In this paper, the thermal wave technique and microfocus Raman spectroscopy are used to measure the relative quality of thin diamond films deposited on silicon. The thermal wave technique uses a modulated heating laser beam, normal to the diamond film surface, to initiate a thermal wave which propagates into the film, the substrate, and the overlying gas(ses). The accompanying modulated gas density is then interrogated by a second (probe) laser beam. The probe beam is deflected by the corresponding periodic changes in the gradient of the refractive index of the gas. The measured probe beam deflection versus offset position is fitted, using a theoretical solution of the three-dimensional thermal diffusion equation for the gas/film/substrate system. The physically important fitting parameter is the thermal diffusivity of the diamond film. Thermal conductivities derived from our diffusivity measurements using this method compare well to previous measurements on similarly prepared films by other methods. Our measured values for the thermal conductivity of the highest-quality polycrystalline diamond films are of the order of 12 W/cm-K. Our measured values of thermal conductivity for diamond films range between this value and the thermal conductivity of graphite. We have also made measurements on bulk diamond using the thermal wave technique, and we obtain a thermal conductivity of 21 W/cm-K, in excellent agreement with values found in the literature. A multi-scan, microfocus ratio of “graphitic” material to diamond material for a relative assessment of film quality.

Diamond thin films have been synthesized at low pressures by chemical vapor deposition (CVD) and, recently, at ambient atmosphere with an oxygen-acetylene welding torch. By the application of appropriate thermal or mechanical stresses to the substrate, the diamond films can be delaminated. The delaminated films which are only a few microns thick have been fractured by manual bending. Scanning electron microscopy (SEM) examination of fractured CVD diamond films shows the presence of primarily intragranular fracture attesting to the inherent strength of the films. Using transmission electron microscopy (TEM), twinning and stacking faults are seen within the crystallites of the films along the fracture surfaces. By combining SEM and TEM examination, the relative degree of intragranular fracture found in films synthesized by both CVD and oxygen-acetylene torch has been investigated. Possible mechanisms for the intragranular fracture and the relative strength of such films are discussed.

High quality polycrystalline diamond films grown on Si substrates by microwave plasma enhanced chemical vapor deposition were characterized in a far-infrared spectroscopic study. The spectroscopic transmissivity data were used to derive a model for the complex refractive index (n – ik) as a function of wavelength in the 10 to 200 cm−1 frequency regime. Similar transmissivity and reflectivity data from samples of varying thickness were used to validate this model. The continuum of measured transmissivity and reflectivity data from 10 to 200 cm−1 were shown to be in excellent agreement with the values calculated from the refractive index model. The films were shown to have low loss in this frequency regime.

The red luminescence band which is a strong broad band that occurs in natural diamonds, showing a zero phonon line at 2.145 eV and a coupling to a nearly localized phonon of 30 meV with a Huang-Rhys factor of 10, and a constant intensity up to room temperature, is shown to present tunable stimulated emission at room temperature. The stability of the band towards strong pumping conditions is discussed. Another strong luminescent band (S3) is shown to present excited state absorption.

We describe the electrical characteristics of boron doped homoepitaxial diamond films fabricated using a plasma assisted CVD process, formation of ohmic contacts, high temperature (580°C) Schottky diodes, and a rudimentary diamond MESFET. We also report reversible changes of the conductive state of the diamond surface by various surface treatments for both natural and thin-film diamonds.

Current-voltage characteristics of type Ia synthetic diamond, type IIb natural diamond and free-standing diamond films were measured before and after hydrogenation. The diamond films were polycrystalline, deposited on sacrificial silicon substrates using a microwave chemical vapor deposition process. On hydrogenation, all the samples showed several orders of magnitude increase in conductivity. Hydrogenation was carried out under controlled conditions to study the changes in the I-V characteristics of the samples. The concentration of electrically active hydrogen was determined from the I-V data. Hydrogen passivation of deep traps in diamond is clearly demonstrated.

