A simple, fast and cost-effective etching technique to create oriented nanostructures such as pyramidal and cylindrical shaped nanopores in diamond membranes by self-assembled metallic nanoparticles ...is proposed. In this process, a diamond film is annealed with thin metallic layers in a hydrogen atmosphere. Carbon from the diamond surface is dissolved into nanoparticles generated from the metal film, then evacuated in the form of hydrocarbons and, consequently, the nanoparticles enter the crystal volume. In order to understand and optimize the etching process, the role of different parameters such as type of catalyst (Ni, Co, Pt, and Au), hydrogen gas, temperature and time of annealing, and microstructure of diamond (polycrystalline and nanocrystalline) were investigated. With this technique, nanopores with lateral sizes in the range of 10-100 nm, and as deep as about 600 nm, in diamond membranes were produced without any need for a lithography process, which opens the opportunities for fabricating porous diamond membranes for chemical sensing applications.
We report on a detailed analysis of the transport properties and superconducting critical temperatures of boron-doped diamond films grown along the $\{100\}$ direction. The system presents a ...metal-insulator transition (MIT) for a boron concentration ($n_B$) on the order of $n_c \sim 4.5 \times 10^{20}$ cm$^{-3}$ in excellent agreement with numerical calculations. The temperature dependence of the conductivity and Hall effect can be well described by variable range hopping for $n_B n_c$) present a superconducting transition at low temperature. The zero temperature conductivity $\sigma_0$ deduced from fits to the data above the critical temperature ($T_c$) using a classical quantum interference formula scales as : $\sigma_0 \propto (n_B/n_c-1)^\nu$ with $\nu \sim 1$. Large $T_c$ values ($\geq 0.4$ K) have been obtained for boron concentration down to $n_B/n_c \sim 1.1$ and $T_c$ surprisingly mimics a $(n_B/n_c-1)^{1/2}$ law. Those high $T_c$ values can be explained by a slow decrease of the electron-phonon coupling parameter $\lambda$ and a corresponding drop of the Coulomb pseudo-potential $\mu^*$ as $n_B \rightarrow n_c$.
The electrical properties of Schottky contacts on the (100) surface of Boron doped diamond films epitaxially grown on Ib substrates are investigated in this work. The role of Boron doping ...concentration and extended defects detected by cathodoluminescence is correlated to current voltage characteristics, rectifying efficiency and high voltage performance of the diodes up to 1
kV and more. The influence of surface treatment prior to metal deposition is highlighted and the choice of metal for the Schottky contact is discussed. The paramount importance of using an oxidised diamond surface at the Schottky contacts and outside is demonstrated. Decreasing the series resistance of diodes is obtained with a stack of two layers, the upper one being lightly doped while the deeper one contains Boron concentrations close to the metallic conductivity threshold (4
×
10
20
B/cm
3). Several architectures are studied. The ohmic contact directly laid on the heavily doped layer permits forward current densities of 66
A/cm
2 under 4
V at room temperature and switching times in the nanosecond range. This set of results shows that p-type diamond is an adequate semiconductor for implementing high speed, high power and high voltage electronic rectifiers.
► Bulk and surface properties of diamond influence Schottky diode characteristics. ► Extended defects and Boron concentrations > 10
16 B/cm
3 worsen the reverse current. ► Electrical and chemical passivation of the free surface and interface are demonstrated. ► A stack of lightly and heavily doped layers leads to high forward current densities. ► Fast switching and high breakdown field rectifiers can be implemented on diamond.
As a result of the larger covalent radius of boron (
r
B
=
0.88 Å) when compared to that of carbon (
r
C
=
0.77 Å), the introduction of substitutional boron into diamond leads to an expansion δ
a/
a ...of the lattice parameter. This has been found previously to follow a linear interpolation (Vegard law) as long as the boron content is lower than about 0.5 at.% in MPCVD epilayers or 1.5 at.% in HPHT bulk crystals.
