Boron-doped Diamond Layers Research Articles

Photovoltaic Schottky ultraviolet detectors fabricated on boron-doped homoepitaxial diamond layer

A photovoltaic diode using tungsten carbide (WC) Schottky contact for deep ultraviolet (DUV) light detection is developed using a lightly boron-doped homoepitaxial diamond layer. The photodiode shows a quick dc response time lower than an instrumental time constant of 0.3 s. The responsivity varies linearly with the DUV light intensity. A discrimination ratio of 105 between 210 nm and visible light is achieved at zero bias. The short-circuit photocurrent at 220 nm decreases with increasing the temperature from 300 to 373 K, whereas the Schottky barrier height under illumination remains unchanged. Numerical and experimental analyses reveal that the interface states between diamond and WC play a major role in reducing the zero-bias responsivity at elevated temperatures.

Electronic properties of boron-doped diamond on the border between the normal and the superconducting state

We report on measurements of resistivity and magnetoresistivity, Hall effect and upper critical field on normal and superconducting heavily boron-doped diamond layer produced by microwave plasma assisted chemical vapour deposition. The magnetoresistivity shows a characteristic change as a function of the boron concentration with strong evidence for a closed Fermi surface for superconducting samples. Although experimental and theoretical results favour a conventional, weak coupling electron–phonon interpretation of the superconducting mechanism, the observed dependence of the transition temperature TC on the hole concentration cannot be consistently described by the conventional theory.

Tungsten carbide Schottky contact to diamond toward thermally stable photodiode

We use tungsten carbide-based Schottky and ohmic contacts for the fabrication of deep ultraviolet (DUV) photodiodes on boron-doped homoepitaxial diamond layers. The photodiode is isothermally annealed at 500 °C in argon ambient in order to investigate the thermal stability of the electrical and optical properties. The ideality factor is improved to be an ideal value of unity after annealing for 1 h and becomes around 1.5 after subsequent annealing for longer time durations. The leakage current for at least 30 V reverse bias is lower than 10 − 14 A before and after annealing for 4 h. The photoresponsivity at 220 nm is enhanced dramatically by a factor of 10 3 after annealing, resulting in a DUV/visible blind ratio as large as 10 6 at the reverse bias of 2 V. The work is expected to open a way for developing thermally-stable Schottky contacts to diamond.

Excitonic emission and N‐ and B‐incorporation in homoepitaxial CVD‐grown diamond investigated by cathodoluminescence

Diamond is a very large bandgap material arising high expectations either for optoelectronic applications or for active semiconducting layers in specific electronic devices to be used under extreme conditions of pressure, temperature, wear or radiation, as well as in chemically aggressive environments. Unintentionally boron-doped diamond layers were grown by microwave plasma-assisted chemical vapour deposition (CVD) on {001}-oriented undoped Ib substrates with the addition of oxygen gas during growth. The relative quantities of nitrogen and boron incorporated in the diamond lattice are evaluated by cathodoluminescence (CL) spectra recorded at 5 K. Two different effects are shown to limit nitrogen incorporation: the substrate crystalline quality and the addition of oxygen into the precursor during the growth. First, the CL spectra are shown to change strongly near the edges of the substrate in the regions corresponding to different bulk crystal growth modes. Some regions show a luminescence governed by UV emission while in other regions, where the H3 defect-related luminescence of the substrate is much stronger, the film UV emission is reduced. Second, the relative importance of the free exciton emission with respect to those from the nitrogen-related H3 centre and from the boron-bound exciton is shown to increase with the addition of oxygen during growth. Such observations are of first importance to improve the spectral emission and absorption threshold of the diamond material in the deep UV range. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Response function measurement of layered type CVD single crystal diamond radiation detectors for 14 MeV neutrons

