Phosphorus-doped Diamond Films Research Articles

Characterization of n-Type Doped Homoepitaxial Diamond Thin Films

The successful n-type doping of epitaxial diamond films grown on (111) oriented synthetic type Ib crystals is shown. Fourier Transform Infrared spectroscopy, cathodoluminescence, and Hall effect were employed to characterize a set of phosphorus-doped diamond films grown under similar conditions by CVD with different phosphine concentrations in the reactant gas ([P]/[C] = 250 to 500 ppm). The activation energy of the conductivity shows a good agreement with the value known for phosphorus-doped sample (about 0.6 eV). Infrared measurements show the characteristic absorption peaks related to neutral substitutional phosphorus. Hall effect measurements clearly indicate n-type conductivity with mobility equal to 40 cm2/Vs at room temperature and a phosphorus concentration in the film of about 1018 cm—3. Cathodoluminescence measurements showed the free excitons and bound exciton peaks related to phosphorus. Bound-exciton recombination without phonon emission was also observed.

Phonon-assisted electronic transitions in phosphorus-doped n-type chemical vapor deposition diamond films

One year ago we published the first results on the electronic structure of the P-level in 1000 ppm PH 3/CH 4 doped {111}-oriented n-type diamond films, using the quasi-steady-state photocurrent technique (PC) and photothermal ionization spectroscopy (PTIS). In this work we have extended our measurements at various temperatures (4.2–77.4 K) to samples with various doping levels (100, 500 and 1000 ppm PH 3/CH 4). This allowed us to obtain more precise results for the electronic structure of the phosphorus defect in homoepitaxial n-type CVD diamond films, making use of the 155 meV LO-phonon to explain the oscillatory photoconductivity. These results are confirmed by the PTIS maxima and Fourier transform infra-red (FTIR) data. In addition we present first measurements on a 2000-ppm doped {100}-oriented sample.

Electron emission process of phosphorus-doped homoepitaxial diamond films

Electron emission is investigated for phosphorous (P)-doped homoepitaxial diamond films grown by microwave plasma chemical vapor deposition. A comparative study of field emission characteristics is performed for P-doped homoepitaxial diamond films with different electrical resistivities and with different cathode metals. A reduction in the turn-on voltage occurs with decreasing electrical resistivity. A variation in the turn-on voltage occurs with cathode metals. It is revealed that the internal electron emission at the diamond/metal contact has an influence on the field emission characteristics. Moreover, field emission characteristics are measured at various spacings between the anode electrode and diamond surface and at various distances from the cathode metal to the diamond surface just below the anode electrode. No significant change of the average electric field strength between the anode electrode and diamond surface is found between P-doped homoepitaxial diamond films with low and high electrical resistivities. It is suggested that space charge limited current is flowing in the diamond film with high resistivity.

Field emission from phosphorus-doped polycrystalline diamond films

Field emission characteristics have been investigated for P-doped polycrystalline diamond films. It is demonstrated that the turn-on voltage of the electron emission decreases with increasing temperature for the P-doped diamond film, while no variation in the turn-on voltage occurs for the undoped diamond film. The temperature-dependent field emission characteristics are found to be inherent to the P-doped diamond film. A behavior of the field emission characteristics can be well explained by means of the thermionic field emission model combined with the temperature dependence of the ionized donor concentration. This means that an increase of the ionized donor concentration with increasing temperature may lead to a reduction in the tunnel barrier width at the interface between the diamond and the cathode, resulting in an enhancement of the internal emission current. It is suggested that the internal electron emission is important to the field emission characteristics of the P-doped diamond films. A variation in the field emission characteristics of P-doped diamond films with various cathode metals and with various P-doping concentrations can be consistently understood on the basis of the internal electron emission model.

