implantation of Bi into GaP. II. channeling studies

The channeling technique has been used to investigate the properties of Bi-implanted Gap. Measurements of the crystal disorder for 100 keV room temperature implants indicate a damage vs dose curve corresponding to ～13000 displacements/ion in the linear region and saturation at ～1.5 × 10¹³ Bi ions/cm². Annealing of the radiation damage has been observed and indicates two annealing steps at ～450°C for light damage and ～750°C for implants in the 1 × 10¹⁴/cm² range. Difficulties associated with the thermal decomposition of the implanted area have been overcome with the use of SiO _x coatings. The experimental details associated with the use of the SiO _x layer and with the use of a C¹² beam to obtain better depth and mass resolution in the backscattering spectrum are discussed. The lattice location measurements of the Bi impurity show ～50 per cent of the Bi atoms to be along the 〈110〉 string after a 900°C anneal for a 7.5 × 10¹³/cm² implant. In addition, the spectra show ～25 per cent of the Bi atoms have diffused to the surface. Correlations of these lattice location results with measurements of the photoluminescent intensity of the GaP (Bi) isoelectronic trap show an agreement in trend with anneal temperature but indicate a factor of ～10 more substitutional ions in the channeling measurement as compared to the photoluminescence results.     

Ion implantation of sulphur into GaAs,GaP and ge monocrystals

The possibility of using ion implantation to form high concentration junctions in semiconductors has been explored for the specific case of sulphur in GaAs, GaP and Ge. The effects of ion dose, ion energy, crystal orientation and target temperature have been investigated by means of radiotracers and sectioning techniques.

It is shown that high concentration junctions can be formed using an incident ion having high electronic stopping cross-section and implanted along the <110< channeling directions of the crystals. A large increase in junction concentration may be obtained when the GaAs and GaP crystals are maintained at 150 °C during the implantation process, but this is not the case with Ge. Rutherford back-scattering of 1 MeV He⁺ ions has been used to measure the ion-bombardment induced damage in the crystals and to show how this damage can be annealed by heating the crystal during the implantation. The annealing, at temperatures up to 150 °C, is most effective in GaAs and least effective in Ge.     

Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing

Silicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1?×?10¹² to 2?×?10¹⁵ cm^?2, corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si–Si and C–C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8?dpa (i.e. ion fluence of 3?×?10¹⁴ cm^?2). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8?dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 °C up to 1500 °C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 °C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 °C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures.     

The measurement of cone length and range in etched plastics

Abstract

Group V impurities implanted at 400 keV into silicon have been detected in substitutional lattice positions by EPR. Three samples of VFZ, p-type 1200–1500 ohm-cm silicon from the same ingot were implanted with As⁷⁵, Sb¹²¹, and Sb¹²³, respectively. The EPR spectrum of each implanted substitutional impurity was observed after annealing the lattice damage. Only the isotope implanted in each sample was seen. Since only those donors which are electrically active can be observed, this technique measures the electrically active fraction of the implanted species. Upon annealing to 970°C, most of the antimony was active whereas only about 1/5 of the arsenic was observed. Comparisons with backscattering results indicate that between 350 and 600°C, ～95 per cent of the implanted antimony is substitutional but ～0 per cent is electrically active. The increase in electrical activity at 600°C is due to the rise of the Fermi level to the donor level as the residual lattice damage anneals. The paramagnetic damage centers observed were those also seen in oxygen-implanted silicon, Si-P3 and Si-Pl, but the Si-P3 center was not as well resolved and grows upon annealing to 200°C.     

The annealing of damage in ion implanted gallium arsenide

Photoluminescence measurements at 77°K and Rutherford scattering of 450 keV protons were used to study radiation damage and annealing in ion implanted GaAs. The characteristic band edge luminescence (8225 Å) in GaAs is completely quenched by ion implantation. Photoluminescence measurements on samples which were isochronally annealed show a single annealing stage at 600°C. A luminescence peak at 9140 Å is introduced into the spectra of all implanted and annealed samples. This peak is attributed to an acceptor level created by As vacancies. The intensity of the peak is greatly reduced by protecting the surface of implanted layers with SiO₂ during annealing. Rutherford scattering measurements on isochronally annealed samples reveal two annealing stages. A 300°C annealing stage is observed on samples which have an initial aligned yield less than random while a 650°C stage is observed on samples which have an initial aligned yield equal to random.     

