蓝宝石衬底上单晶InN外延膜的RF-MBE生长

采用低温氮化铟(InN)缓冲层,利用射频等离子体辅助分子束外延(RF-MBE)方法在蓝宝石衬底上获得了晶体质量较好的单晶InN外延膜.用光学显微镜观察所外延的InN单晶薄膜,表面无铟滴.InN(0002)双晶X射线衍射摇摆曲线的半高宽为14′;用原子力显微镜测得的表面平均粗糙度为3.3nm;Hall测量表明InN外延膜的室温背景电子浓度为3.3×1018cm-3,相应的电子迁移率为262cm2/(V·s).     

蓝宝石衬底上单晶InN外延膜的RF-MBE生长

采用低温氮化铟(InN)缓冲层,利用射频等离子体辅助分子束外延（RF-MBE）方法在蓝宝石衬底上获得了晶体质量较好的单晶InN外延膜．用光学显微镜观察所外延的InN单晶薄膜,表面无铟滴．InN（0002）双晶X射线衍射摇摆曲线的半高宽为14′;用原子力显微镜测得的表面平均粗糙度为3.3nm;Hall测量表明InN外延膜的室温背景电子浓度为3.3e18cm－3,相应的电子迁移率为262cm2/（V·s）．     

HVPE法制备GaN过程中GaAs衬底的氮化

在自制的立式氢化物气相外延(HVPE)系统炉中,一定温度下通入一定流量的NH3使GaAs(111)衬底氮化一层GaN薄膜,以防止高温外延生长GaN时GaAs分解,进而提高了之后GaN外延生长的晶体质量。实验主要通过XRD检测氮化层的质量,研究了氮化温度和时间对氮化层的影响。实验发现,氮化温度过高会使GaAs表面分解,氮化层为多晶。氮化时间过短,氮化层致密性低,不能起到保护衬底的作用;时间过长则氮化层质量降低,GaN(002)半高宽(FWHM)较大。分析结果表明,在500℃氮化2min的工艺条件下,获得的氮化层质量相比其他条件较好,致密性高。     

外延GaN基薄膜表面晶体结构RHEED图像研究

论述了反射高能电子衍射(RHEED)作为外延薄膜进行原位监测的一个重要手段以及RHEED图像与外延薄膜的表面形貌的关系,提出了以RHEED图像分析外延GaN基薄膜晶格结构的演变情况,并从衬底α-Al2O3的等离子体清洗、氮化进行了具体的分析和演算.结论指出,RHEED不仅是进行外延薄膜原位监测,而且还可以作为分析外延薄膜晶体结构演变的一个有力手段.     

Si衬底的氮化处理对ZnO薄膜质量的影响

用氮化处理的方法对Si衬底的表面进行钝化,外延生长出高质量的ZnO薄膜。ZnO薄膜的质量通过X 射线(XRD)、阴极射线(CL)谱和光致发光(PL)谱来表征。氮化的作用主要表现在生长ZnO薄膜的XRD的半高宽由未经氮化的0.25°;减小为经氮化后的0.20°,CL谱的紫外发光增强,深缺陷发光变弱。这说明,在ZnO外延生长前,对Si表面的氮化是一种提高其质量的有效方法。并对氮化处理提高ZnO薄膜质量的机理进行了探索。     

蓝宝石上生长高质量InN单晶薄膜的研究发展

通过介绍蓝宝石衬底上生长氮化铟(InN)单晶薄膜的发展历程,阐述了生长该单晶薄膜的几种方法及生长过程中存在的一些问题和改进措施,说明了生长高质量InN单晶薄膜的有效途径,为InN的生长及应用提供了理论与技术指导。     

氮化时间对脉冲激光沉积AlN薄膜性能的影响

应用脉冲激光沉积(PLD)技术在氮化处理后的蓝宝石衬底上外延生长AlN薄膜。研究了氮化处理时间对AlN薄膜结构性能和表面形貌的影响,利用原位反射式高能电子衍射(RHEED)对生长过程进行实时观测,利用高分辨X射线衍射仪(HRXRD)和扫描电子显微镜(SEM)对AlN薄膜的结构性能以及表面形貌等进行表征和分析。结果表明,随着氮化时间的增加,AlN形核种子数量增加并逐渐有序,促进AlN薄膜由多晶转为单晶并提高其晶体质量,有利于AlN薄膜由三维生长转为二维生长,改善AlN薄膜表面形貌。为采用PLD技术制备高质量AlN基器件提供了一种新思路。     

