SHI induced re-crystallization of Ge implanted SiO2 films

Ge nanocrystals embedded in SiO₂ matrix have been synthesized by swift heavy ion irradiation of Ge implanted SiO₂ films. In the present study, 400 keV Ge⁺ ions were implanted into SiO₂ films at dose of 3 × 10¹⁶ ions/cm² at room temperature. The as-implanted samples were irradiated with 150 MeV Ag¹²⁺ ions with various fluences. Similarly 400 keV Ge⁺ ions implanted into Silicon substrate at higher fluence at 573 K have been irradiated with 100 MeV Au⁸⁺ ions at room temperature (RT). These samples were subsequently characterized by XRD and Raman to understand the re-crystallization behavior. The XRD results confirm the presence of Ge crystallites in the irradiated samples. Rutherford backscattering spectrometry (RBS) was used to quantify the concentration of Ge in the SiO₂ matrix. Variation in the nanocrystal size as a function of ion fluence is presented. The basic mechanism of ion beam induced re-crystallization has been discussed.     

Photoluminescence induced by Si implantation into Si3N4 matrix

Up to the present, photoluminescence (PL) was obtained from near stoichiometric or amorphous Si nitride films (SiN_x) after annealing at high temperatures. As a consequence, the existence of PL bands has been reported in the 400–900 nm range. In the present contribution, we report the first PL results obtained by Si implantation into a stoichiometric 380 nm Si₃N₄ film. The Si excess is obtained by a 170 keV Si implantation at different temperatures with a fluence of Φ = 10¹⁷ Si/cm². Further, we have annealed the samples in a temperature range between 350 and 900 °C in order to form the Si precipitates. PL measurements were done using an Ar laser as an excitation source, and a broad PL band basically centered at 910 nm was obtained. We show that the best annealing condition is obtained at T_a = 475 °C for the samples implanted at 200 °C, with a PL yield 20% higher than the obtained at room temperature implantation. Finally, we have varied the implantation fluence and, consequently, the Si nanocrystals size. However, no variation was observed nor in the position neither in the intensity of the PL band. We concluded that the PL emission is due to radiative states at the matrix and the Si nanocrystals interface, as previously suggested in the literature.     

Nanometer-thick SGOI structures produced by Ge+ ion implantation of SiO2 films and subsequent hydrogen transfer of Si layers

Nanometer-thick silicon-germanium-on-insulator (SGOI) structures have been produced by the implantation of Ge⁺ ions into thermally grown SiO₂ layer and subsequent hydrogen transfer of silicon film on the Ge⁺ ion implanted substrate. The intermediate nanometer-thick Ge layer has been formed as a result of the germanium atom segregation at the Si/SiO₂ bonding interface during annealing at temperatures 800–1100 ^оС. From a thermodynamic analysis of Si/Ge/SiO₂ system, it has been suggested that the growth of the epitaxial Ge layer is provided by the formation of a molten layer at the Si/SiO₂ interface due to the Ge accumulation. The effect of germanium on the hole mobility in modulation-doped heterostructures grown over the 3–20 nm thick SGOI layers was studied. An increase in the Hall hole mobility in SGOI-based structures by a factor of 3–5 was obtained in comparison with that in respective Ge-free SOI structures.     

Avalanche Injection of Holes into SiO2

Avalanche injection techniques are used to provide hole currents through MOS capacitors and study the trapping of holes in the oxide layer. Although radiation is not in any way involved in these experiments, the trapped positive charge and surface states resulting from hole injection are similar to those obtained using radiation. The processing and oxide thickness dependence of hole trapping phenomena are also investigated. Prolonged post-oxidation annealing treatments are shown to lead to enhanced hole trapping in "hardened" oxides. Hole trapping cross-sections between 10-13 and 10-14 cm2 and trap densities between 1012 - 1013 cm-2 are measured depending on the processing conditions. The effective charge density is studied over the range of oxide thickness between 200 ? and 600 ? as a function of post-oxidation anneal in these "hardened" oxides. While the effective charge density is only weakly dependent on oxide thickness in unannealed oxides, in annealed oxides it exhibits a strong linear dependence of trapping on oxide thickness. The dependence on post-oxidation anneal time and ambient are also discussed. These results indicate a strong similarity between hole trapping induced by avalanche injection and by radiation.     

