  We consider pairing of massless Dirac electrons and holes located on opposite
surfaces of thin film of "strong" three-dimensional topological insulator. Such
pairing was predicted to give rise to topological exciton condensate with
unusual properties. We estimate quantitatively achievable critical temperature
of the pairing with taking into account self-consistent screening of the
Coulomb interaction, disorder and hybridization of electron and hole states
caused by a tunneling through the film. Increase of the gap above the
hybridization value when the temperature is lowered can be observable signature
of the pairing. System parameters required to observe the electron-hole pairing
are discussed.
