H. Katsumata

Optical absorption and photoluminescence studies of β‐FeSi2 prepared by heavy implantation of Fe+ ions into Si

Mass‐separated 56Fe+ ions were implanted into Si(100) at 350 °C using three different energies and doses of 140 keV (1.32×1017 cm−2), 80 keV (6.20×1016 cm−2), and 50 keV (3.56×1016 cm−2). Their optical properties were investigated as a function of subsequent annealing temperature and its duration time. X‐ray diffraction analysis revealed that polycrystalline semiconducting β‐FeSi2 layers are formed in the as‐implanted and annealed samples. From Rutherford backscattering spectrometry analysis, the formation of β‐FeSi2 up to the surface was confirmed, and the average thickness and composition of the layers at peak concentration were estimated to be 70–75 nm and Fe:Si=1:2.0–2.2, respectively. The types of optical transition and the inverse logarithmic slope (E0) of the Urbach tail were investigated using room temperature optical absorption measurements. All the synthesized β‐FeSi2 layers exhibited a direct transition with direct band‐gap energies (Egdir) of 0.802–0.869 eV and with high optical absorption coe...

Effect of Multiple-Step Annealing on the Formation of Semiconducting β-FeSi2 and Metallic α-Fe2Si5 on Si (100) by Ion Beam Synthesis

Polycrystalline semiconducting β- FeSi2 layers on Si (100) have been formed by ion beam synthesis. Results from two different annealing processes, either two-step (2SA) annealing up to 900° C or three-step annealing (3SA) up to 1100° C, are discussed. β- FeSi2 grown by 3SA has shown a typical direct band-gap energy (E g dir) of 0.88 eV and a high localized defect density (N0) of 1.0×1018 cm-3, the latter being due to crystallographic mismatches or relevant defects at grain boundaries introduced during the transformation process from β to α. On the contrary, β- FeSi2 grown by 2 SA has shown a lower E g dir of 0.80 eV and a smaller N0 of 1.7×1017 cm-3, the former arising from a deviation of the stoichiometric composition to the Si-rich side. Broad PL bands near 0.8 eV have been observed at 2 K from both 2SA and 3SA samples, and we assign these PL bands to optical radiative transitions intrinsic to β- FeSi2.

Structural and optical characterization of β-FeSi2 layers on Si formed by ion beam synthesis

Abstract Structural and optical properties have been investigated for surface β-FeSi2 layers on Si(100) and Si(111) formed by ion beam synthesis using 56Fe ion implantations with three different energies (140–50 keV) and subsequent two-step annealing at 600 °C and up to 915 °C. Rutherford backscattering spectrometry analyses have revealed Fe redistribution in the samples after the annealing procedure, which resulting in a Fe-deficient composition in the formed layers. X-ray diffraction experiments confirmed the existence of /gb-FeSi2 by annealing up to 915 °C, whereas the phase transformation from the β to α phase has been induced at 930 °C. In photoluminescence measurements at 2 K, both β-FeSi 2 Si (100) and β-FeSi 2 Si (111) samples, after annealing at 900–915 °C for 2 h, have shown two dominant emissions peaked around 0.836 eV and 0.80 eV, which nearly coincided with previously reported PL emissions from the sample prepared by electron beam deposition. Another β-FeSi 2 Si (100) sample has shown sharp emissions peaked at 0.873 eV and 0.807 eV. Optical absorption measurements at room temperature have revealed the allowed direct bandgap of 0.868–0.885 eV as well as an absorption coefficient of the order of 104 cm−1 near the absorption edge for all samples.

Synthesis of metastable group-IV alloy semiconductors by ion implantation and ion-beam-induced epitaxial crystallization

In order to synthesize metastable group-IV binary alloy semiconductor thin films on Si, Si(100) substrates were implanted with 17 keV C ions for Si 1-y C y /Si and alternatively with 110 keV Sn ions for Si 1-z Sn z /Si. Subsequent ion-beam-induced epitaxial crystallization (IBIEC) with 400 keV Ar ions at 300-400°C has induced a good epitaxial growth up to the surface both for Si 1-y C y /Si (y=0.014 at peak concentration) and for Si 1-z Sn z /Si (z = 0.029 at peak concentration). X-ray diffraction measurements have shown a growth of Si 1-y C y /Si with smaller tensile strain than for Si 1-y C y /Si grown by solid phase epitaxial growth (SPEG) up to 650°C. Photoluminescence measurements have revealed properties of defect related to I 1 (Ar) line and G line emissions for IBIEC-grown Si 1-y C y /Si samples. IBIEC has induced an incomplete crystalline growth and a loss of implanted Sn atoms for Si 1-z Sn z /Si (z = 0.086 at peak concentration).

