利用氮化矽插入層成長低差排密度氮化鎵磊晶層及物理特性之研究

Abstract

本論文中，我們使用有機金屬化學氣相沉積(MOCVD)系統成長氮化鎵(GaN)薄膜，並藉由調整氮化矽插入層成長時矽甲烷的流量來控制氮化矽的覆蓋面積以及氮化矽上方氮化鎵的成長模式。接著進行掃描電子顯微鏡、X光繞射以及光激螢光等量測。 由掃描電子顯微鏡的結果可以推測出氮化矽的覆蓋面積會影響到其上方成長氮化鎵的島狀物密度。隨著矽甲烷濃度增加，氮化鎵磊晶層由三維成長轉換成二維成長所需的厚度增加，使得80nmol/min氮化鎵表面尚未完全聚結。而從X光繞射的結果可以計算出薄膜中的差排密度，隨著矽甲烷的濃度增加，a-type差排密度也持續下降(由 8×108 cm-2 降低至 2×108 cm-2)，直到薄膜表面無法聚結時再度開始增加。此差排下降的機制為差排在三維成長時會彎折，使得原本垂直傳遞、不會相遇的差排能夠互相接近而消除，但是當薄膜無法聚結時此機制受到限制，因此密度再度上升。最後由光激螢光的結果可以證明隨著差排密度下降，發光的強度也會增加，當a-type差排由8×108 cm-2 降低至 2×108 cm-2時，發光強度增加了四倍。

In this thesis, we use Metalorganic Chemical Vapor Deposition (MOCVD) reactor to growth GaN epilayer. We insert SiN layer before main eplayer, and by varying SiH4 flow rate, we can control SiN coverage condition and the growth mode of GaN on top of it. We then perform Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Photoluminescence (PL) experiments. From SEM result, we know that the SiN coverage condition will affect GaN island density on top of SiN, which led to uncoalescence surface when flow rate as high as 80nmol/min. We calculate dislocation density from XRD result, and a-type dislocation density decrease with increasing SiH4 flow rate until the film can’t coalescence (From 8×108 cm-2 to 2×108 cm-2), then it increase again. The reason is dislocation bending during 3D growth, it increase the probability of dislocation reaction and annihilation, but when the film fail to coalescence, this mechanism is hindered, so the dislocation density rise again. In the end, the PL result shows up to 4x intensity increase by reducing dislocation density from 8×108 cm-2 to 2×108 cm-2.