蕭基二極體特性之理論研究

Abstract

在本論文中, 我們分析金屬引入能隙能態以及負缺陷在形成蕭基能障時所 扮演的角色. 從我們的分析發現金屬引入能隙能態和負缺陷不僅能擾動電 場穿入金屬的強度, 並且能建構一額外的界面電雙極使得蕭基能障的高度 產生改變. 由於界面電雙極的結構在某一功函數附近急劇地變化, 蕭基能 障與金屬功函數間的關係不是線性而應是分段線性.接著, 我們分析在金 屬-砷化鎵接觸所發現的費米能階栓住的現象 . 經由我們的分析發現空洞 是造成金屬-砷化鎵接觸內費米能階栓住的主因. 所以, 砷化鎵的不當量 特性將決定栓住費米能階的位置.除了蕭基能障的形成, 我們亦分析順向 偏壓下的蕭基二極體之電容 -電壓特性. 藉著考慮能障變化引入界面態電 荷的變化, 我們發展出一新的界面態電容模型. In this thesis, we study the roles of the metal-induced gap states(MIGS) and the native defects in the Schottky-barrier formation. From our analyses, the presence of MIGS and native defects at metal-semiconductor interface not only perturb the strength of the field penetration into metal but also build up extra interface dipoles to change the Schottky barrier height. Since the structure of the interface dipole change abruptly at a critical value of metal work function, the corrrelation between Schottky barrier height and metal work function is not linear but rather piece-wisely linear. Furthermore, the well- known Fermi-level-pinning phenomenon in metal-GaAs contacts is also analyzed. We found that vacancy in GaAs is the dominant mechanism for Fermi-level-pinning in metal-GaAs contacts. Therefore, the type of nonstoichiometry in GaAs will determine the pinning position of the Fermi level. Besides the Schottky- barrier formation, the capacitance- voltage characteristics of forward-biased Schottky diodes is analyzed. By considering the barrier-height-variation-induced feedback effect on the modulation of interface state charge, a new model for the interface state capacitance is developed.