Diamond Metal Oxide Semiconductor Research Articles

Dynamic switching operation of diamond MOSFETs with NO2 p-type doping and Al2O3 gate insulation and passivation

Diamond metal–oxide–semiconductor field-effect transistor (MOSFET) exhibited durable and stable dynamic switching characteristics at an unprecedentedly high voltage of −105 V. Switching turn-on and turn-off times were measured to be 7.64 and 4.93 ns, respectively, with a corresponding total switching loss of 20.03 pJ for a load resistance of 50 Ω. No Miller effect was observed due to the low Miller capacitance of 11 pF/mm. This study suggests the potentiality of diamond MOSFETs in prospective high-voltage, high-speed applications.

Impact of water vapor annealing treatments on Al2O3/diamond interface

Our group developed the first inversion-type p-channel diamond metal–oxide–semiconductor field-effect transistor, which featured normally off properties by employing water vapor annealing treatments for the oxygen-terminated diamond surface. Despite the comprehensive device-grade characterization, the impact of water vapor annealing treatments on the Al2O3/diamond interface has not been investigated in detail. In this work, we fabricated four diamond metal–oxide–semiconductor (MOS) capacitors without and with water vapor annealing treatments for various times of 30 min, 1 h, and 2 h and conducted the cycle capacitance–voltage (C–V) and simultaneous C–V measurements. The large cycle C–V shift existed in the sample without water vapor annealing treatment, whereas it was significantly suppressed by water vapor annealing treatments, indicating the effective passivation of the traps with long time constants. The simultaneous C–V results showed a similar trend that the frequency dispersion of the simultaneous C–V was dramatically reduced with water vapor annealing treatments, and the interface quality of Al2O3/diamond had a slight dependence on the water vapor annealing times. Based on simultaneous C–V measurements, the interface state density (Dit) at an energy level of 0.2–0.6 eV from the valence band edge of diamond was extracted for the different MOS capacitors. The Dit was reduced by one order of magnitude with water vapor annealing treatments, and it almost did not change with the water vapor annealing times. Besides, the flat band voltage shift and effective fixed charge were also dramatically reduced by water vapor annealing. The possible physical reason for the interface improvement by water vapor annealing treatments was discussed.

High quality SiO2/diamond interface in O-terminated p-type diamond MOS capacitors

Metal oxide semiconductor (MOS) capacitors were fabricated based on oxygen-terminated p-type (100) oriented diamond and SiO2 grown by atomic layer deposition. A detailed electrical characterization consisting of I–V, C–V, and C–F was performed in order to analyze the electrical properties of the structure. The MOS capacitor presented no detectable leakage current in forward and very low leakage current in reverse sustaining at least 6 MV/cm without degradation. The C–V measurements showed depletion and deep depletion regimes in forward and accumulation regimes in reverse, with a low density of interface states of ∼1011 cm−2 along the diamond bandgap. The latter results were further validated by conductance and capacitance vs frequency measurements.

Evidence of distributed energy border traps at Al2O3/p-diamond interface

Diamond metal-oxide-semiconductor (MOS) devices are potential candidates for future high-power applications. Al2O3 is the preferred choice for the gate oxide/dielectric owing to multiple advantages, including appropriate band-alignment, interface quality, and compatibility with diamond. The success of diamond MOS devices depends significantly on the quality of the Al2O3/diamond interface. There has been an intense effort in this direction to understand and improve the quality of the interface. While the understanding of this hetero-interface has improved, there are still significant challenges. This work provides further insight where we show the evidence of border traps for p-type O-diamond MOS structure with atomic-layer-deposited (ALD) Al2O3 as a gate dielectric, which has hitherto been neglected. The experimental data shows frequency dispersion of capacitance in the accumulation region for frequencies 1 Hz to 10 MHz. A distributed border traps model fitted to the plot of capacitance versus the logarithm of frequency demonstrates an average border trap density of 1.2 × 1020 cm−3 eV−1 for an oxide thickness of 50 nm. The data is analyzed at three different temperatures of 300, 350, and 400 K. The extracted activation energy for the capture cross-section is 2.96 eV. The origin of border traps is correlated to the presence of Al vacancy in Al2O3, suggesting room for ALD process optimization towards a better interface quality.

