P型氮化鎵之歐姆接觸研究

Abstract

在本篇論文中，我們研究了兩種P型氮化鎵之歐姆接觸：鎳/金以及鎳/金/氧化銦錫。兩者在適當的溫度下進行快速熱退火後皆可達到歐姆接觸的特性。在快速熱退火後，鎳傾向於擴散出表面與氧反應形成氧化鎳。金傾向於擴散進入金屬-半導體介面和鎵反應形成金-鎵合金。反應後在氮化鎵表面產生鎵空缺，這些鎵空缺在氮化鎵內有著受體的作用。當氮化鎵表面出現大量鎵空缺，P型氮化鎵表面形成p+結構使空乏區寬度縮減及蕭基能障降低。載子可藉由穿隧效應傳輸而得到P型氮化鎵歐姆接觸。 在鎳/金/氧化銦錫系統中，氧化銦錫中銦原子可能會與金反應形成合金，降低接觸的功函數。此外在濺鍍過程中，濺擊出來帶有高能量的氧化銦錫分子也有可能會破壞已蒸鍍上之鎳/金薄膜。這些因素皆會破壞接觸的品質，使鎳/金/氧化銦錫之特徵接觸阻抗較鎳/金來的高。不過鎳/金/氧化銦錫有著較好的穿透率以及較佳的電流擴散效果，在製作發光二極體時仍然是較佳的選擇。

We have discussed two kinds of the p-GaN ohmic contacts: Ni/Au and Ni/Au/ITO ohmic contacts. After thermal annealing at proper temperature, both contacts show ohmic characteristics. Ni diffuses out of the interface and reacts with O2 forming NiO after RTA. Au diffuses into GaN matrix and forms Au-Ga solid solution which helps the generation of Ga vacancies. The Ga vacancies act as acceptors in p-type GaN. With a large amount of Ga vacancies the surface p-type GaN becomes p+-GaN which results in the depletion region narrowing and SBH reduction. Ohmic contact on p-type GaN is then obtained. In Ni/Au/ITO system, In atoms in ITO may form alloy with Au and leading to the reduction of the contact work function since the work function of In is low. During ITO sputtering, the ITO atoms with high energy could damage the thin Ni/Au film which is already deposited on the GaN. Thus the Ni/Au/ITO shows poorer specific contact resistivity as compared with Ni/Au. But with much better transmittance and good conductivity for current spreading, Ni/Au/ITO is still a candidate of p-type GaN for LED fabrication.