Diamond film electrical properties

A.H. Deutchman and R.J. Partyka (Beam Alloy Corporation observe, "Characterization and classification of thin diamond films depend both on advanced surface-analysis techniques capable of analyzing elemental composition and microstructure (morphology and crystallinity), and on measurement of macroscopic mechanical, electrical, optical and thermal properties. Because diamond films are very thin (I to 2 micrometers or less) and grain and crystal sizes are very small, scanning electron microscopy... 

Deguchi, M., Kitabatake, M. and Hirao, T. (1996), Electrical properties of boron-doped diamond films prepared by microwave plasma chemical vapour deposition. Thin Solid Films,... 

Amorphous carbons, carbon black, soot, charcoals, and so on, are forms of graphite or fullerenes. The physical properties depend on the nature and magnitude of the surface area. They show electrical conductivity, have high chemical reactivity due to oxygenated groups on the surface, and readily intercalate other molecules (see later). Graphite and amorphous carbons as supports for Pd, Pt, and other metals are widely used in catalysis and for the preparation of diamond films.18... 

The electrical properties of single crystal diamond will be useful to study those of heteroepitaxial diamond films. As a reference. Figures 13.1 (a)-(c) show the resistivity, mobility, and carrier density of single crystal diamond as a function of temperature [107]. Figures 13.2 (a) and (b) are the resistivity and mobility as a function of the carrier density. A more thorough study on B-doped homoepitaxial diamond is presented in Ref. [416], where AFM observation of the layer surface. Hall measurements at different temperatures, and other data are presented. 

Activation and conductivity at room temperature are problems that can be addressed by the incorporation of other electronic structures that increase carrier transport. Crystal morphology is an important parameter in the boron doping process to determine uncompensated acceptors (Aa-Ad) for different crystal facets as a function of doping concentration. The temperature coefficient of resistance for a CVD diamond film can be changed by boron doping. As conductivity depends on the crystal phase, the combined electromechanical properties can be exploited in sensor applications both for resistive temperature detectors and for pressure transdu-cers. " As electrical conductivity is related linearly with boron concentration, a better-controlled process may allow for the development of better semiconductor devices improving crystal quality and operating limits. ... 

Highly boron-doped diamond films, which have been widely studied in electrochemistry, can be grown by chemical vapor deposition (CVD) and are electrically conductive. Different electrochemical properties of boron-doped diamond films have been studied, such as reactivity [133] and electronic structure [134]. Different characterization techniques have been used to study the electrochemistry of diamond, such as scanning electron microscopy [123, 135] and Raman spectroscopy [125,136]. 

The electrical properties of the diamond films or free-standing discs are largely determined by the boron-doping level. Resistivities of useful diamond OTEs are in the range of 0.5-0.05 H-cm. Boron-doping levels associated with this resistivity are ca. 1-10 x 10 B/cm, as determined by boron nuclear reaction analysis measurements. Very preliminary Hall effect measurements for the diamond/quartz (Fig. 23A, 2) and diamond/ Si (Fig. 23B, 7) OTEs have revealed carrier concentrations between 10 and 10 cm and carrier mobilities (holes are the majority carrier in boron-doped films) of 1-100 cm /V-s. 

In contrast to the sp /sp ratio determining the electrical properties, the microstructure of the carbon film plays a vital role in its electrical properties. An anisotropy in resistivity is found with magnetron-sputtered carbon, which shows a diamond and a graphitic phase below and above a deposition temperature of 100°C. These phenomena are considered to be due to peculiarities of the film microstructure [67]. 

We note here the relationships between the particular crystal faces of diamond and the characteristics of the crystal growth. It has been reported that contaminants can be incorporated into the growing (ill) face to a greater extent than into the (100) face during CVD diamond crystal growth [29]. This explains why, first, the dopant (e.g., boron) tends to be incorporated into the (lOO) face at lower concentrations compared to the (ill) face. For example, when the relative boron concentration in the carbon source feedstock is 10,000 ppm (atomic ratio, i.e., 1 at%), which would correspond to lO i cm if incorporated into the diamond crystal, the actual boron concentrations in the (lOO) and (ill) homoepitaxial BDD thin films were found to be ca. 10 cm and 10 cm, respectively [6]. These values correspond to materials that would exhibit electrical properties somewhere between... 

In addition to silicon and metals, a third important element being deposited as thin films is diamond (Celii and Butler, 1991 May, 2000). For many years, diamonds were synthesized by a high pressure/high temperature technique that produced bulk diamonds. More recently, the interest in diamonds has expanded to thin films. Diamond has a slew of properties that make it a desired material in thin-film form hardness, thermal conductivity, optical transparency, chemical resistance, electrical insulation, and susceptibility to doping. Thin film diamond is prepared using chemical vapor deposition, and we examine the process in some detail as a prototypical chemical vapor example. Despite its importance and the intensity of research focused on diamond chemical vapor deposition, there remains uncertainty about the exact mechanism. 

Another amorphous phase of carbonitride, C N phase with sp bonding, was shown to be a stable phase which exhibits high electrical resistivity and thermal conductivity similar to that of diamond-like films. The diamond-like properties and non-diamond-like bonding make C N an attractive candidate for applications such as thermal management in high-performance microelectronics. 

---