Mössbauer study of 57Fe in GaAs and GaP following 57Mn+ implantation

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken ⁵⁷Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive ⁵⁷Mn^?+? ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T?> 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.     

Lattice location and thermal annealing behaviour studies of GaAs single crystals implanted with Co-atoms

Co-atoms have been implanted into n-type GaAs single crystals up to a dose of 2×10¹⁵ atoms/cm². Mössbauer Spectroscopy was used together with Proton Induced X-ray Excitation and Rutherford Backscattering Spectrometry in Channeling geometry to study the recovery of the GaAs-crystal from the implantation damage and the final lattice locations of the Co-atoms. Epitaxial regrowth of the GaAs was found to take place in the annealing temperature region from 300°–450°C. At 900°C rapid thermal annealing an epitaxial Co-phase was found at the surface with the Co-atoms partially blocking the GaAs <110> channel.     

ion implantation of bismuth into GaP. I. photoluminescence

Photoluminescence from the bismuth isoelectronic trap implanted into GaP is investigated for various ion doses and annealing conditions. A thin coating of silicon oxide is found to be essential to prevent thermal decomposition of the implanted surface during annealing. In isochronal anneal studies the intensity of the Bi luminescence increases rapidly between 650 and 800°C. For 200 keV implants, the dose for maximum luminescence is ～3.5 × 10¹² ions/cm², corresponding to an average concentration of ～10¹⁸/cm³. However, for the optimum dose and anneal, one observes only ～10 per cent of the light intensity expected from the estimated number of substitutional ions, and the emitting ions are situated in lattice sites with strong local strain. This strain is evident in the photoluminescence spectrum by the appearance of a strong no-phonon line which results from an otherwise forbidden transition when strain or an external field are present. The luminescence data are correlated with channeling experiments reported in a companion paper.     

Properties investigation of GaN films implanted by Sm ions under different implantation and annealing conditions

GaN films grown by MOCVD were implanted by Sm ions under different implantation and annealing conditions, in order to optimize the implantation parameters. The structural and magnetic measurements indicated a reduction of defect concentration and an increase of saturation magnetization when samples were implanted at 400°C, most probably due to the increased substitutional fraction of Sm ions. While the subsequent annealing process further decreased the damage in GaN lattice, but reduced the saturation magnetization on the contrary, caused by the decomposition of the surface layer and the formation of Sm-defect complexes during high-temperature annealing.     

Low energy boron and phosphorus implants in silicon (a) electrical sheet measurements

Silicon wafers were implanted in 〈111〉-direction with boron and phosphorus ions of 7 keV at room temperature. Doses between 10¹² and 10¹⁸ ions/cm² were applied. After successive annealing steps the electrical properties of the implanted layers have been determined by Hall effect and sheet resistivity measurements. The annealing characteristics of the implants depend on ion dose and species. Three annealing stages can be distinguished: (I) the temperature range below 500°C, (II) 500—700°C, (III) 700—900°C.

After annealing at 90°C the apparent electrical yield is proportional to dose for all implants and amounts to approx. 80 per cent for boron and 40 per cent for phosphorus.

Sheet resistivity vs. dose curves were derived for the annealing temperature of 400°C and used for the fabrication of position sensitive detectors. The position characteristics were found to be linear within ～1 per cent for resistive layers as long as 20 cm.     

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.     

