鍺奈米線合成與其鍺化物之電性量測

Abstract

近年來，由於追求電子元件之微型化，一維奈米結構之半導體材料逐漸受到重視，其中鍺奈米線因具有較大的載子移動率和良好的量子侷限效應，故在研究上備受矚目。 本論文利用熱蒸鍍法，藉以合成單晶成長之鍺奈米線，利用鍺奈米線覆蓋銅電極，以退火形成銅鍺化物/鍺/銅鍺化物之軸向異質結構奈米線，並對其電性量測作探討。 在合成鍺奈米線方面，由熱蒸鍍法配合氣-液-固成長機制合成鍺奈米線，在爐管下利用調控持溫溫度和腔體壓力以控制鍺奈米線的合成。由實驗結果顯示，在固定壓力6 torr和溫度為550 ℃時，鍺奈米線的成長密度和形貌較為理想。另外，針對不同晶面，以矽(111)面基板成長之鍺奈米線具有垂直於基板成長之現象。由TEM分析可發現鍺奈米線以[111]及[110]方向為優選方向成長，其中以[111]方向成長之鍺奈米線，具有較好的磊晶成長。 而在電性量測方面，以TEM對退火形成之銅鍺化物作分析，可確定其生成相為鍺化三銅，利用鍺奈米線製成場效電晶體對其作施以背相閘極作電性分析，可知鍺奈米線為一p型通道型半導體，而其電洞移動率為2.279 cm2V-1S-1。對多根不同線徑鍺奈米線作電性量測可發現奈米線線徑大小對電阻率為正向關係。最後，進行多次退火下，銅鍺化物奈米線的成長速率對溫度作分析，可知在170 ℃下，銅鍺化物奈米線成長速率約為8.5 nm/min。而利用生成之銅鍺化物奈米線作為串聯電極，在多次退火下亦可知鍺奈米線電阻率随銅鍺化物奈米線的成長而逐漸下降。 由本論文實驗結果可知，銅鍺化物/鍺/銅鍺化物軸向異質結構奈米線的形成，有助於降低蕭特基能障，使鍺奈米線與連接電極間，形成歐姆接觸。

As the miniaturization of electronic components, one-dimensional semiconductor nanomaterials, especially germanium (Ge) nanowires, have attracted great interest for their good quantum confinement effects and high carrier mobility in recently year. In this thesis, the thermal evaporation was used to synthesize single crystalline Ge nanowires via vapor-liquid-solid (VLS) mechanism under different chamber temperature and total pressure. The best growth parameters for Ge nanowires were 550 °C and 6 torr. The SEM image showed that Ge nanowires were found to grow vertically on silicon (111) substrate. From TEM analysis, the main growth direction of Ge nanowires is [111] and [110]. In addition, we successfully fabricated the Cu3Ge/Ge/Cu3Ge heterostructure by covering copper contact on both sides of Ge nanowire. According to the TEM analysis, the phase of forming copper-germanide was Cu3Ge. The electrical measurement of Ge nanowire, utilized back-gate field effect transistor (FET), reveals that Ge nanowire was p-type channel semiconductor, and the value of hole mobility was 2.279 cm2V-1S-1. Furthermore, the resistivity of Ge was proportional to the diameters. The growth rates of copper-germanide nanowires with different times of annealing were also investigated. With several times of annealing, the gradually growth of copper-germanide nanowire exhibited lower resistivity as the portion of copper-germanide increase. Finally, it was found that the Schottky barrier can be lower by forming copper-germanide/germanium/copper-germanide axial heterostructure nanowire.