 eV is found only in Ni/4H-SiC SBDs. The vertical Ni/GaN SBD exhibits a promising SBH of 0.83 eV, and two electron traps at E-C-0.18 eV and E-C-0.56 eV are identified from deep-level transient Fourier spectroscopy. A peculiar two-diode model behavior is detected at metal/GaN/AlGaN/GaN interface of high-electron mobility transistor (HEMT); the first diode (SBH-1 of 1.15 eV) exists at the standard Metal/GaN Schottky junction, whereas the second diode (SBH-2 of 0.72 eV) forms due to the energy difference between the AlGaN conduction band and the heterojunction Fermi level. The compensational Fe-doping-related buffer traps at E-C-0.5 eV and E-C-0.6 eV are determined in the AlGaN/GaN HEMT, through the drain current transient spectroscopy experiments.

Vertical Metal–Insulator–Semiconductor (MIS) capacitors with an Al2O3 thin film as a gate insulator have been fabricated on homoepitaxial GaN-on-GaN samples. The effect of the annealing treatments on the MIS characteristics has been investigated exploring two different approaches: Post-insulator-Deposition-Annealing (PDA) and Post-gate-Metallization-Annealing (PMA), i.e., annealing on the bare Al2O3 layer and annealing after the gate metallization deposition on Al2O3. The direct comparison between PDA and PMA is crucial to understand the impact of the metal/dielectric interface quality on the behavior of the Al2O3/GaN MIS capacitors. The efficacy of annealing has been monitored as a function of metal gates having different work functions: nickel (Ni), molybdenum (Mo), and tantalum (Ta). It has been found that both PDA and PMA approaches are equally able to improve the Al2O3/GaN interface electrical quality. However, the PMA demonstrates an additional beneficial effect on the metal/Al2O3 interface. In particular, the possible chemical reactions activated by the annealing process at the metal/dielectric interface can perturb the known metal/dielectric dipole responsible for Fermi-level pinning phenomena, causing a positive shift of the flat voltage (VFB), which depends on the metal, and approaching the theoretical value in the case of Mo and Ta.

In this study, pseudo-vertical GaN-on-Sapphire PiN diodes with different mesa radii were designed, fabricated and characterized. First, critical process stages, such as mesa etching, ohmic contacts on GaN and passivation, are presented and reviewed to obtain functional diodes. Ion beam etching, with an optimized USG hard mask, seems the best solution to achieve reliable devices. Our results also show the impact of different passivation solutions on Au/Ni ohmic contact. Finally, the diodes with varying radii of the mesa (20, 40 and 60 mu m) exhibit turn-on voltages of approximately 3.5 V and achieve a specific on-resistance of 0.56-1.7 m ohm center dot cm(2). More, the devices show low capacitance versus frequency properties up to 40GHz. Further adjustments on designs and fabrication processes are requested to enhance performance.