| Summary: | 碩士 === 國立交通大學 === 電子物理系所 === 95 === The annealing effect of a nitrogen-induced state on the electron emission in InAs self-assembled quantum dots (QDs) has been investigated by high resolution transmission electron microscope (HRTEM), photoluminescence (PL), current-voltage (I-V), capacitance-voltage (C-V), admittance spectroscopy, and deep level transient spectroscopy (DLTS). As grown and four different annealing temperature and time samples are studied. Without N incorporation, electron emission from the QD to the GaAs conduction band occurs by tunneling through the first excited state with 0.058 eV, corresponding to the energy spacing between the QD electron ground and the first-excited states. With N incorporation, a deep defect trap in the QD is induced and we can investigate the effect of the electronic band structure of the QD on the electron emission with this trap. For as grown sample, the electron-emission properties in the QD region is governed by two emissions: a strong and broad emission E1 with 0.38 eV and a weak emission E2 with 0.15 eV, corresponding to the energy spacing between defect level and GaAs conduction band, the quantum dots ground state and GaAs conduction band edge, respectively. We find that annealing can weaken E1(defect) emission, enhance E2(quantum) emission, and significantly reduce the electron emission time and energy. A continuous reduction of electron-emission energy in quantum dots is observed from as grown to annealing 5 minutes at 800oC. This change of emission time and energy is explained by tunneling through the QD state. The N-induced traps in the GaAs bottom layer can induce additional carrier depletion and suppress tunneling emission rates. Annealing can remove the traps there and recovers the electrons in the QD. Increasing annealing temperature enhances the tunneling emission, leading to the continuous reduction of emission time and energy. Thus, by placing a defect state in the QD, annealing can be used to modify its electron-emission time by controlling the tunneling rate.
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