| 摘要: | 在本論文中，我們主要研究原生（as-grown）P 型氮化鎵薄膜， 經由離子佈植方式摻雜矽原子後，對其電性的改變。藉由高劑量的摻 雜，接著在氮氣、氧氣、空氣不同環境下活化，成功的使所有的P 型 氮化鎵薄膜活化成n 型（使得在原生P 型氮化鎵薄膜形成一層n 型氮 化鎵），而經由1000℃ 30 分鐘的高溫熱處理後，原生P 型和n 型氮 化鎵薄膜皆活化成n＋型，載子濃度值約5.5×1019㎝-3（面載子濃度值 約3×1015 ㎝-2），活化率約27﹪。矽離子佈植的條件為40KeV/2E15 ㎝- 2 , 100KeV/5E15 ㎝- 2 , 200KeV/5E15 ㎝- 2。藉由多次的矽離子佈 植，調整不同的能量與劑量，在氮化鎵薄膜內形成一均勻的摻雜區 域。降低離子佈植劑量為40KeV/8E14 ㎝ -2,100KeV/2E15 ㎝ -2, 200KeV/2E15 ㎝-2重複上述實驗，經由1100℃ 60 分鐘氮氣環境下活 化，發現n 型氮化鎵薄膜載子濃度值由8×1016 ㎝-3 變成4×1019 ㎝-3 （面載子濃度值約2.5×1015 ㎝-2），活化率提高至53﹪。 在歐姆電極方面，我們以電子束蒸鍍 鈦/鋁/鉑/金作為離子佈植 試片之n 型歐姆接觸。將矽離子佈植試片以1000℃ 30 分鐘活化後， 其特徵接觸電阻值（specific contact resistance ñc）為5×10-4 Ω -㎝ 2，經過600℃氮氣環境下熱處理後特徵接觸電阻值降低到1×10-6 Ω-㎝ 2。而相同的矽離子試片以1000℃ 15 分鐘及30 分鐘活化後鍍 上透明電極（ITO），其特徵接觸電阻值ñc 分別為2×10-4 Ω-㎝ 2 及8 ×10-5 Ω-㎝ 2。而極薄的金屬層 鎳/金（Ni/Au＝40Å/100Å）作為P 型氮化鎵薄膜之歐姆接觸以改善藍光二極體的透光性。 利用氦-鎘雷射量測光激螢光譜，發現所有活化後的n 型氮化鎵薄 膜都不發光。我們推測應是高劑量（1.2×1016 ㎝- 2）摻雜造成氮化鎵 薄膜表面及結構的破壞。 最後，經由簡單的黃光製程，我們成功的 作出藍色發光二極體，藉由p-n 接面之電流電壓特性曲線來驗證前述 的霍爾系統量測的結果。在40mA 的電流驅動下其發光波長及半高寬 分別為415nm 及80nm。在80mA 的電流驅動下其發光波長及半高寬分 別為385nm 及80nm。在20mA 的電流驅動下具有約34V 之順向偏壓 (Vf)。在-10ìA 的電流驅動下具有約-19V 逆向偏壓(Vr) In this thesis, we focus our efforts on the Silicon ion implantation in GaN, activation of Mg-doped GaN, Hall measurement and fabrication of GaN n＋-p junction. In addition, the device processing technologies were also paid attention to investigate the low resistance ohmic contacts of GaN. The current-voltage (I-V) characteristics were measured at room temperature using an HP4145B semiconductor parameter analyzer. The characteristics of multiple high dose Si implanted GaN were studied. 28Si+ implantation into Mg-doped and unintentionally doped GaN, followed by thermal annealing in N2, air, Oxygen ambiences has been performed to achieve n+-GaN layers. We have successfully convert all p-GaN to n type for annealing temperature from 750℃~1000℃. Multiple implantations are used to form a uniform Si implanted region. The implantation conditions (dose/energy) were 2´1015 cm-2/40 KeV, 5´1015 cm-2/100 KeV and 5´1015 cm-2/200 KeV. The carrier concentration of the film changed from 3×1017 cm-3 ( p-type ) to 5×1019 cm-3 ( n-type, Sheet carrier concentration ns ＝3×1015 cm-2 ) when the Si-implanted p-type GaN was annealed in N2 ambience at 1000℃. The activation efficiency of Si in Mg-doped GaN is 27%. Decrease the implantation dose to 8´1014 cm-2/40 KeV, 2´1015 cm-2/100 KeV and 2´1015 cm-2/200 KeV, the carrier concentration of the film changed from 8×1016 cm-3 ( n-type ) to 4.2× 1019 cm-3 ( n-type, Sheet carrier concentration ns＝2.5×1015 cm-2 ) when the Si-implanted un-doped n-type GaN was annealed in N2 ambience at 1100℃. The activation efficiency of Si in un-doped GaN is as high as 53 ﹪. In addition, specific contact resistance( rc ) of Ti/Al/Pt/Au ohmic contacts to n＋-GaN, which formed by 28Si+ implantation in p-type GaN, were also evaluated by transmission line model( TLM ). The rc is as low as 1.5×10-6 W-cm2 when the metal contact was annealed in N2 ambience at 600℃. The specific contact resistance ( rc )of Indium tin Oxide（ITO） as-deposited on n＋-GaN which formed by 28Si+ implantation in p-type GaN and annealing 1000℃ 15min and 30min were 2×10-4 Ù-㎝ 2 and 8 ×10-5 Ù-㎝ 2 . The as-grown material and these implanted samples were also characterized by photoluminescence (PL) using a 10mW He-Cd Laser (325nm) excitation source with the spectra taken at room temperature. The PL spectra showed that no emission peaks of these implanted samples, this may be attributed that surface damages and amorphized structure of GaN by high dose (1.2E16 cm-2) 28Si+ implantation. The activation of metal organic chemical vapor deposition-grown Mg-doped GaN by N2 annealing has been investigated. P type conductivity with a net acceptor concentration of 1×1018 cm-3 and a mobility of 4 ㎝2/VS was obtained by annealing 750℃. Variable temperature Hall measurement have revealed that activation energy of Mg-acceptor was 109meV after 750℃ anneal. Finally , the n＋-p LED by 28Si+ implantation are fabricated and characterized at room temperature(RT). The room temperature (RT) current-voltage characteristic exhibits that a turn on voltage measured at 100ìA was equal to 1.5V; the forward voltage measured at 20mA was equal to 34V. The breakdown voltage measured at -10ìA was equal to -19V. The room temperature (RT) electroluminescence (EL) is dominated by an emission at 415nm(2.98eV) with a linewidth of 80nm(600meV) at injection current of 10~50mA. When the injection current increases up to 60mA~80mA, the emission is dominated by the peak at 385nm(3.22eV). The EL intensity linearly increases with increasing injection current. As mentioned above of n＋-p junction, this supports the Hall effect data for convert the p-GaN to n type conduction. |
