Nitrogen centers in GaP produced by hot implantation

Backscattering yields of 1.5 MeV?He⁺ ions and low temperature photoluminescence (PL) spectra were measured in GaP crystals implanted with 200 keV?N⁺ ions as functions of ion-dose, temperature during implantation and annealing temperature after implantation. Backscattering results indicate that hot implantation at 500°C greatly reduces radiation damage. The PL intensities of NN lines become maximum in the sample implanted with N⁺ ions of 3 × 10¹⁴cm^?2 at 500°C, and annealed at 1000°C for 1 hr with aluminum glass. The PL intensity is comparable to that of the nitrogen-doped sample during liquid phase epitaxy which is widely accepted as the best method of introducing nitrogen into GaP crystals. In the case of 500°C—hot implantation, the radiation damage produced during implantation is annealed out at 700 ~ 800°C and the implanted nitrogen substitutes for the phosphorous sites after annealing at 900 ~ 1000°C. Some kinds of defects or strains remain around the NN centers even in implanted samples with a maximum PL efficiency. These defects or strains don't seem to reduce the PL efficiency. In the case of room temperature implantation, PL efficiency decreases to one-hundredth or one-thousandth due to the formation of the non-crystalline state compared with hot implantation.     

Beam transport

Abstract

Dopant distribution, electrical activity and damage annealing of high-dose (～5 × 10¹⁵ cm²) Ga-implanted silicon samples annealed by conventional thermal annealing have been studied by alpha particle back-scattering, differential Hall effect and ellipsometry measurements. Back-scattering spectra show that there is no long tail of Ga atoms in the as-implanted samples. Upon annealing these samples the damaged amorphous layer recrystallizes at about 570°C by solid phase epitaxy. During the epitaxial regrowth the dopant atom distribution seems to be modified. Further, very high levels of electrical activaton of Ga-atoms (～3 × 10²⁰ cm^?3), much higher than the maximum solubility limit of Ga in Si (4.5 × 10¹⁹ cm^?3), is achieved by thermal annealing of the sample at ～570°C. This is comparable to the doping achieved by laser annealing of the Ga implanted Si. All the above three measurements show that there is residual damage in the high dose (?10¹⁵cm^?2) implanted samples after the recrystallization at about 570°C. This may be related to strain in the lattice at the high concentrations of metastable substitutional Ga atoms. Annealing at higher temperature reduces the electrical activity of Ga atoms, possibly by driving out the metastably high substitutional concentrations of Ga-atoms into electrically inactive clusters or precipitates.     

Formation of Cu nanoparticles in GaAs using MeV ion implantation followed by thermal annealing

Analytical electron microscopy, high-resolution X-ray diffraction and combined Rutherford backscattering spectrometry and channeling experiments have been used to investigate the radiation damage and the effect of post-implantation annealing on the microstructure of GaAs(100) single crystals implanted with 1.00 MeV Cu⁺ ions to a dose of ≈ 3×10¹⁶ cm^-2 at room temperature. The experiments reveal the formation of a thick and continuous amorphous layer in the as-implanted state. Annealing up to 600 °C for 60 min does not result in the complete recovery of the lattice order. The residual disorder in GaAs has been found to be mostly microtwins and stacking fault bundles. The redistribution of implanted atoms during annealing results in the formation of nano-sized Cu particles in the GaAs matrix. The X-ray diffraction result shows a cube-on-cube orientation of the Cu particles with the GaAs lattice. The depth distribution and size of the Cu particles have been determined from the experimental data. A tentative explanation for these results is presented. Received: 15 February 1999 / Accepted: 18 February 1999 / Published online: 28 April 1999     

Electron-microscopy study of Fe-implanted InP

InP implanted with 200 keV Fe ions to a dose of 1 × 10¹⁴ atoms/cm² has been investigated by Transmission Electron Microscopy (TEM). The as-implanted sample exhibits an amorphous surface region. At the annealing temperature of 650°C, nearly complete solidphase epitaxial regrowth is achieved only for annealing times greater than 1.5 h. For annealing times up to 2 h, however, the samples still contain extended defects such as stacking-fault tetrahedra of vacancy-type and dislocation loops of interstitial-type, mostly concentrated in a band which corresponds to the region of transition between amorphous top layer and crystalline substrate, as was detected in the as-implanted sample. Stacking-fault tetrahedra and loops have also been observed above and below this band, respectively. The origin of these defects is discussed.     

Damage anneal of antimony/phosphorus double implants in silicon

A method is presented for avoiding the dislocation generation in (100) silicon implanted with phosphorus doses up to 5×10¹⁵ ions/cm² at 50 keV. The residual defects after the damage anneal are considerably reduced if the phosphorus implant is combined with a low dose, e.g. 1×10¹⁴ ions/cm², antimony implant which produces a deeper surface layer of amorphous silicon. It is essential that the phosphorus ions are implanted shallower than the antimony ions, and come to rest within the amorphous layer. Subsequent thermal annealing proceeds by a solid phase epitaxial regrowth mechanism.     

