There is no dedicated high tech zone in the game, all industry (except agriculture) uses both medium and high density industral zones. If there's enough demand for I-HT, those buildings will grow. When you have a solid I-D and I-M industry already, you can try rising the taxes for those a tiny bit, so the demand for them will lower, hence only I-HT will grow.
Or you can use T-Wrecks' "Industrial Revolution Mod" (IRM), which is based on a suggestion that I once made. It restricts all I-D and most I-M lots to medium density zones and moves all I-HT lots into high density, so when you zone the appropriate density, only the desired buildings will grow.