外延GaN基薄膜表面应变演变RHEED分析

介绍了反射式高能电子衍射仪(RHEED)衍射原理以及半导体薄膜表面原子间距与其衍射图像间距成反比例关系。分析了采用ECR-PEMOCVD生长技术,在α-Al2O3衬底上低温外延GaN基薄膜(氮化层、缓冲层、外延层)工艺过程。通过对RHEED图像分析软件获取不同工艺过程中的外延薄膜衍射条纹间距的数据分析、计算、比较,得到薄膜表面衍射图像间距的大小,依据RHEED衍射图像与原子面间距之间的对应关系,分析薄膜表面的应变状态演变情况。分析计算结果表明生长20min氮化层、20min缓冲层的表面原子层处于压应变状态,而生长180min的AlN外延层,表面则处于完全弛豫状态。     

CeO2高K栅介质薄膜的制备工艺及其电学性质

研究了CeO2作为高K(高介电常数)栅介质薄膜的制备工艺,深入分析了衬底温度、淀积速率、氧分压等工艺条件和利用N离子轰击氮化Si衬底表面工艺对CeO2薄膜的生长及其与Si界面结构特征的影响,利用脉冲激光淀积方法在Si(100)衬底生长了具有(100)和(111)取向的CeO2外延薄膜;研究了N离子轰击氮化Si衬底表面处理工艺对Pt/CeO2/Si结构电学性质的影响.研究结果显示,利用N离子轰击氮化Si表面/界面工艺不仅影响CeO2薄膜的生长结构,还可以改善CeO2与Si界面的电学性质.     

CeO_2高K栅介质薄膜的制备工艺及其电学性质

研究了 Ce O2 作为高 K (高介电常数 )栅介质薄膜的制备工艺 ,深入分析了衬底温度、淀积速率、氧分压等工艺条件和利用 N离子轰击氮化 Si衬底表面工艺对 Ce O2 薄膜的生长及其与 Si界面结构特征的影响 ,利用脉冲激光淀积方法在 Si(10 0 )衬底生长了具有 (10 0 )和 (111)取向的 Ce O2 外延薄膜 ;研究了 N离子轰击氮化 Si衬底表面处理工艺对 Pt/ Ce O2 / Si结构电学性质的影响 .研究结果显示 ,利用 N离子轰击氮化 Si表面 /界面工艺不仅影响 Ce O2 薄膜的生长结构 ,还可以改善 Ce O2 与 Si界面的电学性质     

Effect of shroud flow on high quality InxGa1−xN deposition in a production scale multi-wafer-rotating-disc reactor

High quality InGaN thin films and InGaN/GaN double heterojunction (DH) structures have been epitaxially grown on c-sapphire substrates by MOCVD in a production scale multi-wafer-rotating-disc reactor between 770 to 840°C. We observed that shroud flow (majority carrier gas in the reaction chamber) is the key to obtaining high quality InGaN thin films. High purity H₂ as the shroud flow results in poor crystal quality and surface morphology but strong photolumines-cence (PL) at room temperature. However, pure N₂ as the shroud flow results in high crystal quality InGaN with an x-ray full width at half maximum (FWHM)_InGaN(0002) of 7.5 min and a strong room temperature PL peaking at 400 nm. In addition, InGaN/GaN single heterojunction (SH) and DH structures both have excellent surface morphology and sharp interfaces. The full width at half maximum of PL at 300K from an InGaN/GaN DH structure is about 100 meV which is the best reported to date. A high indium mole fraction in InGaN of 60% and high quality zinc doped InGaN depositions were also achieved.     

