鋁奈米薄膜磊晶成長與特性分析

Abstract

本論文研究分子束磊晶技術成長結晶性鋁薄膜於砷化鎵基板上，已達成大面積、連續性且高品質結晶性鋁薄膜成長；文中對於鋁薄膜的材料特性、電性、超導特性進行量測與分析。即使在鋁晶格常數與砷化鎵晶格常數約39%的晶格不匹配情況下，依然可成長表面平整度達一個原子層的鋁薄膜；鋁薄膜主要晶向為(111)並擁有孿晶結構，在20 nm鋁薄膜中孿晶趨近1:1的高比例，其結構可能是高應變力且低溫環境下成長所促成。由於製程與量測都是在成長腔體外執行，當鋁接觸到大氣容易氧化使表面形成自我保護的氧化層，極致3 nm鋁薄膜仍有導電特性。電性量測使用四點量測的方式，電阻率值隨厚度有振盪的趨勢，推測可能是量子效應所影響；在液氦極低溫實驗中能證實鋁薄膜擁有超導的兩大物理特性:零電阻與抗磁性，並隨鋁薄膜厚度減薄，超導溫度上升，此結果與理論計算的文獻趨勢相符。本研究對於鋁的量子尺寸效應有初步瞭解，期望後續能將鋁奈米薄膜應用於元件中。

The thesis studies the growth of aluminum thin films on gallium arsenide substrate by using molecular beam epitaxy (MBE), which successfully grow large-area, continuous, and high-quality crystallinity aluminum thin films. The material characteristics, electrical properties, and superconductivity of aluminum are measured and analyzed. Even though there is about 39% of lattice mismatch between aluminum and gallium arsenide due to the different lattice constant, an aluminum film with atomic-scale surface roughness can still be grown. The main crystal orientation of aluminum is (111), and there are twinning structure in aluminum film. The ratio of twinning structure can reach to 1:1 at the 20 nm aluminum film, and twinning structure may cause by high strain and low temperature growth condition. Aluminum will be oxidized as the ex-situ processes and measurements, and it will form the self-protection oxide layer. The extremely 3 nm aluminum film is still conductive. The eletrical property are measured in four-terminal method, and the resistivity has the trend of oscillation along with the film thickness, which may be affected by quantum effect. The superconducting characterisitics of aluminum can be observed in liquid helium ultra-low temperature condition, which has exactly zero electrical resistance and expulsion of magnetic flux fields. When the thicknes of aluminum film decreases, the superconducting temperature rises, which is consistent with the theoretical model in the reference. This study has a preliminary understanding of the quantum size effect of aluminum, and it is expected that aluminum nanofilms can be used in devices.