利用有機化學氣相沉積法成長高品質砷化銦鎵在砷化鎵基板上以及材料成長機制研究和其在 金氧半電容器之應用

Abstract

本博士論文主要研究以金屬有機化學氣相沉積系統(Metalorganic chemical vapor deposition)磊晶成長砷化銦鎵(In0.5Ga0.5As)於砷化鎵(GaAs)基板上於金氧半電容(MOSCAP)元件之應用。首先，將研究磊晶成長條件與偏角度砷化鎵基板對砷化銦鎵(In0.3Ga0.7As)表面形貌與磊晶品質之影響。本論文使用漸變緩衝層(step graded buffer layer)技術成長砷化銦鎵(In0.3Ga0.7As)磊晶層於不同角度(001)砷化鎵基板上，並於研究過程中觀察到當磊晶溫度為490度時，砷化銦鎵(In0.3Ga0.7As)磊晶層表面形貌最為平坦(平均粗糙度:1.5nm)；經由穿透式電子顯微鏡(TEM)結果顯示使用此磊晶條件所成長砷化銦鎵(In0.3Ga0.7As)層之線缺陷密度(threading dislocation density)約為1x106 cm-2；此外，螢光光譜於300K與77K下之分析結果亦顯示出砷化銦鎵(In0.3Ga0.7As)磊晶層中再結合中心(recombination center)含量很少。以上結果可知本研究已成功使用漸變緩衝層技術將砷化銦鎵(In0.3Ga0.7As)磊晶層成長於砷化鎵基板上。 本研究亦嘗試將砷化銦鎵化合物中銦含量提升至50%，並成功成長砷化銦鎵(In0.5Ga0.5As)磊晶層於砷化鎵基板上。由穿透式電子顯微鏡(TEM)之剖面圖可清楚觀察到砷化鎵與砷化銦鎵(In0.5Ga0.5As)磊晶層間缺陷可被漸變緩衝層有效的侷限住，而不會延伸至砷化銦鎵(In0.5Ga0.5As)磊晶層，導致砷化銦鎵(In0.5Ga0.5As)磊晶層之缺陷密度可降低至1x106 cm-2，此結果亦顯示因晶格不匹配所導致的應力可藉由漸變緩衝層有效的被釋放(relaxed)。同時，藉由時間解析光激螢光(time-resolved photoluminescence)分析結果證明砷化銦鎵(In0.5Ga0.5As)磊晶層中再結合中心含量被有效減少，說明此磊晶成長技術可有效釋放因晶格不匹配所造成之應力之外，亦可提高砷化銦鎵(In0.5Ga0.5As)磊晶品質。 本論文利用上述磊晶技術將高品質砷化銦鎵(In0.5Ga0.5As)磊晶層成長於砷化鎵基板上，並將其結構製作成高效能砷化鎵/砷化銦鎵(In0.5Ga0.5As)金氧半電容。研究過程中亦針對砷化鎵/砷化銦鎵(In0.5Ga0.5As)金氧半電容與傳統利用分子束磊晶(MBE)設備所成長之磷化銦(InP)/砷化銦鎵(In0.53Ga0.47As)金氧半電容做比較，結果顯示利用漸變緩衝技術所成長砷化鎵/砷化銦鎵(In0.5Ga0.5As)金氧半電容具有較佳電容-電壓(capacitance-voltage, C-V)與較低頻率發散(frequency dispersion)等特性。由並聯傳導曲線(parallel conductance contours)中顯示閘極電壓之費米能階狀況，與在砷化鎵/砷化銦鎵(In0.5Ga0.5As)金氧半電容中砷化銦鎵價電帶上方0.64-0.52 eV處量測到其Dit(interface trap density)值約5x1011-2x1012 eV-1cm-2。

Future CMOS technology will aim at the integration of InGaAs semiconductor on silicon substrates for low-cost, light-weight, large area and high-performance logic devices. The first step toward the goal of InGaAs/Si is to obtain high-quality thin GaAs (or Ge) on Si substrate, then, InGaAs compound will be grown on the alternative GaAs (Ge)/Si substrates. Therefore, this dissertation concentrates on the growth of high-quality In0.5Ga0.5As epitaxial films on GaAs substrate for MOSCAP device application by using MOCVD growth method. For the purpose of study, the effects of growth conditions and subtract misorientation degrees of GaAs substrate on crystal quality and surface morphology of In0.3Ga0.7As epilayers were first investigated. The epilayers were grown using step graded buffer layers on different misoriented GaAs (001) substrates. AFM images show that smooth-surface In0.3Ga0.7As film with a RMS roughness of 1.5 nm was obtained at the growth temperature of 490 oC. The threading dislocation (TD) density of about 1x106 cm-2 in the film was determined by TEM. The photoluminescence results obtained at 300 and 77 K indicate that very low recombination centers existed in the epilayer. High-quality smooth surface In0.5Ga0.5As epilayers have been successfully grown on the GaAs substrate. A cross-section study by TEM showed that the TDs have been successfully contained and limited within the buffer layers designed to stop the elongation of TDs into In0.5Ga0.5As epilayers. In our work, a TD density of 1x106 cm-2 in a fully relaxed In0.5Ga0.5As epilayer was achieved. The measurement for lifetimes of n- and p-type In0.5Ga0.5As was performed by using time-resolved photoluminescence, confirmed a great reduction on the recombination centers in the In0.5Ga0.5As epilayers. High-quality In0.5Ga0.5As epilayers allow us to fabricate high-performance In0.5Ga0.5As-based metal-oxide-semiconductor capacitor (MOSCAP) on GaAs substrate. The performance of the MOSCAPs is comparable to that of In0.53Ga0.47As/InP based devices grown by molecular beam epitaxy technique. The devices show a nice capacitance-voltage response, with small frequency dispersion. The parallel conductance contours show the free movement of Fermi level with the gate bias. Acceptable interface trap density Dit value of 5E11-2E12 eV-1cm-2 in the energy range of 0.64-0.52 eV above the InGaAs valence band maximum in In0.5Ga0.5As/GaAs MOSCAPs obtained by conductance methods was shown.