Response function measurement of layered-type chemical vapor deposition single crystal diamond radiation detectors for 14 MeV neutrons was carried out. The detector had a layered structure that was composed of a boron-doped diamond layer of 0.5 μm in thickness and a nondoped diamond layer of 20 μm on an inexpensive high pressure and high temperature-type Ib diamond substrate. The detector had energy resolution of 2.6% for 5.5 MeV α particles. This experiment was mainly carried out in order to understand the present status of the detector as a 14 MeV neutron spectrometer and an extent of charge trapping. As result, a peak caused by the C12(n,α0)9Be reactions was clearly observed; the best energy resolution of 6% as for a synthetic diamond radiation detector was achieved. Detection efficiency was 3.2×10−7 counts/unit neutron fluence. However, taking the energy resolution for α particles, etc., into account, the energy resolution for 14 MeV neutrons was not so high. Further improvement based on better crystal growth is indispensable.

Shallow donors with high n-type electrical conductivity in homoepitaxial deuterated boron-doped diamond layers.

Diamond is a unique semiconductor for the fabrication of electronic and opto-electronic devices because of its exceptional physical and chemical properties. However, a serious obstacle to the realization of diamond-based devices is the lack of n-type diamond with satisfactory electrical properties. Here we show that high-conductivity n-type diamond can be achieved by deuteration of particularly selected homo-epitaxially grown (100) boron-doped diamond layers. Deuterium diffusion through the entire boron-doped layer leads to the passivation of the boron acceptors and to the conversion from highly p-type to n-type conductivity due to the formation of shallow donors with ionization energy of 0.23 eV. Electrical conductivities as high as 2omega(-1) x cm(-1) with electron mobilities of the order of a few hundred cm2 x V(-1) x s(-1) are measured at 300 K for samples with electron concentrations of several 10(16) x cm(-3). The formation and break-up of deuterium-related complexes, due to some excess deuterium in the deuterated layer, seem to be responsible for the reversible p- to n-type conversion. To the best of our knowledge, this is the first time such an effect has been observed in an elemental semiconductor.

Preparation of low-threshold and high current rectifying heterojunction using B-doped diamond grown on Si-treated c-BN crystals

Low-threshold heterojunctions have been formed from a boron-doped p-type diamond layer grown epitaxially on the {1 1 1} surface of a Si-treated single crystalline cubic boron nitride. The resistivity of the Si-treated cubic boron nitride was 0.1 Ω cm. With the resistivity of 0.1 Ω cm, which is lower than that of the sample prepared by conventional high-temperature and high-pressure method, the turn-on voltage and the highest current of the heterojunction are 0.5 V and 1 mA, respectively.

Biotin grafting on boron-doped diamond.

Grafting of biotin on top of a polycrystalline boron-doped diamond layer was achieved by surface oxidation followed by an esterification reaction and revealed by fluorescently labelled streptavidin.

ChemInform Abstract: Ultraviolet Emission from a Diamond pn Junction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Optical Conductivity Studies in Heavily Boron-Doped Diamond

The optical transmittance and reflectance of heavily boron-doped (2 × 10 20 cm -3 < [B] < 2 × 10 21 cm -3 ) epitaxial diamond layers deposited by MPCVD were measured in the infrared range. While T-dependent measurements confirmed the metallic character of such films, the overall spectral features were well reproduced by introducing Drude components in the fitting expression for the optical conductivity. The associated microscopic transport parameters were quantitatively compared to those resulting from preliminary transport measurements performed on the same samples. We show that room-temperature FTIR reflectance measurements provide an easy contactless characterization of the transport properties of such p + films, and we discuss what new information on carrier-phonon interaction as well as on the transport mechanism in the impurity band might be gained from temperature-dependent spectroscopic data.

Ultraviolet emission from a diamond pn junction.

We report the realization of an ultraviolet light-emitting diode with the use of a diamond pn junction. The pn junction was formed from a boron-doped p-type diamond layer and phosphorus-doped n-type diamond layer grown epitaxially on the 111 surface of single crystalline diamond. The pn junction exhibited good diode characteristics, and at forward bias of about 20 volts strong ultraviolet light emission at 235 nanometers was observed and was attributed to free exciton recombination.