Amorphous GaP produced by ion implantation

Two types of non-crystalline states (“disordered” and “amorphous”) of GaP were produced by using ion implantation and post annealing. A structural-phase-transition-like annealing behaviour from the “disordered” state to the “amorphous” state was observed.The ion dose dependence and the annealing behaviour of the atomic structure of GaP implanted with 200 keV ? N⁺ ions were studied by using electron diffraction, backscattering and volume change measurements. The electronic structure was also investigated by measuring optical absorption and electrical conductivity.The implanted layer gradually loses the crystalline order with the increase of the nitrogen dose.The optical absorption coefficient α and electric conductivity σ of GaP crystals implanted with 200 keV?N⁺ ions of 1 × 10¹⁶ cm^?2 were expressed as αhν = C(hν ? E₀)ⁿ and log $\text{σ = A ? BT}{}^{\mathrm{<mtext>-</mtext><mtext>1</mtext><mtext>4</mtext>}}$, respectively. Moreover, the volume of the implanted layer increased about three percent and the electron diffraction pattern was diffused halo whose intensity monotonically decreases along the radial direction. These results indicate that the as-implanted layer has neither a long range order nor a short range order (“disordered state”).In the sample implanted at 1 × 10¹⁶ cm^?2, a structural phase-transition-like annealing stage was observed at around 400°C. That is, the optical absorption coefficient α abruptly fell off from 6 × 10⁴ to 7 × 10³ cm^?1 and the volume of the implanted layer decreased about 2% within an increase of less than 10 degrees in the anneal temperature. Moreover, the short range order of the lattice structure appeared in the electron diffraction pattern. According to the backscattering experiment, the heavily implanted GaP was still in the non-crystalline state even after annealing.These facts lead us to believe that heavily implanted GaP, followed by annealing at around 400°C, is in the “amorphous” state, although as-implanted Gap is not in the “amorphous” state but in the “disordered” state.     

Optical waveguides in LiNbO3 formed by ion implantation

Abstract

Ion implantation in LiNbO₃ can be used to modify the refractive index. The change in indices, n ₀ n _e results from the damage formed by energy deposited by the (dE/dx)_nuclear collisions between the ions and the lattice and is independent of the ion species. A saturation change in index of some ?7% occurs after a deposition of 10²³ keV cm^?3 at 300K, greater changes of ?9 % occur with implants at 77K. Annealing studies indicate the optical absorption formed during irradiation is removed below 200°C whereas the index changes exist up to 400°C. For optical waveguide production a negative change in the index is not ideal as the damaged layer cannot directly act as the region of optical confinement. However the (dE/dx)_electronic term is unimportant and so we have been able to form optical waveguides by ion implantation with light energetic ions (e.g. MeV He⁺ ions) because the damaged layer is then formed beneath an unchanged high index surface layer. This retains the desirable electrooptic properties of the single crystal LiNbO₃. The experimentally observed waveguide modes are in accord with our theoretical predictions of the refractive index profiles.     

Hot electron studies of lattice damage created in silicon by implantation of 2.8 MeV protons

Abstract

In this paper we report the results of a study of the annealing properties of the ionized defect density associated with the damage created in the silicon lattice by implantation of 2.8 MeV protons at room temperature. In particular, the annealing of damage created by implanting to a level of 4.43 × 10¹² protons/cm² is reported. The resulting isochronal annealing curve covered the temperature range from 70°C to 460°C. Two major annealing stages are discussed, one a broad stage between 70°C to 200°C and the other an abrupt annealing stage between 440°C to 460°C. Between the temperature range 200°C to 440°C the number of ionized defects remained relatively constant. Above 460°C no detectable effects of the proton implantation remained.     

Lattice disorder produced in GaAs by 60 keV Cd ions and 70 keV Zn ions

Abstract

We have used the standard channeling technique with a 1.0 MeV He⁺ analyzing beam to investigate the lattice disorder produced in GaAs by 60 keV Cd and 70 keV Zn ion implantations made at room temperature. The amount of disorder produced increases linearly with dose and saturates at a dose of approximately 1–2 × 10¹³ Cd ions/cm². The disorder present in low dose implants (～5 × 10¹² Cd ions/cm²) anneals appreciably by 150 °C. With increasing doses of Cd or Zn the samples show a continuous increase in the anneal temperature required to remove a substantial amount of lattice disorder. There is no apparent difference between the anneal of Zn and Cd implants. The rate at which lattice disorder is produced in GaAs by heavy ion implantations and the doses of heavy ions required to saturate the lattice disorder observed are significantly different from the values of the corresponding quantities for Si and Ge.     