We have demonstrated the applicability of DLTS to semiconducting diamond thin films. This paper includes details on the capacitance-voltage measurements, the DLTS spectrum and the DLTS spectra as a function of bias. Our study was done with an aluminum Schottky contact on polycrystalline diamond film. We found a strong temperature dependence of the Schottky diode capacitance with a reduction of effective dopant concentration from 4 × 1014 cm−3 at 300K to 2 × 1014 cm−3 at 200K. The DLTS signal had a good signal to noise ratio, characteristic line-shape and clear peaks. The trap concentration was 8 × 1013 cm−3 (at 400/s rate window) with an activation energy of 0.31 eV and a capture cross section of 1.15 × 10−18 cm−2. The spectra showed a bias dependence of peak height and position.

First-principles calculations were used to study Li, Na, and P as prospective shallow donors in diamond. As expected, P prefers the substitutional site while Li and Na are interstitial donors. All three impurities were found to be shallow. However, their solubilities are very low, which makes them unsuitable for incorporation into diamond via in-diffusion. Instead, kinetic trapping during growth or ion implantation must be used. Interstitial impurities are particularly appropriate for ion implantation, since there is no need to replace host atoms. Considering the stability of the impurity at the dopant site, substitutional P is expected to diffuse by the vacancy mechanism and to have a high activation energy by analogy to self-diffusion. For Li and Na, the activation energies for interstitial channel diffusion are 0.85 and 1.6 eV, respectively. Li is thus a fast diffuser even at room temperature, while Na would remain stable up to moderate temperatures.

We have investigated the challenging problem of doping diamonds, by co-implanting boron, nitrogen or phosphorus together with carbon into natural insulating type -a1 diamonds. All the implantations were done at liquid nitrogen temperature and then the samples were rapidly heated to 1100 °C. Unlike the previous attempts to dope diamond by room temperature or high temperature ion implantations, this method is expected to yield a higher doping efficiency for the implanted atoms. We have characterized the implanted diamonds with electrical and electron spin resonance (EPR) measurements. Boron doped samples showed low electrical resistivities and the EPR signal showed a strong dependence on the boron fluence, indicating a high substitutional fraction of boron atoms. The samples in which nitrogen and phosphorus were co-implanted with carbon showed lower resistivities compared with samples implanted with carbon only. Preliminary thermo-emf measurements indicated n-type conduction in these samples.

We have employed a 32 atom cyclic-cluster and the Modified Intermediate Neglect of Differential Overlap (MINDO/3) method to compute the lattice constant, band structure, heat of formation and other properties of cubic boron nitride, diamond and silicon nitride. The computational scheme we have employed will permit studies of defects in these materials.

Polycrystalline boron-doped diamond thin films were prepared by microwave-enhanced plasma-assisted chemical vapor deposition. Ti, V, Ta, Nb, Al, Mo and W contacts were prepared by physical vapor deposition and their behavior was studied as a function of the annealing temperature, atmosphere and duration. For Ti contacts, short heat treatments (less than 60 minutes) at 500 °C under argon atmosphere were found to make ohmic contacts for applied voltages up to 50 V. Longer annealing times, more reactive atmospheres, and higher temperatures degraded the contact characteristics. In order to obtain a more complete picture of the interface structure, the capacitance-voltage characteristics and the impedance spectra of the systems were measured between 10 K and 1000 K. The interface contribution to the overall dielectric behavior of the system shows much shallower depletion widths in Ti-diamond (ohmic) contacts than with the non-linear Nb and Ta contacts. The higher values of the contact resistance and the shallower depletion width with Ti can be explained in terms of formation of a thin carbide-like region at the metalsemiconductor interface. The space-charge region width as well as the distribution of localized states in the band gap were also determined. The effect of the microstructure on the electrical properties of the systems is discussed in comparison with the behavior of metal-contacts on single-crystal diamonds.

B doped diamond films were synthesized by microwave plasma CVD and electrical contacts were fabricated by R F sputtering. Rc was obtained for Pt, Ni, TaSi2, and Al asdeposited contacts at room temperature. Pt gave the minimum Rc and Al gave the maximum Rc of the metals investigated on films containing a carrier concentration of 5 × 1018/cm3. The minimum Rc, 8.6 × 10−4 Ω cm 2, was obtained on heavily B doped diamond films with a carrier concentration of 2.7 × 1020/cm3. After nnealing at 400 °C, the Rc of Pt contacts on B doped diamond films with a resistivity of 2×104 Ω1 cm decreased by approximately one order of magnitude.