In situ boron doping of chemical-vapor-deposited diamond films

A systematic investigation of the boron doping of microwave-plasma-deposited diamond films was performed. Doping with levels up to 550 ppm was carried out in situ on undoped diamond film substrates in a microwave-plasma-assisted chemical vapor deposition with liquid trimethyl-, triethyl-, and tripropylborate and gaseous trimethylborane as doping sources. The dependence of the boron incorporation probability on the doping sources and on the process parameters was studied with secondary ion mass spectrometry. The doping-induced variations of phase quality and morphologic characteristics of the boron-doped diamond layers were investigated by means of scanning electron microscopy and Ramon spectroscopy. The incorporation of other impurities (i.e., hydrogen, nitrogen, oxygen, and silicon) were also determined by secondary ion mass spectrometry. The relations of the concentration of these impurities to the boron incorporation were also studied.

Modification on the band structure and the related emission characteristics of defective diamond films doped with boron

Electron field emission properties of multilayer diamond films containing an undoped diamond layer grown on top of boron-doped diamond layer are observed to be significantly superior to that of the single layer diamond films, boron-doped or undoped. The electron emission capacity ( J e) of the multilayer diamonds increases as the thickness of the undoped layer reduces, with the turn-on field ( E 0) and effective work function ( ϕ e) essentially unchanged. This phenomenon is accounted for by the bending of the electronic band structure, such that the electrons in the acceptor levels of the underlying boron-doped layer can jump across the junction to the impurity bands in the top undoped layer, and then readily field emitted. The optimum electron emission properties obtained are: J e=4890 μA/cm 2 (at 35 V/μm), E 0=26 V/μm and ϕ e=0.28 eV.

Underpotential Deposition of Lithium on Aluminum in Ultrahigh-Vacuum Environments

The electrochemical properties of clean aluminum in LiClO4(PEO) solutions have been investigated in ultrahigh vacuum using as electrodes both foils and thin films vapor deposited on boron-doped diamond (BDD) layers supported on Si substrates. Voltammetric scans recorded at temperatures of about 55 °C yielded a set of deposition/stripping peaks at potentials positive to the onset of Li/Al alloy formation, attributed to Li underpotential deposition on Al. The positions of these peaks were found to be in relatively good agreement with those predicted by Gerischer−Kolb's work function correlation, as well as with recent theoretical calculations reported by Lehnert and Schmickler. In the case of Al films supported on BDD/Si, the charge under the stripping peak obtained after polarizing the Al electrode at potentials slightly positive to Li bulk deposition was found to increase with the film thickness. Further optimization of this type of experiments, by using, for example, a quartz crystal microbalance to determine the actual amount of Al deposited on the BDD/Si substrate, will make it possible to measure the stoichiometry of the alloy as a function of the applied potential.

Ultraviolet cathodoluminescence from diamond layers after doping by means of boron-ion implantation

Boron-doped diamond layers have been generated in insulating (type IIa) diamonds by means of ion implantation. Cathodoluminescence measurements were used to monitor the layers during this process. It was found that the activation of the boron acceptors, followed by suitable annealing, gave rise to the appearance of two ultraviolet luminescence bands around 3.5 and 4.6 eV. These same bands had been observed previously in natural, as well as synthetically grown, boron-doped, type IIb diamonds. The results reported in this study, support the conclusion that these bands are related to the presence of boron acceptors and show, in addition, that the acceptor density NA need not be more than the density of the compensating donors ND, as had been postulated.

Boron-Doped Homoepitaxial Diamond Layers: Fabrication, Characterization, and Electronic Applications

