獨立式氮化鎵基板之研發

Abstract

本論文利用氫化物氣相磊晶系統成長氮化鎵厚膜，並配合雷射剝離系統將厚膜分離以製作獨立式氮化鎵基板。有鑒於異質磊晶產生高缺陷濃度使得元件的特性及壽命有很大的影響，故加入成長面控制側向成長法調變溫度、壓力與反應氣體五三比以控制氮化鎵成長面的形成進而有效降低缺陷濃度，經由原子力顯微鏡觀察蝕刻點密度，缺陷濃度降低至5.2*10^7cm-2。另外在成長厚膜的部份，由於應力的因素使得厚膜尺寸與厚度的關係成反比，如何成長出大尺寸與厚度符合基板需求的厚度為本論文的重點。最後，本實驗結果已可以穩定製作1.5英吋與厚度250μm以上的高晶格品質獨立式氮化鎵基板。

In the present study, hydride vapor phase epitaxy (HVPE) technology is used to grow thick GaN films on sapphire substrates. To reduce the high defect densities induced by large lattice mismatch during the heteroepitaxial growth, facet-controlled epitaxial lateral overgrowth (ELOG) technique is adopted. By adjusting the temperature, the gas pressure, and the gas phase V/III ratio during the growth, directional growth of GaN can be obtained. Defect propagations and hence defect densities can then be effectively reduced. Etching pit densities (EPDs) measured by atomic force microscopy (AFM) on the thick HVPE GaN films thus prepared show typical defect densities in the 10^17 cm-2 range. Due to the strain, the thickest GaN films achievable, without breaking, is inversely proportional to the diameters of the films. In the present study, by using laser lift-off technique, free-standing GaN films with the thickness above 250μm and 1.5 inch diameter can be routinely separated from the sapphire substrates.