A diamond Schottky PIN diode (SPIND) with the highest reported current density to date of 116 kA/cm2 is demonstrated carrying a total current of 1.3 A through a 50 micron wide pseudo-vertical diode structure. The diamond SPIND also provides a maximum power handling capacity of 1.85 MW/cm2 and a low specific on-resistance Ron,S of 0.05 mOhm-cm2 at a forward bias of 16 V. The diamond SPIN diode also shows excellent rectification characteristics with a current on-off ratio of 6e12. An analytical model including thermionic emission and space charge limited current is presented together with Silvaco ATLAS TCAD simulations, to accurately reproduce the experimental J-V characteristics using multiple single trap levels and other physical models emulating a real device. Theoretical analysis from the analytical models in conjunction with ATLAS simulations shows that further improvement in the device turn on voltage and Ron,S can be achieved by reducing the defect density and contact resistance in order to approach the ultimate performance in the Mott-Gurney space charge limited current regime

Two-dimensional materials hold promise for advanced complementary metal-oxide-semiconductor (CMOS) and beyond-CMOS electronics, including neuromorphic and in-memory computing. Hexagonal boron nitride (hBN) is particularly attractive for non-volatile resistive-switching devices (that is, memristors) due to its outstanding electronic, mechanical and chemical stability. However, integrating hBN memristors with Si-CMOS electronics faces challenges as it requires either high-temperature synthesis (exceeding thermal budgets) or transfer methods that introduce defects, impacting device performance and reliability. Here we introduce the synthesis of hBN films at CMOS-compatible temperatures (<380 °C) using electron cyclotron resonance plasma-enhanced chemical vapour deposition to realize transfer-free, CMOS-compatible hBN memristors with outstanding electrical characteristics. Our studies indicate a polycrystalline structure with turbostratic features in as-deposited hBN films and good wafer-level uniformity in morphology (size, shape and orientation). We demonstrate a large array of hBN memristors achieving high yield (~90%), stability (endurance, retention and repeatability), programming precision for multistate operation (>16 states) and low-frequency noise performance with minimal random telegraph noise. Furthermore, we directly integrate memristive devices on industrial CMOS test vehicles to demonstrate excellent endurance, achieving millions of programming cycles with a high technology readiness level. This represents an important step towards the wafer-scale CMOS integration of hBN-memristor-based electronics.

Diamond-based junction field effect transistor can be used as non-volatile photo-switches. The photo-controlled memory effect in these transistors arises from the absence of ionized nitrogen donors in the neutral region of the Ib diamond substrate gate, forming a pn junction with the p-type diamond conduction channel. In this work, we study the impact of illumination and gate designs on transistor dynamics. Electro-optical characterization, including current transients under different illumination conditions, reveal dependencies on wavelength and light power density. This study shows that optimized geometries of this device pave the way for fast switching and high-voltage applications.

This review explores the properties of diamond and boron nitride as a promising materials combination for high electron mobility transistors, HEMTs. These ultra-wide bandgap materials exhibit excellent electronic properties as well as high thermal conductivity for superior heat dissipation. The lattice mismatch between cubic boron nitride (c-BN) and diamond is similar to 1.4% allowing for the epitaxial growth of heterojunction devices. However, to demonstrate a viable c-BN/diamond HEMT technology a number of significant challenges remain, including: the epitaxial growth of single crystal heterojunctions on large area substrates; control of phosphorus dopant incorporation for n-type channels; and achieving low specific contact resistance to source and drain regions. There has been recent progress towards achieving these goals, paving the way for a new generation of high-power electronic devices for DC and RF applications.

