【作者】 王党会；

【导师】 郝跃；

【作者基本信息】 西安电子科技大学 ， 微电子学与固体电子学， 2013， 博士

【摘要】 以Ⅲ族氮化物为研究对象的固体发光技术，带动了与之密切相关的蓝光、绿光和发光二极管（Light-emitting Diode，LED）照明与紫外探测器的应用。在这个方兴未艾的领域里，虽然很多技术瓶颈已经取得了突破，但是仍然有不少问题尚未解决，例如，虽然紫外半导体激光器和紫外LED、绿光LED技术已经取得了长足的进步，但它们的内量子效率仍然不高；即使是蓝光LED内量子效率已经很高了，但是随着工作电流的增加，其输出效率会急速降低（Efficiency-Droop Effect）。我们知道，位错的量级在固体发光特性中扮演着非常重要的角色，是引起发光效率降低的主要因素。因此，在Ⅲ族氮化物半导体器件大规模商业化的同时，对Ⅲ族氮化物外延层薄膜结晶质量做更进一步的提高依然十分重要；对Ⅲ族氮化物半导体外延层薄膜生长和表征的深入研究依然是当前的研究热点。本文从Ⅲ族氮化物半导体材料的生长和表征出发，重点研究了AlGaN、InGaN的生长和表征技术、GaN非谐效应的变温Raman散射以及LED发光转变机制的低频噪声表征等问题。主要的成果如下：1.提高AlGaN外延层结晶质量的低温加高温AlN成核层技术的生长与表征采用金属有机化学气相沉积（Metal-Organic Chemical Vapor Deposition，MOCVD）法，通过在高温AlN成核层与衬底之间插入一薄层低温AlN成核层结构，有利于提高AlGaN外延层的结晶质量。通过高分辨XRD结果表明，AlGaN外延层薄膜的线位错密度明显降低；原子力显微镜（Atomic Force Microscope，AFM）结果表明，AlGaN外延层的表面相貌得到改善，表面粗糙度降低。2. AlGaN外延层结晶质量进一步提高的自支撑GaN衬底与低温加高温AlN成核层技术的生长与表征采用低温加高温AlN成核层的MOCVD法生长AlGaN外延层，通过与蓝宝石衬底进行对比，研究了AlGaN外延层的相关缺陷行为和发光特性。发现以自支撑GaN衬底生长的AlGaN外延层，虽然表面形貌的起伏较大，但结晶质量和发光性质均得到了明显地提高，刃位错密度和总位错密度得到了较大幅度的降低。3.温度对InGaN外延层薄膜结晶质量的影响在不同温度下，对InGaN外延层薄膜的发光特性与结晶质量和In组分之间的关系进行了研究。提出在较低温度（650℃）时生长的InGaN外延层薄膜，在In组分（15.36%）较高时InGaN外延层的结晶质量、表面形貌与发光特性均得到了明显地提高，线位错密度明显降低。4.插入AlN成核层结构的InGaN/GaN MQW LED光电转换效率的模拟研究采用STR公司的SimuLED5.2软件，对插入AlN成核层结构的多量子阱LED的能带结构、发射光谱、Auger电流密度、非辐射复合电流等方面进行模拟研究。结论表明，插入AlN成核层结构的多量子阱具有较高的内量子效率；随着偏置电压的逐渐增大，IQE下降幅度较小。5. GaN外延层的非谐效应进行变温Raman表征通过对不同温度段（整个测试温度段，高温段和临界温度）Raman频移与温度的分析，提出了采用一阶指数衰减数学模型，可以对样品的非谐效应进行对比。在忽略高能声子衰变的情况下，进一步采用该模型还可以计算出热膨胀系数或者Grüneisen参数。6. InGaN/GaN多量子阱发光二极管发光机制转变的低频电流噪声表征以低频1/f噪声理论为依据，研究了InGaN/GaN多量子阱（Multiple QuantumWell，MQW）发光二极管（Light-emitting Diode，LED）发光机制转变的低频噪声表征方法。在电流从0.1mA到10mA之间变化时，对InGaN/GaN多量子阱结构LED的电流1/f噪声进行了测试，结论表明：（1）随着电流逐渐增大，InGaN/GaN多量子阱结构发光二极管的电流噪声从产生复合噪声（Generation-recombination，g-r）类型逐渐过渡为低频1/f噪声；（2）载流子的复合机制从非辐射复合过渡为载流子之间的辐射复合，并具有标准1/f噪声谱的趋势。更多还原

