<p>This thesis reports on a systematic investigation of the ion implantation damage in Si, Ge, GaP and GaAs at ≤50K. The damage has been measured "in-situ" using the channeling-backscattering technique. Implantation energies have ranged from 10-250 keV with Z₁ in the interval 2 ≤ Z₁≤ 81.</p> <p>The study has been divided into two parts, depending on Z₁. For low Z₁ (Z₁ < or ∼ 30), the damage profiles in Si, GaP and GaAs have been extracted at 50K. Discrepancies from the theoretical profiles are evident and can be accounted for in terms of the previously reported Z₁-oscillations in the electronic stopping powers. The radial distribution of displaced atoms is examined in these three materials by systematically introducing small misalignments (ψ ≤ 0.36 ψ₁) between the analyzing beam direction and crystal axis. This "Off-Axis" effect is examined as a function of Z₁, ion dose, and depth. Significant atom relaxations are concluded to extend perpendicular to the channel row by up to ~ 40% of the channel radius. While atom relaxations do not contribute to the measured damage at low ion doses, they can account for up to 50-70% of the measured damage at high ion doses. A quantitative model of the damage-done behaviour has been developed, in which the atom relaxation component is incorporated as being directly proportional to the measured damage.</p> <p>The number of displaced atoms/ion is found to be greater than the prediction derived from collision theory by up to an order of magnitude for high-Z₁ bombardment. Therefore, the second section of the thesis contains a detailed study of the effect for 7 ≤ Z₁ ≤ 81 in Si and Ge at 35K. The deviation is not an artifact of the channeling-bakscattering technique. It is concluded that an "energy-spike" may be initiated by the high-Z₁ bombardments; the energy-spike induces a local amorphous zone in the semiconductor, thereby accounting for the increased damage. A semi-empirical model of the data is developed, which divides the damage into collisional and energy-spike components. Extensive use is made of molecular ion bombardments, since they provide a simple method of varying the individual ion-induced collision cascade energy density; this allows for a test of the energy-spike concepts. It is concluded that spikes will influence the damage up to energies corresponding to a lower energy density limit of 0.1 eV/atom in Si and 0.01 eV/atom in Ge. The lower energy limit for spike effects is evidently «10 keV. In Si it appears that the amorphization process is best described by a thermal-spike mechanism, whereas in Ge, it is inferred that the athermal collapse of the unstable lattice is more probable. To support the arguments and concepts of the energy-spike, a Monte Carlo computer code has been written to simulate the collision cascade and provide insight into the parameters of the individual ion-induced cascades.</p> / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/12717 |
| Date | 07 1900 |
| Creators | Walker, Sulis Robert |
| Contributors | Thompson, D.A., Electrical Engineering |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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