Characterization of Substrate-Trap Effects in Hydrogen-Terminated Diamond Metal–Oxide–Semiconductor Field-Effect Transistors

Mechanisms of trap effects are crucial to improving diamond-based transistor electrical performance. Here, the trap effects in hydrogen-terminated diamond metal–oxide–semiconductor field-effect transistors (HD MOSFETs) are investigated by separating the effects of gate dielectric bulk alumina (BA) and diamond substrate (DS) for the first time. First, the location of traps and their impact on the dynamic drain current are characterized by pulsed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characterization. The dynamic drain current is degraded by traps in both BA and DS. Furthermore, the quiescent-bias-point-dependent trapping effects are studied by different quiescent bias points to reveal the response intensity of these two kinds of traps. Second, to further respectively characterize the effects of traps in the BA and the DS on HD MOSFETs, the threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> ) instability was characterized under negative gate bias stress (NGBS) conditions. Strong gate biases ranging from −4 to −8 V are selected to activate traps in DS. An extraordinary nonmonotonic change in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> is found under the −8 V NGBS condition. Moreover, the corresponding variation in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> is, unexpectedly, smaller than −4 and −6 V NGBS conditions. These phenomena indicate that the detrapping effect in the DS become dominant with increasing stress duration in the variation in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> under an NGBS of −8 V. Finally, based on these results, an improved kinetic model is proposed to separately describe the effects of traps in the BA and the DS. These results are useful for improving the performance of HD MOSFETs.

Characterization of deep interface states in SiO2/B-doped diamond using the transient photocapacitance method

We fabricated a diamond metal oxide semiconductor structure with a silicon dioxide (SiO2) film as the gate dielectric on B-doped diamond grown by a high-power-density microwave-plasma chemical vapor deposition method. The SiO2/B-doped diamond interface was characterized using a transient photocapacitance technique. The concentration of B in the B-doped diamond film was estimated to be 4.0 × 1017 cm−3, based on the intensity ratio of the exciton emissions observed in the cathodoluminescence measurements at approximately 80 K. Acceptor-type defects could be observed at approximately 1.28 and 1.82 eV above the valence-band edge. The observed defect at approximately 1.82 eV above the valence-band edge is expected to be an interface state of the SiO2/B-doped diamond.

345-MW/cm² 2608-V NO₂ p-Type Doped Diamond MOSFETs With an Al₂O₃ Passivation Overlayer on Heteroepitaxial Diamond

Diamond metal oxide semiconductor field effect transistors (MOSFETs) on high-quality heteroepitaxial diamond (Kenzan diamond <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> ) with NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> p-type doping and an Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation overlayer exhibited a high off-state breakdown voltage of −2608 V. The 100-nm-thick Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation overlayer on the hole channel increased the high-voltage-handling capability of the MOSFETs by substantially suppressing the off-state drain leakage currents. The MOSFET showed a specific on-resistance of 19.74 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a maximum drain current density of −288 mA/mm, with an extremely low gate leakage current <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 10^{-{6}}$ </tex-math></inline-formula> mA/mm. The Baliga’s Figure-Of-Merits was experimentally determined to be 344.6 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the maximum DC power density was observed to be 21.0 W/mm.

