On the growth of gallium phosphide layers on gallium phosphide substrates by MOVPE

We have investigated the growth and luminescence of gallium phosphide layers grown by MOVPE at atmospheric pressure using trimethylgallium and phosphine in a hydrogen ambient. Both the morphology and the type of luminescence were found to be strongly dependent on growth conditions. Hexagonal defects are observed on the epitaxial surfaces, changing to rhombic defects when the growth takes place with a low V/III ratio. The origin of these defects is stacking faults. The density of these defects is dependent on the growth temperature. Photoluminescence studies at 2 K were also carried out. In the bound exciton spectrum of the gallium phosphide layers, the silicon impurity appears on the gallium site with sufficient phosphine excess and at sufficiently high growth temperatures. A deep impurity level, related to silicon on a phosphorus site, is present when growth takes place with a low phosphine excess. We explain all observations by a model that implies that the growing surface can be either gallium-rich (resulting in phosphorus vacancies) or phosphorus-rich, resulting in gallium vacancies. The phosphorus-rich surface enables smooth epitaxial layers to be grown. With growth taking place at a phosphine to trimethylgallium ratio greater than 2.5, the surface is in a configuration stabilized by phosphorus reconstructions.     

Correlation between nitrogen and carbon incorporation into MOVPE ZnO at various oxidizing conditions

Nitrogen-doped ZnO films with preferential (0 0 0 1) orientation were synthesized on c-Al₂O₃ and Si substrates by metal organic vapor phase epitaxy (MOVPE) using tertiary butanol (t-BuOH) and/or N₂O as oxidizers for diethylzinc (DEZ). A striking correlation between nitrogen and carbon incorporation into ZnO was revealed by concentration versus depth profiling employing secondary ion mass spectrometry (SIMS), consistently with recently reported simulations of nitrogen-carbon complexing.     

ZnO growth on Si with low-temperature CdO and ZnO buffer layers by molecular-beam epitaxy

Low-temperature (LT) buffer-layer techniques were employed to improve the crystalline quality of ZnO films grown by molecular-beam epitaxy (MBE). Photoluminescence (PL) spectra show that CdO, as a hetero-buffer layer with a rock-salt structure, does not improve the quality of ZnO film grown on top. However, by using ZnO as a homo-buffer layer, the crystalline quality can be greatly enhanced, as indicated by PL, atomic force microscopy (AFM), x-ray diffraction (XRD), and Raman scattering. Moreover, the buffer layer grown at 450°C is found to be the best template to further improve the quality of top ZnO film. The mechanisms behind this result are the strong interactions between point defects and threading dislocations in the ZnO buffer layer.     

退火温度对生长在TiO2缓冲层上的ZnO薄膜的影响

采用电子束蒸发技术在TiO2缓冲层上沉积了ZnO薄膜,研究了不同的退火温度对薄膜晶化质量及发光性质的影响.利用X射线衍射仪和扫描探针显微镜分析了薄膜样品的结构性质,利用荧光光谱仪研究了薄膜样品的光致发光性质.分析结果表明,退火处理后的ZnO薄膜都沿c轴择优牛长.在600℃下退火的样品具有最强的(002)衍射峰、最强的紫外发射和最弱的可见光发射,其晶粒大小均匀.紧密堆积.而对于在500和700℃下退火的样品,其可见光发射较强.这表明在600℃下退火的样品具有最好的晶化质量.     

退火温度对生长在TiO2缓冲层上的ZnO薄膜的影响

采用电子束蒸发技术在TiO2缓冲层上沉积了ZnO薄膜,研究了不同的退火温度对薄膜晶化质量及发光性质的影响. 利用X射线衍射仪和扫描探针显微镜分析了薄膜样品的结构性质,利用荧光光谱仪研究了薄膜样品的光致发光性质. 分析结果表明,退火处理后的ZnO薄膜都沿c轴择优生长. 在600℃下退火的样品具有最强的（002）衍射峰、最强的紫外发射和最弱的可见光发射,其晶粒大小均匀,紧密堆积. 而对于在500和700℃下退火的样品,其可见光发射较强. 这表明在600℃下退火的样品具有最好的晶化质量.     

