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Phonons confined in mechanical resonators can be coupled to a variety of quantum systems and are expected to be applied to hybrid quantum systems. Diamond surface acoustic wave (SAW) devices are capable of high efficiency in phonon interaction with color centers in diamond. The temperature dependence of the quality factor is crucial for inferring the governing mechanism of coupling efficiency between phonons and color centers in diamond. In this paper, we report on the temperature dependence of the quality factor of an AlN/diamond SAW device from room temperature to 5 K. The temperature dependence of the quality factor and resonant frequency suggests that the mechanism of SAW dissipation in the AlN/diamond SAW resonator at 5 GHz is the phonon–phonon scattering in the Akheiser regime and that further cooling can be expected to improve the quality factor. This result provides a crucial guideline for the future design of AlN/diamond SAW devices. [ABSTRACT FROM AUTHOR]

The longest spin coherence times for nitrogen-vacancy (NV) centers at room temperature have been achieved in phosphorus-doped n-type diamond. However, difficulty controlling impurity incorporation and the utilization of highly toxic phosphine gas in the chemical vapor deposition (CVD) technique pose problems for the growth of n-type diamond. In the present study, n-type diamond samples were synthesized by CVD using tert-butylphosphine, which is much less toxic than phosphine. The unintentional incorporation of nitrogen was found to be suppressed by incrementally increasing the gas flow rates of H2 and CH4. It was found that the spin coherence time (T2) increased with decreasing the nitrogen concentration, which suggests that the nitrogen concentration limits the length of T2. In the sample with the lowest nitrogen concentration, T2 increased to 1.62 ± 0.10 ms. Optically detected magnetic resonance spectra indicated that all of the measured NV centers were aligned along the [111] direction. Hall measurements confirmed n-type conduction in three measured samples prepared under different growth conditions. The highest measured Hall mobility at room temperature was 422 cm2/(V s). This study provides appropriate CVD conditions for growing phosphorus-doped n-type diamond with perfectly aligned NV centers exhibiting long spin coherence times, which is important for the production of quantum diamond devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We studied the charge-state stabilization of shallow nitrogen-vacancy (NV) centers in (111) diamond using graphene/diamond junctions. Measurement of the fluorescence stability and evaluation of the charge-state stability were conducted on the NV centers at the graphene and the graphene-free region. The results revealed that about half of the total NV centers (NV0 + NV−) at the graphene-free region were unstable, while over 90% of the measured NV centers at the graphene region were stabilized as NV− centers. Graphene/diamond junctions contribute significantly to charge-state stabilization of shallow NV− centers in (111) diamond. [ABSTRACT FROM AUTHOR]

n-Type (phosphorus-doped) diamond is a promising material for diamond-based electronic devices. However, realizing good ohmic contacts for phosphorus-doped diamonds limits their applications. Thus, the search for non-conventional ohmic contacts has become a hot topic for many researchers. In this work, nanocarbon ohmic electrodes with enhanced carrier collection efficiency were deposited by coaxial arc plasma deposition. The fabricated nanocarbon ohmic electrodes were extensively examined in terms of specific contact resistance and corrosion resistance. The circular transmission line model theory was used to estimate the charge collection efficiency of the nanocarbon ohmic electrodes in terms of specific contact resistance at a specific voltage range (5–10 V); they exhibited a specific contact resistance of 1 × 10−3 Ωcm2. The result revealed one order reduction in the specific contact resistance and, consequently, a potential drop at the diamond/electrode interface compared to the conventional Ti electrodes. Moreover, the fabricated nanocarbon electrodes exhibited high mechanical adhesion and chemical inertness over repeated acid treatments. In device applications, the nanocarbon electrodes were evaluated for Ni/n-type diamond Schottky diodes, and they exhibited nearly one order enhancement in the rectification ratio and a fast charge collection at lower biasing voltages. [ABSTRACT FROM AUTHOR]

A normally-off inversion p-channel metal-oxide-semiconductor field-effect transistor (MOSFET) with a nitrogen (N)-doped diamond body deposited using microwave plasma-enhanced chemical vapor deposition (MPECVD) was fabricated. The MOSFET exhibited a drain current density of −1.7 mA/mm. Thus far, this value is similar to the device performance of the inversion p-channel MOSFET fabricated using a phosphorus (P)-doped n-type diamond body. The N2 used for N-doping is safer than the PH3 used for P-doping; moreover, the doping concentration is highly controllable. Because the MOSFET, which is a classical electronic device, is driven by a gate voltage, smooth functioning was possible even at a deep donor level. The observed characteristics of the classic MOSFET operating via an N-doped body are crucial for the development of diamond power devices. In this paper, we discuss the significance of the N-doped diamond body and electrical characteristics of the inversion p-channel MOSFET fabricated using an N-doped diamond body. [ABSTRACT FROM AUTHOR]

