Ion Beam Induced Epitaxial Crystallization Research Articles

Quantitative characterization of occupational sites of implanted P atoms in diamond

The authors implanted P atoms at 50 and 140-keV energies with respective fluences of 1×1014 and 2×1014/cm2 into diamond thin films synthesized by chemical vapor deposition on the type-Ib diamond substrate formed by high-pressure and high-temperature conditions. The occupational sites of implanted P atoms were determined in each processing stage of P implantation, ion-beam-induced epitaxial crystallization (IBIEC) annealing by 3-MeV-Ne2+ ion irradiation at 750°C, and thermal annealing at 850°C in vacuum, by quantitatively comparing the random and channeling yields in Rutherford backscattering (RBS) measurements. In the analysis of RBS spectra, simulated distributions were fitted to the experimentally obtained spectra and we quantitatively identified the occupational sites and ratio of implanted P atoms. In addition, we investigated the diffusion phenomenon of implanted P atoms during annealing processes from the depth profile of scattered He ions. Consequently, the averaged occupational ratio in the substitutional lattice site was stably recorded around 50%. From the depth profile in the RBS spectra, thermal diffusion of implanted P atoms was clearly observed during the last thermal annealing after MeV-IBIEC annealing. We finally discuss the potentials of the MeV-IBIEC irradiation at relatively low temperatures applying to useful and credible annealing methods for electrical activation as well as recovery of damaged crystallinity.

Epitaxial growth of a deposited amorphous Si layer formed on hydrogen-terminated Si(001) surfaces by ion beam induced epitaxial crystallization combined with ion beam mixing

We have investigated the crystallization process of an amorphous Si layer deposited on hydrogen-terminated Si(001) surfaces by ion beam induced epitaxial crystallization (IBIEC) combined with the ion beam mixing (IBMX) method, aiming at the clarification of the essential IBMX effect on crystallization. In this study, we deposited a 10−15 nm thick amorphous Si layer on clean and two kinds of H-terminated Si(001) surfaces of dihydride (DH) and monohydride (MH), and then carried out the IBMX by 10-keV Si+ ion irradiation with a fluence of 1 × 1015 ions cm−2 at RT near the amorphous/crystalline interface followed by the IBIEC treatment by 180-keV Ar+ ion irradiation with fluences of 5 × 1015 and 1 × 1016 ions cm−2 at 300 °C–500 °C. The thickness of the crystallized layer was quantitatively measured by the Rutherford backscattering channeling method. We found that the epitaxial crystallization of the amorphous Si layer formed on both DH and MH surfaces can be realized by IBMX followed by IBIEC treatments at significantly lower temperatures than 500 °C in all processes. This fact suggests that the epitaxial crystallization of the amorphous layer formed on the crystalline substrate surface terminated by the obstructive layer is effectively enhanced, regardless of the structure and coverage of the interfacial layers. It should be emphasized that the IBIEC combined with IBMX treatments make it possible to epitaxially crystallize the amorphous layers formed on obstructive layers covering crystalline substrates at significantly low temperatures.

The RBS analysis for a thin amorphous Si layer formed on clean and H-terminated Si(0 0 1) surfaces followed by medium-energy IBIEC treatments

We have investigated the crystallization process of an amorphous Si layer grown on a clean and hydrogen-terminated Si(0 0 1) surfaces by ion beam induced epitaxial crystallization (IBIEC). It is widely known that the amorphous/crystalline (a/c) interface should be atomically controlled to achieve the high-quality Si epitaxy. In this study, we quantitatively clarify the influence of interfacial H amount to the IBIEC rate of the deposited amorphous Si layer. We initially prepared a typical H-free pristine Si(0 0 1)-(2 × 1) surface and two kinds of chemically H-terminated surfaces of as-treated and sequentially annealed at 350 °C in ultrahigh vacuum, corresponding to high (dihydride) and low (monohydride) hydrogen coverage, respectively. An amorphous Si layer was then in-situ deposited on these three types of surfaces by an electron bombardment evaporator at room temperature. The samples were irradiated by 180-keV Ar+ ions with an ion fluence of 5 × 1015 ions cm−2 at 300–500 °C. The Rutherford backscattering (RBS) analysis showed that the deposited Si on the dihydride surface is not crystallized at these temperatures; whereas, that on the monohydride surface is crystallized by Ar+ irradiation at 500 °C. The crystallization on the MH surface was found at significantly higher temperature than that on the H-free clean surface. The behavior of the interfacial H atoms during IBIEC process is discussed by means of RBS analysis.