Photoluminescence study of Ge nanocrystals irradiated by reactor neutron flux

Samples of Ge nanocrystals (Ge-ncs) embedded in amorphous SiO₂ film were prepared by Ge ion implantation and subsequent primary thermal annealing. These samples were irradiated by neutron flux in a nuclear reactor followed by the second annealing. Irradiation with thermal neutrons leads to doping of nanocrystals with Ga, As and Se impurities due to nuclear transmutation of isotope ⁷⁰Ge into ⁷¹Ga, isotope ⁷⁴Ge into ⁷⁵As, isotope ⁷⁶Ge into ⁷⁷Se, respectively (neutron transmutation doping, NTD). Irradiation with fast neutrons leads to appearance of radiation damages, which are expected to be removed after the second annealing. Photoluminescence (PL) measurements show that PL is quenched after neutron irradiation, and restored after annealing higher than 500 °C. The PL spectra of doped Ge-ncs samples show more intense exciton radiative luminescence than of undoped Ge-ncs sample, which is related to that the donor and acceptor impurities recombine the nonradiative centers in the interface of Ge-ncs and SiO₂ matrix, and enhance the probability of exciton recombination.     

Characterization of extended defects in SiGe alloys formed by high dose Ge implantation into Si

The synthesis of SiGe/Si heterostructures by Ge⁺ ion implantation is reported. 400 keV Ge⁺ ions were implanted at doses ranging from 3 × 10¹⁶ to 10 × 10¹⁶ ions/cm² into (001) Si wafers, followed by Si⁺ amorphisation and low temperature Solid Phase Epitaxial Regrowth (SPER). TEM investigations show that strained alloys can be fabricated if the elastic strain energy (E_el) of the SiGe layer does not exceed a critical value (E′_el) of about 300 mJ/m², which is independent of the implantation energy. Our analysis also suggests that “hairpin” dislocations are formed as strain relieving defects in relaxed structures. A “strain relaxation” model is proposed to explain their formation.     

荧光EXAFS研究镶嵌在SiO2中的Ge纳米晶的局域结构

用荧光扩展X射线吸收精细结构(EXAFS)研究了磁控溅射法制备的镶嵌在SiO2中的Ge纳米晶的局域结构.结果表明,在Ge的摩尔分数为25%和60%的初始样品中,Ge原子主要是以非晶GeO2和Ge物相存在,其中在Ge的摩尔分数为25%的样品中,以GeO2物相为主.经1073 K退火后,样品中生成了Ge纳米晶.在Ge的摩尔分数为25%的样品中,Ge纳米晶只是来源于初始样品中的非晶Ge,而在Ge的摩尔分数为60%的样品中Ge纳米晶除了来源于初始样品中的非晶Ge外还来自于部分GeO2.进一步分析表明在Ge的摩尔分数为60%的样品中,有摩尔分数为20%的GeO2与来自衬底的Si发生还原反应生成Ge纳米晶.     

Ti离子注入SiO_2合成TiO_2纳米颗粒及其光学性质

将105 keV的Ti离子注入到SiO_2玻璃至1×10~(17)、2×10~(17) cm~(-2),并在氧气气氛下进行热处理,借助紫外可见分光光度计、掠入射X射线衍射光谱仪、透射电子显微镜、原子力显微镜等多种测试仪器,详细研究了Ti O2纳米颗粒的形成、结构、分布及其光吸收和催化性能。研究结果表明,高注量Ti离子注入结合氧气气氛热处理可以在SiO_2基底中形成TiO_2纳米颗粒,并以金红石相为主。合成的TiO_2纳米颗粒的形貌明显依赖于离子的注量,随离子注量增加,形状不规则且分散排列的TiO_2纳米颗粒会转变成尺寸较为均匀、分布致密的纳米颗粒,进而形成了TiO_2类颗粒膜结构。另外,光催化降解实验结果表明,合成的纳米颗粒对罗丹明B溶液具有一定的降解作用。     

