  Employing scaling analysis of the localization length, we deduce the critical
exponent of the metal-topological insulator (TI) transitions induced by
disorder. The obtained exponent nu~2.7 shows no conspicuous deviation from the
value established for metal-ordinary insulator transitions in systems of the
symplectic class. We investigate the topological phase diagram upon carrier
doping to reveal the nature of the so-called topological Anderson insulator
(TAI) region. The critical exponent of the metal-TAI transition is also first
estimated, shown to be undistinguishable from the above value within the
numerical error. By symmetry considerations we determine the explicit form of
Rashba spin-orbit coupling in systems of C4v point group symmetry.
