獨立式氮化鎵氮極性面蕭特基二極體表面處理後之特性探討

Abstract

本實驗主要針對「在氮極性面獨立式氮化鎵基板所製作垂直式蕭特基二極體做不同的表面處理，並探討其造成的影響」。氮極性面 n-type 獨立式氮化鎵基板是由 HVPE磊晶，接著背部 laser lift off 剝離，最後再由 CMP 拋光所產生。第一種表面處理方式是對鍍完蕭特基接觸的氮極性面進行變溫氮氣快速熱退火後處理。實驗結果顯示，適當溫度的氮氣退火可以提升蕭特基能障、降低理想因子以及逆偏下漏電流。我們嘗試以退火過程中會產生鎳氮化合物解釋以上現象。第二種表面處理方式是在鍍蕭特基接觸前先鍍一層鎳薄膜並進行變溫氧氣快速熱退火前處理。此時發現隨著氧氣退火溫度提高，蕭特基能障會提高，逆偏下漏電流最多降低五個數量級。推論是氧氣退火過程中形成金屬氧化物並導致鎵空洞產生，提升表面能帶彎曲，進而使蕭特基能障提高。

This study focus on the influence of surface treatments for the vertical GaN Schottky diodes by the N face freestanding GaN substrates. The Ga face unintentional n-doping epitaxial GaN layers was grown by Hydride Vapor Phase Epitaxy (HVPE) process, then followed by GaN substrate back side laser lift off (LLO) and chemical mechanical polishing (CMP) to get the N face freestanding GaN substrates. We investigate how to improve the electrical properties on the N face vertical GaN Schottky diodes by two different kinds of surface treatments. One of the methods was applied the post-annealing treatment under N2 ambient on Schottky contact and the other was deposited a thin Ni film and applied pre-annealing under O2 ambient before forming the Schottky contact. According to the electrical characterizations of experiments, both of surface treatments can successfully improve the Schottky barrier height, ideality factor and leakage current. For the first method, the improvement on electrical properties was attributed to Ni4N compounds formation during post N2 annealing process. For the second method, the great improvement could come from certain elements diffusion and forming some acceptor-like Ga vacancies near the metal-semiconductor interface during pre-annealing process, which improved the Schottky barrier height because of the increment in the surface band bending