  We report transport studies on a three dimensional, 70 nm thick HgTe layer,
which is strained by epitaxial growth on a CdTe substrate. The strain induces a
band gap in the otherwise semi-metallic HgTe, which thus becomes a three
dimensional topological insulator. Contributions from residual bulk carriers to
the transport properties of the gapped HgTe layer are negligible at mK
temperatures. As a result, the sample exhibits a quantized Hall effect that
results from the 2D single cone Dirac-like topological surface states.