Field Emission Characteristics of Phosphorus-Doped Diamond Films

Field Emission Characteristics of Phosphorus-Doped Diamond Films

Low-temperature spectroscopic study ofn-type diamond

A spectroscopic study of epitaxial phosphorus-doped n-type diamond films, prepared by the chemical vapor deposition (CVD) technique, was carried out using the constant photocurrent method (CPM). Liquid nitrogen temperature CPM data show two new optically active defects in the gap of the P-doped CVD diamond film. A theoretical fitting of the optical cross-section data yields 0.56 eV optical excitation energy for the first level (denoted as ${X}_{\mathrm{P}1})$ and 0.81 eV for the second level (denoted as ${X}_{\mathrm{P}2}).$ The ${X}_{\mathrm{P}1}$ optical data are in good agreement with Hall measurements, showing about the same value for the (thermal) activation energy of the carrier concentration for P-doped samples. The ${X}_{\mathrm{P}2}$-defect level remains unidentified. Liquid helium temperature measurements for a high-electrical mobility n-type diamond sample show P-related oscillatory photoconductivity.

Field emission characteristics of phosphorus-doped homoepitaxial diamond films

Field emission characteristics were measured for phosphorous-doped homoepitaxial diamond films grown by microwave plasma assisted chemical vapor deposition. A variation in the turn-on voltage with cathode metals and various temperatures is observed for the sample with high electrical resistivity. This behavior of the turn-on voltage demonstrates that the internal electron emission at the diamond/metal contact influences field emission characteristics. A reduction in the turn-on voltage is found for the diamond film with low electrical resistivity.

Behavior of electron emission from phosphorus-doped epitaxial diamond films

Abstract The behavior of electron emission is investigated for phosphorus-doped homoepitaxial diamond films grown by microwave plasma assisted chemical vapor deposition. Field emission characteristics are measured at various spacings between the anode electrode and diamond surface and at various distances from the cathode metal to the diamond surface just below the anode electrode. A variation in the turn-on voltage occurs with cathode metals. This behavior of the turn-on voltage demonstrates that the electron injection at the diamond/metal contact has an influence on the field emission characteristics. Moreover, a reduction in the turn-on voltage is found for the diamond film with a low electrical resistivity. This is due to a decrease of voltages for the electron injection and for the electron transport in the diamond film.

Temperature dependence of field emission characteristics of phosphorus-doped polycrystalline diamond films

Temperature dependence of the field emission characteristics is investigated for the phosphorus(P)-doped polycrystalline diamond film in comparison with that of the boron(B)-doped one. The threshold voltage decreases with increasing temperature for the P-doped diamond film, while no variation in the threshold voltage occurs for the B-doped diamond film. It is considered that an increase of the ionized donor concentration with increasing temperature leads to a reduction in the tunnel barrier width at the interface between the diamond and the cathode, resulting in an enhancement of the emission current. Field emission characteristics in the higher voltage region are featured by the space charge limited current. The activation energy estimated from the Arrhenius plot of the emission current suggests the upward band bending at the diamond surface.

Synthesis of phosphorus-doped homoepitaxial diamond by microwave plasma-assisted chemical vapor deposition using triethylphosphine as the dopant

Abstract Triethylphosphine [TEP, P(C2H5)3] was used as a dopant for homoepitaxial (100) and (111) phosphorus-doped diamond films. which were formed by microwave plasma-assisted chemical vapor deposition using CH4 as the carbon source. The growth rate of TEP-doped (100) diamond increased with increasing atomic ratio of phosphorus to carbon in the gas phase, from 300 nm h−1 at 0 ppm to 800 nm h−1 at 10 000 ppm at 850 C. TEP-doped (100) diamond films deposited at temperatures below 850 C were smooth and homoepitaxial, whereas those deposited above 950 C as well as the TEP-doped (111) films formed at 750–1050 C were polycrystalline. Phosphorus was found to be uniformly incorporated into the diamond film, as evidenced by secondary ion mass spectrometry. The Hall conductivity of the TEP-doped films remained low.

Growth and characterization of phosphorus doped diamond films using trimethyl phosphite as the doping source

Phosphorus doped polycrystalline diamond films were grown by hot-filament chemical vapor deposition using trimethyl phosphite as the doping source. Phosphorus incorporation into the diamond films was established using secondary ion mass spectroscopy. Current–voltage characteristics were measured and the resistivities of the films were found to be of the order of 1012 Ω cm at room temperature. The diamond films gave indications of n-type behavior when electron beam induced current studies were performed.