In this work, nanodiodes comprised of n-GaN nanowires on p-diamond substrates are investigated. The electric transport properties are discussed on the basis of simulations and determined experimentally for individual p-diamond/n-GaN nanodiodes by applying conductive atomic force microscopy. For low doping concentrations, a high rectification ratio is observed. The fabrication of a prototype nanoLED device on the basis of ensemble nanowire contacts is presented, showing simultaneous electroluminescence in the UV and the green spectral range which can be ascribed to hole injection into the n-GaN nanowires and electron injection into the p-diamond, respectively. In addition, the operation and heat distribution of the nanoLED device are visualized by active thermographic imaging. [ABSTRACT FROM AUTHOR]

Two photoluminescence (PL) components with peaks around 2.8–3.0 and 3.8 eV were induced in hafnium silicates by the irradiation of synchrotron radiation photons at 8.0 eV, while two similar ones were induced in zirconium silicates around 2.7–3.0 and 3.8 eV. By examining PL excitation spectra, PL decay characteristics, and vacuum-ultraviolet absorption spectra, it is assumed that the origin of the PL component around 2.7(2.8)–3.0 eV is the same as that of the PL component around 2.7–2.9 eV observed in hafnia and zirconia. In the band gaps of hafnium silicates, zirconium silicates, hafnia, and zirconia, luminescent centers responsible for the PL components around 2.7(2.8)–2.9(3.0) eV have their respective upper and lower states with a certain constant energy difference that does not change by the hafnium or zirconium content. Electrons (or holes) excited by ultraviolet photons to tail states at the band edges first relax to the upper state of the luminescent centers, and then they are deexcited to the lower state, which induces the PL components. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) spectra induced by ultraviolet photons were measured for amorphous hafnia and zirconia deposited by plasma-enhanced chemical-vapor deposition (PECVD), amorphous hafnia deposited by pulse laser deposition, and crystalline yttria-stabilized zirconia. Two kinds of samples were prepared for both hafnia and zirconia deposited by PECVD using different source alkoxides in different deposition chambers. A PL peak was observed around 2.8 eV similarly in all hafnia and zirconia samples, irrespective of the difference in crystallinity, oxygen deficiency, source alkoxide, deposition method, or the substrate material. The decay profile of this PL is also similar in all the samples. These facts clearly show that neither impurities, oxygen vacancy, nor defects at the interface between the sample and the substrate are responsible for the PL. It is a luminescence inherent in hafnia and zirconia and is most likely due to radiative recombination between localized states at the band tails. When the samples were annealed in oxygen, a new PL peak appeared around 4.2 eV in all the amorphous samples. Its decay profile is also in common with these samples. Vacuum-ultraviolet absorption measurements and PL excitation measurements indicate that the 4.2-eV PL is excited due to the interband absorption. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) measurements were performed on a series of hydrogenated amorphous silicon oxynitride and silicon nitride films with different nitrogen contents deposited by plasma-enhanced chemical-vapor deposition. From the PL and PL excitation spectra, the Urbach energy of the sample is found to be proportional to its PL half-maximum width, regardless of whether the sample is silicon oxynitride or silicon nitride. Time-resolved PL measurements showed that PL peak energy varies with time after the excitation, showing a systematic dependence on the chemical composition in the two materials. That the PLs observed in the two materials have very similar characteristics regardless of the presence of oxygen strongly indicates that the PLs result from the same chemical structure, more specifically Si-N bonds, and that the two materials have similar band-tail states associated with the static disorder. In the two materials, it is found that the electrons and holes photoexcited into such band-tail states recombine first through an excitonlike recombination process and then through a radiative tunneling recombination process. [ABSTRACT FROM AUTHOR]

Deposition of hafnium silicate films with various hafnium contents was tried by plasma-enhanced chemical vapor deposition using tetraethoxysilane and a hafnium alkoxide. From x-ray photoelectron spectroscopy, the deposited films are confirmed to be silicate with Hf-O-Si bonds but without any Hf-Si bonds. The permittivity calculated from the capacitance of the accumulation layer increases monotonically with an increase in the hafnium content, whereas the optical band gap energy estimated from vacuum ultraviolet absorption spectra decreases. Similar results were obtained from zirconium silicate films deposited using tetraethoxysilane and a zirconium alkoxide. If we compare the films with the same hafnium or zirconium content, the hafnium silicate exhibits a higher permittivity and a larger band gap energy than the zirconium silicate. [ABSTRACT FROM AUTHOR]