MOVPE growth of GaAsN: surface study by AFM and optical properties

We report on the growth of GaAs_1−xN_x thin films on GaAs substrates (2° off) by metalorganic vapor-phase epitaxy, in the temperature range 500–600°C. A mixture of N₂ and H₂ was used as the carrier gas. Using dimethylhydrazine as nitrogen source, we incorporated up to 3.5% of nitrogen, at 530°C. The growth condition dependence of nitrogen content was studied, and it reveals a distribution coefficient 350 times lower for nitrogen than for arsine at 530°C. Nitrogen incorporation is controlled by surface kinetics. The evolution of surface morphology has been investigated by atomic force microscopy as a function of the nitrogen composition and of growth temperature. For nitrogen content up to 2%, the GaAsN vicinal surface is characterized by a step–terrace structure with bunched steps, and the step edges straighten when increasing the growth temperature. For higher nitrogen content terraces are no longer observed and, above 3%, widely-spaced cross-hatch lines, characteristic of a partial relaxation of strain in the epilayers, appear. Optical properties were studied by low (7 K) and room-temperature photoluminescence and photoreflectance. As usual for this material, a degradation of optical characteristics is observed with increasing N content along with the evolution of surface morphology.     

The photoassisted MOVPE growth of ZnSSe using tertiary-butylmercaptan

We have conducted a study of the compositional control of epitaxial ZnS_ySe_1-y grown by photoassisted metal organic vapor phase epitaxy (MOVPE) (250 torr, 340°C, UV=14 mW/cm²) on GaAs (100) substrates. We have achieved lattice matched ZnSSe films on GaAs substrates using photoassisted growth using dimethylzinc (DMZn), dimethylselenide (DMSe), and tertiary-butylmercaptan (t-BuSH) as precursors. In addition, we have obtained sulfur compositions (y), ranging from 0.023 to unity (ZnS). The growth rate of the ZnS was 1 μm/h, which was previously unattainable by our group using diethylsulfur. The closely lattice matched sample (y=0.07 as determined by high resolution x-ray diffraction) showed a near band edge peak intensity (NBE) to deep level emission intensity (DLE) ratio of 77 to 1, as determined by room temperature photoluminescence measurements. We have examined the sulfur incorporation as a function of source mole fractions, UV intensity, and growth temperature and found that optimized growth conditions (optimized for range of compositions possible, and NBE/DLE ratio) are X_DMZn=1.5 × 10⁻⁴, X_DMSe=3×10⁻⁴, UV=14 mW/cm², growth temperature=340°C. X_DMZn and X_DMSe are the mole fractions of DMZn and DMSe, respectively. We have found the growth rate to be 1 μm/h for y=0.023 to 0.24 for these optimized conditions. It was found that to achieve sulfur compositions of less than 0.9, the t-BuSH mole fractions had to be kept low. Higher UV intensities increased the incorporation of selenium, while also lowering the material quality (NBE/DLE ratios). We have shown that the optical material qualities of ZnSSe films grown with t-BuSH are much better than ZnSSe films grown with DES.     

ZnO和Al2O3缓冲层对AZO透明导电膜薄膜性能的影响

采用射频磁控溅射法,以纯度为99.9%,质量分数98%ZnO、2%Al2O3陶瓷靶为溅射靶材,在预先沉积了ZnO和Al2O3的玻璃衬底上制备了Al2O3掺杂的ZnO薄膜。研究并对比了两种不同的缓冲层对ZnO∶Al(AZO)薄膜的微观结构和光电性能的影响。并借助X线衍射(XRD)仪、扫描电子显微镜(SEM)、紫外可见光谱仪(UV-Vis)等方法测试和分析了不同缓冲层,对AZO薄膜的形貌结构、光电学性能的影响。结果表明:加入缓冲层后,在衬底温度为200℃时,溅射30min,负偏压为60V、在氮气气氛下经300℃退火处理后,制得薄膜的可见光透过率为83%～87%,AZO薄膜的最低电阻率,从9.2×10-4Ω.cm(玻璃)分别下降到8.0×10-4Ω.cm(ZnO)和5.4×10-4Ω.cm(Al2O3)。     

MOVPE growth and optical properties of gan deposited on c-plane sapphire

We address combined utilization of temperature dependent reflectance, photo-luminescence, and Raman spectroscopy measurements to optimize the struc-tural and electronic properties of GaN epilayers deposited on sapphire. Last, we study residual strain fields in such epilayers.     