Radiation hardened H-diamond MOSFET (RADDFET) operating after 1 MGy irradiation

Although the surface conductivity of a hydrogen-terminated diamond (H-diamond) enables production of high-performance field effect transistors (FETs), the total ionizing dose effect is yet to be clarified for H-diamond FETs. We fabricated a RADiation hardened H-terminated Diamond metal–oxide–semiconductor FET (RADDFET) using an oxide gate dielectric deposited at high temperatures. This paper describes its stable operation after 1 MGy irradiation. H-diamond films were prepared using microwave plasma assisted chemical vapor deposition with a p+ layer for reduction of contact resistance. The Al2O3 passivation layer was deposited by atomic layer deposition at 450 °C to achieve operation in high-temperature environment; then a RADDFET was fabricated on them using a Ru electrode. Several current–voltage characteristics were compared before irradiation and after certain dose levels up to 1 MGy. Before they were irradiated in air, the dose rate was measured using a cellulose triacetate film dosimeter. Even after an irradiation level of 1 MGy, the off-current at gate bias voltage (VG) of 3 V was more than six orders of magnitude lower than the on-current at VG of −6 V. Variation of the drain current density (JDS) in the measurements was less than 2%. The threshold voltage shifted approximately 1.7 V with 3 kGy of x ray irradiation, but no marked degradation was confirmed at higher levels. The subthreshold swings were 238, 215, and 264 mV/decade, respectively, after irradiation of 100 kGy, 300 kGy, and 1 MGy. These results indicate that the RADDFET was very stable at higher doses after initial stabilization.

C–Si bonded two-dimensional hole gas diamond MOSFET with normally-off operation and wide temperature range stability

A C–Si bonded SiO2/diamond interface is formed under a SiO2 mask during the selective diamond growth at a high temperature in a H2 atmosphere including methane (5%). A few monolayers with C–Si bonding at the SiO2/diamond surface are confirmed through X-ray photoelectron spectroscopy at the C1s and Si2p core levels from 290 eV to 271 eV and 107 eV–95 eV, respectively. In addition, secondary ion mass spectroscopy results suggest that the C–Si bonds, and not C–H bonds, are majority at the interface and are mainly responsible for the field effect transistor (FET) operation. Two-dimensional hole gas C–Si diamond metal–oxide–semiconductor FET (MOSFETs) are fabricated using the C–Si diamond sub-surface as a p-channel. The MOSFETs in which the actual length from the source to the drain (LSD) is 12 μm–6 μm show appreciable field-effect mobility (e.g. 140 cm2V−1s−1 at LSD = 12 μm and 300 K) and normally-off operation. The wide temperature characteristics of the C–Si MOSFETs are confirmed and the device shows high stability, and a high on/off ratio of 106 is maintained at 673 K. The C–Si bonding at the SiO2/diamond interface provide a lower interface state density which makes the MOSFET show high drain current density and field-effect mobility with normally-off operation.

Enhanced interface properties of diamond MOSFETs with Al2O3 gate dielectric deposited via ALD at a high temperature* *Project supported by the National Natural Science Foundation of China (Grant No. 61922021), the National Key Research and Development Project, China (Grant No. 2018YFE0115500), and the Fund from the Sichuan Provincial Engineering Research Center for Broadband Microwave Circuit High Density Integration, China.

The interface state of hydrogen-terminated (C–H) diamond metal–oxide–semiconductor field-effect transistor (MOSFET) is critical for device performance. In this paper, we investigate the fixed charges and interface trap states in C–H diamond MOSFETs by using different gate dielectric processes. The devices use Al2O3 as gate dielectrics that are deposited via atomic layer deposition (ALD) at 80 °C and 300 °C, respectively, and their C–V and I–V characteristics are comparatively investigated. Mott–Schottky plots (1/C 2–V G) suggest that positive and negative fixed charges with low density of about 1011 cm−2 are located in the 80-°C- and 300-°C deposition Al2O3 films, respectively. The analyses of direct current (DC)/pulsed I–V and frequency-dependent conductance show that the shallow interface traps (0.46 eV–0.52 eV and 0.53 eV–0.56 eV above the valence band of diamond for the 80-°C and 300-°C deposition conditions, respectively) with distinct density (7.8 × 1013 eV−1⋅cm−2–8.5 × 1013 eV−1⋅cm−2 and 2.2 × 1013 eV−1⋅cm−2–5.1 × 1013 eV−1⋅cm−2 for the 80-°C- and 300-°C-deposition conditions, respectively) are present at the Al2O3/C–H diamond interface. Dynamic pulsed I–V and capacitance dispersion results indicate that the ALD Al2O3 technique with 300-°C deposition temperature has higher stability for C–H diamond MOSFETs.