The GaP(001) surface and the adsorption of Cs

GaP(001) cleaned by argon-ion bombardment and annealed at 500°C showed the Ga-stabilized GaP(001)(4 × 2) structure. Only treatment in 10^?5 Torr PH₃ at 500°C gave the P-stabilized GaP(001)(1 × 2) structure. The AES peak ratio $\text{P}\text{Ga}$ is 2 for the (4 × 2) and 3.5 for the (1 × 2) structure. Cs adsorbs with a sticking probability of unity up to 5 × 10¹⁴ Cs atoms cm^?2 and a lower one at higher coverages. The photoemission measured with uv light of 3660 Å showed a maximum at the coverage of 5 × 10¹⁴ atoms cm^?2. Cs adsorbs amorphously at room temperature, but heat treatment gives ordered structures, which are thought to be reconstructed GaP(001) structures induced by Cs. The LEED patterns showed the GaP(001)(1 × 2) Cs structure formed at 180°C for 10 h with a Cs coverage of 5 × 10¹⁴ atoms cm^?2, the GaP(001)(1 × 4) Cs formed at 210°C for 10 hours with a Cs coverage of 2.7 × 10¹⁴ atoms cm^?2, the GaP(001)(7 × 1) and the high temperature GaP(001)(1 × 4), the latter two with very low Cs content. Desorption measurements show three stability regions: (a) between 25–150°C for coverages greater than 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.2 eV; (b) between 180–200°C with a coverage of 5 × 10¹⁴ atoms cm^?2, and an activation energy of 1.8 eV; (c) between 210–400°C with a coverage of 2.7 × 10¹⁴ atoms cm^?2, and an activation energy of 2.5 eV.     

Self-consistent surface calculation of electron-hole drops in gallium phosphide

Self-consistent Kohn-Sham method is used to investigate the surface structure of electron-hole drops (EHD) in GaP. If the conduction bands are located on the X-point and have a degeneracy of 3, the surface tension is found to be 85 × 10^?4 erg cm^?2. In the presence of a “camel's-back” structure and a conduction band degeneracy of 6, the surface tension is calculated to be 130 × 10^?4 erg cm^?2. The surface charge on the EHD is found to be negative irrespective of whether the conduction band degeneracy is 3 or 6.     

57Fe conversion electron Mössbauer spectrometric study of boron and carbon ion implanted irons

Amorphous layers produced at the surface of iron by B⁺ and C⁺ implantation (50 kV, 1×10¹⁸ ions cm⁻²) were analyzed by CEMS. The CEM spectrum of B⁺ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400°C brought about precipitation of FeB, which was converted to Fe₂B by annealing at 500°C. The P(H) for C⁺ implanted iron was resolved to 3 subpeaks with H values of 11.0, 18.0 and 22.5 T. The amorphous FeC phase was strongly correlated to crystalline Fe₅C₂ and Fe₂C, which precipitated at 300°C and were transformed into Fe₃C at 500°C. The amorphous layer disappeared by annealing at 600°C.     

用椭圆偏光法研究硅中砷离子注入的损伤和退火效应

我们用椭圆偏光法对As⁺离子注入Si的损伤和退火效应进行了测量。对As⁺注入能量为150keV、注入剂量为10¹⁶cm^-2的情况,测得的折射率分布呈现平台型,表明出现了非晶质层。在600—700℃间有一转变温度,高于此温度退火,可消除非晶质层。实验结果表明椭圆偏光法亦是测定辐射损伤的有用工具。 关键词：     

Formation of ordered helium pores in amorphous silicon subjected to low-energy helium ion irradiation

Thin transparent (for transmission electron microscopy, TEM) self-supported Si(001) films are irradiated on the (110) end face by low-energy (E=17 keV) He⁺ ions at doses ranging from 5×10¹⁶ to 4.5×10¹⁷ cm⁻² at room temperature. The TEM study of the irradiated Si films along the ion range shows that an a-Si layer forms in the most heavily damaged region and helium pores (bubbles) with a density of up to 3×10¹⁷ cm⁻³ and 2–5 nm in diameter nucleate and grow across the entire width of this layer. The growth of nanopores in the a-Si layer is accompanied by their linear ordering into chains oriented along the ion tracks. The absence of pores in the region that remains crystalline and has the maximal concentration of implanted helium is explained by the desorption of helium atoms from the thin film during the irradiation. After annealing at 600°C, the volume of immobile pores in the remaining a-Si layer increases owing to the capture of helium atoms from the amorphous matrix. Solid solution is shown to be the prevalent state of the helium implanted into the amorphous silicon. Linear features with a diameter close to 1 nm and density of about 10⁷ cm⁻¹ discovered in the helium-doped a-Si layer are identified as low-energy He⁺ ion tracks.     

