| With the size of semiconductor devices continuously shrinking, nanowires become an important sort of material for nano-device fabrication. As a main factor that crutially affect the performance and reliability of nanodevices, the physical properties of the nanowires, as well as their structure stabilities, play an important role. Hence, investigation of the correlation between their structural evolution and physical properties is valuable for future device design. Zn2GeO4 (ZGO) and ZnSe nanowires have quite attractive physical properties, their synthesis strategy is feasible to scale up and compatible with current silicon-based fabrication techniques, so they have been widely investigated in new electronic devices, especially for those photovoltaic and ultraviolet detectors. Therefore, exploaration of the structure, composition and electrical characteristics of these nanowires have drawn reserachers’ great intrerest.However, the previous studies mostly focused on the electrical characterization of the macroscopic wires and the correlation between their structure and properties is unclear. With the development of in-situ electron-microscopy techniques, it is now able to realize their structure-dependent property evolution in real-time. In this thesis, by using the in-situ transmission electron microscopy, we study the electrical properties of ZGO nanowires and ZnSe nanowires and the effect of Joule heating and electron beam irradiation on the electrical properties of ZGO nanowires. The specific contents include:1. The structure and electrical properties of single crystal and twinning ZGO nanowires. The structure of single crystal ZGO nanowire belongs to the hexagonal system. The Ⅰ-Ⅴ curve of single crystal ZGO nanowire is a symmetrical S-shaped curve. The resistance of the single crystal ZGO nanowire, whose diameter and length are 300nm and 1.7 μm respectively, is 18.3 MΩ, together with resistivity 30.6 Ω·cm, carrier concentration 7.2 × 1014 cm-3, electron mobility 454 cm2/V · s, respectively; Twinning ZGO nanowires have grain boundaries due to different crystal orientations on both sides. The measured current of twinning ZGO nanowire is almost zero when axially contacted, possibly owing to its own grain boundaries, which may prevent the movement of the conductive carriers and thereby show high resistance characteristics. The current of twinning ZGO nanowire is slightly asymmetric S-shaped curve when radial contacted. Due to the different effective contact area that nanowire contacted with the two electrodes, when the effective contact area of reverse biased Schottky junction is larger, current is larger.2. The structure and electrical properties of ZnSe nanowires. The structure of ZnSe nanowires are sphalerite. The Ⅰ-Ⅴ curve of ZnSe nanowires is a symmetrical S-shaped curve. When a axial compressive force is applied, the structure of ZnSe nanowires will change, the Ⅰ-Ⅴ curve turns into asymmetric, the corresponding Ⅰ-Ⅴ curve will appear a turning point with the current surge and then shock in a certain range, showing the breakdown characteristics. The resistance of ZnSe nanowire, whose diameter and length are 88nm and 262 nm respectively, is 11 MΩ together with resistivity is 25.5 Ω·cm, carrier concentration is 7.7 × 1016 cm-3, electron mobility is 3.2 cm2/V · s.3. The effects of Joule heating on the electrical properties of ZGO nanowires. Continuous electrical test is applied on the same ZGO nanowire. It is found that with the number of tests increased, the current increases and the threshold voltage of Ⅰ-Ⅴ curve decreases and then tends to be stable. Electrical load induced Joule heat is mainly accumulated in the contact interface and leads to the temperature increase of the contact region. This thermal effect may release the surface adsorbates, resulting in the variation of the contact resistance of the nanowires-based devices. Therefore Joule heating will improve the contact status between the nanowires and the metal electrodes.4. The effects of electron beam irradiation on the electrical properties of ZGO nanowires. With different intensity of electron beam irradiation, electrical tests were carried out based on the same ZGO nanowires. It is found that with the increase of irradiation intensity, the current through the nanowire is increased and the threshold voltage of the Ⅰ-Ⅴ curve is decreased. It indicates that some electrons in metal electrode may be excited by the high energy electron beam, which could ease the span of schottky barrier between metal and semiconductor parts. Therefore, in order to obtain more accurate measurement results, the influence of electron beam irradiation in the process of in-situ TEM electrical tests should be taken into account. |
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