Influence of Substrate Temperature on Structural Properties and Deposition Rate of AlN Thin Film Deposited by Reactive Magnetron Sputtering

Aluminum nitride (AlN) thin films with c-axis preferred orientation have been prepared by reactive direct-current (DC) magnetron sputtering. The degree of preferred crystal orientation, the cross-sectional structure, and the surface morphology of AlN thin films grown on Si (100) substrates at various substrate temperatures from 60°C to 520°C have been investigated by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Results show that the substrate temperature has a significant effect on the structural properties, such as the degree of c-axis preferred orientation, the full-width at half-maximum (FWHM) of the rocking curve, the surface morphology, and the cross-sectional structure as well as the deposition rate of the AlN thin films. The optimal substrate temperature is 430°C, with corresponding root-mean-square surface roughness (R _rms) of 1.97?nm, FWHM of AlN (002) diffraction of 2.259°, and deposition rate of 20.86?nm/min. The mechanisms behind these phenomena are discussed. Finally, film bulk acoustic resonators based on AlN films were fabricated; the corresponding typical electromechanical coupling coefficient (k _t ² ) is 5.1% with series and parallel frequencies of 2.37?GHz and 2.42?GHz, respectively.     

A simple chemical route to synthesize the umangite phase of copper selenide (Cu3Se2) thin film at room temperature

Copper selenide (Cu₃Se₂)thin films have been synthesized with Se as the precursor in aqueous solution by chemical bath deposition technique at room temperature. We have investigated the influence of the growth time ranging from 30 to 90 min on structural, optical and electrical properties of Cu₃Se₂ thin films. The as-grown film at 60 min exhibits a tetragonal structure and is (101) oriented. The maximum value of crystal size D= 55 nm is attained for Cu₃Se₂ films grown at 60 min. The Raman spectrum reveals a pronounced peak at 259 cm^-1, which is assigned to vibrational (stretching) modes from the covalent Se-Se bonds. The optical band gap energy is 1.91 to 2.01 eV with growth time increased from 30 to 90 min. The scanning electron microscopy (SEM) study reveals that the grains are uniform and spread over the entire surface of the substrate of the film at 60 min. The Hall effect study reveals that the film exhibits p-type conductivity. The synthesized film showed good absorbance in the visible region which signifies that synthesized Cu₃Se₂ films can be suitable as a sensitized material in semiconductor sensitized solar cells.     

Effects of surface porosity on tungsten trioxide(WO3) films’ electrochromic performance

In this paper, the correlation between the electrochromic performance and the surface morphology of the tungsten trioxide (WO₃) thin films sputtered by dc reactive magnetron sputtering with widely varying target-substrate distances was investigated. It is found that the optical density change (ΔOD) of films is strongly affected by the target-substrate distance. The coloration efficiency (CE) at 633 nm was also found to be sensitive to the target-substrate distance, with 16 cm²/C of film sputtered at 6 cm and 50 cm²/C at 18 cm. X-ray diffraction showed that the crystal structure of films was amorphous. By using atomic force microscope to identify the surface porosity of the sputtered WO₃ films, we found that the film at longer target-substrate distance was rough, porous, and having a cone-shaped columns morphology, thus offering a good electrochromic performance for opto-switching applications.     

Characterization of nanocrystalline PbS thin films prepared using microwave-assisted chemical bath deposition

Nanocrystalline lead sulfide (PbS) thin films were synthesized on glass substrates using microwave-assisted chemical bath deposition (CBD) method. Various deposition periods of time ranging from 30 to 120 min were used. Results demonstrated that the thickness of the thin films increased with longer deposition time. X-ray diffraction (XRD) measurement revealed that all thin films have cubic rock salt (NaCl) type structure. The surface morphology studied using scanning electron microscopy (SEM) showed that the films have uniform surface morphology over the entire substrate and were of good quality. AFM images confirm that the films have a smooth surface with good adherence to the substrate, a narrow particle size distribution, and that the surface roughness increased with increasing deposition time. Energy gap E_g decreases as the deposition time increases. Electrical measurements revealed that all films were p-type and that the conductivity decreased as the deposition time increased.     

Nanoscale structural characteristics and electron field emission properties of transition metal–fullerene compound TiC60 films

Transition-metal compound TiC₆₀ thin films were grown by co-deposition from two separated sources of fullerene C₆₀ powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C₆₀ structure with certain amount of sp³ bonds and a rough surface with a large number of nanoclusters. z–V tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm² and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC₆₀ thin films can be ascribed to structural variation of C₆₀ in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C₆₀ matrix.     

