Plate-like β-FeSi2 bulk crystals with size of 10×10 mm2 and thickness of 1 mm were fabricated by annealing CVT (chemical vapor transport)-grown plate-like α-Fe2Si5 at 800°C in Ar atmosphere. Before annealing, α-Fe2Si5 crystals were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM) to be single crystals with flat surfaces. XRD measurements of β-FeSi2 crystals subjected to annealing showed that they had a po lycrystalline structure. The mean Fe/Si co mposit ion rat io of β-FeSi2 crystal measured by energy dispersive x-ray spectroscopy (EDX) was 31/69 and it was the same as that of α-Fe2Si5 bulk crystal before annealing. SEM, Raman scattering and electron probe micro-analysis (EPMA) measurements identified that there existed small Si precipitates mixed in the matrix of β-FeSi2 crystals. At annealing temperature of 800°C, the plate-like β-FeSi2 bulk was obtained even the annealing duration time was as short as 5 hours.

Low-energy N2+ molecular-ions were irradiated during the epitaxial growth of GaAs. Ion acceleration energy and ion beam current density were varied in the range of 30-200 eV and 3-37 nA/cm2, respectively. GaAs growth rate was kept constant at 1µm/ h and the thickness of N-doped GaAs layer was about 1 µm. N concentration was obtained by using secondary ion mass spectroscopy. Strong N-related emissions were observed in the low-temperature photoluminescence spectra, which indicates that N atom is efficiently substituted at As site and is optically active as an isoelectronic impurity

The role of hydrogen (H) in carbon (C)-doped GaAs was examined by co-doping of C and H atoms using low-energy hydrocarbon (CH+ and CH3+) ions. Experiments were carried out using the combined ion beam and molecular beam epitaxy (CIBMBE) system. Samples were characterized by low-temperature photoluminescence at 2K and Hall effect measurements at room temperature. Results show that incorporated C atoms are optically and electrically activated as acceptors even by hydrocarbon ion impingement. The effect of H incorporation was found to be noticeable when impinged current density of CH3+ ion beam is high that produces equivalent net hole carrier concentration greater than ∼1018 cm−3

High-energy (400 keV) implantation of carbon (C) ions was made into LEC-GaAs substrates with C concentration ([C]) of 1019− 1022Cm−3. 2 K photoluminescence (PL) and Hall effect measurements indicated that activation rate of C in LEC GaAs is both optically and electrically extremely low even after furnace-annealing at 850 °C for 20 min. For [C] = 1×1022 cm−3, two novel strong emissions were obtained and PL measurements as a function of excitation power and sample temperature suggested that the two emissions one at 1.485 eV and the other at 1.305 eV should reflect the formation of a new alloy between GaAs and C. Dual implantation of C+ and Ga+ ions was carried out to improve the activation or substitution rate. We found that nearly 90% activation rate can be achieved for C dose of 2.2 × 1013 cm−2.

Manganese ions implantation into ultrapure GaAs layers grown by molecular beam epitaxy were investigated by photoluminescence technique systematically in a wide range of manganese concentration up to 1×1020cm-3. Five shallow emission bands denoted by (Mn°, X), “G”, “G' “ “H” and (D, A)2 are formed in the implanted layers in addition to the well known Mn impurity related emission at ~880nm. With increasing manganese concentration to 1×1019cm-3, “G” exhibits no energy shift, suggesting that “G” is different from the behavior of [g-g] emission that is commonly formed in shallow acceptor (such as C) incorporated ultrapure GaAs. (Mn°, X), “G” and “G' “ present no energy shift with increasing excitation intensity, while “H” and (D, A)2 indicate peak energy shift greatly showing typical donor-acceptor pair characteristics. “G” and (Mn°, X) are found to hold similar radiative origin which is different from “G”. Temperature dependence measurement reveals that emission “G” has a thermal activation energy of 5.4meV.

