Infrared-detector and FET applications and velocity modulation effect using hetero-coupling

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We consider devices that consist of two coupled quantum structures. One can vary drastically the physical properties of such devices by controlling the strength of coupling between the two either electrically or optically. This opens up a possibility for us to fabricate novel devices with unique features that could not have been realized by standard single quantum structure devices. We have therefore studied the following phenomena in order to discuss the possibility of producing FETs using the velocity modulation effect or infrared detectors.(1) We have designed and fabricated an FET that consists of double quantum wells, only one of which is doped with donors. In this device, under normal operational conditions, the electrons confined in the channel with high mobility dominate the transport property of the device. However, by adjusting the gate voltage so that the two quantum wells are in resonance, all electrons will be influenced by the impurities and the mobility will be significa … More ntly reduced. Under such a condition, we observed a negative mutual-conductance.(2) We have designed and fabricated an FET structure that consists of self-assembled InAs quantum dots buried in between channel and gate in an reverse HEMT structure of which the interface of GaAs and n-AlGaAs layrs acts as the transport channel. With this device, we observed that electrons in the channel can be trapped into the quantum dots by controlling the gate electric field, and as a result exhibit velocity modulation or function as a memory device.(3) We have fabricated an FET by growing n-AlGaAs on a vicinal GaAs (111) substrate that consists of multi-atomic steps at an interval of about 20nm. With this device we have investigated the possiblity of controlling electron scattering that occur at step interfaces.(4) In a structure that consists of two quantum wells, photo-generated electrons and holes under electric field relax into diffrent wells. By excitating electrons to the excited states with excitated states in resonance, we observed inter-band luminescence since the electrons can move back and forth between the wells. Less