P-i-N and Schottky P-i-N diamond diodes are a promising technology for high-power limiters. Receivers, solid-state amplifiers, and detectors commonly use P-i-N and/or Schottky diodes for protection from high power incident signals. Here, we report on the RF power handling and power dissipation capability of diamond P-i-N and Schottky P-i-N diodes. We fabricate P-i-N diodes as vertical structures, with both majority and minority carriers involved in charge transport. Similarly, we fabricate vertical Schottky P-i-N diodes, with the doping in the n-layer reduced compared to P-i-N diodes such that the n-layer becomes fully depleted during operation, resulting in a majority-carrier device with a fast recovery time. Both P-i-N and Schottky P-i-N diodes were packaged in shunt-configuration and matched for 3 GHz operation, with a small signal insertion loss of ∼1.25 dB. P-i-N diodes operated up to 40 dBm before failing nondestructively at 45 dBm, demonstrating power dissipation handling that exceeds that of commercially available Si P-i-N diodes by more than a factor of five. Schottky P-i-N diodes operated up to 49 dBm before non-recoverable failure at 50 dBm.

We demonstrate threshold switching behaviors with working temperatures up to 500 $^{\circ}$ C based on GaN vertical p-n diodes, and these devices survived a passive test in a simulated Venus environment (460 $^{\circ}$ C, 94 bar, CO $_{\text{2}}$ gas flow) for ten days. This is realized via interface engineering through an etch-then-regrow process combination with a Ga $_{\text{2}}$ O $_{\text{3}}$ interlayer. It is hypothesized the traps in the interfacial layer can form/rupture a conductive path by trapping/detrapping electrons/holes, which are responsible for the observed threshold switching behaviors. To the best of our knowledge, this is the first demonstration of two-terminal threshold-switching memory devices under such high temperatures. These results can serve as a critical reference for the future development of GaN-based memory devices for harsh environment applications.

In this Letter, low-temperature (400 °C) chemical vapor deposition-grown boron nitride (BN) was investigated as the gate dielectric for AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) on a Si substrate. Comprehensive characterizations using x-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, atomic force microscope, high-resolution transmission electron microscopy, and time-of-flight secondary ion mass spectrometry were conducted to analyze the deposited BN dielectric. Compared with conventional Schottky-gate HEMTs, the MISHEMTs exhibited significantly enhanced performance with 3 orders of magnitude lower reverse gate leakage current, a lower off-state current of 1 × 10−7 mA/mm, a higher on/off current ratio of 108, and lower on-resistance of 5.40 Ω mm. The frequency-dependent conductance measurement was performed to analyze the BN/HEMT interface, unveiling a low interface trap state density (Dit) on the order of 5 × 1011–6 × 1011 cm−2 eV−1. This work shows the effectiveness of low-temperature BN dielectrics and their potential for advancing GaN MISHEMTs toward high-performance power and RF electronics applications.

This Letter reports the device and material investigations of enhancement-mode p-GaN-gate AlGaN/GaN high electron mobility transistors (HEMTs) for Venus exploration and other harsh environment applications. The GaN transistor in this work was subjected to prolonged exposure (11 days) in a simulated Venus environment (460 °C, 94 bar, complete chemical environment including CO2/N2/SO2). The mechanisms affecting the transistor performance and structural integrity in harsh environment were analyzed using a variety of experimental, simulation, and modeling techniques, including in situ electrical measurement (e.g., burn-in) and advanced microscopy (e.g., structural deformation). Through transistor, Transmission Line Method (TLM), and Hall-effect measurements vs temperature, it is revealed that the mobility decrease is the primary cause of reduction of on-state performance of this GaN transistor at high temperature. Material analysis of the device under test (DUT) confirmed the absence of foreign elements from the Venus atmosphere. No inter-diffusion of the elements (including the gate metal) was observed. The insights of this work are broadly applicable to the future design, fabrication, and deployment of robust III-N devices for harsh environment operation.

