- 學位論文
鎂摻雜之p型氮化鎵的活化與鈍化技術在p-i-n元件上之特性分析
Activation and Passivation of Mg-doped GaN - Application in p-i-n Diodes
摘要
在本次實驗中，我們將活化技術與鈍化技術分別使用在氮化鎵材料之元件上。 我們使用快速熱退火(Rapid thermal annealing)與雷射退火的方式來活化p型摻雜之氮化鎵磊晶層，並且顯著地降低此層與金屬間的接觸電阻。霍爾量測中顯示，快速熱退火或是雷射退火的方式，普遍能幫助p型氮化鎵(鎂摻雜)的電洞濃度從1017/cm3上升至2 × 1017/cm3，另外，使用雷射退火搭配鎳金屬膜的磊晶片，能使接觸電阻由10-2 Ωcm2 降至1.6×10-4 Ωcm2，最後，我們將此組實驗的方式引用到元件上做驗證。在順向偏壓時，發現有使用與沒使用雷射退火技術的元件在導通電壓值(Turn on voltage)上比較，會出現接近7.5%的減少，此值是在電流密度為100 A/cm2的情況下所量得，因此，又再一次地驗證此方法是可行的。 另一方面，我們使用CHF3電漿來抑制p-i-n功率元件側壁上的漏電流，實驗結果顯示，在逆向偏壓時，崩潰電壓有接近20%的提升，另外，元件之微分電阻在比較片與電漿處理過後的片子上可以得到分別為0.5 mΩ-cm2和0.48 mΩ-cm2，最後，我們在CHF3電漿處理過後的元件上得到非常高的Baliga品質因子為827 MW/cm2，這可以說是目前成長在藍寶石上的氮化鎵材料之p-i-n功率元件裡，最好的一個實驗結果。
並列摘要
In this work appropriate activation and passivation techniques have been introduced to p-GaN and applied to improve the electric characteristics of GaN p-i-n diodes. In order to better activate the p-GaN to further reduce the contact resistance, the rapid thermal annealing (RTA) and laser annealing system are studied. It is shown that RTA or laser annealing of Mg-doped GaN (about 0.5 um in thickness) in general helps activate acceptors and increase the average hole concentration by a factor of about 2 from low to mid of 1017/cm3 determined by the Hall measurement. Use of laser annealing of p-GaN coated with Ni and removal afterwards prior to depositing conventional Ni/Au ohmic-contact films, however, greatly improves the contact resistance from 10-2 to 1.6×10-4 Ωcm2. As a result, the forward voltage of p-i-n diodes can be as low as 3.7 V with a current density at 100 A/cm2 which is a 7.5 % reduction compared with control sample. The trifluoromethane-containing plasma is used to passivate the mesa surfaces and suppress the surface current leakage of GaN p-i-n rectifiers. Reduction of surface leakage enhances the reverse blocking voltage by 20% (from 509 to 630 V) measured at J＝1 A/cm2. Differential forward resistances of control samples and plasma-treated ones are 0.5 mΩ-cm2 and 0.48 mΩ-cm2, respectively, and an excellent Baliga’s Figure-of-merit of 827 MW/cm2 is achieved for GaN diodes fabricated on sapphire substrates.