Microwave-pumped GaAs far infrared photoconductor
This proposal introduces an innovative concept which significantly enhances the performance of a far-infrared GaAs photoconductor. This method employs a microwave source, in the range of 90 to 120 GHz, to assist the photoionization process by pumping the infrared-generated electrons from the excited states to the continuum. Since the microwave photons are low in energy, they are not available to directly ionize the ground state of the shallow donors. Therefore, the microwave pumping process is not expected to generate additional leakage current and the associated noise. This will allow us to cool the detector as low as necessary to reduce the thermal leakage current and improve the detector's noise performance. The proposed concept is not limited to GaAs and may be applied in a broader scope. Since the excited state response of a photoconductor lies at lower frequencies (longer wavelengths), an important use of this method would be to extend the detector's long-wavelength response. For a photoconductor, such as Ge:Ga, whose excited state response is non-existent at its optimum operating temperature due to insufficient thermal energy, microwave pumping can provide the additional energy and essentially extend its long-wavelength response.
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