We report an investigation of the bulk optical, bulk acoustic, and surface acoustic phonons in thin films of turbostratic boron nitride (t-BN) and cubic boron nitride (c-BN) grown on B-doped polycrystalline and single-crystalline diamond (001) and (111) substrates. The characteristics of different types of phonons were studied using Raman and Brillouin-Mandelstam light scattering spectroscopies. The atomic structure of the films was determined using high-resolution transmission electron microscopy (HRTEM) and correlated with the Raman and Brillouin-Mandelstam spectroscopy data. The HRTEM analysis revealed that the cubic boron nitride thin films consisted of a mixture of c-BN and t-BN phases, with c-BN being the dominant phase. It was found that while visible Raman spectroscopy provided information for characterizing the t-BN phase, it faced challenges in differentiating the c-BN phase either due to the presence of high-density defects or the overlapping of the Raman features with those from the B-doped diamond substrates. In contrast, Brillouin-Mandelstam spectroscopy clearly distinguishes the bulk longitudinal and surface acoustic phonons of the c-BN thin films grown on diamond substrates. Additionally, the angle-dependent surface Brillouin-Mandelstam scattering data show the peaks associated with the Rayleigh surface acoustic waves, which have higher phase velocities in c-BN films on diamond (111) substrates. These findings provide valuable insights into the phonon characteristics of the c-BN and diamond interfaces and have important implications for the thermal management of electronic devices based on ultra-wide-band-gap materials.

Phosphorus doped diamond films were prepared by plasma-enhanced chemical vapor deposition (PECVD) utilizing a 200ppm trimethylphosphine (TMP) in hydrogen gas mixture. The phosphorus doped diamond growth was characterized by in situ residual gas analysis (RGA), which identified a growth species (PH) formed in the hydrogen plasma. A rapid analysis response was achieved through an engineered differentially pumped component. Secondary ion mass spectroscopy (SIMS) was employed to evaluate the phosphorus incorporation in the doped diamond epilayers. For phosphorus doped diamond homoepitaxy, control of the dopant source temperature effected a more uniform doping concentration with a maximum phosphorus concentration of 4.5·1019cm-3. This was the highest phosphorus concentration achieved on a (111) CVD type II substrate with moderate miscut utilizing a diluted TMP doping source.

Cubic boron nitride (c-BN) is an ultrawide-bandgap (UWBG) semiconductor with many potential applications in high-power and high-temperature devices due to its large bandgap of 6.4 eV, breakdown field greater than 15 MV/cm, and thermal conductivity of ∼940 W/m.K.However, synthesis of c-BN is challenging since epitaxial growth methods often result in nucleation of metastable phases, namely sp 2 -bonded hexagonal (h-) or sp 3 -bonded wurtzite (w-BN) [1].Our previous study of c-BN growth focused on an in-depth analysis of growth chemistry, substrate type and growth temperature (T s ) in efforts to achieve the cubic phase [2].In this current research, transmission electron microscopy (TEM) and electron-energy-loss spectroscopy (EELS) have been used to evaluate nucleation conditions and different surface preparation methods to further improve the crystal quality and phase purity.The films were grown using electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD).Samples suitable for cross-sectional TEM observation were prepared by focused-ion beam (FIB) milling using a Thermo-Fisher Helios 5UX dual-beam instrument with initial thinning at 30 keV and further thinning at 5 keV and 2 keV.A Philips-FEI CM-200 FEG TEM operated at 200 kV and a probe-corrected JEOL ARM200 operated at 200 kV were used for imaging and EELS analysis, respectively.Fig. 1 shows an EELS spectrum analysis across the BN-diamond interface of the sample prepared with H 2 /BF 3 ratios of 0.75 for the initial 44 mins, and 1, for the next 105 mins, with T s = 850 °C.Prior to growth, the diamond substrate was annealed at 830 °C to remove adsorbed oxygen, and then further cleaned with H 2 plasma at 750 °C for 1.5 hrs.Fig. 1(a) shows identical spectrum images that combine EELS data for low-loss energies in the range from 0 to 460 eV.The EELS spectra from the ∼2-3 nm thick nucleation layer near the interface (B, C, and D) show significant π* peaks at ∼191 eV, indicating the presence of sp 2 -bonded BN.This undesired nucleation of the sp 2 layer can likely be attributed to defects introduced by the aggressive substrate cleaning procedure.A second sample was prepared with a modified cleaning method, where the substrate was plasma-cleaned for only 10 minutes and a growth duration of 40 minutes with H 2 /BF 3 ratio = 0.75.Fig. 2(a) shows markedly reduced defect density in the substrate and a reduced proportion of w-BN islands at the interface, with no visible h-or t-BN phases.Fig. 2(b) shows a high magnification TEM image of an almost epitaxial c-BN.Further experiments are in progress to identify optimal cleaning and nucleation conditions to yield the pure cubic phase [3].