Local structure study of GeMn recrystallization process by helium ion beam-induced epitaxial crystallization

In this study, GeMn thin films were fabricated by implantation of Mn ions at room temperature. Post-annealing was performed using 2MeV of He+ ion irradiation. The recrystallization phenomena of the GeMn thin films were analyzed by Raman scattering. High-resolution transmission electron microscopy was also used to characterize the recrystallization process before and after ion beam annealing. A structure phase transition-like behavior of the recrystallization process of GeMn thin films was observed in the Raman spectra.

Ion beam induced epitaxial crystallization of α-Al2O3 at room temperature

The structure of single crystal α-Al2O3 irradiated with 175keV zirconium ions to fluences of 7.5×1015 and 1.5×1016 Zr/cm2 at room temperature, was investigated using Rutherford backscattering spectroscopy with ion channeling (RBS-C) and transmission electron microscopy (TEM). A buried amorphous layer was observed in samples irradiated at room temperature to a fluence of 1.5×1016 Zr+/cm2 (175keV). The buried amorphous region is sandwiched between two highly-damaged crystalline regions. Nano-beam electron diffraction confirmed that both the near-surface damaged layer and the deeper damaged layer remained crystalline, but the buried amorphous region is lacking in long-range atomic order. Post irradiation using 55keV oxygen ions at room temperature into pre-Zr-implanted samples produced ion beam-induced epitaxial crystallization (IBIEC) of the amorphous region adjacent to the near-surface damaged layer. Growth of the metastable polymorph γ-Al2O3 was observed at the amorphous/near surface damaged crystalline interface, as a result of this oxygen ion irradiation.

Regrowth characteristics of SiGe/Si by IBIEC and SPEG

Single crystalline Si1−xGex/Si with three kinds of Ge contents (x: 0.05, 0.1, and 0.2) with thicknesses of 400–440nm were amorphized by 500keV (x: 0.05 and 0.1) and 600keV (x: 0.2) Ge ion beam bombardment to a fluence of 1.0×1016ions/cm2 at room temperature. The regrowth behavior of the damaged layers were compared between ion beam induced epitaxial crystallization (IBIEC) by 2.0MeV Ge ions at 300°C to fluences of 1.0–3.0×1016ions/cm2 and solid phase epitaxial growth (SPEG) carried out in a flowing N2 ambient for up to 40min at 600°C. Rutherford backscattering spectroscopy (RBS) with channeling techniques revealed that crystallinity improvement by IBIEC tended to be saturated with increasing fluence while crystallinity improvement by SPEG was proceeded with increasing annealing time and relatively high quality SiGe layers were obtained. Crystallinity improvement was more rapid and pronounced for SiGe with higher Ge concentration both in IBIEC and SPEG. In contrast to the case of SPEG at 600°C, transmission electron microscope (TEM) image in SiGe treated by IBIEC showed that bunches of dislocation loops remained as islands surrounded by single crystalline lattice layers image, leading to the high RBS aligned yield even after completion of the layer-by-layer regrowth.

Ferromagnetic GeMn thin film prepared by ion implantation and ion beam induced epitaxial crystallization annealing

Ferromagnetic GeMn was prepared by Mn implantation followed by ion beam-induced epitaxial crystallization annealing. The damage caused by Mn implantation was repaired by subsequent helium ion irradiation. Various structural analyses were performed and Mn ions were found to incorporate uniformly into the Ge lattice without the formation of any secondary phases. The remnant magnetic moment exhibited room temperature ferromagnetism. Anomalous Hall effect and field dependent magnetization were measured at the same time at room temperature indicating spin polarized free carrier transport. Additional measurement using x-ray magnetic circular dichroism also revealed that the carriers were spin-polarized.

