侧向外延生长六方相GaN中堆垛层错的同步辐射表征

本文采用低温光致发光谱研究了蓝宝石(0001)衬底上MOCVD侧向外延生长的六方相GaN中的堆垛层错, 并使用同步辐射XRD方法研究了该堆垛层错以及立方相和六方相GaN的相对取向.     

外延在蓝宝石衬底上的非掺杂GaN研究

采用改变生长条件的方法制备GaN薄膜,在(0001)面蓝宝石衬底上利用金属有机物化学气相沉积技术制备了不同样品,并借助X射线双晶衍射仪(XRD)、PL谱测试仪和光学显微镜对材料进行了分析。XRD(0002)面和(1012)面测试均表明TMGa流量为70 cm3/min时样品位错密度最低。利用该TMGa流量进一步制备了改变生长温度的样品。XRD和PL谱测试结果表明,提高生长温度有利于提高GaN样品的晶体质量和光学性能。最后,利用光学显微镜对样品的表面形貌进行了分析。     

国产SiC衬底上利用AIN缓冲层生长高质量GaN外延薄膜

采用高温AlN作为缓冲层在国产SiC衬底上利用金属有机物化学气相外延技术生长GaN外延薄膜.通过优化AlN缓冲层的生长参数得到了高质量的GaN外延薄膜,其对称(0002)面和非对称(1012)面X射线衍射摇摆曲线的半峰宽分别达到130 arcsec和252 arcsec,这是目前报道的在国产SiC衬底上生长GaN最好的...     

N极性GaN薄膜的MOCVD外延生长

采用MOCVD技术在c面蓝宝石衬底上外延制备了N极性GaN薄膜。通过KOH腐蚀的方法判定了GaN外延薄膜的极性。通过X射线双晶衍射(XRD)摇摆曲线和光致荧光(PL)谱测试研究了成核层生长时间对N极性GaN薄膜晶体质量和发光性能的影响。研究结果表明,成核层生长时间为300 s时,N极性GaN薄膜样品的位错密度最低,发光性能最好。采用拉曼(Raman)光谱对样品的应变状态进行了分析。     

GaN1-xPx薄膜的结构特性研究

用金属有机物化学气相沉积技术在蓝宝石衬底上外延了高P组分的GaN1-xPx 薄膜.利用x射线衍射仪和拉曼光谱仪研究了P对GaN1-xPx晶体结构的影响.研究结果表明:随着P组分比的增加,GaN1-xPx(0002)衍射峰逐渐向小角度移动,即晶格常数变大;与非掺杂GaN相比,GaN1-xPx薄膜的拉曼光谱中出现了4个新的振动模式,将它们分别归因于P族团引起的准局部振动模式、Ga-P键振动引起的间隙模,以及来自缺陷引起的无序激活散射.同时,随着P组分比的增加,A1(LO)模式的频率向低频方向移动,这种红移现象起因于合金化和应变的影响.     

金属有机化合物气相外延生长GaN薄膜的电子微结构研究

研究了金属有机化合物气相外延(MOVPE)方法在(0001)氧化铝基底上生长的GaN薄膜的微结构,目的在于解释GaN缓冲层在二步法生长过程中的作用及其对外延层晶体质量的影响.在缓冲层中观察到了高密度的结构缺陷,并发现了两种晶体结构(立方和六角)的GaN.进而对两种结构GaN的成因进行讨论,并对缓冲层和外延层中结构缺陷的关系进行了研究.     

腐蚀时间对蓝宝石衬底上外延生长GaN质量的影响

使用熔融的KOH在高温下对c面蓝宝石衬底进行不同时间的腐蚀,借助扫描电镜、原子力显微镜对衬底表面进行了表征,然后利用金属有机物化学气相沉积设备在不同腐蚀时间的衬底样品上进行了GaN材料的外延生长。通过X射线衍射结果比较了两组衬底上外延材料的质量,利用原子力显微镜结果对外延层表面形貌进行了分析,最后论述了腐蚀时间的调整对蓝宝石衬底上外延生长氮化镓质量的影响机理。     

MOCVD生长Si衬底上HT-AlN缓冲层低生长压力对GaN薄膜的影响

采用金属有机化学气相沉积（MOCVD）技术在Si（111）衬底上外延GaN薄膜,对高温AlN（HT-AlN）缓冲层在小范围内低生长压力（6.7~16.6 kPa）条件下对GaN薄膜特性的影响进行了研究。研究结果表明GaN外延层的表面形貌、结构和光学性质对HT-AlN缓冲层的生长压力有很强的的依赖关系。增加HT-AlN缓冲层的生长压力,GaN薄膜的光学和形貌特性均有明显改善,当HT-AlN缓冲层的生长压力为13.3 kPa时,得到无裂纹的GaN薄膜,其（002）和（102）面的X射线衍射峰值半高宽分别为735 arcsec和778 arcsec,由拉曼光谱计算得到的张应力为0.437 GPa,原子力显微镜（AFM）观测到表面粗糙度为1.57 nm。     

