Radical assisted metalorganic chemical vapor deposition of CdTe on GaAs and carrier transport mechanism in CdTe/n-GaAs heterojunction

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Abstract
The growth and carrier transport mechanism in CdTe on the GaAs substrate is reported. Epitaxial layers of CdTe were grown on n- and semi-insulating GaAs substrates by the hydrogen radical assisted metalorganic chemical vapor deposition technique at a low pressure. Dimethylcadmium and diethyltelluride were used as the source materials. The growth was carried out in the substrate temperature range of 150-300°C. The grown films have high resistivity in the order of 107Ωcm for the entire growth range. Applicability of this heteroepitaxial CdTe layer on n-GaAs as an x-ray detector was then investigated. The carrier transport mechanism of the CdTe/n-GaAs heterojunction was studied by means of current-voltage measurements at different temperatures. The forward current was characterized by multitunneling capture-emission current and space charge limited current. The reverse current was considered as the generation current from the heterojunction interface states through the analysis of capacitance-voltage measurement. It is found that for devices using minority carriers, this heterojunction alone is not useful because of the high concentration of interface states. A suitable modification, like an isotype heterojunction between GaAs and CdTe before forming the p-n junction, seems to be necessary

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