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Reverse characteristics of diamond PiN diodes were studied under high reverse bias for high voltage applications. We have fabricated vertical diamond PiN diode structures consisting of a phosphorus-doped n-type diamond layer and an undoped intrinsic diamond layer on a heavily boron-doped p-type diamond substrate with Au/Pt/Ti Ohmic contacts on both the top and the bottom surfaces. Temperature dependent current-voltage ( I- V) and capacitance-voltage ( C- V) measurements were carried out to reveal the diode characteristics. The fabricated PiN diodes exhibited a sharp and repeatable reverse breakdown with positive temperature dependence indicating an avalanche mechanism. The obtained maximum breakdown field was 2.3 MV cm−1 (920 V) which is comparable to the ideal dielectric breakdown field of SiC. The reverse breakdown field and the leakage current were correlated with the hillock density. This research indicates that robust diamond power devices with high breakdown reliability can be achievable after improvement the quality of the intrinsic layer. [ABSTRACT FROM AUTHOR]

We fabricated diamond lateral p-n junction diodes by selective growth of n+-type diamond and evaluated their structural and electrical properties. The phosphorus-doped n+ diamond was selectively grown by microwave chemical vapor deposition at the side of a boron-doped p-type layer to form lateral p-n junction diodes. No distinct defects are observed at the interface of the p-n junction diode by cross-sectional transmission electron microscopy, implying the good homoepitaxial growth of the n-type diamond. Electron beam induced-current measurements directly confirmed the existence of the depletion layer in p-n junction diode. The electrical properties of the lateral p-n junction diodes were investigated at room temperature to 773 K. The devices show normal diode characteristics at all temperatures. A very low leakage current <10−14 A in the reverse bias was obtained at room temperature, resulting in a high rectification ratio of 108. Although the rectification ratio decreases with increasing temperature, it possesses 106 even at 573 K. A breakdown voltage was examined to be more than 100 V. [ABSTRACT FROM AUTHOR]

Abstract: We have realized low specific on-resistance and ideal built-in potential simultaneously for a (111)-oriented homoepitaxial diamond p–n + junction. As the p–n + junction, the heavily phosphorus doped n +-type layer, which shows variable range hopping conduction, was formed on the (111)-oriented boron doped p-type one. By using this hopping conduction, the resistivity of the n +-type layer becomes lower by three orders of magnitude than that of a lightly P-doped layer. Current density–voltage characteristics showed a rectification ratio of 106 at ±15 V at room temperature. The current density and the specific on-resistance at forward bias voltage of 15 V at room temperature are over 100 A/cm2 and 8×10−2 Ωcm2, respectively. This low specific on-resistance corresponds to the lower resistivity of the n +-type layer by three orders of magnitude than that of conventional lightly P-doped n-type layer. The existence of the space-charge layer at the vicinity of the p–n + junction was confirmed from capacitance–voltage (C–V) characteristics. From C −2–V characteristics at 200 °C, the built-in potential was estimated as approximately 4.4 eV, which is identical to that of conventional diamond p–n junction. [Copyright &y& Elsevier]

Abstract: Phosphorus (P) doping of (001) diamond was investigated focusing on [CH4]/[H2] and [PH3]/[CH4] gas flow ratio dependence during homoepitaxial growth. P concentration was primarily controlled by gas flow ratio in the same manner as (111) doping, although the controllable range stayed narrow due to lower doping efficiency. Electrical properties of (001) P-doped diamond films were investigated by Hall effect measurements and the doping level dependence of carrier compensation was discussed. The compensation ratio remained almost constant with increasing P concentration, indicating that P doping itself induces acceptor states compensating P donors. [Copyright &y& Elsevier]

Abstract: We have succeeded in fabricating (001)-oriented diamond p–n junctions with clear diode characteristics and conformed ultraviolet (UV) light emission by current-injection at room temperature. As p–n junctions, a phosphorus doped n-type layer was formed on (001)-oriented boron doped p-type one by applying an optimized homoepitaxial growth technique based on microwave plasma-enhanced chemical vapor deposition. Current–voltage characteristics showed a rectification ratio of 103 at ±30 V at room temperature. The existence of the space-charge layer at the vicinity of the p–n junction was confirmed from capacitance–voltage (C–V) characteristics. From C −2–V characteristics at 773 K, the built-in potential was estimated as approximately 4.7 V. A strong UV light emission at 235 nm due to free exciton recombination with transverse-optical phonon was observed at forward current over 36 mA in these p–n junctions. [Copyright &y& Elsevier]

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]

