| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 88 === Modulation-doped photodetector (MODPD) grown on GaAs substrate by molecular beam epitaxy (MBE) has been shown to exhibit an excellent responsitivity in the sub-bandgap range (0.9-1.3 m). The device is basically a conventional modulation doped field effect transistor (MODFET) structure with its channel region made of low-temperature (LT) MBE-grown GaAs. In this work, we report the performances of three MODPDs with different channel materials of LT GaAs, LT InGaAs, and Si-doped LT GaAs. The effect of width and separation of the interdigitated electrodes on the performance of MODPD is also presented.
The I-V characteristics of all the MODPDs show the typical FET-like behavior with output current modulated by the power of the incident light. The MODPD with Si-doped LT GaAs as the channel layer is found to have the maximum gain. The large amount of photo-excited electrons originated from the Si dopants is attributed to be responsible for the high gain in the device. Analytical approaches based on the conventional MODFET have been developed to describe the measured I-V characteristics of the MODPDs. For the detectors under the same illuminated area, the device with narrower width and separation has larger gain. The enhanced response is due to the increment of electrodes.
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