For electronic applications, a series of boron-doped homoepitaxial diamond layers of high crystal quality have been grown on (100)-cut diamond substrates using the microwave plasma CVD method. The B-concentration varies from 3 × 1017 to 3 × 1020 atoms/cm3. The layers are selectively grown into the shape of Hall bars using a sputtered SiO2 mask. The diamond substrates are 3×3×1 mm3 in size. Gold wires are bonded to ohmic contacts on the Hall bars formed by an electron beam evaporated Mo/Pt/Au sandwich annealed at 950 °C for 30 min. Electrical characterization is performed in eight samples over the temperature range from 100 to 1300 K. The results are discussed in detail. For diamond layers grown on synthetic nitrogen-doped (type Ib) substrates, current-voltage characteristics of diode type can be observed in the temperature range from 360 to 900°C. Green electroluminescent light is emitted from the p-n junction area. High current Schott-ky diodes are also fabricated which consist of a gold contact to a moderately B-doped homoepitaxial layer grown on a synthetic heavily boron-doped (type IIb) substrate. Fur elektronische Anwendungen wird eine Serie von Bor-dotierten homoepitaktischen Dia-maritschichten hoher kristalliner Gute auf (100)-geschnittenen Diamantsubstraten mittels der Mikrowellenplasma-unterstutzten CVD-Methode aufgewachsen. Die B-Konzentration variiert von 3×1017 bis 3 × 1020 Atome/cm3. Die Schichten werden selektiv mittels gesputterter SiO2-Masken als Hallkreuze gewachsen. Die Diamantsubstrate sind 3×3×1 mm3 gros. Golddrahte werden an ohmsche Kontakte gebondet. Diese werden als Mo/Pt/Au-Schichtpakete mittels Elektronenstrahl-Aufdampfen und halbstundigem Tempern bei 950°C hergestellt. Die elektrische Charakterisierung erfolgt bei acht Proben uber den Temperaturbereich von 100 bis 1300 K. Die Ergebnisse werden eingehend diskutiert. Auf synthetischen Stickstoff-dotierten (Typ Ib) Substraten werden Strom/ Spannungs-Charakteristiken vom Diodentyp im Temperaturbereich von 360 bis 900°C beobachtet. Grumes Elektrolumineszenzlicht wird von der p-n-Kontaktflache emittiert. Hochstrom-Schottkydio-den werden ebenfalls hergestellt. Sie bestehen aus einem Goldkontakt zu einer masig B-dotierten homoepitaktischen Schicht, die auf einem synthetischen, hochdotierten (Typ IIb) Substrat aufgewachsen wurde.

P-n Junction diode by B-doped diamond heteroepitaxially grown on Si-doped c-BN

Boron-doped p-type diamond thin film was heteroepitaxially grown on silicon-doped n-type cubic boron nitride (c-BN) bulk crystal by microwave plasma chemical vapor deposition. Utilizing selective etching of the boron-doped diamond layer to the c-BN substrate, a diamond/c-BN heterojunction p-n diode was fabricated for the first time. A small reverse bias leakage current and more than five orders of rectification ratio were obtained for the diode.

Density of states distribution in diamond thin films

Space-charge-limited hole currents in nominally undoped diamond thin films have been studied using thin, highly boron-doped (p+) diamond layers as injecting contacts. The results obtained from these p+-p-Si structures have been analyzed to determine, for the first time, the bulk distribution of localized states N(E) in polycrystalline diamond thin films. The values of N(E), covering an energy range of about 0.8–0.6 eV above the valence band, indicate that the density of states at 0.8 eV is about 1015 cm−3 eV−1 but rises rapidly, within the 0.2 eV, to about 1018 cm−3 eV−1.

Fermi-Dirac statistics and the nature of the compensating donors in boron-doped diamond layers.

Fermi-Dirac statistics have been applied to semiconducting diamond layers doped with boron by means of ion implantation. Suitable limiting equations could be derived to describe the resistance-temperature behavior which relates to acceptor activation and also to hole creation in the valence band by means of compensating-donor neutralization. When applying these equations to the experimental data, it is found that the donor centers have a very large degeneracy weighting factor ${g}_{D}$ and that this parameter depends on the annealing cycle used after ion implantation. This result can be explained by assuming that the donors consist of small aggregates of vacancies which constitute vacancy-lattice ``crystallites.'' In this paper, we shall call these particular vacancy aggregates, which have a stable electronic structure, vacloids. The presence of vacloids may also be invoked to explain some of the optical properties previously observed in diamonds.