Abstract: Electrical properties of homoepitaxial diamond p–n+ junction of boron (B)-doped p-type layer and phosphorus-doped n-type layer on Ib (111) diamond single crystal have been characterized. Current–voltage characteristics show a clear rectifying property with rectification ratio of over 105 at ±10 V. From capacitance–voltage characteristics, it is found that a spatial distribution of space-charge density N i of the p–n+ junction is not uniform and N i at a middle region of the space-charge layer formed at zero bias voltage is higher than that of other region of the space-charge layer. This peculiar characteristic can be explained by superposition of two effects; one is the deep dopant effect due to B atoms in the p-type layer, which makes to reduce N i at around the edge of the space-charge layer formed at zero bias voltage. The other is the compensation of B acceptors by impurity atoms diffusing during the p–n+ interface and incorporating during the growth of p-type layer, which makes to reduce N i at the vicinity of the p–n+ interface. [Copyright &y& Elsevier]

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]

Abstract: Field emission characteristics of heavily phosphorus (P)-doped homoepitaxial diamond is measured. Temperature dependent resistivity measurements indicate that hopping dominant transport in heavily P-doped homoepitaxial diamond. Field emission current versus anode voltage characteristics divide into three distinct regions. The effective electron affinity of O-terminated diamond surface is calculated to be 1.5 eV from F–N plot. This value is in reasonable agreement with data evaluated from total photo-electron yield spectroscopy measurements. Using these data, we introduce field emission process of O-terminated heavily P-doped diamond: i) emission of electrons from the conduction band minimum, ii) depletion of electrons in conduction band and iii) field emission from the phosphorus doping level. [Copyright &y& Elsevier]

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]

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]

A diamond Schottky-pn diode (SPND) was fabricated and its electrical properties were investigated by measuring the current-voltage characteristics. The diode showed high current density (>10 4  A/cm 2 at 7 V) at room temperature with low differential on-resistance (~10 −5  Ωcm 2 ) under a wide temperature range (295–600 K). We constructed Richardson plots based on the characteristics and then estimated the potential barrier height on the hole current. From these results combined with the results of Poisson equation analysis, we viewed the change in hole barrier as a function of applied voltage and obtained the value of the hole activation energy as ~0.06 eV in the p + -type layer around the flat-band voltage. We clarified the transport mechanisms of the SPND and the method for estimating the activation energy in heavily boron-doped diamond exhibiting hopping conduction. [ABSTRACT FROM AUTHOR]

Due to the limits of the physical properties of conventional semiconductors against harsh environments, seeking a suitable material for next‐generation photoconversion devices with high‐temperature stability and strong radiation hardness has become a hot issue. Here, visible‐light photodetectors are fabricated on an N‐doped diamond. Their visible‐light detection via charge‐neutralized impurity levels including multi‐complex mid‐gap states induced crystal defects shows photosensitivity of at least four orders (104), the visible responsivity of 0.08 A W−1, and the detectivity of 3.9 × 1012 Jones. No significant deterioration of such figures of merit of photodetectors is observed even at an environmental temperature of 250 °C and after absorption to 10 MGy in the dose of white X‐ray. N‐doped diamond shows excellent potential to be applicable to visible‐light photodetectors for harsh‐environmental implementations, which conventional visible‐light photodetectors are not capable of so far. [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]

We successfully observed electron emission from hydrogenated diamond (111) p–i–n+ junction diodes with negative electron affinity during room temperature operation. A heavily doped layer and p–i–n junction structure, rather than a p–n junction structure, play important roles in obtaining high diode and emission currents. The emission started when the applied bias voltage was equal to the expected built-in potential, and the emission current reached 8.8 µA during the room temperature operation. In this high current region, we observed an increase in quantum efficiency – a nonlinear increase in emission current. [ABSTRACT FROM AUTHOR]

Heavily phosphorus doping (n+) is a promising technique to reduce the resistance of n-type diamond. We propose a selective <111> direction growth technique on (001) diamond films, which enables n+ diamond to be fabricated even on the (001) orientation. The maximum concentration of about 1020 cm-3 was observed by secondary ion mass spectroscopy, although the distribution of phosphorus depth was not uniform. Electrical properties of selectively grown n+ diamond were characterized by current–voltage experiments. Clear conduction was found along the line and space structure of n+ diamond, and its resistivity was determined to be as low as ∼3×102 Ω cm, which is four orders of magnitude lower than that of the conventional (001) n-type diamond film. [ABSTRACT FROM AUTHOR]