Synchrotron x-ray multiple diffraction in the study of Fe+ ion implantation in Si(0 0 1)

In this work, x-ray multiple diffraction has been used as a three-dimensional high-resolution probe to study the Fe+ ion implantation process in Si(0 0 1). The semiconducting β-FeSi2 crystallographic phase has been synthesized by Fe ion co-implantation in Si(0 0 1) followed by ion-beam-induced epitaxial crystallization (IBIEC) and thermal treatment. This phase was clearly detected by the conventional techniques, micro-Raman scattering spectroscopy, transmission electron microscopy (TEM) and grazing incidence x-ray diffraction. Synchrotron radiation rocking curves (ω-scans) and mapping of the Bragg surface diffraction (BSD) of the Si matrix, as-implanted, after the IBIEC process and thermally treated, have enabled the detection of co-implanted regions formation that present distinct lattices in comparison with the matrix one clearly observed by TEM. Also, the compressive strain of both regions in depth by rocking curve and in-plane has been determined by using BSD, which is one order of magnitude smaller.

English

Swift heavy ions (SHI) available with 15 million Volt Pelletron accelerator at Inter University Accelerator Centre (IUAC) Delhi, formerly known as Nuclear Science Centre, (NSC), provide a unique opportunity to researchers for accelerator based materials science research. The major research areas can be broadly categorised as electronic sputtering, interface modifications, synthesis and modification of nanostructures, phase transitions and ion beam-induced epitaxial crystallisation. In, general, SHI irradiation based-materials may not be economically feasible, still it could be of interest for very specific cases in defence and space research. The paper gives a glimpse of the current research activities in materials science with SHIs, at IUAC.Defence Science Journal, 2009, 59(4), pp.401-412, DOI:http://dx.doi.org/10.14429/dsj.59.1540

English

Studies on MeV heavy ion beam-induced epitaxial crystallisation of a buried silicon nitride layer are reported. Transmission electron micrographs and selected area diffraction patterns have been used to study the recrystallisation of an ion beam-synthesised layer. Complete recrystallisation of the silicon nitride layer having good quality interfaces with the top- and the substrate-Si has been obsorved. Recrystallisation is achieved at significantly lower temperatures of 100 and 200OC for oxygen and silver ions, respectively. The fact that recrystallisation is achieved at the lowest temperature for the oxygen ions is discussed on the basis of energy loss processes.Defence Science Journal, 2009, 59(4), pp.351-355, DOI:http://dx.doi.org/10.14429/dsj.59.1533

Fabrication of ferromagnetic (Ga,Mn)As by ion irradiation

Using Mn + implantation following ion beam-induced epitaxial crystallization (IBIEC) annealing, high Curie temperature ferromagnetic (Ga,Mn)As thin film was fabricated. The crystalline quality of the Mn + implanted layer was identified by X-ray diffraction (XRD) and transmission electron microscopy (TEM). A clear ferromagnetic transition at T c 253 K was observed by magnetization vs. temperature measurement. We infer that IBIEC treatment is a useful method not only for the low-temperature annealing of (Ga,Mn)As thin films but also for other dilute magnetic semiconductor (DMS) samples.

Amorphization/recrystallization of buried amorphous silicon layer induced by oxygen ion implantation

In this paper we discuss the structural modifications observed in a buried amorphous Si (a-Si) layer containing high oxygen concentration level (up to ∼3 at. %) after being implanted at elevated temperature with O+16 ions. For implants conducted at temperatures lower than 150 °C, the a-Si layer expands via layer by layer amorphization at the front and back amorphous–crystalline (a–c) interfaces. When performed at temperatures above 150 °C, the implants lead to the narrowing of the buried a-Si layer through ion beam-induced epitaxial crystallization at both a–c interfaces. Cross section transmission electron microscopy analysis of samples implanted at 400 °C revealed an array of microtwins and a dislocation network band in the recrystallized material. In samples implanted at 550 °C, only a buried dislocation network band is observed.

Ion beam induced epitaxial crystallization of silicon implanted with heavy ions

In this study we focus on the dynamics of heavy ions during the ion beam induced epitaxial crystallization (IBIEC) of the implanted amorphous layer as a function of annealing dose. Dopants used are with very low solid solubility and low diffusivity in Si. Behaviour of such elements was investigated when they are swept by the moving crystal/amorphous interface. Heavy ions, namely Te, Pb and Bi, were implanted at 100 keV into Si, in order to form amorphous layers. IBIEC of the implanted amorphous silicon was induced at 400 °C using a 3 MeV Si beam. Rutherford backscattering/channeling spectra of the resulting structures indicated that substitutional fractions of the all investigated ions (Te, Pb and Bi) after IBIEC were less than those of the conventional solid phase epitaxial growth.