The capability of discharge-pumped vacuum ultraviolet F2 molecular laser for laser annealing of heavily ion implanted semiconductor was demonstrated for the first time using Se+ heavily ion implanted GaAs. Cr-doped semi-insulationg GaAs wafers were used as the substrates, and the Se+ implantation energy and dose were controlled to 100 keV and 1× 1015 cm-2, respectively. Samples were annealed using a F2 molecular laser ( wavelength = 157 nm ) with a single pulse ( width ~ 20 ns ) in the energy density range from 200 to 800 mJ/cm2 in a nitrogen atmosphere. In addition, furnace annealing was done on separate samples at 850 ºC for 20 minutes in a purified hydrogen atmosphere for comparison. Characterization of the samples was carried out using Raman scattering and ellipsometry. The laser annealed samples exhibited intense Raman scattering LO phonon peaks whose intensity increased with increasing laser power density, whereas the furnace annealed samples exhibited a very weak LO phonon peak. It was demonstrated for the first time that VUV photons can be very effective in annealing ion implantation damage as compared with conventional furnace annealing. The behavior of Raman scattering spectra as a function of laser energy density was explained quantitatively by a “spatial correlation” model. The model made it possible to estimate the average size of the recovered crystal regions in samples for any given laser energy density.

Recently, we introduced various acceptor impurities into MBE-grown ultra-pure GaAs by conventional high-energy ion implantation and found many novel shallow emissions associated with acceptor-acceptor pairs. Most of these emissions were easily quenched by extremely small amount of residual donor atoms which were unintentionally introduced during doping processes. For the interpretation of impurity effects, the usage of mass-separated atom as dopant source was strongly suggested. Along this consideration, we developed combined ion beam and molecular beam epitaxy (CIBMBE) technology, in which damage-free doping with high mass purity (M/ΔM=100) is expected to be possible. We here present the results of low-energy (100 eV) carbon ion doping using CIBMBE method. Samples were prepared asa function of growth temperature (Tg=400-700°C) and ion beam current. Net hole concentration, |NA-ND| as high as ~1×1020 cm-3 was obtained in as-grown samples. In 2K photoluminescence spectra, emissions due to acceptor-acceptor pairs exhibit specific energy shift with growing |NA-ND|. Results indicate that carbon doping can be made efficiently even at Tg as low as 500°C without any post heat treatment. These results also tell that by CIBMBE method no serious radiation damages are produced and the undesired impurity contamination can be considerably suppressed.

C-doped GaAs films were prepared by novely a developed, combined ion beam and molecular beam method (CIBMBE) as a function of hyperthermal (30–500 eV) energies (EC+) of carbon ion (C+) beam. Ion beams of a fixed beam current density were impinged during molecular beam epitaxy growth of GaAs at substrate temperature of 550 °C. Low temperature (2 K) photoluminescence (PL) has been used to characterize the samples together with Hall effects measurements at room temperature. Through the spectral evolution of an emission denoted by [g-g]β which is a specific emission relevant to acceptor-acceptor pairs, the activation rate was confirmed to increase with increasing EC+ for EC+ lower than 170 eV. It was explicitly demonstrated that the most effective Ec+ to establish highest activation rate is located at ~170 eV. This growing activation rate was suggested to be attributed to the enhanced migration of both impinged C and host constituent atoms with increasing EC+. This surmise was supported also by Hall effect measurements which revealed the maximum net hole concentration ( |NA-ND| ) for EC+=170 eV. For EC+ higher than ~170 eV, increasing EC+ was found to induce the reduction of activation rate. It was suggested that this observation is ascribed not to the formation of C donors but to the enhanced sputtering effect of impinged C+ ions with increasing EC+.

Fabrication of Si1-xGex and Si-1-x-yGexCy layers on Si(100) by high-dose ion implantation of 72Ge ions without and with 12C ions and subsequent high-energy and low-energy ion-beam-induced epitaxial crystallization (IBIEC) has been investigated. Structural properties of the surface layers were observed by RBS-channeling technique. Si(100) wafers were implanted with 150keV and 80keV Ge ions at room temperature so as to produce a peak concentration of Ge amounting to approximately 2 and 14 at.%, respectively. C ions were additionally implanted to a fluence of 10% of Ge concentration for the SiGeC samples. IBΓEC experiments performed with 400keV 18Ar ion bombardments have induced crystallization of the amorphous layers of SiGe and SiGeC on Si up to the surface at 400°C for both samples with low Ge concentration (2%) and high Ge concentration (14%). IBIEC using 72Ge ions with energies whose projected ranges are within the amorphous layer was alternatively performed for SiGe layer on Si. Bombardments of 140keV and 40keV Ge ions at 400°C have induced crystallization up to the surface with a slight disorder in the grown layer. Present experimental results suggest a novel ion beam synthesis method of fabrication of SiGe (SiGeC) on Si at low temperatures.