Ge nano-layer fabricated by high-fluence low-energy ion implantation

A Ge nano-layer embedded in the surface layer of an amorphous SiO₂ film was fabricated by high-fluence low-energy ion implantation. The component, phase, nano-structure and luminescence properties of the nano-layer were studied by means of Rutherford backscattering, glancing incident X-ray diffraction, laser Raman scattering, transmission electron microscopy and photoluminescence. The relation between nano-particle characteristics and ion fluence was also studied. The results indicate that nano-crystalline Ge and nano-amorphous Ge particles coexist in the nano-layer and the ratio of nano-crystalline Ge to nano-particle Ge increases with increasing ion fluence. The intensity of photoluminescence from the nano-layer increases with increasing ion fluence also. Prepared with certain ion fluences, high-density nano-layers composed of uniform-sized nano-particles can be observed.     

Er+ implantation in SnO2:SiO2 layers: Structure changes and light emission

Structure changes and light emission behavior in Er⁺ implanted SnO₂:SiO₂ layers are studied, using transmission electron microscopy (TEM), Rutherford backscattering (RBS) and cathodoluminescence (CL). SnO₂:SiO₂ layers of different composition deposited with RF magnetron sputtering on Si wafers were implanted with 200 keV Er⁺ to a fluence of 3 × 10¹⁵ cm^?2 at room temperature. The implanted structures were then annealed at 600–1000 °C for 30 min, resulting in the formation of crystalline SnO₂ nanoclusters. Cross-section TEM revealed a strong reduction of the SnO₂ crystallite size down to several nanometers in the implanted area of the SnO₂:SiO₂ layer as compared to the undoped layer. In addition, a very narrow layer of SnO₂ nanocrystals appears at the SiO₂/Si interface. Several narrow CL emission peaks and wide bands were found which could be related to the decay of SnO₂ free excitons, to oxygen deficiency centers in SiO₂ and to transitions between the energy levels in the Er ions, apparently located at nanoclusters. The mechanisms of nanostructuring as well as the emission process are discussed.     

Effects of BF2+ implantation on the strain-relaxation of pseudomorphic metastable Ge0.06Si0.94 alloy layers

Metastable pseudomorphic Ge_0.06Si_0.94 alloy layers grown by molecular beam epitaxy (MBE) on Si (1 0 0) substrates were implanted at room temperature by 70 keV BF₂⁺ ions with three different doses of 3 × 10¹³, 1 × 10¹⁴, and 2.5 × 10¹⁴ cm⁻². The implanted samples were subsequently annealed at 800°C and 900°C for 30 min in a vacuum tube furnace. Observed by MeV ⁴He channeling spectrometry, the sample implanted at a dose of 2.5 × 10¹⁴ BF₂⁺ cm⁻² is amorphized from surface to a depth of about 90 nm among all as-implanted samples. Crystalline degradation and strain-relaxation of post-annealed Ge_0.06Si_0.94 samples become pronounced as the dose increases. Only the samples implanted at 3 × 10¹³ cm⁻² do not visibly degrade nor relax during anneal at 800°C . In the leakage current measurements, no serious leakage is found in most of the samples except for one which is annealed at 800°C for 30 min after implantation to a dose of 2.5 × 10¹⁴ cm⁻². It is concluded that such a low dose of 3 × 10¹³ BF₂⁺ cm⁻² can be doped by implantation to conserve intrinsic strain of the pseudomorphic GeSi, while for high dose regime to meet the strain-relaxation, annealing at high temperatures over 900°C is necessary to prevent serious leakages from occuring near relaxed GeSi/Si interfaces.     

Regular surface patterns by local swelling induced by He implantation into silicon through nanosphere lithography masks

Nanopatterning of silicon surfaces by means of He⁺ ion implantation through self-organized colloidal masks is reported for the first time. Nanosphere lithography (NSL) masks with mask openings of 46–230 nm width were deposited on Si(1 0 0) wafers. He⁺ ions were implanted through these masks in order to induce a local cavity formation and Si surface swelling. The surface morphology and the subsurface structure were studied using atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM), respectively, as a function of mask and implantation parameters. It is demonstrated that regular arrays of both individual hillocks and trough-like circular rings can be generated.     