Refractive index change is shown to be induced by the irradiation of ultraviolet photons in hydrogenated amorphous silicon oxynitride films prepared by plasma-enhanced chemical vapor deposition. The mechanism of the index change and its dependence on the nitrogen content were investigated by electron spin resonance and scanning electron microscopy. It is concluded that the index change is due mainly to densification, and that the contribution of the formation of paramagnetic defects is only slight. To demonstrate the versatility of this refractive index change, a planar diffraction grating was fabricated. [ABSTRACT FROM AUTHOR]

We investigated the phosphorus concentration (NP) dependence of the field-effect mobility μFE and interface state density Dit in inversion channel diamond metal-oxide-semiconductor field-effect transistors (MOSFETs). The inversion channel diamond MOSFETs are potentially applicable in high-frequency, high-current, and high-voltage devices because of the material's excellent properties such as a wide bandgap, high breakdown electric field, high carrier mobility, and high thermal conductivity. However, the influences of device design parameters, such as NP in an n-type body and the oxide layer material, on the electrical characteristics of inversion channel diamond MOSFETs have not yet been reported. In this study, we fabricated inversion channel diamond MOSFETs using n-type bodies with various NP values. For decreased NP in the n-type body, μFE was increased, while Dit was decreased. Using the n-type body with the lowest NP of 2 × 1015 cm−3, the maximum μFE of 20 cm2/V·s and the minimum Dit of 1 × 1013 cm−2·eV−1 were obtained. In addition, an inverse correlation was found between μFE and Dit. Specifically, in the low-gate-voltage region of the drain current–gate voltage characteristics, μFE and Dit were strongly inversely correlated. The high Dit suggests that most holes are trapped in the interface state as strong scattering factors in the low-gate-voltage region. Lower Dit values are therefore important for obtaining higher μFE values, the same as in Si and SiC. [ABSTRACT FROM AUTHOR]

Field emission properties of phosphorus (P)-doped homoepitaxial diamonds are measured after hydrogen plasma treatment and wet chemical oxidization. We also measure field emission properties of H-terminated B-doped diamond for comparison. P-doped diamonds are grown on type Ib single crystalline diamond by microwave plasma chemical vapor deposition. The resistivity of the films is in the range of (5–8)×102 Ω cm. Phosphorus concentration measured by secondary ion mass spectroscopy is in the range of (5–7)×1019 cm-3. The threshold voltage for field emission of O-terminated P-doped diamond with positive electron affinity is lower than that of H-terminated P-doped diamond with negative electron affinity. Upward band bending due to ionized phosphorus donors exists at the H-terminated surface. This upward bend bending prevents electrons from reaching to the emitting surface. An effective emission barrier height of O-terminated P-doped diamond surface is estimated to be 1.3 eV using slopes of Fowler-Nordheim plots. This value is in good agreement with the reported electron affinities in literature. [ABSTRACT FROM AUTHOR]

We demonstrate high-efficiency excitonic emission with deep-ultraviolet (DUV) light of 235 nm at room temperature for a (111)-oriented diamond p-i-n junction light-emitting diode (LED) by introducing a thick i-layer. Significant enhancement in excitonic emission efficiency of over 500 times was observed for a diamond LED by increasing the i-layer thickness from 0.1 to 14 μm. Maximum output power and external quantum efficiency of excitonic emission for the LED without any specific device structure were 0.1 mW and 0.006%, respectively, under pulsed-current injection. We also demonstrate the sterilization of Escherichia coli by irradiation with DUV light from the diamond LED. [ABSTRACT FROM AUTHOR]

We have performed high-resolution core level photoemission spectroscopy on a heavily phosphorus (P)-doped diamond film in order to elucidate the chemical sites of doped-phosphorus atoms in diamond. P 2p core level study shows two bulk components, providing spectroscopic evidence for multiple chemical sites of doped-phosphorus atoms. This indicates that only a part of doped-phosphorus atoms contribute to the formation of carriers. From a comparison with band calculations, possible origins for the chemical sites are discussed. [ABSTRACT FROM AUTHOR]

We fabricated a diamond diode, namely a Schottky-pn diode (SPND), which is composed of a fully depleted n-type active layer sandwiched between a highly doped p-type layer and a Schottky metal layer. The SPND has superior characteristics that overcome the weak points of both a Schottky barrier diode and a pn diode. That is, the SPND showed high current density (over 4000 A/cm2) with low specific resistance (0.4 mΩ cm2) at a forward bias of 6 V while maintaining a high rectification ratio of ∼1010. Moreover, the SPND showed extremely fast turn-off speed of nanosecond order. [ABSTRACT FROM AUTHOR]

