S.T. Johnson

Ion beam induced epitaxial crystallisation of silicon

Abstract It is shown that epitaxial crystallisation of amorphous silicon layers can be induced by irradiating samples with energetic light ions at temperatures in the range 673–723 K. This epitaxial process is shown not to be a consequence of macroscopic beam heating. Under certain irradiation conditions Rutherford backscattering/channeling analysis suggests that the regrown silicon is nearly perfect single crystal but TEM analysis, while confirming epitaxial growth, reveals the presence of extended defects which result from the elevated temperature helium bombardment. Evidence is presented to support the view that ion beam induced epitaxy is a consequence of mobile, ion irradiation induced defects created at, or near, the crystal-amorphous interface.

Ion‐beam‐induced epitaxial crystallization kinetics in ion implanted GaAs

Thin amorphous GaAs layers on (100)‐oriented substrates, generated by Si+ ion bombardment at 77 K, have been observed to recrystallize epitaxially during 1.5‐MeV Ne+ bombardment in the temperature range 75–135 °C. Crystallization proceeds linearly with increasing ion fluence, except in the near‐surface region, and the process is characterized by an activation energy of 0.16 eV, which is an order of magnitude smaller than that obtained for conventional thermal annealing at much higher temperatures.

Implantation temperature dependence of electrical activation, solubility, and diffusion of implanted Te, Cd, and Sn in GaAs

The relationship between electrical activity, dopant solubility, and diffusivity was investigated as a function of the substrate temperature during implantation of Te, Cd, and Sn ions into GaAs. Implant doses of these species in the range 5×1012–5×1015 cm−2 were performed in the temperature range −196 to 400 °C, followed by either transient (950 °C, 5 s) or furnace (450–900 °C, 20 min) annealing. The redistribution after such annealing was found to depend on the implant temperature, and was always greatest for Cd followed by Sn and Te. The degree of electrical activation was in the same order, but there was essentially no correlation of electrical activity with dopant solubility. Te, for example, showed soluble fractions of ∼90% for a dose of 1015 cm−2 after annealing at 850 °C or higher, regardless of the initial implant temperature. By sharp contrast, the electrically active fraction under these conditions was in the range 0.8%–3.4%. There was also no apparent correlation of the degree of electrical act...

Ion beam induced epitaxy of (100) and (111) GaAs

Ion implanted amorphous layers on GaAs substrates of both (100) and (111) orientation were subjected to ion beam induced epitaxial crystallization at temperatures between 75 ° C and 165 ° C using 1.5 MeV Ne+ ions. For (100) GaAs a linear growth rate with Ne fluence is observed at low ( < 100° C) temperatures and this contrasts with non linear behaviour observed at higher (∼150° C) temperatures. In the low temperature regime, ion beam induced regrowth proceeds linearly beyond thicknesses which can be successfully regrown by a conventional 270° C furnace anneal. For (111) GaAs, ion beam induced crystallization proceeds faster than for (100) GaAs but the growth rate is non linear at low temperatures. The IBIEC regrowth rate behaviour of (111) GaAs is also shown to exhibit anomalous behaviour compared to that observed during thermal annealing.

Electrical activation of group‐IV elements implanted at MeV energies in InP

The electrical activation and carrier mobility of InP implanted with the group‐IV elements at MeV energies has been studied as a function of implanted atom (C, Si, Ge, and Sn) and rapid thermal annealing temperature (500–800 °C). In addition, electrical results have been correlated with photoluminescence (PL) measurements. In general, for a dose of 5×1014/cm2 and a projected range of ∼1.0 μm, the electrical activation and carrier mobility increase then saturate with increasing annealing temperature. Similarily, PL emission intensity increases with increasing annealing temperature. At a temperature of 750 °C, the electrically active fraction increases from C, Ge, Si, to Sn, respectively, while carrier mobility and PL emission intensity decreases with increasing atomic mass. Thus, Sn exhibits the highest electrical activation yet lowest carrier mobility with little optically observable, postanneal lattice recovery.

Characterisation of MeV neon damage in silicon

Abstract Ion backscattering (RBS)/channeling and transmission electron microscopy (TEM) have been combined to characterise the radiation damage produced in crystalline silicon during irradiation with 1.5 MeV Ne + . The resulting damage structures and distributions are found to be a sensitive function of substrate temperature. In particular, for temperatures between 20 and 300°C the disorder is found to increase gradually from the surface to a peak at the projected ion range, whereas, for temperatures greater than 300°C the disorder is observed to have a very distinctive distribution, consisting of a narrow band of extended defects at the projected ion range but with the surface region essentially defect free to depths of ~ 1.4 μm. This latter structure has been employed to obtain an accurate measure of the channeled to random stopping power ratio (0.53 ± 0.05) for 3 MeV He + incident along a 〈001〉 silicon axial direction.

Solid solubility limits in ion-implanted gallium arsenide

Abstract High dose (4 × 10 14−1 × 10 16ions cm −2) implantation into (100) GaAs wafers of Sn, Sb and Te was carried out at either liquid N 2 temperature or at elevated temperature. Selected samples were capped with sputter deposited SiO 2 and annealed in the solid phase using either a furnace or a rapid incoherent light source. Uncapped samples were annealed using a pulsed ruby laser. Ion channeling of 2 MeV He 2+ indicated that solid solutions of Sn, Sb and Te in the range 10 20−10 21 cm −3 were obtained following 600°C annealing. The maximum measured solubility appeared to be limited by the solute-defect interactions and thus the ability to achieve acceptable crystallinity during annealing. For higher temperature and longer time furnace annealing the maximum solubility can either increase or decrease with temperature and is controlled by both solute trapping at residual defects and precipitation processes.

Mev Ion Beam Applications In III-V Semiconductors

This paper reviews some key areas where MeV ion beams can be applied to III-V semiconductor materials. In particular, ion damage is assessed for various III-V materials in terms of implantation parameters, especially substrate temperature and dose rate. Implant isolation, involving the introduction of damage to remove carriers and achieve highlyresistive layers, is assessed for MeV irradiation. It is concluded that MeV ions can provide deep, uniform damage with a single-energy implant. Finally, improved epitaxy of amorphous InP with MeV ions is demonstrated.

Ion-beam induced isolation of gallium arsenide layers

Abstract Epitaxial (n+−n) layers on semi-insulating GaAs samples were implanted with 60 keV He+ ions at elevated temperatures. Samples were analysed to provide sheet resistivity, Hall mobility and carrier depth profiles using electrical measurement techniques and damage distributions using TEM and Rutherford backscattering and channeling. All of the data were correlated to identify the optimum conditions to achieve electrical isolation. Elevated temperature He+ implants have been found to create uniform, single step isolation of GaAs layers. Isolation of the GaAs layers can be enhanced and stabilised further by a suitable post-implantation annealing process.

Ion beam mixing of Sn layers with GaAs

Thin (∼ 200 A) Sn layers on GaAs have been mixed using Ar+ and Kr+ ions at doses up to 106 ions cm−2 and covering the temperature range from LN2 to 225°C. Both ballistic mixing and radiation enhanced mixing regimes have been identified. In the former regime, peak Sn concentrations exceeding 20 at.% are achievable, but the latter process results in a saturation at a much lower level of ∼ 4 at.%, a result that is consistent with maximum concentrations achievable by laser-induced mixing.