Electron emission characteristics of metal/diamond field emitters

Electron emission characteristics have been investigated for polycrystalline diamond films with negative electron affinity. Phosphorus-doped diamond films are deposited on Si wafers and Cu plates by hot-filament chemical vapor deposition. An Al/diamond contact is formed on the rear side of the diamond film after removing Si substrates. A significant reduction in the applied electric field for the electron emission is achieved by forming Cu/diamond and Al/diamond contacts in comparison to that of diamond on Si. It is revealed that the electron emission characteristics are dominated by electrons injected into the diamond at the metal/diamond contact.

The synthesis and characterization of phosphorus-doped diamond films using trimethyl-phosphite as a dopping source

Producing impurity-doped diamond films is a critical task for modern electronic applications. In this study, the effects of phosphorus in the gas phase on the morphological features of polycrystalline diamond films were investigated. The diamond films were prepared on n-type Si(100) substrates by the microwave plasma chemical vapour deposition. A trimethyl-phosphite vapour was introduced to the CH 4CO 2 gas mixture as a dopant source. Surface morphology changed from well-defined facets to ball-like features by increasing the dopant concentration in the gas phase. Phosphorus-doped diamond films of good quality and well defined facets could be obtained by reducing the carbon concentration of reactant gases. This reduction could be achieved by decreasing the CH 4 flow rates during the deposition process. An increase in the the dopant source caused the growth rate to become lower, the nucleation density to reduce drastically, and the relative intensity of XRD characteristic (110) peak to increase significantly.

Characterization of doped and undoped CVD-diamond films by cathodoluminescence

Nominally undoped and boron- and phosphorus-doped CVD-grown diamond films on silicon substrates were studied by cathodoluminescence in the range from 2 eV to 5.5 eV with and without high spatial resolution. Single crystallites in polycrystalline films exhibit strong free exciton luminescence, which is mostly absent in completely closed films, with a few exceptions. The presence of nitrogen in the layers quenches the free exciton radiation. We observe new, fairly narrow luminescence lines at 5.15 eV and 4.97 eV close to the emission of the boron bound exciton. A broad band at h v = 4.4–4.6 eV recently associated with boron shows an unresolved triplet substructure. All these near-band edge peaks seem to originate from optical centers associated with boron doping.

Growth and characterization of phosphorus doped diamond films

Phosphorus-doped diamond films were grown from CH 4 and H 2 using d.c. and microwave plasmas with PH 3 as the dopant source. The P incorporation which was quantified using secondary ion mass spectrometry varies by more than two orders of magnitude for a given ratio of PH 3 to CH 4 in the gas phase. The lowest incorporation occurs in single-crystal (homoepitaxial) layers and the highest occurs in the polycrystalline films with the smallest grain size, indicating that P incorporates preferentially at grain boundaries. Conductivities of approximately 10 −10 to 10 −9 Ω −1 cm −1 were measured at room temperature for P-doped films. Significant levels of Si and B impurities are unintentionally present in these films, which may compensate any potential donor behavior of P. The homoepitaxial films were characterized by high resolution X-ray diffraction. The peak widths at half-maximum for the (004) reflection for all films are comparable with that of the bare IIa natural diamond substrates (0.050°), regardless of thickness or doping, suggesting that the crystalline quality of the epitaxial layers is as good or better than that of the substrates.

Phosphorus incorporation in plasma deposited diamond films

Phosphorus-doped polycrystalline and homoepitaxial diamond films were grown using both microwave and dc plasma assisted chemical vapor deposition. P incorporation was quantified using secondary ion mass spectrometry, and was approximately ten times greater for polycrystalline films deposited using dc plasmas compared to microwave plasmas. For microwave-assisted growth, P incorporation was approximately ten times greater in polycrystalline than homoepitaxial films. These effects appear to be due to preferential incorporation at grain boundaries, since higher levels of P are measured in samples with smaller grains. The films were highly electrically resistive, with conductivities of 10−10–10−9/Ω cm at room temperature.