Electron emission current was observed from a hydrogen-terminated n-layer diamond surface of forward biased diamond p–n junction diodes, while there was no electron emission from the same surface after oxidization, suggesting that the phenomenon is related to negative electron affinity (NEA) of the hydrogen-terminated diamond surface. Since electrons in the n-layer flow toward to the p-layer due to forward bias, they cannot directly contribute to the emission current from the n-layer surface. In view of our previous result that the exciton-derived photoelectron emission was observed from the NEA diamond surface by total photoelectron yield spectroscopy, the phenomenon can be explained as electron emission due to exciton diffusion at the forward bias. [ABSTRACT FROM AUTHOR]

The realization of diamond‐based advanced devices is interrelated with the fabrication of practical ohmic contacts. Contrary to boron‐doped, the phosphorus‐doped diamonds with interface carbide forming Ti‐based conventional ohmic contacts find their limitation in device fabrication due to the high contact resistance. Herein, nanocarbon ohmic contacts are deposited by a coaxial arc plasma gun on semiconducting diamonds, and their composite structure which facilitates exceptional contact properties is explored. A comparative electrical characterization between nanocarbon ohmic contacts and conventional Ti‐based contacts is performed on a heavily phosphorus‐doped diamond, and they exhibited one‐order declination in specific contact resistance. In addition to the low contact resistance, an ideal ohmic electrode is preferable to have good mechanical adhesion and corrosion resistance for device applications. The contact behavior of n‐type diamond/nanocarbon against an extremely corrosive environment realized by boiling H2SO4 + HNO3 solution is analyzed. The nanocarbon ohmic contacts exhibit excellent corrosion resistance and mechanical adhesion over conventional Ti‐based contacts. A similar trend is also observed for nanocarbon contacts on boron‐doped diamonds. The modest effect on the transfer length of the nanocarbon contacts with respect to acid treatment sessions indicates a tightly bonded diamond/nanocarbon interface and actively suggests their application in highly‐corrosive and harsh environments. [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]

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]

We successfully fabricated the inversion-type p-channel metal–oxide–semiconductor field-effect transistor (MOSFET) on heteroepitaxially grown free-standing diamond using silicon-based substrates. The drain current–drain voltage (I ds – V ds) and drain current–gate voltage (I ds – V gs) characteristics were examined. The maximum drain current density and the peak field effect mobility (μ FE) were around 0.35 mA/mm and 2.7 cm2 V−1s−1, which were lower than our reported results of the homoepitaxial diamond MOSFETs fabricated on high-pressure, high-temperature (HPHT) substrates. The interface state density (D it) extracted from the subthreshold region was around 5.5 × 1012 cm−2eV−1, comparable to our reported results of the homoepitaxial diamond MOSFET. To further examine the reason for the low μ FE , atomic force microscopy (AFM) measurements were performed for the n-type body of the heteroepitaxial diamond MOSFET, and we found that the surface roughness was much larger than our reported ones of the homoepitaxial diamond MOSFET. It can be deduced that the surface roughness would be one main limiting factor for the field effect mobility of the heteroepitaxial diamond MOSFET. The imperfect diamond heteroepitaxy would also degrade the field effect mobility. This work explores the potential of the inversion-type p-channel heteroepitaxial diamond MOSFETs, which would facilitate the practical application of diamond power devices. Image 1 [ABSTRACT FROM AUTHOR]

We demonstrated and characterized Schottky barrier diodes (SBDs) fabricated on heteroepitaxial diamond films grown onto 3C-SiC/Si substrates. SBDs showed clear diode properties with rectification ratios above 109 at ±5 V and maintained above 108 even at 500 K. Temperature dependence of the Schottky barrier height (SBH) and the ideality factor was explained by assuming inhomogeneous Schottky barriers following the Gaussian distribution. For leakage current analysis, two types of defects, linear pits (LPs) and nonepitaxial crystals (NCs), were shown to be fatal defects, causing the flow of leakage currents. The leakage current was found to be an exponential function of the length of the LPs and a linear function of the size of the NCs. These defects can be suppressed by highly oriented heteroepitaxial diamond films with reduction of tilt and twist spread for diamond nuclei and optimized growth condition. Moreover, intrinsic layer thickening and inserting a buffer layer stopping propagation of dislocations are also effective. By reducing both crystal defects, we can obtain device properties comparable to SBDs fabricated on homoepitaxial diamond films because the leakage currents can be suppressed. [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]