Low temperature (2° K) photoluminescence (PL) measurements were performed for the wavelength (λ) region from 800 to 1600 nm on Be–doped GaAs grown by molecular beam epitaxy (MBE) for wide range of net hole concentration at room temperature (p) up to 2 x 1020 cm−3 after annealing at 850 °C for 20 minutes. The annealing procedure formed several new PL emission bands associated with deep levels appeared between 0.4 and 1.4 eV. The most intensive new PL band appeared at around 1.2 eV with a band width of about 0.2 eV for all samples investigated. Its peak position and band width were observed to shift slightly toward lower energy side and increase, respectively with increasing p. An additional two sharp bands appeared overlapping the main band at around 1.31 and 1.35 eV for p less than 1 x 1018 cm−3. New broad band formation was also observed at around 1.0 eV in the same samples. In addition, a new prominent PL band was found at about 1.35 eV in the as-grown samples with p = 5 ∼ 6 x 1017 cm−3, which disappeared entirely after annealing. The formation and annihilation mechanism of these deep levels after annealing can be presumably attributed to Be redistribution from Ga sites to As sites and interstitial sites to Ga or As sites, driven by the formation of As vacancies (V As) due to As evaporation from samples during annealing.

The structural effects of low-energy (30-500 eV), mass separated C12 Ion doping of GaAs simultaneous with conventional solid source MBE growth have been studied using room-temperature raman scattering, Hall-effect, transmission electron microscopy and 2K photoluminesence measurements for GaAs epitaxy temperatures of 550 ºC. Results indicate good acceptor activation without detectable residual damage is achieved for ion energies ≤ 240 eV, while at EIon = 500 eV, residual damage is present with a corresponding reduction in electrical activation. Low-energy TRIM calculations indicate that the damage is related to the increased depth distribution of vacancies and interstitials created during the higher (500 eV) implantation process which can not be annealed out at growth temperatures. Constant energy (100 eV) film growth experiments for a range of implantation currents (45 pA/cm2 - 45 nA/cm2) and growth temperatures of 550 and 550 ºC, show LO Raman peak broadening and mode hardening for currents ≥15 nA while maintaining very high C acceptor activation. This is interpreted as residual stress due to small amounts of interstitial C in the highest doped films. Both Hall mobility measurements and photoluminesence show no evidence of C dopant compensation.

The preparation of amorphous insulating films containing nanometer-scaled structures of semiconductors has attracted increased attention since the observation of room temperature emission of light from films containing indirect-bandgap semiconductors such as Ge and Si. While most experimental reports on these Si and Ge nano-scale structures have been based on thin films created using sputter-deposition, in this study we have used conventional ion implantation of Ge to create the non-equilibrium mixture of materials that, upon annealing, develops a nano-crystallite phase embedded in the amorphous matrix. The presence of clusters that are difficult to image in TEM, in addition to microcrystallites, is an issue of interest since the source of light emission is still controversial. The second phase is formed from excess amounts of the semiconductor, in this case added by implantation. In this paper the formation and size distribution of the Ge nano-structures was characterized using Raman scattering and transmission electron microscopy (TEM). Similarly to reported sputtered film results, Raman spectra suggest Ge clusters that are not well formed crystallites may be present for anneals at low temperatures and in unannealed films. For annealing temperatures exceeding 600°C, a mixture of amorphous-like clustering and nano-crystallites may result, depending on the volume fraction of Ge. For low dose samples it was found that temperature and time of annealing could be used to manipulate the nucleation behavior of the nano-crystallites.

Low energy (100 eV) impinging of carbon (C+) ions was made during molecular beam epitaxy (MBE) of GaAs using combined ion beam and molecular beam epitaxy (CIBMBE) technologies for the growth temperature ( Tg ) between 500 °C and 590 °C. 2 K photoluminescence (PL), Raman scattering and Hall effect measurements were made for the samples. In the PL spectra two specific emissions, “g” and [g-g], were observed which are closely associated with acceptor impurities. PL and Hall effect measurements indicate that C atoms were very efficiently introduced during MBE growth by CIBMBE and were both optically and electrically well activated as acceptors even at Tg=500 °C. The results reveal that defect-free impurity doping without subsequent annealing can be achieved by CIBMBE method.

