用MOCVD法在LiGaO2(001)上生长GaN的研究

LiGaO₂单晶是目前所知的GaN最为理想的衬底材料,本研究用金属有机物气相沉积法(MOCVD)在LiGaO₂(001)衬底上进行了外延生长GaN膜的试验,生长出了表面较为平整的GaN外延膜.应用原子力显微镜(AFM)、X射线粉末衍射(XRD)和高分辨X射线双晶衍射分别对衬底对外延膜和衬底材料进行了分析测试.结果表明,用MOCVD法可以在LiGaO₂(001)衬底上生长出较高质量的无掺杂GaN(0001)外延膜.但由于MOCVD法是在高温还原气氛中生长GaN外延膜的,LiGaO₂在这种气氛中不够稳定,实验发现衬底材料在生长过程中部分样品发生开裂,但没有发生相变.     

Si(111)衬底上HVPE GaN厚膜生长

在Si(111)衬底上,以MOCVD方法高温外延生长的AIN为缓冲层,使用氮化物气相外延(HVPE)方法外延生长了15Km的c面GaN厚膜.并利用X射线衍射(XRD)、光致发光谱(PL)、拉曼光谱(Raman)等技术研究了GaN厚膜的结构和光学性质.分析结果表明,GaN厚膜具有六方纤锌矿结构,外延层中存在的张应力较小,...     

GaN材料的横向外延过生长(LEO)及其特性研究

对用LEO技术生长GaN材料的选择生长和横向生长速率进行了实验研究。结果表明，作为LEO生长基板的GaN层的表面质量是实现选择生长的关键，而图形方向对横向生长速率与纵向生长速率之比（L／V）也有重要的影响。通过选择合适的工艺条件，实现了GaN材料的LEO外延生长，所得样品的X射线衍射峰宽比用常规MOCVD法生长的样品减小了1／3。     

外延SCNN电光薄膜生长及研究

用激光脉冲沉积(PLD)法在MgO(001)衬底上成功地生长、制备出了外延铌酸锶钡钠(SCNN)电光薄膜.对生长制备出的SCNN电光薄膜用X射线衍射对其微观结构进行了测量研究;X射线衍射结果显示生长在MgO(001)衬底上的SCNN电光薄膜是外延膜;对生长在MgO(001)衬底上的外延SCNN电光薄膜在200～900nm光谱范围的透射光谱进行了测量研究,通过对薄膜透射光谱的振荡曲线分析计算得到了SCNN电光薄膜的光学常数,结果发现外延SCNN电光薄膜的折射率符合单电子模型.     

射频分子束外延生长AlInGaN四元合金

利用射频等离子体辅助分子束外延（RF-MBE）技术在蓝宝石衬底上外延了铝铟镓氮(AlInGaN)四元合金,通过改变Al源的束流生长了不同组分的AlInGaN四元合金,材料生长过程中采用反射式高能电子衍射（RHEED）进行了在位检测. 通过扫描电镜（SEM）、卢瑟福背散射（RBS）、X射线衍射（XRD）和阴极荧光（CL）等测试手段表征了AlInGaN四元合金的结构和光学特性. 研究结果表明：在GaN层上生长AlInGaN外延层时,外延膜呈二维生长;当铝炉的温度为920℃时,外延AlInGaN四元合金外延薄膜中Al/In接近4.7,X射线衍射摇摆曲线的半高宽最小为5arcmin,四元合金的阴极荧光发光峰的半高宽为25nm,AlInGaN四元合金外延层具有较好的晶体质量和光学质量.     

不同衬底上低温生长的ZnO晶体薄膜的结构及光学性质比较

采用电子束反应蒸发方法,在单晶Si（001）及玻璃衬底上低温外延生长了沿C轴高度取向的单晶ZnO薄膜,并对沉积的ZnO晶体薄膜的结构和光学性质进行了分析比较。通过对ZnO蒲膜的X射线衍射（XRD）分析及光致荧光激发谱（PLE）测量,研究了衬底材料结构特性、生长温度及反应气氛中充O2对ZnO薄膜的晶体结构和晶体光学吸收特性的影响。结果表明：①衬底温度对沉积的ZnO薄膜的晶体结构影响显,玻璃衬底上生长ZnO薄膜的最佳温度比Si(001)衬底上生长的最佳温度要高70℃;②虽在最佳生长条件下获得的ZnO薄膜的的XRD结果（半高宽和衍射强度）相近,但光学吸收特性有较大差异,Si(001)衬底上生长的ZnO薄膜优于玻璃衬底上生长的ZnO薄膜;③反应气氛中的O2分压对XRD结构影响不大,但对PLE谱影响显,充O2后能明显改善吸收边特性。     