【Abstract】 In the past few decade, Ⅲ-nitride (GaN, AlN and InN) and its compounds arebeing established as materials of extreme significance for the next generationhigh-density power devices for applications in solid state lighting field, includingblue-light, green-light and visible-light light-emitting diodes (LED), ultraviolet LEDand detector in deep space exploration. After a long-period of development and research,many key obstacles in this field have been achieved progress. However, there stillremain many problems expecting to be solved. For example, although the opticalefficiency have made great progress in semiconductor lasers, ultraviolet LEDs andgreen-light LEDs, there still existed the lower internal quantum efficiency (IQE). It wasfound that IQE will drop rapidly with increasing current for blue-light LEDs possessedhigher IQE value, which is called as efficiency-droop effect. It is well known that theorder magnitude of dislocation density plays a key role in solid state lighting, andbecomes an important factor that caused the efficiency reduce. Therefore, it is importantto study deeply and character the primary problems in materials and devices ofⅢ-nitride epitaxial films for large-scale and commercialization. This thesis studied thegrowth and characterization based on AlGaN, InGaN epifilms, anharmonic effect ofGaN epifilms using dependent-temperature Raman scattering and transition mechanismfor InGaN/GaN MQW LEDs using low-frequency noise. The main research results areas follows:(1) Growth and characterization of AlGaN layer by combining low-temperatureand high-temperature AlN nucleation layer on c-plane sapphire substrateThick AlGaN layer on c-plane sapphire substrate with low-temperature AlN(LT-AlN) and high-temperature AlN (HT-AlN) nucleation layers have been grown bylow-pressure metal-organic chemical vapor deposition (LPMOCVD). Results indicatethat the insertion of LT-AlN nucleation layer between sapphire substrate andhigh-temperature AlN nucleation layer improves effectively crystal quality, reduces thesurface roughness and eliminates the threading dislocation density.(2) Growth and characterization of AlGaN layer on c-plane sapphire substrate andfree-standing GaN substrateThick AlGaN epilayers have been grown on c-plane sapphire substrate andfree-standing GaN substrate using LT-AlN nucleation layers by LPMOCVD. Resultsindicate that crystal quality can be improved greatly when grown on the free-standingGaN substrate. We calculated the threading dislocation density and found that AlGaN epifilm grown on free-standing GaN substrate is much lower in total threadingdislocation density than that grown on sapphire substrate, although surface morphologyis rougher than that of sapphire substrate.(3) Influence of growth temperature on crystal quality of InGaN epifilmsWe studied the relationships between luminescence properties, crystal quality ofInGaN epifilms and In fraction under different different growth temperatures. Resultsshow that InGaN epitaxial layers possessed better crystal quality and luminescenceproperties when indium fraction increases from4.36%to15.36%at a lower temperature(650℃), and InGaN epifilms have an improved crystal quality, a lower threadingdislocation density and smoother surface morphology.(4) Studying the wall plug efficiency for inserting an AlN nucleation layer inInGaN/GaN MQW LEDs using simulationWe have employed the software named SimuLED5.2to study the wall plugefficiency for InGaN/GaN multiple quantum well (MQW) LEDs based on Chapter IV.We compared the band diagram, emission spectra, non-radiative recombination currentand internal quantum efficiency of the convention InGaN/GaN LEDs with insertionHT-AlN nucleation layer of InGaN/GaN MQW LEDs. Conclusions show that insertingan AlN nucleation layer in InGaN/GaN MQW LEDs is beneficial to IQE, and IQE has alittle reduction with the increasing bias voltage.(5) Studying the relationships between Raman shifts and temperature range fora-plane GaN using temperature-dependent Raman scatteringRaman shifts of a-plane GaN layers grown on r-plane sapphire substrates byLPMOCVD are investigated. We studied the relationships between Raman shift andtemperature for conventional a-plane GaN epilayer with insertion AlN/AlGaNsuperlattice layers for a-plane GaN epilayer using temperature-dependent Ramanscattering. Results indicate that a critical temperature existed in the first-orderexponential decay model, which can characterize anharmonic effect of a-plane GaN indifferent temperature ranges. Further studies can calculate the thermal expansioncoefficient or Grüneisen parameters.(6) Charactering the transition mechanism for InGaN/GaN MQW LEDs usinglow-frequency noiseThe transition mechanism of InGaN/GaN MQW LEDs was investigated using thetool of low-frequency noise within the current range from0.1mA to10mA. We havestudied the relationships between power spectral density (PSD) of low-frequency noiseand frequency. Results indicated that PSD of low-frequency noise increased with thecurrent from0.1mA to10mA. At lower current range (I<1mA), it is g-r (generation-recombination) noise origin that dominated in low-frequency noise; and athigher current range (I>10mA), it is1/f noise origin that dominated in low-frequencynoise. There existed a transition mechanism in InGaN/GaN MQW LEDs between0.1mA to10mA, which indicated that the recombination mechanism of carriers fromnon-radiative recombination to stable carriers number fluctuation.更多还原