M. Kalitzova

Ability of reflection high energy electron diffraction (RHEED) to observe structural modifications in ion-implanted and annealed GaAs

GaAs 〈100〉 wafers were implanted and later annealed by using three different techniques: furnace thermal annealing (FTA), flash lamp (RTA) and low-power laser annealing (LPLA). The resulting modifications of the structure were studied by RHEED. The RHEED pattern analysis indicates that: (a) A well annealed structure is observed after thermal treatment in furnace at 850 °C for 30 min; (b) the particular RTA employed leads to some texturing, but is not sufficient to provide good structural effects; (c) best annealing under our conditions is obtained by the LPLA technique, especially for low ion doses (less than 1013 cm−2); (d) variable-glancing-angle RHEED is an effective and convenient method to investigate the ion induced disorder in crystals at small depths.

Precipitation of superstructured nano-crystals in high-dose implanted Si: an XHRTEM study

Nano-sized precipitation in high-dose implanted Si has been investigated using high-resolution transmission electron microscopy of cross-sectional specimens (XHRTEM). Zn and Bi (50 keV) have been implanted in Si at doses of 5 × 1016 cm−2 and 1016 cm−2, respectively. In spite of the different diffusivities of these species in Si, their low solubility resulted in precipitation of nano-sized metallic inclusions whose inner structures revealed a synthesis of superlattices, composed of the host Si matrix and the implanted species.

High‐dose phenomena in zinc‐implanted silicon crystals

The structure of (100) silicon implanted with Zn+ ions at an energy of 50 keV was studied. The ion doses were varied from 1×1015 to 1×1017 cm−2 and the beam current density was 10 μA cm−2. The analytical techniques employed for sample characterization included cross‐sectional transmission electron microscopy and x‐ray energy dispersion analysis. The energy deposition of the ion beam was calculated by using computer simulation codes. For the two lower doses of 1×1015 and 1×1016 a crystalline‐to‐amorphous transformation was observed in the implanted layer and this was correlated with the thermal history of the implants and the attendant changes in morphology. In contrast, an amorphous‐to‐crystalline transition was found to occur at higher doses, namely 5×1016 and 1×1017, where the formation of a complex, structured layer consisting of an amorphous phase mixed with crystalline grains of Zn and partly recrystallized Si was identified together with other specific structural features. Detailed characterization ...

Radiation defects in Te-implanted germanium Electron microscopy and computer simulation studies

Abstract Direct observation of radiation damage induced by heavy ion implantation in crystalline germanium by means of high-resolution electron microscopy is reported. The dark-field lattice imaging mode is used, under conditions suitable for object like imaging. Conventional TEM is used for estimating the efficiency of creating visibly damaged regions. Heavy ion damage clusters with three types of inner structure are observed: with near-perfect crystalline cores, and with metastable and stable amorphous cores. The MARLOWE computer code is used to simulate the atomic collision cascades and to obtain the lateral spread distributions of point defects created. A comparison of high-resolution electron microscopy (HREM) with computer simulation results shows encouraging agreement for the average cluster dimensions and for the lateral spread of vacancies and interstitials.

Low‐power pulsed‐laser annealing of implanted GaAs

Low‐power annealing by a pulsed laser is used to recover the structure of low‐dose implanted (100) GaAs crystals. Reflection high‐energy electron diffraction with variable glancing incidence is employed to detect the structural changes at different depths in the specimens. The depth dependence of the damage is studied in more detail by Rutherford backscattering analysis. The annealing results depend on the irradiation conditions. A laser energy window below the melting threshold is found within which the structure can be restored to about as high degree of crystallinity as the virgin one, without any visible surface damage. A simple theoretical estimate shows that the temperature rise of the material is far below the melting threshold. This rise is too short in time to cause substantial dopant diffusion; however, it can enhance well the point‐defect mobility.

Amorphization and crystallization in high-dose Zn+-implanted silicon

The nature of amorphization and crystallization of Si brought about by 50 keV Zn ion implantation within the dose range 2×1017–1×1018 cm−2 is studied. The structures are evaluated in the as-implanted state by transmission electron microscopy, transmission electron diffraction, reflection high-energy electron diffraction, selected-area electron diffraction, x-ray energy-dispersive analysis, and Rutherford backscattering spectrometry. It is found that, contrary to the theoretical predictions, the Zn concentration profile does not reach saturation even at a dose as high as 1×1018 cm−2. A common feature of the microstructure of these high-dose implants is the formation of a continuous amorphous layer and concurrent crystallization of Zn and Si in small crystalline clusters. Microscopic beam-heating effects are also believed to play an appreciable role in the development of the specific morphologies observed. The results are interpreted in terms of two recent models proposed in the literature and the concept o...

RHEED and RBS analysis of low-power laser annealed GaAs

〈100〉GaAs crystals were implanted with 140 keV Zn ions at random incidence and a dose of 1014 cm−2. Annealing by a low-power pulsed laser was used to recover the radiation damage. The samples were analysed by RHEED and RBS techniques. The effect of the annealing on the recovery of structure defects in GaAs is reported.

Activation of electrical carriers in Zn-implanted InP by low-power pulsed-laser annealing

Low-power pulsed-laser annealing was applied to Zn+-implanted InP samples. In order to avoid surface oxidation during the treatment, the laser irradiation was carried out in inert ambient of nitrogen at different pressures. The analytical techniques used include Rutherford backscattering spectroscopy, reflection high energy electron diffraction, and electrical measurements. The highest carrier activation, about 80%, was achieved at the same laser power density (6.5 MW/cm2) at which the best crystal recovery was obtained.

Cross‐sectional high resolution electron microscopy of Zn+ implanted and low‐power pulsed‐laser annealed GaAs

High resolution transmission electron microscopy has been used to investigate the lattice damage distribution in Zn+ implanted and implanted plus low‐power pulsed‐laser annealed (LPPLA) GaAs. The damage distribution of implanted samples has been examined in detail showing the presence of a continuous amorphous layer under the surface and stacking fault tetrahedra nuclei at the inner a–c interface. A solid phase epitaxial regrowth of ion implanted GaAs has been induced by LPPLA technique. In the annealed samples, the crystalline recovering is characterized by a low density of residual extended defects lying in the fully recrystallized amorphous layer.

High resolution transmission electron microscopy of elevated temperature Zn+ implanted and low-power pulsed laser annealed GaAs

Cross-sectional high resolution transmission electron microscopy was applied to 140 keV Zn+ implanted GaAs at elevated temperature (110±10 °C). Gaussian-like in-depth distributions of damage clusters, retaining some features of the original crystal lattice, were observed. The distribution maximum was found located between about 55 and 80 nm below the implanted surface. Low-power pulsed-laser annealing of the implanted samples induced both migration and clustering of radiation defects in the region extending from the surface and 80 nm depth, combined with nearly complete recrystallization of the material below this layer.