纳米晶粒受控生长抑制PZNT铁电薄膜中异相形成

在LaAlO3（001）、MgO（001）、SrTiO3（001）衬底以及SrTiO3（001）／PZT（001）种膜上用液相外延方法生长了PZNT薄膜。生长结果表明：在LaAlO3（001）基片PZNT晶粒以三维岛状自发生长。薄膜中有大量的焦绿石异相；在MgO（001）和SrlriO3（001）衬底上，为三维岛状异质外延生长。薄膜中焦绿石异相几乎消失；引入[001]取向的PZT种膜后，岛状三维生长变为二维生长，显著改善了外延膜的质量，获得了完整的PZNT膜。分析了衬底取向对紧邻层纳米尺寸范围的晶粒形成、薄膜晶粒的发育、克服薄膜中异相形成等的影响，总结了获得完整PZNT薄膜的生长条件。     

ZnO/GaN/Al2O3的X射线双晶衍射研究

以H2O作氧源,Zn(C2H5)2作Zn源,N2作载气,以GaN／Al2O3为衬底采用常压MOCVD技术生长了高质量的ZnO单晶膜。用X射线双晶衍射技术测得其对称衍射(0002)面ω扫描半峰宽(FWHM)为404arcsec,表明所生长的ZnO膜具有相当一致的C轴取向;其对称衍射(0004)面ω-20扫描半峰宽为358arcsec,表明所生长的ZnO单晶膜性能良好;同时,该ZnO薄膜的非对称衍射(1012↑-)面ω扫描半峰宽为420arcsec,表明所生长的ZnO膜的位错密度为10^8cm^-2,与具有器件质量的GaN材料相当。     

Si(111) 衬底上3C-SiC的超低压低温外延生长

研究了发展一种Si衬底上低温外延生长3C－SiC的方法。采用LPCVD生长系统，以SiH4和C2H4为气源，在超低压（30Pa) ,低温（900℃）的条件下，在Si(111衬底上外延生长出高质量的3C－SiC薄膜材料。采用俄歇能谱（AES），X射线衍射（XRD）和原子力显微镜（AFM）等分析手段研究了SiC薄膜的外延层组分，晶体结构及其表面形貌。AES结果表明薄膜中的Si/C的原子比例符合SiC的理想化学计量比，XRD结果显示了3C－SiC外延薄膜的良好晶体结构，AFM揭示了3C－SiC薄膜的良好的表面形貌。     

缓冲层对氮化镓二维生长的影响

报道了在射频等离子体（RF-Plasma)辅助的分子束外延（MBE）技术中，使用白宝石（0001）衬底，采用低温缓冲层工艺外延氮化镓（GaN)。通过原子力显微镜（AFM）的表面形貌比较及X射线双晶衍射（XRD）ω扫描摇摆曲线的分析，讨论了低温缓冲层成核机理及缓冲层生长温度与形成准二维生长的关系，确立了缓冲层的三维成核，准二维生长的生长机理，并在此基础上实现了氮化镓外延层更好地二维生长，进一步提高了氮化镓外延层的晶体质量。     

Growth of GaN and AlN thin films by laser induced molecular beam epitaxy

Hexagonal GaN and AlN thin films were grown by laser induced molecular beam epitaxy using Al or Ga metal as target material and N₂as nitrogen source. The films were deposited on sapphire (0001) and SiC (0001) substrates. Epitaxial growth of GaN has been achieved at 730°C and 10⁻³ mbar N₂ pressure. The AlN films were polycrystalline with predominant (0001) orientation.     

Fabrication of GaN epitaxial thin film on InGaZnO4 single-crystalline buffer layer

Epitaxial (0001) films of GaN were grown on (111) YSZ substrates using single-crystalline InGaZnO₄ (sc-IGZO) lattice-matched buffer layers by molecular beam epitaxy with a NH₃ source. The epitaxial relationships are (0001)_GaN//(0001)_IGZO//(111)_YSZ in out-of-plane and [112¯0]_GaN//[112¯0]_IGZO//[11¯0]_YSZ in in-plane. This is different from those reported for GaN on many oxide crystals; the in-plane orientation of GaN crystal lattice is rotated by 30° with respect to those of oxide substrates except for ZnO. Although these GaN films showed relatively large tilting and twisting angles, which would be due to the reaction between GaN and IGZO, the GaN films grown on the sc-IGZO buffer layers exhibited stronger band-edge photoluminescence than GaN grown on a low-temperature GaN buffer layer.     

