Cyclotron resonance has been measured in GaAs and related compounds through the use of a new experimental technique developed for the study of very pure semiconductors called optically detected cyclotron resonance (ODCR). ODCR differs from other forms of magnetospectroscopy in that the intensity of luminescence excited by a visible laser is monitored rather than the direct absorption of far-infrared radiation. The ODCR technique is initially used on an exceptionally pure sample of GaAs and resolves impurity transitions and central cell effects. An accurate measure of the electron effective mass including band nonparabolicity is made. The ODCR signal represents an interaction between the donor bound electron states and the donor bound exciton states. Standard cyclotron resonance measurements on high mobility GaAs/Ga<sub>1</sub>-<sub>x</sub>Al<sub>x</sub>As heterojunctions are performed with tilted magnetic fields. Resonant coupling between the Landau levels and electric subbands gives rise to a splitting of the cyclotron resonance lineshape which can be used to determine the subband energy spacings. This allows for a direct determination of the shape of the confinement potential which changes dramatically under different illumination conditions. A dilution refrigerator is modified in order to measure the cyclotron resonance (CR) to 100 mK of the low density, two dimensional electron system in a heterojunction. Anomalies in the CR spectrum are explained in terms of an interacting electron system composed of carriers in the two spin states of the lowest Landau level. Experimental results are presented in terms of a recent theory offered for cyclotron resonance. A series of undoped GaAs quantum wells is studied with ODCR. The conduction band mass was measured for different well widths. An offset is observed in the cyclotron resonance energy which is strongly dependent on the well width. ODCR is measured on In<sub>0.05</sub>Ga<sub>0.95</sub>As/GaAs superlattices using both the Faraday and Voigt magnetic field orientations. Cyclotron resonance in the Voigt geometry reveals a band structure in the growth direction. The impurity transition in the Voigt configuration shifts dramatically, moving from the bulk 1s-2p + to close to the bulk free electron field.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:240610 |
| Date | January 1994 |
| Creators | Michels, Joseph Gerard |
| Contributors | Nicholas, R. J. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:20ffc752-d7e7-4631-803a-bfeb9b12dfc6 |
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