Surface and Interface Characterization of Ion Beam Re-crystallized Si

ABSTRACTIn the present work we have studied efficacy of ion beam induced epitaxial crystallization (IBIEC) to recover amorphous layers (300 – 350 nm) produced by MeV Kr ions in Si(100) and studied the associated changes occurring on surface and interface of the recrystallized region. IBIEC experiments were carried out at sample temperatures in the range of 200 − 400°C using 1 MeV N+ ion beam. Rutherford backscattering-Channeling technique showed planar and gradual recovery of the amorphous layer as a function of temperature. Transmission electron microscopy measurements show good crystalline structure of the recovered region at 400°C while at lower temperatures nano-crystalline Si formation embedded in the amorphous structure is evident. The surface topography studied by atomic force microscopy shows development of islands after IBIEC. The rms roughness is around 0.5 nm and average height of the islands is found to be 1.8 nm. The observed epitaxial growth and the surface topographical features have been correlated.

Simulation of ion beam induced crystallization and amorphization in (0 0 1) silicon

The ion beam induced epitaxial crystallization (IBIEC) and the ion beam induced interfacial amorphization (IBIIA) in (0 0 1) silicon caused by 3 MeV Si + and 3 MeV Au + irradiation at 293 K and 623 K are investigated by using a combination of binary collision MC simulations and MD simulations. The energy and angular distribution of the primary recoils is calculated by TRIM and the subcascades caused by the primary recoils are treated by classical MD simulations using a correspondingly large MD cell with 49152 atoms. The resulting topological interface structure is analyzed and compared with that obtained by thermally activated solid phase epitaxy. The rates of crystallization and amorphization are calculated and compared with experimental data. Especially, their dependence on the nuclear deposited energy is discussed.

The role of point defects in ion beam induced crystallization of silicon investigated by molecular dynamics simulations

The experimental data and the phenomenological models of ion beam induced epitaxial crystallization (IBIEC) do not yet give unambiguous information about the role of point defects in IBIEC. In this work the influence of vacancies and interstitials present at the amorphous/crystalline (a/c) interface is investigated by classical molecular dynamics (MD) simulations using the Stillinger–Weber (SW) potential. The results show that vacancies near the interface always migrate to the interface and cause crystallization while in the case of interstitials the situation is more complex. The results are discussed with respect to the experimental data and the assumptions made in the different phenomenological models.

Study of ion beam induced epitaxial crystallization of SrTiO3

Amorphous SrTiO3 on single crystal SrTiO3 (100) has been crystallized by He+, Ne+, or Ar+ ions with energy of 200 keV–2 MeV at a substrate temperature of 100–250 °C. Rutherford backscattering spectrometry in channeling geometry and x-ray diffraction were used to evaluate the crystallization. Ion-beam-induced epitaxial crystallization (IBIEC) of SrTiO3 was confirmed and the activation energy of IBIEC observed was about 0.1–0.3 eV, a value about 1/10 relative to thermal solid phase epitaxial crystallization. The observed IBIEC seems to be consistent with previously proposed models in which IBIEC is dominated by point defects produced by ion irradiation and their migration to the amorphous/crystal (a/c) interface. The IBIEC mechanism and point defect behavior are discussed by the use of simple models taking into account the rate limiting processes of IBIEC for both point defect diffusion and atomic rearrangement at a/c interface.

Ion beam induced epitaxy experiments in silicon under channeling and random alignments

This paper examines issues arising in ion beam induced epitaxial crystallisation (IBIEC) of both surface and buried amorphous silicon layers at 320°C under random and channeled alignment of MeV C + beams. These issues include: random versus channeled energy loss, multiple scattering in amorphous layers, direct displacement versus cascade effects on IBIEC and Rutherford backscattering depth scales. Multiple scattering within amorphous layers and channeled energy loss for MeV He + and C + beams were directly measured using Rutherford backscattering/channeling (RBS-C) and markers. When the above issues were taken into account the IBIEC measurements indicated that epitaxial growth is stimulated by silicon displacements very close to the amorphous–crystalline interface. However, effects in buried amorphous layers show that displacements at the interface due to cascades rather than primary ion displacements play a major role in determining random versus channeled behaviour.