We investigated an effect of interface defects in diamond lateral p-n-junction diodes on their reverse-biased leakage currents. Defects at the p–n interface were observed by cross-sectional transmission electron microscopy from different electron incident directions. The observations revealed that the diodes with the large leakage current had a number of defects localized at the p–n interface. The amount of the defects is related to the magnitude of the reverse leakage currents of the devices. Leakage analysis with applying high voltages strongly suggests that the leakage currents originate from the observed defects. Possible origin of the defect formation is discussed. [ABSTRACT FROM PUBLISHER]

To realize an ultra-flat diamond surface with a three-dimensional (3D) structure, we performed dressed-photon-phonon (DPP) etching. A DPP is generated on nano-scale protrusions. Hence, the generation of DPPs results in selective removal of nano-scale protrusions, thereby achieving an ultra-flat surface even on the sidewall of a diamond mesa structure. By controlling the polarization of the incident light, a smooth diamond mesa structure sidewall was obtained, and a higher etching rate was obtained with a perpendicular polarization on the corrugations. In addition, by selective deposition of n-layer diamond on the p-layer diamond mesa structure, smooth n-layer diamond was confirmed on the DPP etched sidewall. Schematic of dressed-photon-phonon (DPP) etching on the sidewall: (a) before and (b) after etching, in which DPP selectively generates on the corrugations and etching automatically stops when the surface was smooth. Scanning electron microscopy image of the selective deposition of the n-layer (c) without and (d) with the DPP etched sidewall. [ABSTRACT FROM AUTHOR]

Abstract: Photocurrent in phosphorous-doped CVD diamond film of the bandgap of 5.5eV with the density of 2×1018 cm−3 decreases with increasing photon energy in the energy range higher than 5.8eV at room temperature (RT). The photocarrier life time is 0.3ms at the excitation energy of 5.8eV and decreases with increasing excitation energy. These show that the photocarriers, ascertained to be electrons by the Hall effect of the photocurrent, are trapped near the surface. The life time of photo-excited holes in Boron-doped CVD diamond film with the density of 9×1017 cm−3 is 35ms at RT and decreases with decreasing Boron density, which is explained from the relation between the Fermi energy and the density. [Copyright &y& Elsevier]

Abstract: We have succeeded in fabricating a (111)-oriented diamond p–i–n junction with high crystalline quality intrinsic layer and with low series resistance. The series resistance of this diamond p–i–n junction was improved by decreasing the resistivity and specific contact resistance of n-type layer, which is allowed to inject higher current while maintaining lower junction temperature. Current density–voltage characteristics showed a rectification ratio of 106 at ±15 V at room temperature. A clear ultraviolet emission at around 235 nm due to free exciton recombination was observed at a forward current, while the broad visible light emission from deep levels was significantly suppressed. Moreover, stronger excitonic emission by two orders of magnitude than that of (001)-oriented diamond p–i–n junctions with high series resistance was realized. [Copyright &y& Elsevier]

The density of dislocations that occur in the intrinsic (i -) layer of a pin diamond diode was estimated from two-photon excitation photoluminescence (2PPL) imaging. Results elucidated data obtained from device characteristic measurements and cathodoluminescence (CL). Generation and diffusion of free carriers for deep-level emission in the i -layer have no effect on emission images observed using the 2PPL method. Therefore, to evaluate the pin diode structure, the influence of free carrier propagation on the adjacent layer can be avoided. However, this effect cannot be ignored when using CL. These findings are expected to be important for assessing diamond device performance. [Display omitted] • Results show distinguishing dislocation densities in the i -layer of pin diode. • Two-photon excitation photoluminescence (2PPL) imaging can be used. • CL measurements are affected by free carrier diffusion to adjacent layers. [ABSTRACT FROM AUTHOR]

Current leakage sites in diamond p–n junction are determined by measuring an electron‐beam–induced current (EBIC) technique and conductive atomic force microscopy (C‐AFM). Current leakage sites in p–n diodes, particularly, can be determined by means of EBIC without destruction of the device structure. From EBIC observation, bright spots with higher signal intensity than these in surrounding region are observed in p–n diodes, and these spots strongly correlate with the leakage current. It is found that these bright spots are originating from pits of comet‐shaped defects observed by a scanning electron microscope. With C‐AFM, the leakage current is detected at pits of comet‐shaped defects. Reduction in comet‐shaped defects shall be reduced using the technique of reduction in dislocation and high‐quality crystal growth to suppress the leakage current. [ABSTRACT FROM AUTHOR]

The coherent control of the orbital state is crucial for realizing the extremely-low power manipulation of the color centers in diamonds. Herein, a neutrally-charged nitrogen-vacancy center, NV 0 , is proposed as an ideal system for orbital control using electric fields. The electric susceptibility in the ground state of NV 0 is estimated, and found to be comparable to that in the excited state of NV - . Also, the coherent control of the orbital states of NV 0 is demonstrated. The required power for orbital control is three orders of magnitude smaller than that for spin control, highlighting the potential for interfacing a superconducting qubit operated in a dilution refrigerator., (© 2024. The Author(s).)