Si(111)衬底上GaN的MOCVD生长

利用LP-MOCVD在Si（111）衬底上,以高温AIN为缓冲层,分别用低温GaN（LT-GaN）和偏离化学计量比富Ga高温GaN（HT-GaN）为过渡层外延生长六方相GaN薄膜。采用高分辨率双晶X射线衍射（DCXRD）,扫描电子显微镜（SEM）,原子力显微镜（AFM）和室温光致荧光光谱（RT-PL）进行分析。结果表明,有偏离化学计量比富Ga HT-GaN为过渡层生长的GaN薄膜质量和光致荧光特性均明显优于以LT-GaN为过渡层生长的GaN薄膜,得到GaN（0002）和（1012）的DCXRD峰,其半峰全宽（FWHM）分别为698s和842s,室温下的光致荧光光谱在361nm处有一个很强的发光峰,其半峰全宽为44．3meV。     

预通三甲基铝对AlN薄膜的结构与应变的影响

采用有机金属化学气相沉积设备用两步生长法在(0001)蓝宝石衬底上制备AlN薄膜。研究了预通三甲基铝(TMAl)使衬底铝化对外延AlN的影响。利用高分辨X射线衍射(XRD)技术和扫描电子显微镜(SEM) 分析了样品的结晶质量以及外延膜中的残余应力。通过SEM观察发现,短时间的预通TMAl处理对AlN薄膜表面的影响不大;但随着预通时间的增加,表面会出现六角形的岛。通过优化TMAl的预通时间可以保护衬底被氮化有利于Al极性面AlN的生长,从而得到的Al极性面AlN表面比较平整;但是预通TMAl时间过长会使衬底表面沉积金属态铝而不容易形成平整的表面。X射线双晶摇摆曲线结果表明:样品的(0002)和(101 2)面的X射线双晶摇摆曲线的半峰宽随着预通TMAl时间的不断增加,由此得出薄膜的晶体质量不断下降。这可以解释为:预通TMAl使形成的晶核不再规则,从而在成核层形成了很多亚颗粒降低了晶体质量。进一步对XRD结果分析,我们也发现了这样的应力变化。这种应力的变化起源可以归结于内应力(岛的合并在其晶界引入的应力)与外应力(晶格失配与热失配引起的应力)共同作用的结果。     

MgxZn1-xO薄膜的生长及其光学性能

利用金属有机化学气相沉积(MOCVD)法在蓝宝石(1120)衬底上生长高质量的Mg_xZn_1-xO合金薄膜,实验研究了各种不同Mg组分对样品光学性能的影响。通过光致发光荧光衰减特性对激子发光寿命的研究表明,激子的寿命随Mg组分的增加而增加,当Mg组分达到50%时,激子的寿命为872 ps。     

Effects of V/III ratio on a-plane GaN epilayers with an InGaN interlayer

The effects of V/Ill growth flux ratio on a-plane GaN films grown on r-plane sapphire substrates with an InGaN interlayer are investigated. The surface morphology, crystalline quality, strain states, and density of basal stacking faults were found to depend heavily upon the V/III ratio. With decreasing V/III ratio, the surface morphology and crystal quality first improved and then deteriorated, and the density of the basal-plane stacking faults also first decreased and then increased. The optimal V/III ratio growth condition for the best surface morphology and crystalline quality and the smallest basal-plane stacking fault density of a-GaN films are found. We also found that the formation of basal-plane stacking faults is an effective way to release strain.     

The effect of single A1GaN interlayer on the structural properties of GaN epilayers grown on Si （111） substrates

High-quality and nearly crack-free GaN epitaxial layer was obtained by inserting a single AlGaN interlayer between GaN epilayer and high-temperature AlN buffer layer on Si (111) substrate by metalorganic chemical vapor deposition. This paper investigates the effect of AlGaN interlayer on the structural properties of the resulting GaN epilayer. It confirms from the optical microscopy and Raman scattering spectroscopy that the AlGaN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer and preventing the formation of cracks. X-ray diffraction and transmission electron microscopy analysis reveal that a significant reduction in both screw and edge threading dislocations is achieved in GaN epilayer by the insertion of AlGaN interlayer. The process of threading dislocation reduction in both AlGaN interlayer and GaN epilayer is demonstrated.     

