ICMCTF2001 Session D3-1: Electrical, Optical and Thermal Characterization and Applications of Carbon and Related Materials

Field emission display (FED) is evolving as a promising technique of flat panel displays in the future. Many factors affect the performance of field emitter arrays including the shape and work function of emission materials, distance between tip and gate, and the environmental vacuum condition. There is an increasing interest in the studies on field emission of diamond films. This is because diamond surfaces terminated with hydrogen atoms have negative affinity (NEA) in addition to superior properties such as chemical inertness and mechanical hardness. Therefore, this material is considered as highly promising applications in electron field emission devices.

In this work, we present a novel scheme that involves a new fabrication process of gate structure metal-insulator-semiconductor (MIS) diode using IC technology. Using a bias assisted microwave plasma chemical vapor deposition (BAMPCVD) system synthesized P-doped completes this process. Deposition of the diamond emitters in this MIS diode forms a dendrite-like diamond in gated field emission arrays (FEAs).

Moreover we compare the gate structure and P-doping concentrations for the influence of emission properties. It is demonstrated that turn-on voltage of electron emission decreases with increasing concentrations for P-doped diamond emitters. Next, the gate aperture diameter could significantly influence the electron field emission characteristics. We have successfully fabricated 4µm-pattern and 1µm-pattern device to enhance emission current density for a given voltage. The detail of result will be presented at conference.

Amorphous carbon film is one of promising materials for the cold emitter of the field emission display (FED). It is need to deposit the amorphous carbon film on metal electrodes, which are formed on glass substrate, at low temperature to fabricate the FED. In this study, we have deposited the amorphous carbon films on the various metal electrodes below the temperature of 100 °C without sample cooling by the deposition of low growth pressure (5x10^-3 torr). Moreover, we have studied the field emission from the amorphous carbon films on the metal electrodes.

The amorphous carbon films were deposited on the Al, Au and Ti electrodes from mixture gas of CH4 and H2 by using the RF plasma CVD equipment. Both gas flow rates of the CH₄ and the H₂ were 5 sccm. The RF power and the growth pressure were kept at 100 W and 5x10^-3 torr, respectively. The negative bias of -30 V was applied to the substrate during the film deposition. The amorphous carbon films with the thickness of 100 nm were deposited by the deposition of 2 hours.

The amorphous carbon film, deposited on the Al electrode, did not exhibit the electron emission up to applied electric field of 20 V/µmm. On the other hand, the amorphous carbon films, deposited on the Au and the Ti electrodes, emitted the electrons by applying the electric field. The threshold electric field for the amorphous carbon film, deposited on the Au electrode, was 5 V/µmm, which was lower than that of Ti electrode. The emission current densities at the electric field of 20 V/µmm were 7x10^-4 and 6x10^-6 A/cm^-2 for the Au and the Ti electrodes, respectively. Moreover, the stability of the field emission for the Au electrode was more stable than that of the Ti electrode. These results indicate that the high efficiency cold emitter is formed by using the Au electrode as the back contact.

The transparency of diamond to a wide range of electromagnetic spectrum makes it an ideal material for fabricating IR windows and optical coatings. The polycrystalline diamond films however contain grain boundaries and defects not present in single crystal stones. The impurities and defects in CVD diamond can induce significant amount of absorption that renders these less perfect diamond useless as IR windows. A detailed study of the influence of nitrogen, hydrogen on optical and thermal properties is there for essential for commercializing its novel properties. Studies of isotopic effect in the properties of diamond films are also equally important.

Diamond sheets were grown by hot filament chemical vapour deposition technique. Methane (CH₄) and Hydrogen (H₂) were used as precursor gases. ¹³CH4 were used to study the isotopic effect. Sheets were characterized using scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The mid-infrared spectral region contains detailed information on molecular vibrations and hence the chemical structures present in the polycrystalline film. Using Fourier Transform Infrared (FTIR) spectroscopy we have studied the one phonon infrared absorption bands for the nitrogen related peaks. Nitrogen also added in a controlled manner to the gas mixture inorder to ascertain the origin of C-N bands. The spectra show several features that have not been reported earlier. The shifts in C-N bands were noticed in one phonon region with the addition of ¹³C. The effect of isotope on thermal conductivity has also been studied. Quantitative calculation of hydrogen in the sheets using elastic recoil detection analysis and FTIR spectroscopy shows that the total hydrogen concentration in the sheets is nearly one order of magnitude higher than the bonded hydrogen. A correlation has been made with thermal and optical properties and the impurities in the sheets.

For practical applications in optics and electronics, large area single crystal (synthesized) diamond thin films on Si or other suitable substrates are very desirable. However due to the lattice mismatch and random nucleation, usually only polycrystalline diamond films were deposited on Si substrates in the past. These polycrystalline diamond films are formed by inter growth of disjointed diamond crystallites and usually have very rough surfaces. Depending on the deposition conditions, the morphology of these diamond films can be altered.

We have grown (100) oriented diamond films using temperature gradient across the Si(100) substrates by hot filament chemical vapour deposition method. Si substrates were treated with 2µm diamond powder. The temperature gradient was developed across the substrates by heating the sample at one end. The heating was done using a thin film heater on the backside of the sample. Deposition was carried out with 0.8% CH₄ in balance hydrogen at average substrate temperature 890°C with varying deposition pressure from 60-140 Torr. Films were characrized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). XRD shows very strong (400) reflection in all the samples. SEM results shows smooth diamond surface comprised of (100) platelets. Because the (100) diamond plates were grown on top of the silicon substrate which is (100) oriented, their faces were more or less aligned parallel with the substrate surface resulting in a relatively smoother diamond surfaces. FTIR studies were carried out in order to determine the impurities present in it. Quantitative analysis was done for the calculation of hydrogen present in the sample. Comparative studies were done between the samples grown by temperature gradient method and steady temperature method.