Diamond Detectors for Ionizing Radiation - HEPHY

CHAPTER 3. MATERIAL PROPERTIES 13
direction, reaching a diameter in the order of 100 m with a diamond lm thickness of
500 m. The section of a CVD grown diamond, visualizing this \cone"-like structure is
shown schematically in g. 3.3 and as a SEM (scanning electron microscopy) photograph
in g. 3.4.
Growth Side
y=D
Substrate Side
y=0
Figure 3.3: Schematic section of a diamond lm.
Figure 3.4: Photograph of the section of a diamond lm.
The dierent grain sizes of substrate and growth sides are clearly visible with the SEM
photographs in g. 3.5. The grain size expands from approximately 2 m at the substrate
side (y =0)toabout 80 m atthe growth side (y = 415 m).
The CVD diamond samples used by the RD42 collaboration have been grown by
the commercial manufacturers St. Gobain/Norton [11] and De Beers [12]. Most of the
samples were grown on 4" wafers in a research reactor and then laser cut into 1 1cm 2
pieces. Recently, several 2 4cm 2 samples were delivered from a production reactor. The
as-grown thickness of the CVD samples ranges from 300 m upto almost 3 mm.
For the detector application, the diamond lm is equipped with contacts on either
side. First a chromium layer of typically 50 nm is sputtered onto the sample, which forms
a carbide with the diamond, providing an Ohmic contact. Then, a gold layer (typically