Abstract
A range of di®erent high-quality single crystal diamonds synthesized under high
pressure and high temperature (HPHT) conditions have been studied in view of their
potential as candidates for specialized electronic devices with emphasis on particle
detectors. The studies incorporated a long range of spectroscopic and electronic
characterization techniques.
Special attention was given to electronic properties and device performance re-
lated to the electrical contacts applied, the type and the concentration of impur-
ities and the crystallographic defects present. The electronic response of a dia-
mond detector as far as impurities are concerned is predominantly determined
by the single substitutional nitrogen (SSN) and boron acceptors. Di®erent tech-
niques were used to assess the role of such impurities in the diamond crystals stud-
ied, as well as to study the dynamics due to the interaction of such impurities
with each other (compensation). Hence, the electron spin resonance (ESR) and the
current-deep level transient spectroscopy (I-DLTS) techniques were used in this re-
spect to extract the information concerning activation energies, nitrogen-boron dy-
namics, and the nitrogen and boron concentrations.
ii
iii
It was found that the SSN content was below 1013 cm¡3 with this result giving the
approximate concentration of boron acceptors, being the same value as of that of
the SSN, or slightly above. Maximum activation energies of boron acceptors were
extracted from three di®erent regions in the bulk of the diamond. The values were
approximately 0.311 eV § 0.0027 eV in the center region, 0.308 eV § 0.007 eV in
the intermediate region and 0.29 eV § 0.007 eV at the edge region, respectively.
The maximum activation energy when boron is fully compensated is about 0.37 eV.
Properties of ohmic and Schottky contacts as a function of concentration of SSN and
boron acceptors were investigated using Current-Voltage characteristic and photo-
current measurements. Di®erent surface treatment conditions and di®erent types of
diamonds (IIa, IIb and Ib) were used.
Electronic properties as a function of contacts were assessed for high purity synthetic
type IIa diamond detector, incorporating a time of °ight (TOF) UV laser set-up.
The maximum hole collection distance at room temperature was found to be 91.00
cm, the maximum transient time for holes was about 1.00 ms and the e±ciency was
approximately 41%, with contacts made of Ti/Pt/Au-Ru. When Ru-Ru contacts
are applied, the maximum hole mobility and the velocity were extracted at room
temperature to be about 17963.44 cm2V¡1s¡1 and 5.02 £107 cms¡1, respectively,
and the e±ciency of the device is about 30%. The maximum applied external
electric ¯elds with Ru-Ru contacts were increased to about 1.32 times that at low
temperature and to about 1.84 times that at room temperature.
iv
Large signals generated by ®-particles from 228Th were obtained without using amp-
li¯cation. However, a full analysis of the pulse was not possible due to the narrow
bandwidth of the electronic probes used.
In a detector made of type Ib diamond, with SSN concentrations of about 50 ppm,
it was found that regions in the bulk exhibiting better charge collection properties
contained small concentrations of uncompensated boron impurity. On the other
hand, the di®erence in the concentrations of SSN between the two type Ib diamonds,
with about 50 ppm and about 200 ppm of SSN concentrations, respectively, resulted
in approximately 70 ps di®erence in the transit time between two detectors made of
these diamonds.
Keywords:
Synthetic diamond, detector, HPHT, type Ib, type IIa, single substitutional ni-
trogen, SSN, ESR, ARP, I-DLTS, metallization, uncompensated boron impurity,
crystallographic defects, rise and decay times, charge carrier life time, charge carrier
mobility, carrier mean free path , charge collection distance, carrier Schubweg.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/4962 |
| Date | 19 June 2008 |
| Creators | Costa, A.M.O.D. da |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 4406364 bytes, application/pdf, application/pdf |
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