Year

1999

Degree Name

Doctor of Philosophy

Department

Department of Physics

Abstract

Far-infrared absorption spectroscopy has been performed on samples of germanium cut from single crystal ingots doped with various shallow acceptors.

The shallowest of the group III acceptors, boron, has been examined with magnetic fields applied up to 7 Tesla with B||〈100〉. The spectra were obtained using the Voigt configuration. From the spectra taken the Zeeman behaviour of the boron ground state and two of the excited states has been able to be deduced. These behaviours have been compared with the results of two theoretical predictions. This comparison shows good agreement for the excited states but not for the ground state.

The resonant states which form in the valence band of germanium when a magnetic field and acceptor impurity are both present have also been studied. At high fields transitions to these states are more intense than those to bound states. These observations have been made for two magnetic field directions; B||〈100〉 and B||〈111〉. For both these directions it has been possible to determine the symmetry of some final states by using knowledge of the ground state Zeeman splitting. In the course of these experiments, the behaviour of one of the lines of phosphorus, 2p±(1) , has also been determined for B||〈100〉. These results show a small splitting of the donor ground state, which has here been attributed to spin splitting.

The effect of uniaxial stresses on thallium acceptor states has been studied for F||〈100〉, F||〈111〉and F||〈110〉. For the first two stress directions the results obtained are in agreement with the theoretical predictions made by calculations of R. Buczko within the effective mass approximation. For the third direction of stress, the splitting of an acceptor state can be predicted from knowledge of the splittings for the other two directions. Here the predicted value is found to be in good agreement with that obtained from experiment. From measurements carried out on boron doped samples with F||〈112〉 it has been determined that for shallow acceptors in germanium the splittings for F||〈112〉and F||〈110〉 are identical.

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