Transform-limited photon emission from quantum emitters is essential for high-fidelity entanglement generation. In this Letter, we report the coherent optical property of a single negatively charged lead-vacancy (PbV) center in diamond. Photoluminescence excitation measurements reveal stable fluorescence with a linewidth of 39 MHz at 6 K, close to the transform limit estimated from the lifetime measurement. We observe 4 orders of magnitude different linewidths of the two zero-phonon lines, and find that the phonon-induced relaxation in the ground state contributes to this huge difference in the linewidth. Because of the suppressed phonon absorption in the PbV center, we observe nearly transform-limited photon emission up to 16 K, demonstrating its high temperature robustness compared to other color centers in diamond.

Diamond possesses excellent physical and electronic properties, and thus various applications that use diamond are under development. Additionally, the control of diamond geometry by etching technique is essential for such applications. However, conventional wet processes used for etching other materials are ineffective for diamond. Moreover, plasma processes currently employed for diamond etching are not selective, and plasma-induced damage to diamond deteriorates the device-performances. Here, we report a non-plasma etching process for single crystal diamond using thermochemical reaction between Ni and diamond in high-temperature water vapour. Diamond under Ni films was selectively etched, with no etching at other locations. A diamond-etching rate of approximately 8.7 μm/min (1000 °C) was successfully achieved. To the best of our knowledge, this rate is considerably greater than those reported so far for other diamond-etching processes, including plasma processes. The anisotropy observed for this diamond etching was considerably similar to that observed for Si etching using KOH.

Single crystal, nanoscale diamond membranes are highly sought after for a variety of applications including nanophotonics, nanoelectronics and quantum information science. However, so far, the availability of conductive diamond membranes has remained an unreachable goal. In this work we present a complete nanofabrication methodology for engineering high aspect ratio, electrically active single crystal diamond membranes. The membranes have large lateral directions, exceeding ∼500 × 500 μm 2 and are only several hundreds of nanometers thick. We further realize vertical single crystal p-n junctions made from the diamond membranes that exhibit onset voltages of ∼10 V and a current of several mA. Moreover, we deterministically introduce optically active color centers into the membranes, and demonstrate for the first time a single crystal nanoscale diamond LED. The robust and scalable approach to engineer the electrically active single crystal diamond membranes offers new pathways for advanced nanophotonic, nanoelectronic and optomechanical devices employing diamond.

The electric field inside semiconductor devices is a key physical parameter that determines the properties of the devices. However, techniques based on scanning probe microscopy are limited to sensing at the surface only. Here, we demonstrate the direct sensing of the internal electric field in diamond power devices using single nitrogen-vacancy (NV) centers. The NV center embedded inside the device acts as a nanoscale electric field sensor. We fabricated vertical diamond p-i-n diodes containing the single NV centers. By performing optically detected magnetic resonance measurements under reverse-biased conditions with an applied voltage of up to 150 V, we found a large splitting in the magnetic resonance frequencies. This indicated that the NV center senses the transverse electric field in the space-charge region formed in the i-layer. The experimentally obtained electric field values are in good agreement with those calculated by a device simulator. Furthermore, we demonstrate the sensing of the electric field in different directions by utilizing NV centers with different N-V axes. This direct and quantitative sensing method using an electron spin in a wide-band-gap material provides a way to monitor the electric field in operating semiconductor devices.

Bilayer graphene was synthesized at low temperature using surface wave microwave plasma techniques where poly(methyl metacrylate) (PMMA) and methane (CH 4 ) were used as carbon sources. Temperature-dependent Hall effect measurements were carried out in a helium atmosphere. Sheet resistance, sheet carrier density and mobility showed weak temperature dependence for graphene from PMMA, and the highest carrier mobility is 740 cm 2 V -1 s -1 . For graphene from CH 4 , tunneling of the domain boundary limited carrier transport. The difference in average domain size was determined by Raman signal maps. In addition, residuals of PMMA were detected on graphene from PMMA. The low sheet resistances of graphene synthesized at a temperature of 280 °C using plasma techniques were explained by the PMMA related residuals rather than the domain sizes.