本論文主題是蕭特基接觸與在未摻雜A面氮化鎵上的光檢測器特性之研究，採用的試片為利用MOCVD在R面藍寶石(sapphire)基板上成長A面氮化鎵薄膜，藉由不同的金屬功函數如鉑、鎳、鉻、鈦，製作在未摻雜的氮化鎵上，形成蕭特基能障。於A面氮化鎵上由鉑、鎳、鉻、鈦所形成的蕭特基能障高度分別為0.88eV、0.81eV、0.69eV、0.68eV且得到半導體電子負性值:S為0.156。發現蕭特基接觸於A面氮化鎵和在C面氮化鎵上相比較有較大的費米釘札效應。當鉑、鎳、鉻和鈦四種不同金屬蒸鍍在A面未摻雜的氮化鎵，注入偏壓為-4V時，漏電流分別為 8.36x10-7A、1.71x10-6A、4.18x10-5A、7.171x10-5A.。漏電流會隨著偏壓大幅度的增加主要是由於高密度的缺陷造成例如: 缺陷和線差排會由A面氮化鎵成長在R面氮化鋁基板產生。高密度缺陷的存在同時也產生載子的漏電路徑和費米釘札效應。
為了有效降低漏電流，選擇在鎳和A面氮化鎵中間以低溫成長的氮化鎵或絕緣體(SiO2)當覆蓋層，以鎳-金為金屬薄膜於A面氮化鎵製作成蕭特基光檢測器。當注入偏壓為-4V時，若採用30nm低溫成長的氮化鎵為覆蓋層，漏電流將會減少到2.79x10-7A，但選擇10nm的絕緣體(SiO2)當覆蓋層時，漏電流會進一步減少到2.90x10-10A。以絕緣層(SiO2)為覆蓋層於A面氮化鎵上的蕭特基二極體在光響應鑑別度(355nm/400nm)上比用低溫成長的氮化鎵當覆蓋層部分遠大於一個數量級以上。實驗結果顯示，選擇在鎳和A面氮化鎵中間以SiO2當覆蓋層製成的金屬-絕緣-半導體(MIS)光檢測器能有效的抑制電流，以及提升光性和電性。
此外，由於A面氮化鎵受到非等向性的應力，造成不同方向的極化光會有吸收程上的不同。所以當改變整個元件的應力時，發現也會影響極化光吸收的靈敏度。

The study of the subject was characteristics of Schottky contact and Schottky photodetector of A-plane undoped GaN. We adopt the sample which was deposited A-plane GaN film on R-plane Al2O3 substrate. Different metal contacts including Pt, Cr, Ni and Ti were evaporated on undoped-GaN layer to serve as Schottky barrier. The Schottky barrier heights of the Pt, Cr, Ni, and Ti on undoped A-plane GaN were 0.88eV, 0.81eV, 0.69eV, and 0.68eV, respectively. And the S parameter of the A-plane GaN Schottky contact was 0.156. We found that the Schottky contact of A-plane GaN had a strong surface pining effect compared with Schottky contact of C-plane GaN. The leakage current at -4V of the Pt, Cr, Ni, and Ti on undoped A-plane GaN were 8.36x10-7A, 1.71x10-6A, 4.18x10-5A, and 7.171x10-5A, respectively. The significant leakage current might be from the high density defects such as pits, threading dislocations, of the A-plane GaN on R-plane Al2O3. The existence of the high density defects could cause the leakage path of the carriers and the Fermi-level pinning effect at the metal/semiconductor interface, revealing a weak dependence of Schottky barrier height.
In order to reduce the leakage current effectively for the application of the photodetectors, we selected the LT-GaN or SiO2 to serve as inserting layer in between Ni and A-plane GaN interface. The reverse leakage current at -4V of Au/Ni/A-plane GaN Schottky diode was reduced to 2.79x10-7A by introducing the 30nm-thick LT-GaN inserting layer and could be further suppressed to 2.90x10-10A by using the 10nm-thick SiO2 inserting layer. However, the rejection ratio (355nm/400nm) of the Au/Ni/SiO2/A-palne GaN Schottky photodiode is about one more order better than the Au/Ni/LT-GaN/A-plane GaN Schottky photodiode.The experimental results displayed the SiO2 inserting layer in between the Ni and A-plane GaN interface could effectively reduce the leakage current and elevate the optical property.
Because the A-plane GaN was suffered by anisotropic strain, it had the optical polarization anisotropy characteristics of light absorption. We find the modification of anisotropic strain can also effect the polarization sensitive.

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