Oxidation and annealing of GaP and GaAs (111)-faces studied by AES and UPS

The annealing behaviour after argon sputtering and the first steps of oxidation of the polar GaP and GaAs (111)-faces are studied by AES and UPS. The Auger spectrum of GaP is briefly discussed. In contrast to GaAs, the GaP surfaces show a gallium accumulation after argon sputtering, but they become stoichiometric by annealing. The photoemission spectra show an additional emission due to oxygen with its maximum at about 5 eV below the valence band edge. The decrease of the emission near the valence band edge by oxidation shows the existence of surface sensitive states. Comparing the results of the two polar faces and for different surface compositions, it is concluded that these states are mainly As- and P-derived, respectively. A linear relationship is found between the UPS and Auger signal of oxygen.     

Hg ION implantation in silicon: Lattice disorder created and hg atom lattice location

Abstract

The lattice disorder produced by 42-keV and 75-keV Hg ions implanted in Silicon at room temperature and the lattice location of the Hg atoms were studied by means of the channeling technique with a 2.0 MeV ⁴He⁺ beam. The damage produced was found to increase linearly with ion dose until a saturation value, connected to the ion range, is reached. The number of Si atoms displaced for Hg ion implanted was evaluated and compared with the theoretical expectation. The substitutional Hg fraction is connected to the disorder produced: the replacement mechanism is discussed.     

Study of radiation-induced damage to type III–V semiconductor compounds irradiated with γ quanta and protons using positron annihilation spectroscopy

The effect of proton and ?? radiation on characteristics of the spectra for the angular distribution of annihilation photons (ADAP) have been studied in the case of positron annihilation in GaAs and GaP single crystals. Relative variations in defect accumulation and annealing under irradiation and subsequent isochronous annealing of the samples have been studied using variations in the basic parameters of the ADAP spectra. In both cases (GaAs and GaP), the variations in the ADAP spectral parameters as functions of the annealing temperature have a steplike character, which is interpreted as the formation of a certain type of defects with different annealing activation energies.     

Characteristics of molecular beam epitaxy-grown GaFeAs

Diluted magnetic semiconductors GaFeAs were grown by molecular beam epitaxy and characterized. Ga_1−xFe_xAs ternary alloys were obtained at the growth temperature T_s=200 °C ranging from x=0.005 to 0.03. The effects of thermal treatment on behaviors of defects, affecting to the magnetic properties of GaFeAs layer were particularly elucidated. As-grown samples were annealed at temperatures varying from 400 to 600 °C. From the measurement of double crystal X-ray diffraction, we observed Fe-related peak which shifted to a higher diffraction angle as the Fe content increased, indicating that the lattice constant decreases with increasing Fe content. In contrast, above the annealing temperature 500 °C, the lattice constant becomes smaller than that of GaAs. Using the deep level transient spectroscopy, various defects in GaFeAs layer were observed and identified in conjunction with magnetic properties.     

Structural defect recovery in GaP after heavy ion implantation

The channeling and blocking effect of electrons and positrons emitted in nuclear decay allows the lattice site location of radioactive impurities implanted into single crystals at small concentrations (ppm) and low implantation fluences (10¹²/cm²). We applied this emission channeling technique to the localization of ^112mIn and ^111mCd after implantation into si-GaP single crystals at different temperatures. After implantation at low temperature and subsequent annealing an increase of the fraction of substitutional probe atoms and a recovery of the local lattice structure between 300 and 500 K were observed. GaP tends to anneal at higher temperatures than GaAs (200–350 K), but compared to GaAs the channeling effects observed in GaP are more pronounced, indicating a more complete recovery of implantation defects.