W. Wesch

Ion-beam induced damage and annealing behaviour in SiC

Abstract The paper presents the damage accumulation in silicon carbide (SiC) as a function of the ion mass, the ion energy and the implantation temperature. A defect-interaction and amorphization model is used to analyse the dose dependence of defect production, as obtained by the various methods. The temperature dependence of the amorphization dose can be represented assuming a thermally enhanced annealing within the primary collision cascades. On the basis of such a model, a critical implantation temperature is obtained, which was found to vary with the ion mass and the implantation energy. The concurrent influence of implantation temperature and ion fluence on the resulting damage distribution in SiC is demonstrated. The damage annealing of ion implanted SiC is investigated for low, medium and high damage concentrations. The effect of the implantation temperature and the concentration of implanted atoms, both influencing the kind of defects obtained after implantation, on the annealing behaviour is analysed.

Silicon carbide: synthesis and processing

Abstract Silicon carbide with its outstanding physical properties is a material of choice for special optoelectronic and electronic devices working under extreme conditions. Synthesis as well as processing are complicated compared to other materials. The present paper summarizes some aspects of crystal growth and processing and discusses arising problems.

Damage formation and annealing at low temperatures in ion implanted ZnO

N, Ar, and Er ions were implanted into ZnO at 15 K within a large fluence range. The Rutherford backscattering technique in the channeling mode was used to study in situ the damage built-up in the Zn sublattice at 15 K. Several stages in the damage formation were observed. From the linear increase of the damage for low implantation fluences, an upper limit of the Zn displacement energy of 65 eV could be estimated for [0001] oriented ZnO. Annealing measurements below room temperature show a significant recovery of the lattice starting at temperatures between 80 and 130 K for a sample implanted with low Er fluence. Samples with higher damage levels do not reveal any damage recovery up to room temperature, pointing to the formation of stable defect complexes.

Structural processing of enstatite by ion bombardment

During their lifetime, cosmic dust silicates suffer from a continuous processing by annealing, cosmic ray and UV irradiation, destruction and possibly also interstellar recondensation. Since the discovery that a significant proportion of star- dust silicates leaves their star in crystalline form, the question arose as to why the interstellar silicate dust component does not show any indication of crystallinity. Amorphization due to ion irradiation is one possible explanation for the effect. In this paper, the results of irradiation experiments of submicrometre-sized clinoenstatite (MgSiO3) particles with 400 keV Ar + and 50 keV He + ions are presented. The irradiation doses have been varied between 1×10 16 and 1×10 18 ions/cm 2 for He + ions and 1×10 14 up to 5×10 14 ions/cm 2 for Ar + ions. These doses are comparable to those values that an interstellar silicate grain should be exposed to during its average life-time of 4×10 8 years. Threshold values for amorphization have been amounted to 1×10 17 and 3×10 14 ions/cm 2 for 50 keV He + and 400 keV Ar + ions. Besides the structural changes in the microcrystallites morphological modifications in the grains, but no change of the chemical composition are found. Conclusions of potential astrophysical relevance have been drawn.

Three-step amorphisation process in ion-implanted GaN at 15 K

GaN layers were implanted at 15 K with 150 keV O, 300 keV Ar or 800 keV Xe ions. The subsequent damage analysis was performed by Rutherford backscattering of He ions in channelling configuration at the same temperature. At this low temperature thermal effects can be widely excluded. However, the dependence of the damage concentration on the ion fluence suggests that the damage evolution in GaN is dominated by a pronounced recombination of the primarily produced defects within the collision cascades. Furthermore, a strong influence of the ions themselves has to be assumed in order to understand the experimental results. Such effects occur already at rather low ion fluences. Our results indicate an amorphisation of GaN proceeding in three steps.

Defect production during ion implantation of various AIIIBV semiconductors

The present paper gives a survey about the defect generation caused by ion implantation of GaAs, InAs, GaP, and InP. By combining Rutherford backscattering spectrometry, optical spectroscopy, and transmission electron microscopic methods, further information concerning the kinetics of the defect production as well as the type of defects created is obtained. Generally, the defect concentration in the region of implantation parameters investigated can be described by the energy density deposited into nuclear processes. Below critical values of the nuclear deposited energy density in GaAs weakly damaged layers containing point defects and point defect clusters are produced. With increasing nuclear deposited energy density an increasing number of amorphous zones is created due to manifold overlap of the initial defect clusters. The results indicate that in GaAs and InAs already at relatively low implantation temperatures, the amorphization occurs via homogeneous defect nucleation. The results obtained for GaP...

Growth of silicon nanowires by chemical vapour deposition on gold implanted silicon substrates

Silicon nanowires (SiNWs) were synthesized by the vapour–liquid–solid (VLS) growth mechanism using gold implanted silicon substrates. Implantation of high ion fluences leads to an amorphized silicon layer at the wafer surface. During annealing the Au in the implanted region agglomerates and yields Au droplets at the surface upon recrystallization of the amorphous layer. The structural quality of nanowires grown from implanted substrates is comparable to those grown on wafers with evaporated gold films. This opens up new possibilities for local growth of SiNWs by implanting through masks or using a focused ion beam technique.

Two-beam irradiation chamber for in situ ion-implantation and RBS at temperatures from 15 K to 300 K

In order to investigate the primary eAects of ion‐solid interaction, low-temperature implantation and measurement of the irradiated samples without warming up are necessary. A corresponding experimental setup is described, which allows one to perform ion-implantation at constant temperatures between 15 K and 300 K and the defect analysis by Rutherford backscattering spectrometry (RBS) without changing the target temperature. 200 keV Ar a implants into GaAs are done at 15 K and RBS spectra are collected with the detector placed under a backscattering angle of 110∞. Under these conditions a very good agreement of the measured defect profiles with those calculated with the TRIM code is obtained. The defect profiles were calculated from the RBS spectra with due consideration for the lattice vibrations. The Debye temperatures of GaAs at diAerent temperatures are thus determined. ” 2001 Elsevier Science B.V. All rights reserved.

Defect production during ion implantation of various A/sub III/B/sub V/ semiconductors

The present paper gives a survey about the defect generation caused by ion implantation of GaAs, InAs, GaP, and InP. By combining Rutherford backscattering spectrometry, optical spectroscopy, and transmission electron microscopic methods, further information concerning the kinetics of the defect production as well as the type of defects created is obtained. Generally, the defect concentration in the region of implantation parameters investigated can be described by the energy density deposited into nuclear processes. Below critical values of the nuclear deposited energy density in GaAs weakly damaged layers containing point defects and point defect clusters are produced. With increasing nuclear deposited energy density an increasing number of amorphous zones is created due to manifold overlap of the initial defect clusters. The results indicate that in GaAs and InAs already at relatively low implantation temperatures, the amorphization occurs via homogeneous defect nucleation. The results obtained for GaP...

Damage production in semiconductor materials by a focused Ga+ ion beam

The semiconductor materials Si, SiC, GaP, InP, GaAs, and InAs were irradiated at normal incidence and room temperature with a focused Ga+ ion beam in order to investigate the damage production at high current densities on the order of some A cm−2. The samples were irradiated with ion fluences between 2×1013 and 2×1015 Ga+ cm−2 at an ion energy of 50 keV. The critical ion fluences for amorphization were determined by Rutherford backscattering spectrometry and by Raman spectroscopy. It was found that for SiC, GaP, and InP the number of displacements per atom necessary for amorphization is about the same one as that required for irradiation at low current densities, but in the cases of Si, GaAs, and InAs the high and low current density results differ remarkably. The reason for the different behavior of these materials is discussed.