The growth temperatures dependence of optical and electrical properties of InN films

InN films grown on sapphire at different substrate temperatures from 550°C to 700°C by metalorganic chemical vapor deposition were investigated. The low-temperature GaN nucleation layer with high-temperature annealing (1100°C) was used as a buffer for main InN layer growth. X-ray diffraction and Raman scattering measurements reveal that the quality of InN films can be improved by increasing the growth temperature to 600°C. Further high substrate temperatures may promote the thermal decomposition of InN films and result in poor crystallinity and surface morphology. The photoluminescence and Hall measurements were employed to characterize the optical and electrical properties of InN films, which also indicates strong growth temperature dependence. The InN films grown at temperature of 600°C show not only a high mobility with low carrier concentration, but also a strong infrared emission band located around 0.7 eV. For a 600 nm thick InN film grown at 600°C, the Hall mobility achieves up to 938 cm²/Vs with electron concentration of 3.9 × 10¹⁸ cm⁻³. Supported by the National Basic Research Program of China (Grant No. 2006CB6049), the National Natural Science Foundation of China (Grant Nos. 6039072, 60476030 and 60421003), the Great Fund of the Ministry of Education of China (Grant No. 10416), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050284004), and the Natural Science Foundation of Jiangsu Province of China (Grant Nos. BK2005210 and BK2006126)     

The influence of AlN/GaN superlattice intermediate layer on the properties of GaN grown on Si（111） substrates

AlN/GaN superlattice buffer is inserted between GaN epitaxial layer and Si substrate before epitaxial growth of GaN layer. High-quality and crack-free GaN epitaxial layers can be obtained by inserting AlN/GaN superlattice buffer layer. The influence of AlN/GaN superlattice buffer layer on the properties of GaN films are investigated in this paper. One of the important roles of the superlattice is to release tensile strain between Si substrate and epilayer. Raman spectra show a substantial decrease of in-plane tensile strain in GaN layers by using AlN/GaN superlattice buffer layer. Moreover, TEM cross-sectional images show that the densities of both screw and edge dislocations are significantly reduced. The GaN films grown on Si with the superlattice buffer also have better surface morphology and optical properties.     

常压化学气相沉积技术生长ZnO:H薄膜的光学性质

采用常压金属有机物化学气相沉积技术(AP-MOCVD),以二乙基锌(DEZn)为Zn源,去离子水(H2O)为氧源,N2作载气,在外延ZnO薄膜的反应气氛中通入少量氢气,在c-Al2O3衬底上生长出了ZnO∶H薄膜。用X射线双晶衍射和光致发光谱对ZnO∶H薄膜的结晶性能和光学性质进行表征。结果表明,ZnO∶H薄膜(002)和(102)面的Ω扫描半峰全宽分别为46.1 mrad和81.4 mrad,表明该薄膜具有良好的结晶性能;室温下,ZnO∶H薄膜具有较强的紫外光发射(380 nm),在低温10 K光致发光谱中观测到位于3.3630 eV处与氢相关的中性施主束缚激子峰(I4)及其位于3.331 eV处的双电子卫星峰(TES)。采用退火的方法,通过观测I4峰的强度变化,研究了氢在ZnO∶H薄膜中的热稳定性。发现随着退火温度的升高,I4峰的强度逐渐减弱,表明在高温下退火,氢会从ZnO薄膜中逸出。     

常压化学气相沉积技术生长ZnO∶H薄膜的光学性质

采用常压金属有机物化学气相沉积技术(APMOCVD),以二乙基锌(DEZn)为Zn源,去离子水(H2O)为氧源,N2作载气,在外延ZnO薄膜的反应气氛中通入少量氢气,在cAl2O3衬底上生长出了ZnO∶H薄膜。用X射线双晶衍射和光致发光谱对ZnO∶H薄膜的结晶性能和光学性质进行表征。结果表明,ZnO∶H薄膜(002)和(102)面的Ω扫描半峰全宽分别为46.1 mrad和81.4 mrad,表明该薄膜具有良好的结晶性能；室温下,ZnO∶H薄膜具有较强的紫外光发射(380 nm),在低温10 K光致发光谱中观测到位于3.3630 eV处与氢相关的中性施主束缚激子峰(I4)及其位于3.331 eV处的双电子卫星峰(TES)。采用退火的方法,通过观测I4峰的强度变化,研究了氢在ZnO∶H薄膜中的热稳定性。发现随着退火温度的升高,I4峰的强度逐渐减弱,表明在高温下退火,氢会从ZnO薄膜中逸出。     

Effects of SiNx on two-dimensional electron gas and current collapse of A1GaN/GaN high electron mobility transistors

SiNx is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors (HEMTs). In this paper, the effects of SiN x passivation film on both two-dimensional electron gas characteristics and current collapse of AlGaN/GaN HEMTs are investigated. The SiNx films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results.