利用電漿輔助化學氣相沉積法於低溫下成長氮化鎵奈米線

Low Temperature Growth of GaN Nanowires by Plasma-Enhanced Chemical Vapor Deposition

本文主要以電漿輔助化學氣相沉積法藉由氣－－液－－固成長機制（vapor-liquid-solid mechanism, VLS） 成長氮化鎵 （gallium nitride, GaN） 奈米線。此實驗系統以氮電漿作為氮化鎵成長所需的氮源，氮電漿反應性比熱化學氣相沉積法所使用的氨氣高且氮電漿解離率與溫度間的關聯性不大，故能在低成長溫度下得到高品質氮化鎵奈米線。在本研究中，氮化鎵奈米線的成長溫度範圍由900°C 到550°C，以穿透式電子顯微鏡 （transmission electronmicroscopy, TEM）、光激發螢光光譜 （photoluminescence, PL） 及X 光繞射儀（X-ray diffraction, XRD） 對製備出的氮化鎵奈米線進行分析。相較於熱化學氣相沉積法需要接近1000°C 的高溫來成長高品質晶體，利用電漿輔助系統可在900°C 下成長出高品質的氮化鎵奈米線，當成長溫度下降到700°C 時，經由TEM 與PL 的分析，證實在這個系統中仍可維持奈米線的晶體品質，但當成長溫度降到550°C 時，由於成長氣氛轉為N-rich 及低的表面溫度，造成鎵原子在基板及奈米線表面的擴散能力大幅下降，奈米線內部及表面因而產生許多缺陷，使奈米線外型彎曲且晶體品質下降。

In this work, a novel plasma-assisted chemical vapor depositionmethod was developed to fabricate GaN nanowires by the Vapor-Liquid Solid Mechanism. Nitrogen plasma was used as a nitrogen source togrow GaN crystals. Compared to NH3 used in thermal CVD systems,nitrogen plasma is more active and its ability to produce active nitrogenradicals is insensitive to temperature, making it more suitable for lowtemperature growth of GaN crystals. The growth temperature of GaNnanowires varied from 900 to 550°C followed by transmission electronmicroscopy (TEM), photoluminescence (PL) and X-ray diffraction analysisto investigate the effect of growth temperature on the crystal structure andquality. High quality GaN nanowires were grown at 900°C, which waslower than the normal growth temperature of 1000°C in thermal CVD.According to TEM and PL analysis, the crystal quality was still high, evenafter lowering the growth temperature to 700°C. When the growthtemperature was further reduced to 550°C, defects formed in the bulk andon the surface of nanowires due to the slow surface diffusion of Gaadatoms on the sidewall of nanowires resulting from the N-rich growthenvironment and low surface temperature.