常压MOCVD生长Ga2O3薄膜及其分析

以去离子水(H₂O)和三甲基镓(TMGa)为源材料,用常压MOCVD方法在蓝宝石(0001)面上生长出β-Ga₂O₃薄膜.用原子力显微镜(AFM)、X射线衍射(XRD)以及二次离子质谱(SIMS)实验表征Ga₂O₃外延膜的质量.在X射线衍射谱中有一个强的Ga₂O₃(102)面衍射峰,其半峰全宽(FWHM)为0.25°,表明该Ga₂O₃外延膜是(102)择优取向.在二次离子质谱中除了C、H、O和Ga原子外,没有观测到其他原子.     

Syntheses, X-ray structures and CVD studies of trimethylphosphite stabilized silver(I) methanesulfonates

The preparation of {[(MeO)₃P]_n·AgO₃SCH₃} (n = 1, 2a; n = 2, 2b) is described. The molecular structure of 2a was determined by using X-ray single crystal analysis. Complex 2a contains an Ag₄ rectangular make-up, the centroid of which constitutes an inversion center. Complex 2b was used as precursor in the deposition of silver films using metal organic chemical vapor deposition (MOCVD) technique for the first time. The silver films obtained were characterized using scanning electron microscopy (SEM) and energy-dispersion X-ray (EDX) analysis.     

MOCVD技术制备的ZnS:Mn电致发光薄膜结晶性及Mn2+分布

本文报导了用MOCVD技术制备的ZnS:Mn电致发光薄膜为立方晶相,结晶取向性好,颗粒大。从高倍率的扫描电镜拍摄的照片观察到薄膜的表面平滑。SIMS测量表明Mn2+在ZnS薄膜纵向分布均匀,但在两侧有起伏,可能的原因是在生长的初终阶段流量的突变使化合物的化学计量比偏离而产生位错,引起原子的局部堆积,并且由于初终阶段ZnS:Mn生长的衬底不同使原子堆积层厚度不同。     

Tin(II) aminoalkoxides and heterobimetallic derivatives: the structures of Sn6(O)4(dmae)4, Sn6(O)4(OEt)4 and [Sn(dmae)2Cd(acac)2]2

Tin(II) methoxide reacts with N,N′‐dimethylaminoethanol (dmaeH) to yield Sn(dmae)₂ ( 1 ) along with small amounts of the hydrolysis product Sn₆(O)₄(dmae)₄ ( 2 ). The geometrically more regular iso‐structural cage Sn₆(O)₄(OEt)₄ ( 3 ) was obtained as the only tractable product isolated from reaction of 2 and Sb(OEt)₃, while 1 reacted with CdX₂ (X = acac, I) to afford Sn(dmae)₂Cd(acac)₂ ( 4 ) and Sn(dmae)₂CdI₂ ( 5 ). The X‐ray structures of 2, 3 and 4 are reported. Decomposition of 4 under aerosol‐assisted chemical vapour deposition conditions leads to amorphous tin oxide films with no detectable cadmium (i.e. ca < 2% cadmium), rather than a stoichiometric Sn:Cd oxide. Copyright © 2006 John Wiley & Sons, Ltd.     

ZnO-Si不同退火条件对生长ZnSe薄膜的影响

研究了作为缓冲层的ZnO薄膜在不同的退火时间、退火温度下退火对Si衬底上生长ZnSe膜质量的影响。当溅射有ZnO膜的Si(111)衬底的退火条件变化时，从X射线衍射谱（XRD）和光致发光谱（PL）中可见，ZnSe(111)膜的晶体质量有较大的变化。变温的PL谱表明，Si衬底上生长的具有ZnO缓冲层的ZnSe膜的近带边发射峰起源于自由激子发射。     

优质GaAs/Si和AlGaAs/Si材料的MOCVD生长研究

用自制常压MOCVD装置,在Si衬底上生长GaAs和AlGaAs外延层,在高温去除Si衬底表面氧化膜之后,采用两步法,即低温生长过渡层,再提高温度生长外延层。得到了表面镜面光亮的优质GaAs和AlGaAs外延层。X射线双晶衍射仪测试GaAs外延层,其回摆曲线半峰宽是200孤秒,GaAs和AlGaAs外延层在77K温度下,PL谱半峰宽分别是17meV和24meV。     

