為了改善氮化鎵成長過程所產生的缺陷，係利用不同基板結構，作為磊晶成長的基板。首先，為了成長高效能之氮化鎵光偵測器，先利用顯影與電漿離子矽蝕刻吃出圖案化藍寶石基板，其寬度與間距皆為3 微米；深度為150 奈米，再利用有機金屬化學氣相沉積法成長元件主動層。針對圖案化藍寶石基板與傳統藍寶石基板之元件效能之比較，前者，除了暗電流與光響應有大幅改善外，其對稱面之半高寬亦優於傳統基板。再透過蕭基位障計算，可計算出圖案化藍寶石基板之理想因子和蕭基位障為1.53、0.79電子伏特，其因缺陷密度改善，位障高於傳統基板所成長之元件！經由計算，傳統基板所成長的元件，其蕭基位障，僅0.69電子伏特。更深入地利用閃爍雜訊測量，分析元件晶格品質，計算兩元件之低頻雜訊等數據。於2伏特下，雜訊等效功率與標準化偵測能力各為9.08×10-11 W、1.74×1010 cmHz0.5W-1，亦優於傳統基板所製造的光偵測元件利用圖案化藍寶石基板成長的元件，其光電特性數據皆優於傳統元件的表現，亦可證明其晶格缺陷遠小於傳統式成長方式。
除了圖案化藍寶石基板技術外，我們亦利用自我對準技術與電漿離子矽蝕刻吃出奈米等級之奈米棒，奈米棒的平均直徑為350奈米，密度為3×108 cm-2。最後，經由有機金屬化學氣相沉積法成長光偵測元件。透過X光繞射分析儀器，其非對稱角（缺陷方向）的半高寬為422角秒，優於傳統基板的525角秒。其暗電流與光拒次比，兩者相比，暗電流改善3個級數，光拒次增為350倍。於2伏特下，雜訊等效功率與標準化偵測能力各為7.00×10-10 W、2.26×109 cmHz0.5W-1，優於傳統基板所製造的光偵測（3.56×10-6 W、4.44×105 cmHz0.5W-1）。
最後，我們更提出一種新而便利的方式，改善光偵測器的光電效益。係利用鎳金屬催化製程，先擷取我們於P型氮化鎵所得到的最佳化數據，係利用10奈米厚度的鎳金屬層，搭配不同的回火溫度、時間，增強元件表面的蕭基位障，可有效地抑制暗電流，且氧化鎳的高透光性，不影響元件本身的光響應特性。利用最佳化的鎳催化條件，元件本身的蕭基位障、理想因子從0.698電子伏特，增強至1.008電子伏特；理想因子從1.822減至1.263。暗電流與光響應亦皆有改善，而光拒次比則由104增強至12149。於2伏特下，雜訊等效功率與標準化偵測能力各為1.74×10-11 W、9.07×1010 cmHz0.5W-1，優於未經過鎳金屬催化的元件之光偵測能力（9.95×10-8 W、1.57×107 cmHz0.5W-1）。

The fabrication of GaN-based Schottky barrier PDs on patterned sapphire substrate (PSS) was investigated. The stripe width and spacing of PSS template were both 3 μm. The depth of the groove was controlled at 150 nm by ICP etching. A high quality GaN Schottky barrier PD was prepared on PSS by metalorganic chemical vapor deposition (MOCVD). Comparing with the PD prepared on conventional flat sapphire substrate (FSS), it was found that we can reduce dark current and enhance responsivity. Furthermore, it was found that full-width-half-maxima (FWHMs) measured the samples prepared on from FSS and PSS were 255 and 186 arcsec, respectively. The significantly smaller FWHM observed from the sample prepared on PSS again be attributed to the smaller TD density. We also determine Schottky barrier height (ΦBE) and ideality factor (n) from the forward I-V characteristics, it was found that ΦBE and n for the PD prepared on FSS were 0.69eV and 1.82, respectively, while ΦBE and n for the PD prepared on PSS were 0.79eV and 1.53, respectively. The larger turn-on voltage, the larger ΦBE and smaller n observed from the PD prepared on PSS should again be attributed to the reduced TD density. Under -2 V applied bias, it was found that noise equivalent power (NEP) and normalized detectivity (D*) were 9.08×10-11 W and 1.74×1010 cmHz0.5W-1, respectively, for the PD prepared on PSS. These values were also better than those achieved from the PD prepared on flat sapphire substrate.
Besides PSS approach, we report the preparation of nanorod (NRs) templates with a simplified NRELOG method and the fabrication of GaN Schottky barrier PDs on the nanorod template. In this thesis, GaN nanorods were vertically aligned with an average diameter of 350 nm. It was also found that density of the GaN nanorods was around 3×108 cm-2. Comparing with conventional substrate, it was found that FWHMs measured from NR_PD and PD were 422 and 525 arcsec, respectively. In dark current and rejection contrast, the significant three orders of magnitude and 350 times are reduction in reverse leakage current and responsivity observed from NR_PD, respectively. With -2 V applied bias, it was found that noise equivalent power (NEP) and normalized detectivity (D*) were 7.00×10-10 W and 2.26×109 cmHz0.5W-1, respectively, for the PD prepared on nanorods template. With the same -2 V bias, it was found that NEP and D* were 3.56×10-6 W and 4.44×105 cmHz0.5W-1, respectively, for the PD prepared on a conventional sapphire substrate.
Finally, we reveal a new method to improve the performance of PDs that use Ni treatment. In first stage, we deposited Ni catalytic films with different thicknesses onto the as-grown Mg-doped GaN epitaxial layers and subsequently annealed the samples by conventional furnace annealing. It was found that surface of the Ni catalytic films became rough with numerous island structures after thermal treatment. With a 10 nm-thick Ni film, it was found that we achieved a hole concentration of 4.35×1017 cm−3 with a 400 ℃ annealing. Without the Ni catalytic film, we could achieve p-type conduction only when the annealing temperature was equal to or larger than 600 ℃. SIMS results show that H concentration was reduced and a certain amount of Ni atoms seem to penetrate into the GaN epitaxial layers after annealing. Furthermore, it was found that we could only achieve p-GaN with high hole concentration at the sample surface by using the Ni catalytic films.
On the contrary, we first try to use this methodology to improve GaN-based PD performance. It was found that ΦBE and n for the PD prepared on Ni treatment sample were 1.008 eV and 1.263, respectively, while ΦBE and n for the PD prepared on as-grown sample were 0.698 eV and 1.822, respectively, at 600 ℃, O2 ambient. It was found that we can reduce dark current and enhance responsivity, too. The rejection contrast is raised from 104 (without Ni treatment) to 12149 (with Ni treatment at 600 ℃). It can be seen clearly that NEP increased while D* decreased monotonically with the increase of applied reverse bias. With -2 V applied bias, it was found that NEP for the PDs prepared without and with Ni treatment were 9.95×10-8 and 1.74×10-11 W, respectively. At the same applied bias, it was found that D* for PDs prepared without and with Ni treatment were 1.57×107 and 9.07×1010 cmHz0.5W-1, respectively. The smaller NEP and higher D* observed from the PD prepared with Ni treatment indicate we can also improve noise characteristics of GaN-based UV PDs by using Ni treatment methodology.

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