Effects of ammonia concentration on property of Cd1−xZnxS films by chemical bath deposition

Cd_1−xZn_xS thin films were grown on soda–lime glass substrates by chemical-bath deposition (CBD) at 80 °C with stirring. All the samples were annealed at 200 °C for 60 min in the air. The crystal structure, surface morphology, thickness and optical properties of the films were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), step height measurement instrument and spectrophotometer respectively. The results revealed that Cd_1−xZn_xS thin films had cubic crystal structure and the intensity of the diffraction peak increased gradually as ammonia concentration rose and the grain size varied from 5.1 to 8.3 nm. All of Cd_1−xZn_xS thin films had a granular surface with some smaller pores and the average granule sizes increased from 92 to 163 nm with an increase in ammonia concentration. The Cd_1−xZn_xS thin films had the highest transmittance with ammonia concentration of 0.5 M L⁻¹, whose thickness was 50 nm and band gap was 2.62 eV.     

Unveiling the Nanoparticle‐Seeded Catalytic Nucleation Kinetics of Perovskite Solar Cells by Time‐Resolved GIXS

Recently, a new seeding growth approach for perovskite thin films is reported to significantly enhance the device performance of perovskite solar cells. This work unveils the intermediate structures and the corresponding growth kinetics during conversion to perovskite crystal thin films assisted by seeding PbS nanocrystals (NCs), using time‐resolved grazing‐incidence X‐ray scattering. Through analyses of time‐resolved crystal formation kinetics obtained from synchrotron X‐rays with a fast subsecond probing time resolution, an important “catalytic” role of the seed‐like PbS NCs is clearly elucidated. The perovskite precursor‐capped PbS NCs are found to not only accelerate the nucleation of a highly oriented intermediate phase, but also catalyze the conversion of the intermediate phase into perovskite crystals with a reduced activation energy E_a = 47 (±5) kJ mol^?1, compared to 145 (±38) kJ mol^?1 for the pristine perovskite thin film. The reduced E_a is attributed to a designated crystal lattice alignment of the perovskite nanocrystals with perovskite cubic crystals; the pivotal heterointerface alignment of the perovskite crystals coordinated by the Pb NCs leads to an improved film surface morphology with less pinholes and enhanced crystal texture and thermal stability. These together contribute to the significantly improved photovoltaic performance of the corresponding devices.     

Effects of different precursors on Cu2ZnSnS4 thin film solar cells prepared by sputtering method

In this study, the impacts of different precursors on Cu₂ZnSnS₄ thin film solar cells were investigated. The two kinds of precursors of (Cu+Sn)/Zn and (Cu+Sn)/ZnS were deposited on Mo-coated soda lime glasses by magnetron sputtering. Cu₂ZnSnS₄ (CZTS) films based on different precursors were fabricated by soft annealing and following two-step sulfurization in sulphur vapour. The crystal structure, phase purity, surface morphology, composition and optical properties of CZTS films from different precursors were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), energy dispersive spectrometry (EDS) and UV–vis–NIR spectroscopy, respectively. As a result, the CZTS thin films with smooth surface and uniform compositional ratio distribution were obtained from the precursors of (Cu+Sn)/ZnS. The best conversion efficiency of the fabricated CZTS film solar cell based on (Cu+Sn)/ZnS precursors was 3.36%.     

Tuning the Properties of CZTS Films by Controlling the Process Parameters in Cost-Effective Non-vacuum Technique

Highly dispersive Cu₂ZnSnS₄ (CZTS) nanoparticles were successfully synthesized by a simple solvothermal route. A low cost, non-vacuum method was used to deposit CZTS nanoparticle ink on glass substrates by a doctor blade process followed by selenization in a tube furnace to form Cu₂ZnSn (S,Se)₄ (CZTSSe) layers. Different selenization conditions and particle concentrations were considered in order to improve the crystallinity and surface morphology; the annealing temperature was varied between 400°C and 550°C and the annealing time was varied between 5 min and 20 min in a selenium-nitrogen atmosphere. The influence of annealing conditions on structural, compositional, optical and electrical properties of CZTSSe thin films was studied. An improvement in the structural and surface morphology was observed with increasing of annealing temperature (up to 500°C). An enhancement in the crystallinity and surface morphology were observed for thin films annealed for 10–15 min. Absorption study revealed that the band gap energy of as-deposited CZTS thin film was approximately 1.43 eV, while for CZTSSe thin films it ranged from 1.15 eV to 1.34 eV at different annealing temperatures, and from 1.33 eV to 1.38 eV for different annealing times.