Comparison between the reversal temperature of IBIEC–IBIIA transition and critical temperatures of damage formation in ion irradiated InP and InAs

The critical temperature of damage formation in crystalline semiconductors, TC, and the reversal temperature TR of the ion beam induced epitaxial crystallization (IBIEC)–ion beam induced interfacial amorphization (IBIIA) transition are studied for ion irradiated InP and InAs. It is shown that both temperatures, TC and TR, depend on the number of primary displacements per ion and unit depth, N∗displ, and on the dose rate j according to (N∗displ)2j∼exp(−Ea/kTC/R). That means this relation which was first derived to explain TR data of ion irradiation into amorphous/crystalline interfaces in Si, holds well to describe the critical temperature of damage formation in crystalline semiconductors, too. The values of Ea estimated from the dependences of TC and TR given above are almost the same. This is related to the fact that both processes are dominated by the thermal mobility of point defects. TC was found to be always less than TR, i.e., amorphization at an amorphous crystalline interface proceeds at somewhat higher temperatures where amorphization of crystalline material is no longer possible.

Annealing of ion-implanted defects in diamond by MeV ion-beam irradiation

Defects and amorphous C layers or clusters in a type-Ib diamond formed by C- or P-ion implantation under certain doses are clearly annealed or epitaxially crystallized during thermal annealing at 750 \ifmmode^\circ\else\textdegree\fi{}C or during mega-electron-volt (MeV) ion-beam irradiation at 750 \ifmmode^\circ\else\textdegree\fi{}C. Implanted P atoms are incorporated into substitutional sites after complete crystallization by using MeV-ion-beam irradiation. This is confirmed by using the Rutherford-backscattering-spectroscopy channeling method. A considerable amount of defects or amorphous clusters are formed by C-ion implantation at a 50-keV energy for a $1\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose. However, they are crystallized epitaxially to the crystalline diamond by using only thermal annealing at 750 \ifmmode^\circ\else\textdegree\fi{}C or by using MeV-ion-beam irradiation at 750 \ifmmode^\circ\else\textdegree\fi{}C. Above $2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ C doses, continuous amorphous layers are formed internally in the substrate and epitaxial crystallizations proceed from both the crystalline substrate and the crystalline-surface region. Moreover, the rate of crystallization is higher for annealing with MeV-ion-beam irradiation than for thermal annealing at the same temperature. Epitaxial crystallization of the internal amorphous layer, however, stops in both thermal annealing and MeV-ion-beam irradiation, even if annealing time or irradiation dose increases. This is probably due to amorphous C changing into the graphite layers that occurs during thermal annealing or MeV-ion-beam irradiation. Graphite formation is also observed for the as implanted sample before annealing. Direct evidence of graphite formation is given from the channeling yield difference between samples for a $2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose and for a $3\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose, showing clearly the stopping power difference between ${\mathrm{sp}}^{2}$ (graphite) and ${\mathrm{sp}}^{3}$ (diamond) bonding. Amorphous layers in diamond can be formed by C-ion implantation at a more than one order of magnitude smaller amount of doses, compared with those needed for the amorphization of the Si substrates. A calculated number of vacancies created per incident C ion in Si is larger than in diamond. Nevertheless, diamond is amorphized faster than Si. A mechanism is proposed for forming the amorphous layer in diamond. This consists of a bond-breaking process due to inelastic electronic scattering and the movement process of C atoms after bond breaking with the assistance of elastic nuclear scattering without recoil, induced by ion implantation. Atomistic models for ion-beam-induced epitaxial crystallization (IBIEC) and for low-temperature crystallization of implantation-amorphized epitaxial Si layer formed by ultrahigh vacuum chemical-vapor deposition are proposed and discussed, putting particular emphasis on the role of both nuclear and electronic scattering of incident MeV-ion beam. A similar atomistic model for the inclusion of implanted P atoms into substitutional sites is also proposed, based on this atomistic IBIEC model.