Design of an end station for a high current ion implantation system

Single crystal silicon has been implanted with nitrogen and phosphorus ions at MeV energies to fluences between 10¹⁶ and 1.6 × 10¹⁸ ions/cm₂. Infrared transmission and reflection spectra in the range of 1.25 to 40 μm were measured for as-implanted samples and after various annealing treatments. Interference fringes were observed in the IR spectra which are produced by the interference of light which has been multiply reflected between the front surface and the buried layers. By detailed theoretical analyses of the interference fringe structure, we obtained refractive index profiles, which, under suitable interpretation, provide accurate measurements and several quantities of interest. These quantities are the range and straggling of the implanted ions, the depth of disordered layers, and the width of the order-disorder transition. Mechanisms for the refractive index changes which have been identified include amorphization of the implanted silicon, bulk compositional change in the buried layer, localized vibrational mode dispersion, and free electron dispersion. Experimental results and theoretical predictions are presented, demonstrating each of these mechanisms.     

Low temperature thermal annealing-induced α-FeSi2 derived phase in an amorphous Si matrix

Thermal annealing-induced recrystallisation in Fe ion-implanted Si was investigated by transmission electron microscopy. Single crystals of Si(111) were implanted with 120 keV Fe ions to a fluence of 1.0×10¹⁷ cm^-2 at cryogenic temperature. A buried amorphous Fe-Si layer in an amorphous Si matrix was formed in the as-implanted sample. Nanobeam electron diffraction revealed that metastable α-FeSi₂ precipitates embedded in the amorphous Si matrix were formed after annealing at 350 °C for 8 h. The formation of this α-FeSi₂-derived phase was unusual, because it has been observed only in epitaxially grown thin films. Based on the Fe_1-xSi (0<x<0.5) phase with the CsCl structure, which is another metastable phase in the Fe-Si binary system, we discuss the formation process of the metastable α-FeSi₂ in the amorphous matrix. PACS 61.43.Dq; 61.14.Lj; 61.80.Jh     

Evidence for charmed baryon “elastic” production in neutrino reactions at the CERN SPS

Evidence for charmed baryon “elastic” production is found in a sample of 55 000 charged-current neutrino interactions in the bubble chamber Gargamelle exposed to the SPS wide-band neutrino beam. The product of the average cross section times the branching ratio into modes including a Λ⁰ or a $\text{K}$⁰p system is found to be α·B=(14.3 ± 7.4) × 10^?40 cm² for ν+n reactions and α · B<3.3×10^?40 cm² (90% CL) for ν+p reactions.     

Gettering of implanted Au in MeV?C implanted Si

The gettering behavior of 1 MeV?C implantation induced defects for Au (1.5 MeV, 2.2×10¹⁵ cm^-2), implanted into FZ Si(111), has been investigated using Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. The gettering efficiency of the C implanted layer has been studied as a function of C dose, annealing temperature and time. For a C dose of 2×10¹⁶ cm^-2, a 2 h anneal at 950 °C has been found to result in a gettering efficiency going beyond ?90%. Thermal stability of the gettered Au in the C implanted layer has subsequently been investigated over a temperature range of 950–1150 °C using isochronal annealing. The gettered amount has been found to be stable up to 1050 °C beyond which there is a release. We have observed nanovoids in the C implanted layer surrounded by ?-SiC precipitates along with patches of a-SiC. Up to about 1050 °C, these nanovoids act as efficient gettering centers beyond which they seem to release the trapped Au. Four distinct regimes in annealing temperature with different mechanisms for Au gettering have been observed.     

Mössbauer study of the defect structures around Te implanted in Al x Ga1−x As

^129mTe-atoms were implanted in Al _x Ga_1?x As-samples (withx varying from 0 to 1) with a dose of 2×10¹³ atoms/cm². After rapid thermal annealing to 900°C, a variation in the Mössbauer spectra as a function ofx is observed. Forx between 0.2 and 0.7, a component with a large electric field gradient is dominant in the spectra, while for the other values ofx a single line dominates. The presence of the component with a large electric field gradient coincides with the presence of the so-called “DX-center”.     

