Damage formation and annealing studies of low energy ion implants ...

abundance of 92.23 % (3). This has a small bearing on the MEIS spectra and is
discussed in section 4.2.2.
Figure 3.1 Si unit cell. From (2).
Figure 3.2 Si (100), (110) and (111) planes. From (3)
Intrinsic (undoped) Si has a band gap of 1.1 eV at room temperature and will
have an equal (low) concentration of holes and electrons (5). Extrinsic (doped) Si will
have an excess of holes or electrons depending on the doping type. Usually doping is
with group III and V atoms although group II and VI are also used. To be electrically
active these atoms have to replace a Si atom being covalently bound to Si atoms,
creating an unsatisfied bond (hole) if a group III ion or with an extra electron not
involved in bonding, available of conduction, if group V dopant.
Si oxidises in air to form a native SiO2 layer. This SiO2 is amorphous and is an
electrical insulator. The native oxide can easily be removed in a HF dip. Thin oxide
layers are used as the insulating gate oxide and can easily be grown on the surface of Si
to the required thickness. Mechanisms for oxide growth are discussed in (6) and
references therein. Oxygen molecules react with surface Si atoms to form SiO2. Further
growth is due to the diffusion of oxygen through the SiO2 layer which reacts with Si at
31