CRYSTALLIZATION OF SISN AND SISNC LAYERS IN SI BY SOLID PHASE EPITAXY AND ION-BEAM-INDUCED EPITAXY

Abstract For the synthesis of novel group-IV semiconductors, crystalline growth of amorphous Si1−xSnx and Si1−x−ySnxCy layers in Si formed by Sn and C ion implantation has been investigated with solid phase epitaxial growth (SPEG) and ion-beam-induced epitaxial crystallization (IBIEC). Si(100) wafers were implanted at RT with 110 keV or 270 keV 120Sn ions to a dose up to x = 0.03 at peak concentration and 17 keV or 35 keV 12C ions up to y = 0.025 at peak concentration. SPEG experiments at 750°C have shown epitaxial crystallization of the strained alloy layer in the Si 1−x Sn x Si sampl (x = 0.03) and strain-compensated layer in the Si 1−x−y Sn x C y Si sample with medium C concentration (x = 0.03 and y = 0.019). IBIEC experiments performed with 400 keV Ar ions at 350°C have also induced epitaxial crystallization for the Si 1−x Sn x Si sample (x = 0.025), whereas those of Si1−x−ySnxCy (x = 0.025 and y = 0.014) have shown a collapse of epitaxial growth. Photoluminescence (PL) from SPEG-grown Si1−xSnx and Si1−x−ySnxCy samples has shown neither prominent I1 nor G peaks. Present results have revealed features in crystalline growth properties, in both techniques, for the non-thermal equilibrium fabrication of these new alloy semiconductors.

Fabrication of epitaxial silicides thin films by combining low-energy ion beam deposition and silicon molecular beam epitaxy

We have developed successfully the combined ion beam and molecular beam epitaxy (CIBMBE) system with a newly designed Knudsen cell for Si effusion. The CIBMBE system was applied to the epitaxial growth of Sil., Cx alloy thin films on Si using low-energy ( 100 – 300 eV ) C + ion beam. Preliminary results on the characterization of the deposited films suggest high potential and reliability of the new Knudsen cell for Si effusion, as well as high ability of the CIBMBE method to produce thermally non-equilibrium materials. In addition, they indicate that the value of x decreases with increasing I C , which suggests that the selective sputtering for deposited C atoms by incident C + ion beams takes place during CIBMBE processing. Precipitates of β-SiC were also found to be formed in the deposited films, whose amount was observed to increase with increasing I C .

Ion-beam-induced epitaxial crystallization (IBIEC) and solid phase epitaxial growth (SPEG) of Si1−xCx layers in Si fabricated by C ion implantation

Amorphous Si1−xCx layers in Si(100) (0.013 ≤ x ≤ 0.032 at peak concentration) formed by 35 keV 12C implantation were crystallized by solid phase epitaxial growth (SPEG) up to 850°C and by ion-beam-induced epitaxial crystallization (IBIEC) with 400 keV Ar or Ge ions at 300–400°C. SPEG process has induced the epitaxial growth up to the surface for samples with x ≤ 0.019 and IBIEC process has induced that for samples with x ≤ 0.025. Rutherford backscattering spectrometry (RBS) measurements have revealed a direct scattering peak due to extended defects around the depth of peak C concentration both in SPEG-grown samples (x = 0.019) and IBIEC-grown sample (x = 0.025). X-ray diffraction (XRD) has shown a growth with smaller tensile strain in both SPEG- and IBIEC-grown samples than in fully strained layers. Photoluminescence (PL) measurements at 2 K have shown a strong I1 line emission in IBIEC-grown samples, which can be attributed to vacancy clustering. The local configuration of defects around C atoms in the IBIEC-grown samples is thought to be an origin of the smaller tensile strain.

Electrical properties of /spl beta/-FeSi 2 bulk crystal grown by horizontal gradient freeze method

The growth of bulk iron silicide by Horizontal Gradient Freeze (HGF) method was achieved using different growth and annealing conditions. Two types of annealing process, in-situ annealing and ex-situ annealing, were examined. Three types of samples were prepared and examined; (i) samples which were not applied any annealing processes, (ii) samples which were applied in-situ annealing, and (iii) samples which were applied both in-situ and ex-situ annealing. The influence of annealing and growth conditions upon the material qualities was examined and discussed, putting special emphasis on the structural properties and electrical properties. Results of the X-ray diffraction revealed that only the in-situ annealing was not sufficient for the peritectic reaction from /spl alpha/+/spl epsi/ eutectic to peritectic /spl beta/-phase. However, it was revealed that, if the ex-situ annealing is applied after the in-situ annealing, the condition of 900/spl deg/C for 200 hours is enough for the ex-situ annealing to obtain almost single /spl beta/-phase. It was also confirmed in the aspect of electrical properties that ex-situ annealing at 900/spl deg/C for 300 hours is enough to realize electrically semiconducting /spl beta/-FeSi/sub 2/. The sample prepared under such a condition exhibited p-type conductivity with hole concentration and hole mobility about 5.68/spl times/10/sup 17/ cm/sup -3/ and 1.36 cm/sup 2/Ns, respectively.

Growth of Ge 1-xC x alloys on Si by combined low-energy ion beam and molecular beam epitaxy method

A combined ion beam and molecular beam epitaxy (CIBMBE) method was applied for the deposition of a Ge 1- x C x alloy on Si(100) using a low-energy ( 50 – 100 eV ) C + ion beam and a Ge molecular beam. Metastable Ge 1- x C x solid solutions were formed up to x = 0.047, and the CIBMBE method was shown to have a very high potential to grow metastable Ge 1- x ,C x alloys. It was also revealed that the sticking coefficient of C + ions into Ge was ∼28% for E i , = 100 eV and ∼18% for E i = 50 eV. Structural characterization suggests that the deposited films are single crystals grown epitaxially on the substrate with twins on {111} planes. Characterization of lattice dynamics using Raman spectroscopy suggested that the deposited layers have a small amount of ion irradiation damage.