Energy distribution of Al2O3/diamond interface states characterized by high temperature capacitance-voltage method

In our previous work, we demonstrated the world’s first inversion-type p-channel diamond metal–oxide–semiconductor field-effect transistor (MOSFET). However, it exhibited low channel mobility due to high interface state density (Dit). In this study, the electronic states of Al2O3/diamond interfaces above the valence band edge (Ev) were carefully examined by capacitance–voltage (C–V) measurements in a wide frequency range of 1 Hz–10 MHz at 300, 350, and 400 K, providing an accurate characterization of deeper interface state density compared with our previous work (from 10 Hz to 10 kHz at room temperature) within the limitations of the high-low method. We observed humps in C–V curves, which became wider as the temperature increased and the frequency decreased, indicating the presence of interface states at deep energy levels. They can act as Coulomb scattering centers in diamond MOSFETs; thus, their characterization at low frequencies and high temperatures is necessary. The energy distribution of Dit was estimated using the high-low method at 400 K, indicating that Dit was in the range of (0.4–1.5) × 1012 cm−2eV−1 within 0.23–0.76 eV from Ev of diamond. More effective passivation techniques are required to reduce interface states at deep energy levels.

145-MW/cm2 Heteroepitaxial Diamond MOSFETs With NO2 p-Type Doping and an Al2O3 Passivation Layer

In this study, we investigated diamond metal oxide semiconductor field effect transistors (MOSFETs) with NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> p-type doping and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation layer fabricated on a high-quality heteroepitaxial single crystal (001) diamond substrate called Kenzan diamond <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> . MOSFETs with a gate length of 1.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> and nearly zero source-gate spacing exhibited a high drain current density of −776 mA/mm with a negligible gate leakage current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; 0.1~\mu \text{A}$ </tex-math></inline-formula> /mm). MOSFETs with a gate-to-drain length of 4.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> delivered a high off-state breakdown voltage (−618 V) at an average breakdown field of 1.2 MV/cm and a specific on-resistance of 2.63 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Baliga’s Figure-Of-Merits was calculated as 145 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the anticipated maximum power density was 12 W/mm. The diamond MOSFET was improved with high crystal quality.

Oxidized Si terminated diamond and its MOSFET operation with SiO2 gate insulator

During selective epitaxial growth of diamond through SiO2 masks, silicon terminations were formed on a diamond surface by replacing oxygen terminations under the masks. The high temperature of selective growth and its reductive atmosphere possibly allowed Si atoms in SiO2 to interact with the diamond surface, resulting in silicon terminated diamond (C–Si diamond) composed of a monolayer or thin multi-layers of carbon and silicon bonds on diamond. Diamond metal oxide semiconductor field effect transistors (MOSFETs), with a C–Si diamond channel and selectively grown undoped or heavily boron-doped (p+) source/drain (S/D) layers, have been fabricated. Both the MOSFETs with undoped and p+ S/D exhibited enhancement mode (normally off) FET characteristics. The drain current (IDS) of the undoped device reached −17 mA/mm with threshold voltage (VT) −19 V; the p+ device attained a high IDS −165 mA/mm with a VT of −6 V being one of the best normally off diamond FETs. Transmission electron microscopy and energy dispersive x-ray spectroscopy confirmed the presence of C–Si diamond under the SiO2 masking area. The field effect mobility and interface state density at the C–Si/SiO2 (220 nm)/Al2O3 (100 nm) MOS capacitor are 102 cm2 V−1 s−1 and 4.6 × 1012 cm−2 eV−1, respectively. The MOSFET operation of C–Si diamond provides an alternative approach for diamond.