Low resistive contacts were formed on heavily phosphorus-doped diamond (n+) films with phosphorus concentration of over ∼1020 cm-3 grown on (111) diamond substrates by microwave plasma enhanced chemical vapor deposition with precise control of growth conditions. The specific contact resistance was determined by characterizing the current-voltage relations by means of transfer length method. It was found that the resistance of Ti/n+ contact was significantly reduced down to the order of ∼10-3 Ω cm2 even at room temperature, which indicates that the barrier width would be narrow for tunneling through the barrier to take place by heavy phosphorus doping. [ABSTRACT FROM AUTHOR]

We report about field emission from reconstructed phosphorus-doped diamond surfaces. In order to reconstruct the surface, annealing at 950 °C for 60 min in a high vacuum system has been applied. Field emission shows the lowest threshold field for the reconstructed surface of 16 V/μm, while the threshold fields for oxidized and hydrogen-terminated surface are 28 and 44 V/μm, respectively. A model is introduced to discuss these results, which takes into account effective electron affinities and tunneling of electrons from conduction band and donor levels. [ABSTRACT FROM AUTHOR]

Surface conductive layers (SCL) on oxidized (111) diamonds with smooth surfaces after exposure to air were detected and characterized by Hall effect measurements. Hall effect measurements show that the conductivity is p type with sheet hole concentrations around of 1012 cm-2 and Hall mobilities between 5 and 130 cm2/V s. The SCL vanishes by thermal annealing at a temperature higher than 460 K in He atmosphere, and recovers in air. These characteristics are similar to those generated by hydrogen termination. The experiments revealed that these SCLs are present on boron doped (111) and undoped (111) diamond films with smooth surfaces and natural IIa (111) diamonds, but not on (111) diamond films with rough surfaces and not on (100) diamonds. [ABSTRACT FROM AUTHOR]

n-type doping of (001)-oriented single-crystalline diamond has been achieved using PH3 as doping gas and applying a newly optimized homoepitaxial growth technique based on plasma-enhanced chemical vapor deposition. Hall-effect measurements indicate n-type conductivity with highest mobilities of ∼350 cm2/Vs. Phosphorus doping is confirmed by secondary-ion mass spectroscopy. [ABSTRACT FROM AUTHOR]

The mechanism of electroluminescence in hydrogenated amorphous silicon oxynitride was investigated. The luminescence can be observed only in the samples with high nitrogen content and annealed at high temperatures. It depends on the direction of the applied electric field, and its peak photon energy decreases from 2.3 to 1.8 eV as the nitrogen content increases. From the measurements of conduction current and Fourier transform infrared absorption spectroscopy, it was found that the electrical conduction in the electric field region where the luminescence was observed is governed by the Poole–Frenkel process at the defect centers induced by the high temperature annealing. The electroluminescence is considered to be caused by electronic transition between the band-tail states, at least one of which is related to N or Si–N bonds. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A good ideality factor and rectification ratio were obtained in a p+-i-n+ diamond diode with p+ and n+ doping levels of ∼1020 cm-3, where the hopping conduction mechanism dominates in the bulk p+ and n+ layers. The diode characteristics show a rectification ratio of 108 at ±10 V and an ideality factor of n=1.32. This diode showed ruggedness with a large current density of over 15 000 A/cm2 at +35 V. These results indicate the possibility of large-current devices. [ABSTRACT FROM AUTHOR]

Charge-states modulation of nitrogen-vacancy (NV) centers incorporated into single crystal diamond films attracts increasing attention for solid-state qubits applications. Here, we discuss the electro- and photoluminescence emission properties of NV centers incorporated by gas phase nitrogen delta-doping of the intrinsic diamond layer of a positive-intrinsic-negative (PIN) junction diode. The experiments show that the charge state of NV centers can be intentionally controlled by applying well-defined external bias voltages. It can be switched from the negatively charged state NV- to the neutral charged state NV0 when a strong forward bias potential is applied. This can be switched back by application of reverse potentials. These results will be discussed assuming basic electronic properties of diamond PIN diodes, including the variation of spectral properties as well as the dynamics of charge state transitions. [ABSTRACT FROM AUTHOR]

A broad photoluminescence (PL) around 2.6–2.9 eV is known to appear in hydrogenated silicon oxynitride. Although its origin was reported to be Si–N bonds, it is not so clear since the material contains hydrogen. In the present research, we have confirmed that the same PL appears in silicon oxynitride grown by nitriding of silicon dioxide. The depth profile of the PL intensity agrees with that of the nitrogen concentration. Furthermore, the emission spectrum, excitation spectrum, and decay constant of this PL agree with those of the PL observed in silicon nitride. Based on these results and theoretical discussion, the origin of the 2.6–2.9 eV PL is estimated to be Si–N bonds. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]