- 學位論文
Al2O3/Y2O3/GaAs 異質磊晶結構之介面特性研究
Interfacial Investigation of Al2O3/Y2O3/GaAs Hetrostructures
摘要
在超高真空下，利用分子束磊晶及電子束蒸鍍的技術，高品質奈米氧化釔薄膜以及作為保護層的氧化鋁可成功成長於砷化鎵基材上。 本研究利用Ｘ光電子能譜分析技術(XPS)可詳盡地分析氧化釔薄膜與砷化鎵介面的化學反應。利用此分析技術配合電性比較，可知若氧化釔沒有保護層，由於其吸水性，暴露在空氣中後,會與水氣反應形成氫氧化釔，而在薄膜與基材介面形成氧化砷以及氧化鎵造成費米能階釘扎(Fermi-level pinning)。而若先成長約三奈米厚的氧化鋁作為氧化釔保護層，即使試片在去離子水中浸洗十分鐘後也未發現在薄膜中有氫氧化物形成，表示水氣無法進入到薄膜中進而破壞氧化釔與基材介面，也保證了氧化釔成長在砷化鎵上可得到良好的電性。 然而，室溫成長非晶氧化釔與高溫成長結晶氧化釔表現出大不相同的電性。高溫(約550 °C)成長的氧化釔電性較佳。假設氧化鋁之介電常數為8，結晶氧化釔之介電常數約8.6-11.1，而非晶氧化釔之介電常數則僅3.7-4.6。故我們懷疑因為成長溫度的不同造成氧化釔與砷化鎵之間化學反應相異,並影響二者電性。在本研究中，溫度效應造成氧化釔薄膜與砷化鎵的化學反應變化將藉由Ｘ光電子能譜分析技術探討，期望能找出造成電性差異的原因。
並列摘要
Freshly grown GaAs epi-layers were passivated with in situ electron beam evaporated nano-thick Y2O3 films in ultrahigh vacuum condition, followed by in situ deposition of a Al2O3 capped layer. The formation of hydroxides in the films and arsenic oxide at Y2O3/GaAs interface after exposed to air will be reported. In the Al2O3/Y2O3/GaAs hetero-structure, neither hydroxides, nor arsenic oxides, were found in the sample; even it was exposed to air and dipped in DI water for 10 min. Moreover, the hetero-structure exhibits well-behaved inversion and accumulation characteristics in capacitance-voltage curves. However, Y2O3 in amorphous and crystalline phase deposited on GaAs at room and elevated temperatures capped with Al2O3 exhibit significant different electrical properties. Let the dielectric constant of Al2O3 be assumed about 8, then the dielectric constants of a-Y2O3 (1.8 nm) and c-Y2O3 (2.5 nm) are estimated to about 3.7-4.6 and 8.6-11.1, respectively. It is suggested that the different growth temperature results in different chemical reactions of Y2O3 with GaAs, thus affecting the electrical properties. XPS will be used to study the chemical reactions of Y2O3 on GaAs at different temperature.