硅基体的金属钼反冲注入

在某基体的表面,真空蒸镀一层其它材料的薄膜,用离子轰击时将引起原子级联碰撞而导致基体原子和薄层原子的混合,特别是在界面区域的混合。所谓反冲注入是指薄层原子在此过程中进入基体的现象。目前,离子束混合已开始应用到半导体器件及金属等材料改性的领域中。     

High temperature silver ion implantation into glass

Soda-lime-silicate glass has been implanted with 55 keV Ag⁺ ions at five different temperatures: room temperature, 100, 225, 350 and 600°C. Rutherford backscattering spectroscopy was used to provide depth profiles for the implants. All samples show a low retention of silver and this varies with temperature. In the room temperature and 100°C implants the silver diffuses to, and is lost from the surface. This also occurs in the higher temperature implants, but in these cases there is a significant amount of inward diffusion by the silver. This diffusion extends to at least 500 nm: greatly in excess of the predicted range for a standard implant. Optical measurements on the samples show that those with the inward diffusion have formed an enhanced-index waveguide.     

High-dose iron implantation into silicon and metals

High-dose implantations of Fe into metals and semiconductors have been performed with energies up to 1 MeV at the UNILAC injector at GSI. Unusually high concentrations of 70 at.% for Si and 20 at.% for Cu have been obtained, with doses of 10¹⁸ Fe/cm² in the case of Si and several times 10¹⁷ Fe/cm² in the case of Cu. For Si the thicknesses of the layers were determined by Rutherford backscattering to be 4500 Å. These results are consistent with calculations, which show that these high concentrations are due to the reduction of the sputter yield at the relatively high particle energies. The cases of Si, Cu and Pb will be discussed. Samples have been characterized using several complementary methods (Mossbauer spectroscopy (MS), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and X-ray diffraction (XRD)).     

半绝缘GaAs材料中的Si、Be双重离子注入

GaAs集成电路要求FET有一致的夹断特性,而半绝缘GaAs衬底的质量对Si全离子注入的MESFET有着重大影响。这是由于高阻衬底中的Cr在离子注入和高温退火后的再分布,注入后载流子分布出现翘尾,使部分器件呈现出异常输出特性,表现为夹断电压偏高,小电流时跨导偏低,难以获得均匀的夹断电压。在N型有源层之下,用离子注入工艺形成一个隐埋的P型层,可以大大改善夹断电压的均匀性。已有报道,通过在沟道层和衬底之间引入一P型层,亚微米栅GaAs MSFET的短沟道效应有效地被抑制了,背栅效应对于GaAs集成电路无疑是有害的,模拟计算也表明,使用近补偿的衬底材料或缓冲层可使背栅沟道电容减至最小。     

Swift-heavy-ion-induced shaping of spherical Ge nanoparticles into disks and rods

The work reports on experimental features and theoretical studies of swift-heavy-ion-induced shaping of Ge nanospheres into disks. A stack of alternating Ge and SiO₂ layers was sputtered on an oxidized Si wafer. The Ge layer thicknesses varied from 2.5 to 7.5 nm. Thermal treatment above the melting temperature of Ge transformed each Ge layer into a layer of Ge nanospheres. With growing Ge layer thickness the mean diameter increases from 8 to 37 nm. Irradiation with low fluences (～10¹⁴ cm^?2) of 38 MeV I⁷⁺ shaped medium-sized Ge nanospheres into disks, whereas smaller ones became rod-like and larger ones remained unchanged. At higher fluences, the larger Ge nanospheres shrink due to Ge loss and shape into disks too. A new model is presented and atomistic Monte-Carlo simulations are shown which describe the shaping evolution and the size thresholds for shaping quantitatively. The volume change of Ge upon melting has been identified as driving force.     

Morphology of the implantation induced disorder in GaAs

Disorder is introduced into GaAs by implantation of ³⁰Si⁺ ions, using a very wide range of ion doses, and studied by Raman scattering (RS) and Rutherford backscattering and ion channeling (RBS). A comparative analysis of mechanisms influencing RS and RBS signals has been made. This analysis revealed that, due to different sensitivity of each method to various defect structures, it is possible to distinguish several different types of implantation induced disorder. RS results indicate that a second type of amorphous structure, having medium-range order, grows at the expense of the continuous-random-network structure, even at doses beyond the threshold for complete amorphization.