The transfer length method (TLM) was used to investigate Ohmic contact properties using the tri-layer stack Ti/ Pt/Au on a nitrogen-doped n-type conducting nanocarbon (nanoC) layer grown on a diamond (100) substrate. Room temperature electrical measurements were taken, and samples were annealed to observe changes in electrical conductivity. Low specific contact resistivity values between the electrode and nanoC layer of 8 x 10-5 omega cm2 were achieved, which is almost two orders of magnitude lower than previously reported values. The results were attributed to the increased nitrogen incorporation, and the presence of electrically active defects which leads to an increase in conduction in the nanocarbon film.

We report on the low-frequency electronic noise in (Al$_x$Ga$_{1-x}$)$_2$O$_3$ Schottky barrier diodes. The noise spectral density reveals 1/f dependence, characteristic of the flicker noise, with superimposed Lorentzian bulges at the intermediate current levels (f is the frequency). The normalized noise spectral density in such diodes was determined to be on the order of 10$^{-12}$ cm$^2$/Hz (f=10 Hz) at 1 A/cm$^2$ current density. At the intermediate current regime, we observed the random telegraph signal noise, correlated with the appearance of Lorentzian bulges in the noise spectrum. The random telegraph signal noise was attributed to the defects near the Schottky barrier. The defects can affect the local electric field and the potential barrier, and correspondingly, impact the electric current. The obtained results help to understand noise in Schottky barrier diodes made of ultra-wide-band-gap semiconductors and can be used for the material and device quality assessment.

We report on the low-frequency electronic noise in β-(AlxGa1−x)2O3 Schottky barrier diodes. The noise spectral density reveals 1/f dependence, characteristic of the flicker noise, with superimposed Lorentzian bulges at the intermediate current levels (f is the frequency). The normalized noise spectral density in such diodes was determined to be on the order of 10−12 cm2/Hz (f = 10 Hz) at 1 A/cm2 current density. At the intermediate current regime, we observed the random telegraph signal noise, correlated with the appearance of Lorentzian bulges in the noise spectrum. The random telegraph signal noise was attributed to the defects near the Schottky barrier. The defects can affect the local electric field and the potential barrier and, correspondingly, impact the electric current. The obtained results help in understanding the noise in Schottky barrier diodes made of ultra-wide bandgap semiconductors and can be used for the material and device quality assessment.

Favorable material properties such as extreme thermal conductivity, high input power attenuation, low on resistance and high reliability make diamond among the most promising materials for high power RF applications such as limiter/receiver protector systems. RF diodes are the core component in receiver protector systems. To meet the needs of this application, we demonstrate successful diamond-based RF diode fabrication, starting with plasma enhanced chemical vapor deposition growth of p-i-n layers on <100> diamond substrates, microfabrication, and RF characterization. Diode characterization is conducted from dc to 25 GHz with results closely matching RF diode structures fabricated on <111> diamond substrates. Compared to previous <111> devices, we show off-capacitance and small signal resistance values as low as 16.1•10 -9 F/cm 2 and 0.65•10 -3 Ohm•cm 2 as well as additional pathways for further reducing these values and enabling receiver protector circuits with higher power handling requirements.

