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Viadensity functional theory based calculations we show that self-dopingof the surface Dirac cones in three-dimensional Bi2X3(X = Se, Te) topological insulators can be tuned by controllingthe sequence of stacking defects in the crystal. Twin boundaries insidethe Bi2X3bulk drive either n- or p-type self-dopingof the (0001) topological surface states, depending on the preciseorientation of the twin. The surface doping may achieve values upto 300 meV and can be controlled by the number of defects and theirrelative position with respect to the surface. Its origin relies onthe spontaneous polarization generated by the dipole moments associatedwith the lattice defects. Our findings open the route to the fabricationof Bi2X3surfaces with tailored surface chargeand spin densities in the absence of external electric fields. Inaddition, in a thin film geometry two-dimensional electron and holeDirac gases with the same spin-helicity coexist at opposite surfaces. [ABSTRACT FROM AUTHOR]