ZnO nanoparticles as a luminescent down-shifting layer for photosensitive devices

The optical properties of ZnO nanoparticles(NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting(DS) efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device(photodiode),thereby increasing its efficiency.Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency(EQE) characteristics of the final devices were measured.Through comparison of the photodiode’s EQE characteristics before and after the deposition of the ZnO NPs layer,it was concluded that for the photodiode with a low UV sensitivity(about 8%),the ZnO luminescent layer produces a down-shifting effect and the EQE in the UV and blue range improves by 16.6%,while for the photodiodes with a higher initial UV sensitivity(about 50%),the EQE in this range decreases with the ZnO layer thickness,due to the effects competing with DS,like the diminution of the ZnO layer transmittance and an increasing diffusion.     

利用磁控溅射在GaN/蓝宝石衬底上生长ZnO薄膜

Zinc oxide (ZnO) thin films were grown on n-GaN/sapphire substrates by radio-frequency (RF) magnetron sputtering. The films were grown at substrate temperatures ranging from 400 to 700 ℃ for 1 h at a RF power of 80 W in pure Ar gas ambient. The effect of the substrate temperature on the structural and optical properties of these films was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra. XRD results indicated that ZnO films exhibited wurtzite symmetry and c-axis orientation when grown epitaxially on n-GaN/sapphire. The best crystalline quality of the ZnO film is obtained at a growth temperature of 600 ℃. AFM results indicate that the growth mode and degree of epitaxy strongly depend on the substrate temperature. In PL measurement, the intensity of ultraviolet emission increased initially with the rise of the substrate temperature, and then decreased with the temperature. The highest UV intensity is obtained for the film grown at 600 ℃ with best crystallization. oindent     

Epitaxial growth of ZnO on GaN/sapphire substrate by radio-frequency magnetron sputtering

Zinc oxide (ZnO) thin films were grown on n-GaN/sapphire substrates by radio-frequency (RF) magnetron sputtering. The films were grown at substrate temperatures ranging from 400 to 700 ℃ for 1 h at a RF power of 80 W in pure Ar gas ambient. The effect of the substrate temperature on the structural and optical properties of these films was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra. XRD results indicated that ZnO films exhibited wurtzite symmetry and c-axis orientation when grown epitaxially on n-GaN/sapphire. The best crystalline quality of the ZnO film is obtained at a growth temperature of 600 ℃. AFM results indicate that the growth mode and degree of epitaxy strongly depend on the substrate temperature. In PL measurement, the intensity of ultraviolet emission increased initially with the rise of the substrate temperature, and then decreased with the temperature. The highest UV intensity is obtained for the film grown at 600 ℃ with best crystallization.     

Enhancement of ZnO ultraviolet emission by surface plasmon coupling using a rough NiSi_2 layer synthesized by ion implantation

The calculation results of the surface plasmon(SP) energy and Purcell factor of ZnO/NiSi_2 demonstrate the possibility of using NiSi_2 to enhance the UV emission of ZnO by SP coupling.Experimentally,ZnO films were deposited on NiSi_2 layers synthesized by ion implantation,and the roughness of the NiSi_2 layers spans a large range from 3 to 38 nm,providing favorable conditions for investigating SP-mediated emission.An 11-fold emission enhancement from the ZnO film on the roughest NiSi_2 layer was obtained...     

Electrical and optical properties of oxygen doped GaN grown by MOCVD using N2O

Oxygen doped GaN has been grown by metalorganic chemical vapor deposition using N₂O as oxygen dopant source. The layers were deposited on 2″ sapphire substrates from trimethylgallium and especially dried ammonia using nitrogen (N₂) as carrier gas. Prior to the growth of the films, an AIN nucleation layer with a thickness of about 300? was grown using trimethylaluminum. The films were deposited at 1085°C at a growth rate of 1.0 μm/h and showed a specular, mirrorlike surface. Not intentionally doped layers have high resistivity (>20 kW/square). The gas phase concentration of the N₂O was varied between 25 and 400 ppm with respect to the total gas volume. The doped layers were n-type with carrier concentrations in the range of 4×10¹⁶ cm⁻³ to 4×10¹⁸ cm⁻³ as measured by Hall effect. The observed carrier concentration increased with increasing N₂O concentration. Low temperature photoluminescence experiments performed on the doped layers revealed besides free A and B exciton emission an exciton bound to a shallow donor. With increasing N₂O concentration in the gas phase, the intensity of the donor bound exciton increased relative to that of the free excitons. These observations indicate that oxygen behaves as a shallow donor in GaN. This interpretation is supported by covalent radius and electronegativity arguments.     