Two atomic layer etching (ALE) methods were studied for crystalline GaN, based on oxidation, fluorination, and ligand exchange. Etching was performed on unintentionally doped GaN grown by hydride vapor phase epitaxy. For the first step, the GaN surfaces were oxidized using either water vapor or remote O2-plasma exposure to produce a thin oxide layer. Removal of the surface oxide was addressed using alternating exposures of hydrogen fluoride (HF) and trimethylgallium (TMG) via fluorination and ligand exchange, respectively. Several HF and TMG super cycles were implemented to remove the surface oxide. Each ALE process was monitored in situ using multiwavelength ellipsometry. X-ray photoelectron spectroscopy was employed for the characterization of surface composition and impurity states. Additionally, the thermal and plasma-enhanced ALE methods were performed on patterned wafers and transmission electron microscopy (TEM) was used to measure the surface change. The x-ray photoelectron spectroscopy measurements indicated that F and O impurities remained on etched surfaces for both ALE processes. Ellipsometry indicated a slight reduction in thickness. TEM indicated a removal rate that was less than predicted. We suggest that the etch rates were reduced due to the ordered structure of the oxide formed on crystalline GaN surfaces.

Cubic boron nitride (c-BN), with a small 1.4% lattice mismatch with diamond, presents a heterostructure with multiple opportunities for electronic device applications. However, the formation of c-BN/diamond heterostructures has been limited by the tendency to form hexagonal BN at the interface. In this study, c-BN has been deposited on free standing polycrystalline and single crystal boron-doped diamond substrates via electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD), employing fluorine chemistry. In situ x-ray photoelectron spectroscopy (XPS) is used to characterize the nucleation and growth of boron nitride (BN) films as a function of hydrogen gas flow rates during deposition. The PECVD growth rate of BN was found to increase with increased hydrogen gas flow. In the absence of hydrogen gas flow, the BN layer was reduced in thickness or etched. The XPS results show that an excess of hydrogen gas significantly increases the percent of sp(2) bonding, characteristic of hexagonal BN (h-BN), particularly during initial layer growth. Reducing the hydrogen flow, such that hydrogen gas is the limiting reactant, minimizes the sp(2) bonding during the nucleation of BN. TEM results indicate the partial coverage of the diamond with thin epitaxial islands of c-BN. The limited hydrogen reaction is found to be a favorable growth environment for c-BN on boron-doped diamond.

A diamond Schottky p-i-n diode (SPIND) with the highest reported current density to date of ~116 kA/cm 2 is demonstrated, carrying a total current of ~1.32 A through a $50-\mu \text {m}$ wide pseudo-vertical diode structure. The diamond SPIND also provides a maximum power handling capacity of ${1.85}~ \text {MW/c}\text {m}^{{2}}$ and a low specific ON-resistance ${R}_{ \mathrm{ON}}S$ of ${0.05}~ \text {m}\Omega \cdot \text {cm}^{{{2}}}$ at a forward bias of ~16 V. The diamond Schottky p-i-n (SPIN) diode also shows excellent rectification characteristics with a current ON– OFF-ratio of $\sim {6} \times {10}^{{12}}$ . An analytical model including thermionic emission and space charge limited (SCL) current is presented together with Silvaco ATLAS Technology Computer Aided Design (TCAD) simulations to accurately reproduce the experimental ${J}$ – ${V}$ characteristics using multiple single-trap levels and other physical models emulating a real device. Theoretical calculations from the analytical model show that further improvement in the device turn on voltage and ${R}_{ \mathrm{ON}}{S}$ can be achieved by reducing the defect density and contact resistance in order to approach the ultimate performance in the Mott–Gurney SCL current regime.

The paper features the fabrication, characterization, and modeling of diamond Schottky p-i-n diodes grown by plasma enhanced chemical vapor deposition. The electrical measurements are used to extract the parameters for a unified lumped-element SPICE model. The sub-circuit model accurately reproduces the forward and reverse bias DC characteristics, the capacitance-voltage and S-parameter measurements, as well as the large-signal, non-linear properties of the diodes. An early insertion point for diamond electronics will be high power RF passive systems such as receiver protectors and mixers. We validate the model by comparing it to the measured non-linearities produced by the diode in a single-ended unbalanced RF mixer configuration.