Diamond Detectors for Ionizing Radiation - HEPHY

CHAPTER 3. MATERIAL PROPERTIES 12
oxygen gas. When the gas mixture is ionized, carbon based radicals are reduced and
settle on a substrate, usually silicon or molybdenum, and link together with -type bonds,
forming a diamond lattice. Successful diamond deposition is restricted to a well dened
area within the C-H-O ternary diagram shown in g. 3.2. Outside this area, either nondiamond
carbon or nothing at all is grown.
Figure 3.2: The C-H-O ternary diagram. CVD Diamond growth is restricted to the white area
in the center [7].
The properties of the diamond grown in this process depend on the gas mixture,
temperature and pressure. Although this is an easy principle, the growth process is
extremely dicult to control in order to grow material suitable for detector application;
the parameters are not constant throughout the process. The growth speed is typically
about 1 mh ,1 . There are several types of CVD reactors, which dier in the way the gas
is ionized; e.g., this is done by microwaves or by a heating wire. After the growth process,
the substrate is etched from the diamond lm, which is then cut and cleaned.
Initially, there is a large number of small crystal seeds on the substrate, each oriented
individually. As deposition continues, the grains grow together, forming columnar singlecrystals
with grain boundaries between. On the substrate side the lateral grain size is very
small (in the order of micrometers), while the size continuously increases in the growth