Diamond/γ-alumina band offset determination by XPS

γ-Alumina is a promising candidate for fabricating the gate of the diamond metal oxide semiconductor field effect transistor based on oxygen termination due to its high bandgap of 6.7 eV and high static dielectric constant of 9. Besides these properties, having a sufficient barrier for holes is mandatory to avoid carriers leakage through the gate. However, the band offset of the diamond/alumina heterojunction can be affected by the alumina crystallinity and interface bonds, which depend on multiple factors such as deposition and annealing temperature or diamond surface treatment prior to deposition.In this work, the heterojunction of atomic layer deposited alumina and (1 0 0) p-diamond is studied using X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy studies reveal that the deposited alumina layer is 35 nm thick and present the gamma phase. The valence band offset between diamond and γ-alumina is evaluated on a single sample with a new methodology based on an ion etching XPS depth profile. The obtained value for the valence band offset of diamond and γ-alumina is 3.4 eV.

Characterization and Mobility Analysis of Normally off Hydrogen‐Terminated Diamond Metal–Oxide–Semiconductor Field‐Effect Transistors

Hydrogen‐terminated diamond (H‐diamond) metal–oxide–semiconductor field‐effect transistors (MOSFETs) are fabricated, and a partial C–O channel is formed by UV‐ozone treatment of the H‐diamond surface to help realize normally off devices. The first parameterization of the vertical‐field (Feff)‐dependent effective hole mobility (μeff) in a normally off diamond FET is conducted using the fabricated MOSFETs with a gate length of 40 μm fat field‐effect transistors (FATFET). The FATFET with a threshold voltage of −0.69 V shows a low on‐resistance of 475.1 Ω mm and a record high drain current of −3.8 mA mm−1 for normally off H‐diamond MOSFETs with gate lengths over 20 μm. The extracted μeff ranges from 127 cm2(V s)−1 (at VGS = −4.5 V) to 276 cm2(V s)−1 (at VGS = −1.5 V). Both μeff versus Feff and μeff versus VGS relations can be well fitted by the semiempirical formulas used for silicon counterparts. The resulting low‐field mobility without vertical‐field degradation for the two relations is 376 cm2(V s)−1 and 418 cm2(V s)−1, respectively. The origin of this difference is also given.

Threshold Voltage Instability of Diamond Metal–Oxide–Semiconductor Field‐Effect Transistors Based on 2D Hole Gas

Recent marked advances in diamond metal–oxide–semiconductor field‐effect transistors (MOSFETs) have raised the issue of gate reliability. Herein, the threshold voltage stability of MOSFETs based on hydrogen‐terminated diamond surface conductivity is examined. The electrical output characteristic curves are characterized by cyclic gate sweeping from reverse to forward gate bias (RF) and from forward to reverse gate bias (FR), respectively. The characteristics of drain current versus drain voltage are affected by the gate bias sweeping direction. Marked hysteresis is also observed in the transfer curves for the RF and FR gate sweeping. The different gate sweeping directions induce threshold voltage variation and hole mobility change. The facts that 1) no extra interface states are generated due to gate sweeping and 2) the trapped charge density depends on the gate oxide thickness, reveal that charge trapping occurs at the border of the gate oxide.

