利用雙加熱有機金屬化學氣相沉積系統成長低史托克位移氮化銦鎵薄膜之研究

Abstract

本論文以雙加熱有機金屬化學氣相沉積系統成長了四個系列的樣品，分別為調變基板溫度系列、調變上蓋板溫度系列、調變五三比系列以及調變三甲基銦流量系列。我們研究了各個長晶參數對史托克位移的影響，在調變基板溫度系列，隨著基板溫度由675℃降至600℃，史托克位移呈現下降的趨勢，這是因為低基板溫度降低了原子在表面的移動能力，導致銦原子不容易聚集而形成局部富銦的區域；在調變上蓋板溫度系列，上蓋板溫度900至750℃之史托克位移的變化則主要受銦組成的影響，但上蓋板溫度降至700℃時，史托克位移卻開始下降，此現象應和氨的裂解率降低有關，當上蓋板溫度為950℃時，因為高溫時原子移動能力增加或因為寄生反應導致奈米尺寸的粒子溶入，呈現較大的史托克位移；調變五三比的系列，隨著五三比降低，史托克位移跟著降低，因為高上蓋板溫度與高五三比分解出來的氫原子或是 的自由基數量也增加，其界面活化效應增加了三族原子在表面的擴散長度，增加了銦原子彼此碰觸而聚集的機會，導致銦組成更不均勻，而使史托克位移增加。最後，藉由(0002)面X-ray θ-2θ scan譜線半高寬的分析，發現低史托克位移的樣品，其發光來源為母體大範圍的組成波動，而非位能較低的富銦叢集。低史托克位移(低組成波動)為利用雙加熱有機金屬化學氣相沉積系統成長氮化銦鎵薄膜的一大優勢。

In this thesis, four series of InGaN films were grown by two-heater Metalorganic Chemical Vapor Deposition (MOCVD) system. They are varying substrate temperature series, varying ceiling temperature series, varying V/III ratio series, and varying TMIn flow rate series. We investigated the effects of growth parameters on Stokes shift of InGaN films. For varying substrate temperature series, Stokes shift decreases with reducing substrate temperature from 675 to 600℃. This is attributed to reduced surface mobility of atoms at low temperature thus prevents indium accumulation and formation of In-rich region. For varying ceiling temperature series, in the range of 900 – 750℃, solid phase indium composition is the dominant factor for the variation of Stokes shift. But when ceiling temperature is reduced to 700℃, Stokes shift starts to drop. This should be associated with low ammonia cracking efficiency. Because surface mobility of atoms were enhanced or the incorporation of nanoparticles generated by parasitic reaction at high temperature, Stokes shift for the sample with ceiling temperature of 950℃ is large apparently. For varying V/III ratio series, Stokes shift decreases with reducing V/III ratio. Because high ceiling temperature and high V/III ratio will increase hydrogen atoms or radicals generated by decomposition of ammonia, the surfactant effect of them can enhance the diffusion length of group III atoms and increase the probability for indium atoms to collide with each other. Therefore, indium will accumulate and result in inhomogeneous distribution of composition, which is responsible for increasing Stokes shift. Finally, from the analysis of FWHM for (0002) XRD θ-2θ scan spectra, we found that for InGaN films with low Stokes shift, the optical emission is from long range compositional fluctuation of matrix, not from In-rich clusters. InGaN films with low Stokes shift (small compositional fluctuation) can be achieved by using two-heater MOCVD system, and this is one of the advantages of this system.