Photoconductivity storage in Ga1−xAlxAs alloys at low temperatures |
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Authors: | Ashok K Saxena |
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Affiliation: | Department of Electronics and Electrical Engineering, Mappin St. S1 3JD, University of Sheffield, England |
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Abstract: | Intentionally undoped n-type and high purity Ga1?xAlxAs alloys with compositions in the range 0.19≤x≤0.78 are found to show a long life time photoconductivity effect at low temperatures (T < 80 K) when irradiated with white light filtered through a Ge filter and also when the light source is removed after photoexcitation. For the direct gap materials (0≤x≤ 0.43), it is shown that the deep level in the alloys, which controls the electrical properties of the crystals, captures and emits electrons via the first higher energy subsidiary conduction band inima L although the Γ minimum is the lowest in energy. These indirect electron transitions by the deep level, via the L minima, which is found to have an acceptor like nature, provide a natural explanation of the photoconductivity storage at low temperatures. For indirect gap materials (x > 0.43), when X minima are the lowest energy subsidiary minima, the photoconductivity storage at low temperatures is due to the double acceptor nature of the deep level. |
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