Preparation of large area free-standing GaN substrates by HVPE using mechanical polishing liftoff method

In this study, 30×30 mm² free-standing GaN substrates were fabricated from 400–450 μm thick GaN films grown on (0001) sapphire by hydride vapor phase epitaxy (HVPE). The thick films were separated from the substrate by mechanical polishing liftoff method, using a diamond slurry. After liftoff, the bow is only slight or absent in the resulting free-standing GaN wafers.     

Substrate effects on the structure and optical properties of GaN epitaxial films

The phase composition and luminescent properties of GaN films grown by molecular beam epitaxy on (0001) sapphire and 6H-SiC substrates were studied. The films grown on SiC were found to consist only of the hexagonal phase and contain a lower concentration of impurities. Grains of cubic GaN, as well as donor and acceptor impurities, were found in the GaN film grown on sapphire. The formation of impurity centers is caused by the diffusion of oxygen and aluminum from the sapphire substrate during crystal growth.     

The influence of reactor height adjustment on properties in GaN films grown on 6H-SiC by metal organic chemical vapor deposition

The influence of reactor height adjustment on properties in GaN films grown on 6H-SiC by metal organic chemical vapor deposition (MOCVD) was investigated. The property of GaN epilayer was investigated by atomic force microscopy, X-ray diffraction, low-temperature (10 K) photoluminescence and the Raman scattering. It is found that, as the spacing between showerhead and susceptor decreased, the growth rate increased and the tensile stress decreased. This result may be useful to control the stress in GaN thin films grown on silicon carbide substrate by MOCVD.     

GaN负电子亲和势光电阴极材料的生长研究

采用低压金属有机化学汽化淀积法在蓝宝石(0001)衬底上生长2~5μm厚度的P-AlxGa1-xN/GaN层(0     

Influence of double buffer layers on properties of Ga-polarity GaN films grown by rf-plasma assisted molecular-beam epitaxy

Ga-polarity GaN thin films were grown on sapphire (0001) substrates by rf-plasma assisted molecular beam epitaxy (MBE) using a double buffer layer, which consisted of an intermediate-temperature GaN buffer layer (ITBL) grown at 690 °C and a conventional AlN buffer layer deposited at 740 °C. Raman scattering spectra showed that the E₂ (high) mode of GaN film grown on conventional AlN buffer layer is at about 570 cm⁻¹, and shifts to 568 cm⁻¹ when an ITBL was used. This indicates that the ITBL leads to the relaxation of residual strain in GaN film caused by mismatches in the lattice constants and coefficients of thermal expansion between the GaN epilayer and the sapphire substrate. Compared to the GaN film grown on the conventional AlN buffer layer, the GaN film grown on an ITBL shows higher Hall mobility and substantial reduction in the flicker noise levels with a Hooge parameter of 3.87×10⁻⁴, which is believed to be, to date, the lowest reported for GaN material. These results imply that the quality of Ga-polarity GaN films grown by MBE can be significantly improved by using an ITBL in addition to the conventional low-temperature AlN buffer layer.     

立式高真空MOCVD装置CaN外延生长与器件制备

自行设计了一套具有创新性的研究型立式高真空MOCVD装置,能够较好的调节反应气体的流动状态,从而在衬底上生长大面积均匀的外延层.利用该装置在蓝宝石和硅单晶衬底上成功地生长出高质量的GaN晶体薄膜.在蓝宝石衬底上生长出n、p型GaN以及多量子阱多层结构材料,并成功制备了GaN基多层量子阱结构的蓝光发光二极管,性能良好,具有实用价值.     

Synthesis and characterization of heteroepitaxial GaN films on Si(111)

We report crack-free and single-crystalline wurtzite GaN heteroepitaxy layers have been grown on Si (111) substrate by metal-organic chemical vapor deposition(MOCVD). Synthesized GaN epilayer was characterized by X-ray diffraction(XRD), atomic force microscope (AFM) and Raman spectrum. The test results show that the GaN crystal reveals a wurtzite structure with the <0001> crystal orientation and XRD ω-scans showed a full width at half maximum (FWHM) of around 583 arcsec for GaN grown on Si substrate with an HT-AlN buffer layer. In addition, the Raman peaks of E₂^high and A₁(LO) phonon mode in GaN films have an obvious redshit comparing to bulk GaN eigen-frequency, which most likely due to tensile strain in GaN layers. But the AO phonon mode of Si has a blueshit which shows that the Si substrate suffered a compressive strain. And we report that the AlN buffer layer plays a role for releasing the residual stress in GaN films.