Studies of Laser-induced-MOCVDZinc Oxide Films

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氮气氛中高温退火对ZnO薄膜发光性质的影响

以二乙基锌和水汽分别作为锌源和氧源,用LP-MOCVD方法在p型Si(100)衬底上生长了单一取向的ZnO薄膜。对得到的样品在氮气气氛中进行高温热处理,退火温度分别为900,1000,1100℃。利用室温PL谱、XRD、AFM、XPS等方法对样品的性质进行了研究。研究表明:(1)随着退火温度的升高,样品的结晶性质也逐渐提高,从表面形貌观察到晶粒尺寸逐渐增大;(2)当退火温度从900℃升高至1000℃时,样品的光致发光谱中可见光波段的发光强度有所减弱,而紫外波段的发光强度明显增强;当退火温度升高至1100℃时,可见光波段的发光几乎完全被抑制,而紫外波段的发光强度急剧增强。分析认为,高温退火改善晶体结晶质量的同时调制了样品的Zn/O比,氮气气氛下的热处理使得样品内的氧原子逸出,来自受主缺陷OZn的可见发射随温度升高逐渐减弱,而当退火温度达到1000℃以上时样品成为富锌状态,此时与施主缺陷Zni有关的紫外发射急剧增强。     

MOVPE growth and characterization of a ‐plane AlGaN over the entire composition range

We report the metal organic vapor phase epitaxy (MOVPE) growth and characterization of non‐polar (11 0) a ‐plane Al_x Ga_1–xN on (1 02) r ‐plane sapphire substrates over the entire composition range. Al_x Ga_1–xN samples with ～0.8 μm thick layers and with x = 0, 0.18, 0.38, 0.46, 0.66, and 1.0 have been grown on r ‐plane sapphire substrates. The layer quality can be improved by using a 3‐stage AlN nucleation layer and appropriate V/III ratio switching following nucleation. All a ‐plane AlGaN epilayers show an anisotropic in‐plane mosaicity, strongly influenced by Al incorporation and growth conditions. Careful lattice parameter measurements show anisotropic in‐plane strain that results in an orthorhombic distortion of the hexagonal unit cell, making Al composition determination from X‐ray diffraction difficult. In general lower Al incorporation is seen in a ‐plane epilayers compared to c ‐plane samples grown under the same conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pivotal role of ballistic and quasi-ballistic electrons on LED efficiency

Significant progress in the power conversion efficiency and brightness of InGaN-based light emitting diodes (LEDs) has paved the way for these devices to be considered for LED lighting. In this realm, however, the efficiency must be retained at high injection levels in order to generate the lumens required. Unfortunately, LEDs undergo a monotonic efficiency degradation starting at current densities even lower than 50 A/cm² which would hinder LED insertion into the general lighting market. The physical origins for the loss of efficiency retention are at present a topic of intense debate given its enormous implications. This paper reviews the current status of the field regarding the mechanisms that have been put forward as being responsible for the loss of efficiency, such as Auger recombination, electron overflow (spillover), current crowding, asymmetric injection of electrons and holes, and poor transport of holes through the active region, the last one being applicable to multiple quantum well designs. While the Auger recombination received early attention, increasing number of researchers seem to think otherwise at the moment in that it alone (if any) cannot explain the progressively worsening loss of efficiency reduction as the InN mole fraction is increased. Increasing number of reports seems to suggest that the electron overflow is one of the major causes of efficiency degradation. The physical driving force for this is likely to be the relatively poor hole concentration and transport, and skewed injection favoring electrons owing to their relatively high concentration. Most intriguingly there is recent experimental convincing evidence to suggest that quasi-ballistic electrons in the active region, which are not able to thermalize within the residence time and possibly longitudinal optical phonon lifetime, contribute to the carrier overflow which would require an entirely new thought process in the realm of LEDs.