We have investigated the electrical properties of ZnO∕GaN heterostructures by capacitance-voltage (C-V) measurements. ZnO∕GaN heterostructures are fabricated on Ga-polar GaN templates by plasma-assisted molecular-beam epitaxy. The ZnO∕GaN heterostructures exhibit a plateau region of 6.5V in the C-V curves measured at 10kHz and room temperature. Moreover, it is found that a large electron density is accumulated at the interface of ZnO∕GaN, where the concentration approaches ∼1018cm−3. The distinct C-V characteristics are ascribed to large conduction-band discontinuity at the ZnO∕GaN heterointerface. It is suggested that the ZnO∕GaN heterostructure is a very promising material for the application to heterojunction transistors.
An in-plane single-electron memory cell operating at 77 K has been fabricated from a Si-doped thin GaAs film. This device utilizes an artificially fabricated floating node as a storage node and detects the charge stored on the floating node using a single-electron electrometer. Charging of the floating node is evidenced by a large peak in source–drain current as a function of control gate voltage, and is further confirmed by a discrete shift in the peak or threshold voltage.
We have extensively studied electrical properties for ZnO layers grown on GaN templates by molecular-beam epitaxy. First, the Schottky characteristics of Au contacts onto ZnO:N layers have been investigated by current-voltage measurements. Barrier heights and ideality factors for Au/ZnO:N Schottky contacts are systematically varied by controlling the growth temperatures and crystal-polar directions of ZnO:N layers. Second, the capacitance-voltage (C-V) characteristics of ZnO/GaN heterostructures has been investigated. Large plateau regions are observed in C-V characteristics, which are ascribed to the confined charges caused by band offset at the ZnO/GaN heterointerface. Finally, electron-trap centers in ZnO layers have been investigated by capacitance-temperature measurements. ZnO layers exhibit two electron-trap centers ET1 and ET2, whose thermal activation energies are estimated to be 33 and 0.15 eV, respectively.
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