Above those concentrations, the expansion is less pronounced than predicted by Vegard. In order to explain this effect, we have performed ab initio calculations on C:B substitutional alloys. The results show that the presence of interstitial boron and of boron clusters is not necessary to explain the experimental data available in the literature. Moreover, quantitative estimates are proposed for the deformation potential of the valence band maximum and for the steric effect associated to boron pairing. We then apply these conclusions to discuss the different variations of δ
a/
a vs boron contents observed by high resolution XRD experiments performed on “insulating” and metallic (and superconducting) p
++ diamond epilayers grown by MPCVD on (100)- and (111)-oriented type Ib substrates, for which boron concentration profiles have been determined by Secondary Ion Mass Spectroscopy.
In this work, we have used X-ray photoelectron spectroscopy (XPS) to investigate the nature of surface adsorbed species and their sensitivity to the boron concentration B in two sets of as-grown ...diamond films: homoepitaxial {111} and polycrystalline. These sets cover each one at least three of the four doping ranges: low doping (5
×
10
16
<
B
<
1.5
×
10
19
cm
−
3
), high doping (1.5
×
10
19
<
B
<
3
×
10
20
cm
−
3
), heavy doping (3
×
10
20
<
B
<
2
×
10
21
cm
−
3
), and phase separation (B
>
2
×
10
21
cm
−
3
). The results are compared to those we have previously obtained on {100} homoepitaxial films in the same doping ranges.
A detailed description of both the nature and the relative concentrations of the main surface chemical species on every set of films is reported. Besides the usual CH
x bonds on the diamond surface, the following oxygen-related groups: Ether (C–O–C), hydroxyl (C–OH, only on polycrystalline films), carbonyl (>
C=O) and carboxyl (HO–C=O) have been found on the surface of grown diamond films, upon spontaneous oxidation under air (no oxidation treatment has been applied). The evolution of each surface chemical group according to the boron concentration in the films is.
Sets of heavily boron-doped {100}-oriented diamond epilayers have been grown by MPCVD from isotope-enriched gases such as
13CH
4 and
10B
2H
6 or
13CH
4 and naturally abundant
11B
2H
6, and the ...resulting concentration profiles of the various boron isotopes were measured by SIMS. In the particular case of the
13C
10B set, the high absorption cross section of
10B made neutron depth profiling possible for this element.
The vibrational and superconducting properties of these epilayers were compared to those of films grown from gases containing the isotopes in their natural abundance. The critical temperature
T
C values were found to be lower both in the
13C
11B and
13C
10B sets, as expected for a conventional pairing mechanism mediated by phonons. In good agreement with recent studies, the isotope-effect coefficient for
T
C was found to be much higher than the classical 0.5 value. Various origins for this behaviour are suggested.
Defects involving hole traps in diamond are investigated with Fourier Transform Deep Level Transient and Isothermal Spectroscopies in several Boron doped diamond films epitaxially grown on Ib ...substrates in our own reactor, either with or without oxygen in the gas mixture. It is shown that both pre- and post-treatments can stabilize a continuous distribution of traps which was not necessarily present initially. The ionization energy and capture cross section of each trap is determined and compared to previous experimental and theoretical data. From deep trap profiling, it is shown that concentrations are all decreasing below 10
15
cm
−
3
beyond about 250
nm below the interface with the Schottky metal. All these traps do not exist in epilayers prepared with oxygen in the gas mixture. This set of properties strongly suggests that hydrogen is involved in traps, probably associated with either structural defects or Boron.
► In MWPCVD diamond, holes traps stabilized after either pre- or post treatments. ► Ionization energies of holes traps lie in the range 0.7–1.6 eV. ► Concentration profiles of holes traps in diamond shows an inwards decreasing trend. ► Holes traps are likely due to defective sites in which hydrogen atom is present. ► Holes traps are suppressed in diamond epilayers prepared with 0.25% of oxygen.
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