低溫有機金屬氣相磊晶與砷離子佈植砷化鎵薄膜之結構、缺陷及電性研究

Abstract

本論文以有機金屬化學氣相磊晶系統，和離子佈植法將砷離子佈植入 砷化鎵基板來得到高電阻砷化鎵薄膜，並探討這些薄膜的結構與電性之間 的關係，以瞭解高電阻砷化鎵薄膜形成的機制。實驗中以冷激光探討載子 躍遷和缺陷的種類；以電阻隨溫度變化的曲線探討費米能階的位置，進而 推測可能的主要深層能階的位置；以深層能階暫態阱譜來尋找薄膜中所有 可能存在的深層能階，並且探討費米能階和深層能階之間的關係；以穿透 是電子顯微鏡觀察微細結構之變化；以蕭特基二極體研究電流與電壓的關 係，和相關的位能障；並且以 X-ray 光電子譜的測量去瞭解原子環境的 變化。 以有機金屬化學氣相磊晶法在低溫成長砷化鎵薄膜，使用三以 基鎵分別配合三級丁基砷和砷化氫作為磊晶源，在溫度 425 C 到 500 C 之間來成長高電阻砷化鎵薄膜。從實驗結果，以 TEGa 配合 TBAs 在低溫 成長之砷化鎵薄膜，分子源分解的砷和鎵原子沒有堆積到正確的晶格位置 上,使結構不完整,加上沒有足夠的動能提供給原子移動,形成區域性的砷 化鎵成核或聚結成塊,並且具有非計量平衡的缺陷. 可能是這些缺陷捉捕 自由載子,加上不正常的晶體結構,造成載子移動時的散射,使得薄膜具有 高電阻特性. 以離子佈植法將砷離子佈植入基板砷化鎵,形成過量的砷 原子存在於砷化鎵中. 試片在未退火前的結構是非晶體;經過退火後,砷化 鎵晶體再結晶,同時砷原子集結成析出物. 薄膜層內,點缺陷伴隨著巨觀上 的結構及析出物的改變,使得薄膜中原子環境改變,並且影響高電阻特性. In this dissertation, the investigations of structures, defects and electrical properties are performed in GaAs films with high resistivity grown by metalorganic chemical vapor deposition (MOCVD) at low temperatures and films implanted by arsenic ions. Measurement are imployed by photo-luminescence (PL) to observe the transitions between deep levels in films,by temperature-dependent conductance to find out the pinned position of Fermi-level, by deep level transient spectroscopy (DLTS) to identify thespecies of defects, by transmission electron microscopy (TEM) to present the micro structures, by Schottky diodes to demonstrate the current-voltagebehavior and barrier heights, and by X-ray photoelectron spectroscopy(XPS)to find the shifts of As 3d binding energies and the change of atomic environments. The GaAs films grown by MOCVD at low temperature(Tg) from 425 to 500 C are deposited with TEGa accompanied TBAs and AsH3, respectively. At such low Tg, the defifient supply of As atoms from decomposition of TBAs is found. The decomposited atoms from sources do not have enough kinetic energy to move and deposite on the exact sites. Hence a lot of point defects and disordered structures are formed in these films during growth. The explanation for high resistivity in GaAs films may be due to the trapping of carriers fromnon- stoichiometric defects and the scattering in polycrystalline GaAs boundaries. In the arsenic-ion-implanted GaAs layers, the implanting energy and thedosage are 200 keV and 10^16 cm^-2 ,respectively. The implanted SI and N+ GaAsfilms are investigated. During annealing, the precipitating of interstitial As atoms and the incorporation of As atoms to the site of Ga and As in GaAs matrix occur in the process of crystalline regrowth. Due to the formation of point defects and arsenic precipitates and regrowth of GaAs in the implanted film the atomic enviroment and electrical prperty may be influenced.