适用SAW器件的ZnO/Ti/Si薄膜制备及缺陷分析

在Si(100)衬底和Ti/Si(100)衬底上分别制备了ZnO薄膜,探讨了Ti缓冲层对ZnO薄膜结构和缺陷的影响,利用X射线衍射(XRD)测试了ZnO薄膜的晶体结构及择优取向,利用原子力显微镜(AFM)观察ZnO薄膜的表面粗糙度(RMS),利用光致发光(PL)光谱检测了ZnO薄膜的缺陷,利用四探针法测试了ZnO薄膜的电阻率。结果表明,在Ti/Si(100)衬底上、衬底温度350℃的条件下,制备的ZnO薄膜表面光滑、缺陷少、电阻率高且具有高C轴取向。本文这一工作对于压电薄膜缺陷分析及高性能ZnO的声表面波(SAW)器件研制有重要意义。     

自然掺杂及N-Al共掺杂ZnO薄膜的发光特性

采用螺旋波等离子体辅助溅射技术制备了自然掺杂及N-Al共掺杂ZnO薄膜,对两种不同类型掺杂薄膜的低温光致发光(PL)特性进行了研究。实验结果表明,二者均呈现出了较强的与受主能级相关的发光特征,自然掺杂薄膜的光致发光谱在404.0 nm处出现了由于锌空位产生的近带边发光,N-Al共掺杂薄膜的光致发光谱在383.0 nm处出现了N作为受主的施主-受主对(DAP)跃迁发光。两种薄膜的发光特性比较分析表明,N-Al共掺杂技术能够有效提高N的固溶度,N受主能级密度增加使薄膜表现出较强的施主-受主对跃迁发光,表明该技术为实现p型ZnO薄膜制备的有效方法。     

两步法生长ZnO纳米棒的结构及其发光特性

应用两步法在玻璃衬底上制备了高度取向的ZnO纳米棒,并研究了衬底和反应时间等参数对其结构及发光特性的影响。从样品的扫描电镜(SEM)图中发现,利用脉冲激光沉积(PLD)方法在玻璃衬底上生长一层ZnO薄膜作为修饰层,可以明显提高水热法生长的ZnO纳米棒的结晶质量。样品的SEM和光致发光(PL)谱表明,在有ZnO修饰层的玻璃衬底上生长的ZnO纳米棒分布均匀,排列致密,取向性好;缺陷发光的发光强度约是激子发光峰的2倍,且随着反应时间增长,样品的缺陷发光增强而激子发光减弱。     

氮化Si基ZnO/Ga_2O_3制备GaN薄膜

利用射频磁控溅射法在Si衬底上先溅射ZnO缓冲层,接着溅射Ga2O3薄膜,然后ZnO/Ga2O3膜在管式炉中常压下通氨气进行氮化,反应自组生成GaN薄膜。XRD测量结果表明,利用该方法制备的GaN薄膜是沿c轴方向择优生长的六角纤锌矿多晶结构的薄膜,利用SEM观测了其表面形貌,PL测量结果发现了位于351nm处的室温光致发光峰。     

ZnO纳米颗粒表面缺陷对有机太阳能电池性能的影响

用温度控制ZnO纳米 颗粒粒径的大小,研究了颗粒粒径对表面缺陷的影响。由透射电镜(TEM)、紫外-吸收光谱 和荧光光谱测试表明,随着反应温度升高,ZnO纳米颗粒的尺寸增加,比表面积显著下降, 表面缺陷的体密度降低。将不同反应温 度下的ZnO纳米颗粒应用于ITO/ZnO/P3HT:PCBM/MoO₃/Ag结构的有机太阳能电池中,进一 步研究了缺陷对电池性能的影 响。实验结果表明,60℃下ZnO纳米颗粒薄膜作为电子传输层的器件 效果最好,电池效率可以达到3.05%。 这表明在一定范围内,ZnO纳米颗粒越大,缺陷密度越低,越有利于器件中电子的传输从而 提高太阳能电池器件的短路电流密度和光电转化效率。     

Criteria for versatile GaN MOVPE tool: high growth rate GaN by atmosphericpressure growth

Growth rate has a direct impact on the productivity of nitride LED production. Atmospheric pressure growth of GaN with a growth rate as high as 10 μm/h and also Al_0.1Ga_0.9N growth of 1 μm/h by using 4 inch by 11 production scale MOVPE are described. XRD of (002) and (102) direction was 200 arcsec and 250 arcsec, respectively. Impact of the growth rate on productivity is discussed.