Mössbauer and XRD Comparative Study of Host Rock and Iron Rich Mineral Samples from Paz del Rio Iron Ore Mineral Mine in Colombia

The local environment of implanted ¹¹¹Ag (t _1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following the 60 keV low dose (1 × 10¹³ cm⁻²) ¹¹¹Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps, at temperatures ranging from 200 to 1050°C. The results revealed that 42% of the probes are located at defect-free S_Zn sites (ν _Q ∼ 32 MHz, η = 0) in the as-implanted state and that this fraction did not significantly change with annealing. Moreover, a progressive lattice recovery in the near vicinity of the probes was observed. Different EFGs assigned to point defects were furthermore measured and a general modification of their parameters occurred after 600°C. The 900°C annealing induced the loss of 30% of the ¹¹¹Ag atoms, 7% of which were located in regions of high defects concentration.     

Effect of implantation temperature on the blistering behavior of hydrogen implanted GaN

GaN epitaxial layers were implanted by 100 keV H⁺ ions at different implantation temperatures (LN₂, RT and 300 °C) with a fluence of 2.5×10¹⁷ cm^?2. The implanted samples were characterized using Nomarski optical microscopy, AFM, XRD, and TEM. Topographical investigations of the implanted surface revealed the formation of surface blistering in the as-implanted samples at 300 °C and after annealing at higher temperature for the implantation at LN₂ and RT. The physical dimensions of the surface blisters/craters were dependent on the implantation temperature. XRD showed the dependence of damage-induced stress on the implantation temperature with higher stress for the implantation at 300 °C. TEM investigations revealed the formation of a damage band in all the cases. The damage band was filled with large area microcracks for the implantation at 300 °C, which were responsible for the as-implanted surface blistering.     

Doping and radiation damage profiles of P+ ions implanted in silicon along the [110] axis

Several doses of 200 KeV phosphorus ions have been implanted under channeling conditions along the [110] direction in silicon.

Range distribution has been determined for the three implant doses 10¹³, 10¹⁴, 10¹⁵ P⁺/cm² both with the electrical measurements and the neutron activation techniques.

The radiation damage distribution has been determined both with 290 KeV proton back-scattering analysis and with transmission electron microscopy (TEM) observations.

Good agreement has been found between electrical and neutron activation profiles in the samples where 100% of the implanted dose had been electrically activated by means of annealing.

Carrier concentration profiles, from samples implanted with 10¹⁵ P⁺/cm², determined after two different annealing temperatures (500°C and 700°C) have bcen compared with the radiation damage distribution and a correlation between damage and phosphorus electrical activation process seems to be possible.

Maximum damage peak, as determined by back-scattering analysis, shifts from ～0.4 μ depth in the lower dose(5 × 10¹⁴ P⁺/cm²), to ～0.22 pm depth in the higher implanted dose (4 × 10¹⁵ P⁺/cm²). Damage distribution of phosphorus ions random implanted in the same experimental conditions shows 3 peak at ～0.2 μn depth.

In accordance with the back-scattering analysis, T.E.M. observations on 10¹⁵P⁺/cm² implanted samples show the presence of amorphous regions at depth between 0.25 and 0.5 μm from the surface. In the most damaged layer ～0.3μm in depth, a surface density of ～10¹²/cm² amorphous regions 25-50 A diameter was observed.     

Roles of local He concentration and Si sample orientation on cavity growth in amorphous silicon

(111)- and (100)-oriented Si samples were implanted with Si⁺ ions at 1 MeV to a dose of 1?×?10¹⁶?cm^?2 and with 5?×?10¹⁶ He⁺ cm^?2 at 10?keV or 50?keV and eventually annealed in the 800–1000°C temperature range. Sample characterisation was carried out by cross-section transmission electron microscopy, positron annihilation spectroscopy and nuclear reaction analysis. In addition to the formation of He bubbles at the projected range of He, bubbles were observed after solid-phase epitaxial growth (SPEG) of the embedded amorphous Si layer. The He threshold concentration required to obtain thermally stable bubbles in amorphised Si is between one and four orders of magnitude lower than in c-Si. Since bubble formation and growth take place in the a-Si phase, the interaction with SPEG during annealing was studied by considering (100) and (111) Si. Both the SPEG velocity and the resulting defects play a role on bubble spatial distribution and size, resulting in bigger bubbles in (111) Si with respect to (100) Si.     

Ti离子注入和退火对ZnS薄膜结构和光学性质的影响

利用真空蒸发法在石英玻璃衬底上制备了ZnS薄膜,将能量80 keV,剂量1×10¹⁷ cm^-2的Ti离子注入到薄膜中,并将注入后的ZnS薄膜进行退火处理,退火温度500—700 ℃.利用X射线衍射（XRD）研究了薄膜结构的变化,利用光致发光（PL）和光吸收研究了薄膜光学性质的变化.XRD结果显示,衍射峰在500 ℃退火1 h后有一定程度的恢复;光吸收结果显示,离子注入后光吸收增强,随着退火温度的上升,光吸收逐渐降低,吸收边随着退火温度的提高发生蓝移;PL显示,薄 关键词： ZnS薄膜 离子注入 X射线衍射 光致发光