Photoluminescence (PL) measurements have been carried out as a function of temperature and of excitation power on heavily magnesium (Mg) implanted ultra-pure indium phosphide (InP) with a dose concentration, [Mg], ranging from l×lO15cm-3 to 3×1020cm−3. Several undefined emissions have been observed; a strong emission, Z, emerges near the band-acceptor emission for [Mg]= 3×1020cm−3 and two novel emissions, Y1 and Y3 appear below the energy of donor-acceptor pair emission for [Mg] smaller than 3×1018cm−3. In order to obtain more explanation on such emission, temperature and excitation power dependence of the emissions were investigated. Temperature dependent PL experiments revealed that Z is composed of three emissions named ZA, ZBand ZC. Measured activation energies suggest Z represents a pair type transition associated with Mg acceptors. While, Y1 and Y3 emissions are attributed to donor-acceptor type transition because of a significant blue-shift with increasing excitation power.

Mg ion-implantation was carried out into very pure GaAs made by molecular beam epitaxy, in which the dose of Mg atoms, [Mg] was varied from l×1015 to 1×1020 cm−3 . As a method of characterization, low temperature photoluminescence (PL) studies were carried out as a function of [Mg]. A new emission, denoted by [g-g] was observed between bound exciton emissions and the emission due to 1 and-to-acceptor pairs. It was found that [g-g] appears around [Mg]= 2×1016 cm−3 and becomes a dominant emission at [Mg] over l×1017 cm−3. A significant shift of [g-g] towards the lower energy side with increasing [Mg] was reproducibly obtained and its PL properties were carefully investigated in terms of annealing temperature, TA and excitation density. Results revealed that the implanted Mg atoms become optically active at TA over 600 [g-g] was suggested to be acceptor-acceptor pair, which is consistent with the theoretical explanation that its radiative mechanisms is ascribed to the pair between excited-state acceptors. The systematic energy shift inherent to [g-g] was attributed to the growing ionization energy of the pair with increasing pair distance.

Ion implantation of Se+ and Zn+ ions into GaAs was carried out and characterization was performed by photoluminescence and Raman scattering at 2 K and room temperature, respectively. For comparison, implantation of Cd+ ions was also performed and further. a series of Si-doped GaAs samples were prepared by molecular beam epitaxy. In the Se+-implanted samples. with Se concentration between 1×1016 cm−3 and 5×1019 ca−3 the dominant radiative transition was the band-to-band emission, (B-B). No energy shift characteristic of (B-B) was observed but instead, the formation of a complex radiative center between donor impurities and implantation-induced damages, [D.LD] was revealed. This was in contrast to the Si-doped GaAs which displayed a pronounced energy shift of (B-B) towards higher energies with increasing Si concentration. The results suggest that (B-B) (reflecting the raising of the quasi Fermi-energy due to the increase of net free electron concentration) is significantly suppressed in the donor-ion implanted GaAs due to the presence of unremovable damages caused by implantation. In the Zn+ -implanted GaAs, the dominant emission was [g-g] which is formed just below the bound exciton emissions. The energy shift of [g-g] towards lower energies with increasing implanted Zn concentration was reproducibly observed. Thus clear differences in the PL spectra of donor- and acceptor-implanted samples were observed near the fundamental band edge. It was suggested that residual radiation damages suppress (B-B) but have little effect on acceptor-related emissions.

C+ ion-implantation was carried out for extremely pure GaAs gown by moleplar Ieam epitaxy. The dose was very widely varied from 1×1015 to 1×1020 cm−3. Photoluminescence and Raman scattering measurements were performed at 2 K and room temperature, respectively, both as functions of dose and annealing temperature. The results revealed that for a dose less than 5×1017 cm−3, where the dominant damages are point defects, annealing at 200°C is sufficient to attain a damage-free lattice. When the dose is above that value, where the principal damage is a highly disordered lattice, annealing, at least above 550°C, is required. Photoluminescence spectra showed that the well-defined near-band-gap emission, [g-g], (exclusively inherent to acceptors), was a dominant emission in the above mentioned low dose region, but was strongly suppressed in the higher region. These observations indicate that ion-implanted C atoms in GaAs behave as amphoteric impurities when the dose exceeds a critical value, of around 5×1017 cm−3.

Photoluminescence measurements of Be-doped GaAs, grown by molecular beam epitaxy, were carried out at low temperature as a function of acceptor concentration. Results revealed that besides the well-defined emission, [g-g], which is exclusively relevant to acceptor impurities, an additional specific emission, temporarily denoted by [g-g]α is formed near the band-edge, when the concentration of acceptors exceeds 1×1019 cm−3:. From the viewpoint of application it was suggested that also in case of acceptors, photoluminescence spectra can be practically used for the precise determina-tion the acceptor concentration.