A processing technology has been developed to make ohmic contacts to naturally doped semiconducting diamond. The approach follows, as far as possible, conventional photolithographic techniques for metallization of semiconductors currently in use in the microelectronics industry.

Electric properties of the interface between metal and semiconducting CVD diamond formed by microwave plasma chemical vapour deposition (CVD) have been investigated. Much better rectifying property due to Schottky barrier has been obtained in the films formed with CO(5%)/H2 compared with CH4(0.5%)/H2. A high breakdown voltage (200 V) and a high rectification ratio (105) have been observed at the evaporated Al/diamond interfaces formed with CO(5%)/H2. In the point contact interfaces, where the metal-carbon reaction is not expected at room temperature, the rectifying and ohmic property depends on the electronegativity of metals.

Recently, there has been considerable interest in electronic device applications of diamond thin films. The chemical properties of diamond is stable. So diamond thin films become very useful if they are used for electronic devices. We consider diamond thin films as blue like emitting devices because diamond has a wide band gap(about 5.5eV). Some light emitting devices have been known [1]. First of all we have been trying to deposit diamond thin films on the large areas. If they deposit on the large areas, light emitting devices may be massproduced.

The dependence of the electrical properties on the evolving doping profile during diffusion processes was studied, as well as the role of the vacancies in determining the electrical properties of diamonds. To this aim, B was deposited on diamond single-crystal by physical vapor deposition. The element was then thermally diffused into diamond at 800°C under helium atmosphere. The deposited layer was finally removed and subsequent annealing cycles were carried out. The diffusion profiles were tracked by Nuclear Analysis Techniques. For comparison, the same element was implanted in diamonds at 70 K and at room temperature. Electrical contacts of different metals were deposited on diamond and the current-voltage and the capacity-voltage characteristics were measured. A comparative analysis of the electrical behavior of implanted and diffused samples was carried out, which elucidated the electronic activity of point defects in diamond.

Thin diamond films were grown on low resistivity p-type Si wafers by microwave plasma assisted chemical vapor deposition. Using gold contacts, diode-like behavior was observed and forward bias current densities in excess of 5 A/cm2 were obtained. Reverse bias current densities were as low as 5 mA/cm2. Photocurrent was measured when photon energies larger than the Si bandgap were used to illuminate the heterojunction. The same photocurrent spectrum was measured even when the illumination spot was moved several centimeters away from the metal-diamond contact. Photovoltage. photocurrent and hot probe measurements have been used to infer the energy band diagram of the diamond-Si p-p heterojunction.

Thin C films deposited from a CH4/Ar plasma on Si substrates kept at 20C are shown to be semiconducting. The semiconducting properties are associated with the poly-crystalline diamond grains present within the films. Diode type I-V characteristics observed from AVC/Si verticle structures are explained by the action of a C-Si heterojunction. A band gap of 2eV, a resistivity of 106Ω.cm and an electrical breakdown strength of 5.106 V/cm are estimated for the C.

Hydrogenated amorphous carbon (a-C:H) thin films have been prepared by rf glow discharge decomposition of C6H5CH3 gas at 13.6 MHz. Multi-energy boron or phosphorus implantation into these films has been performed to achieve a relatively flat impurity profile and the doping effect as a function of implanted impurity concentration has been studied. It is found that there are critical values of the implanted boron and phosphorus concentration below which there is no significant change observed in the electrical conductivity activation energy Ea, and the room temperature conductivity σRT increases only slightly with the impurity concentration. When the critics values are reached, there are first an abrupt decrease in Ea and an abrupt increase in σRT. Then Ea decreases and σRT increases gradually with further increase in impurity concentraton. The values of the critical concentrations are also found to be dependent on the substrate temperature during deposition. The critical concentrations are lower for lower deposition substrate temperatures. Preliminary results on the comparison between the doping effects by B+ and BF2 implantation show that the doping efficienty by BF2 implantation is much higher.

Diamond-like carbon films have been deposited with a low temperature 2.45 GHz electron cyclotron resonance plasma enhanced chemical vapor deposition system. The bombarding ion energy was independently controlled with a RF bias to the substrate. The production rate of reactant species and the impinging ion energy are decoupled with this system. The optical band gap decreased from 2.7 to 1.2 eV as substrate bias was increased from 0 to -140 V.