Semi-insulating, powder samples of Cadmium Telluride (CdTe) have been
studied using ������In Time Differential Perturbed Angular Correlation (PAC)
Spectroscopy. The samples have been lightly doped (~10���� cm�����) with ������In atoms,
which occupy well-defined metal (Cd) lattice sites and act as probes of the local
environment. These substitutional donors form a single defect complex in CdTe.
This complex has been identified and characterized as a function of temperature.
Those indium probes that are not complexed occupy metal lattice sites with no
defect in the local vicinity.
Samples containing metal vacancy concentrations as large as 500 ppm have
been prepared by a high temperature anneal and quench. The defect complex
involves the trapping of a cadmium metal vacancy bound to the indium probe. The
electric field gradient (EFG) experienced by probe atoms has a coupling constant of
V[subscript Q]=61.5(5) MHz and is not axially symmetric, with the asymmetry parameter
given by ��=0.16(4). It is believed that this asymmetry results from a relaxation of
the chalcogen (Te) atoms adjacent to the metal vacancy, with the tellurium atom
shared by the probe atom and the vacancy providing the dominant contribution.
The fraction of complexed probe atoms increases as the sample
temperature is decreased, and is still increasing at room temperature. Complexed
fractions are reproducible on cycling within the temperature range 40 to 200��C.
The binding energy of the complex has been measured to be 0.15(2) eV and is
independent of metal vacancy concentration, which varies and is dependent on the
details of the quench.
In rapidly cooled samples, a non-equilibrium number of these defect
complexes is observed. This state equilibrates with a time constant of 45(5) hours
at 15��C, implying that at least one of the two constituents involved in the complex
has a significant diffusion rate at this temperature. Under the assumption that
vacancy diffusion mechanisms dominate at this temperature, it is found that the
cadmium vacancies overcome an energy barrier of 0.9(1) eV with a jump time of
20(2) minutes in CdTe at 15��C. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32627 |
| Date | 16 April 2002 |
| Creators | Griffith, John W. |
| Contributors | Gardner, John A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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