Normally-OFF Two-Dimensional Hole Gas Diamond MOSFETs Through Nitrogen-Ion Implantation

Diamond is a promising material for power applications owing to its excellent physical properties. Two-dimensional hole gas (2DHG) diamond metal–oxide–semiconductor field-effect transistors (MOSFETs) with hydrogen-terminated (C-H) channel have high current densities and high breakdown fields but often show normally- ON operation. From the viewpoint of safety, normally- OFF operation is required for power applications. In this letter, we used ion implantation to form a shallow and thin nitrogen-doped layer below the C-H channel region, which realized normally- OFF operation. Nitrogen-ion implanted length is fixed at 5 or 10 $\mu \text{m}$ . Nitrogen is a deep donor (1.7 eV) and the nitrogen-doped layer prevents hole accumulation near the surface. The threshold voltage was as high as −2.5 V and no obvious dependence on the threshold voltage of nitrogen-ion implanted length is observed. The breakdown field was 2.7 MV/cm at room temperature. Of 64 devices with a common gate length, 75% showed normally- OFF operation. We confirmed the threshold voltage shift by a thin and shallow nitrogen-doped layer formed by ion implantation.

Operations of hydrogenated diamond metal–oxide–semiconductor field-effect transistors after annealing at 500 °C

Operations for hydrogenated diamond (H-diamond) metal–oxide–semiconductor field-effect transistors (MOSFETs) after annealing at 500 °C are investigated. SiOx films are employed as oxide insulators for the H-diamond MOSFETs. Before annealing, the current output maximum, on/off ratio, and subthreshold swing for the SiOx/H-diamond MOSFET are −53.3 mA mm−1, 1.4 × 109, and 88 mV dec−1, respectively. After annealing at 500 °C for as long as 60 min, although leakage current density of the SiOx/H-diamond MOS capacitor increases, good operations and distinct pinch-off characteristics are observed for the SiOx/H-diamond MOSFET with the above electrical properties of −2.6 mA mm−1, 1.4 × 104, and 530 mV dec−1, respectively. Stable electrical characteristics are confirmed for the annealed SiOx/H-diamond MOSFET after 35 cycles repeat measurements. This study is meaningful to the development of H-diamond MOSFETs for high-temperature applications.

Heterointerface properties of diamond MOS structures studied using capacitance–voltage and conductance–frequency measurements

The interface properties of Al2O3/hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor (MOS) structures both with and without NO2 p-type doping were studied by measuring the capacitance–voltage (C-V) and conductance–frequency (G–f) characteristics to investigate the effect of NO2 p-type doping at the Al2O3/H-diamond interface. The interface state density was studied by measuring the conductance as a function of frequency and applied voltage. Interface state density (Dit) values are for NO2 p-doped MOS structure varied from ~5.7 × 1012 cm−2 eV−1 at 0.27 eV above the valence band maximum (VBM) to 1.75 × 1012 cm−2 eV−1 at 0.36 eV above VBM. Conversely, MOS structure without NO2 p-type doping exhibits a Dit value of approximately 4.2 × 1012 cm−2 eV−1 within an energy range of 0.27 to 0.39 eV. In addition, border trap density in the Al2O3 layer near the interface is also discussed.

Gate Oxide Electrical Stability of p-type Diamond MOS Capacitors

This paper shows the effect of performing consecutive measurement prior to negative bias stress instability (NBSI) on diamond metal–oxide–semiconductor capacitor (MOSCAP). For the first time, time-dependent stress tests have been carried out in order to investigate the stability of the flatband voltage ( ${V}_{\text {FB}}$ ) of MOSCAPs through capacitance–voltage ( CV ) measurements. Two tests have been performed. In the first test, consecutive CV measurements with the device biased from deep depletion to the accumulation regime were performed to monitor the recovery of the ${V}_{\text {FB}}$ . In the second test, NBSI technique has been applied. ${V}_{\text {FB}}$ stability has been measured by means of a time-dependent bias stress in which the device was polarized at a fixed negative voltage for a specific time interval prior to performing the next CV measurement. As ${V}_{\text {FB}}$ is directly connected to the effective oxide charge ( ${N}_{\text {eff}}$ ), the two different tests allowed the extraction of total amount of ${N}_{\text {eff}}$ that interfered during the measurements. The result observed shows that the postoxidation annealing process induces a strong enhancement of the MOSCAP stability together with a decrease of ${N}_{\text {eff}}$