p 型氮化鎵金屬接觸之電性研究

Abstract

本文中，p型氮化鎵金屬接觸之研究分為二方面：一為利用低功函數之金屬來進行蕭特基接觸之研究；二為利用高功函數的金屬以研究其歐姆接觸之特性。 蕭特基接觸方面，採用了三種低功函數的金屬Ag、Al、及Ti來製作p-型氮化鎵之蕭特基二極體，其功函數分別為4.26、 4.28、及 4.33 eV，並利用室溫Ｉ-Ｖ，變溫Ｉ-Ｖ，及Ｃ-Ｖ量測以進行其蕭特基接觸之電性研究。在室溫Ｉ-Ｖ量測方面，在載子穿隧效應的影響下，所有試片均顯現出遠大於1值的理想因子。而在所有的樣品中，Al之蕭特基接觸具有較大的蕭特基能障；在變溫Ｉ-Ｖ方面，由於受到載子被接觸介面散射及載子穿隧能障的效應下，導致量測之Richardson常數遠低於理想值；在Ｃ-Ｖ量測方面，猜測因接觸金屬表面的氧化導致量測到大於理想值的蕭特基能障。 歐姆接觸之特性研究方面，利用Circular Transfer Length Method (CTLM)研究Pd/Au、Pd/AuZn、及Ti/Pd/Au之接觸電阻，對Pd/Au歐姆接觸方面，在450℃，5分鐘的退火條件下可獲得最小接觸電阻 ；對Pd/AuZn方面，在不經退火處理下即可有最小值 ；對Ti/Pd/Au方面，經450℃，5分鐘的退火處理後有最小接觸電阻 。

Ag, Al, and Ti have the small work function of 4.26, 4.28, and 4.33 eV, respectively. In this study, these three metals are adopted to make Schottky contacts to p-type GaN. The I-V characteristics of Schottky contacts all display large ideality factor due to the tunneling effect. The Al contact shows the larger Schottky Barrier Height (SBH) than the value of the Ag contact. The Ti contact displays the smallest SBH. The I-V-T behaviors exhibited small effective Richardson coefficients owing to the transmission of carriers negotiating the barrier and the scattering of carrier between the interface of metal-semiconductor. The C-V characteristics exhibit the unusually large SBHs due to the surface oxidized metal. Pd/Au, Pd/AuZn, and Ti/Pd/Au contacts are chosen to make Ohmic contacts to p-GaN owing to the large work function. The Ohmic characteristics are investigated using the Circular Transfer Length Method (CTLM). For Pd/Au Ohmic contacts, the lowest specific contact resistance of Ω cm 2 is observed under the annealing condition of 450℃ and 5 min. For the Pd/AuZn contact, the lowest of Ω cm 2 is observed without any thermal annealing treatment. For Ti/Pd/Au contact, the lowest value of Ω cm 2 is observed under the annealing condition of 450℃ and 5 min. However, the value is the largest one among the three contacts.