Phase transitions in two-dimensional electron-hole systems in high magnetic fields

We consider phase transitions with an excitonic condensate formation in quasi-two-dimensional semiconductors in high magnetic fields. The phase diagram is constructed and thermodynamic quantities are calculated for all densities. In the Hartree-Fock approximation all thermodynamic potentials prove to be the same as those of the electron-hole (e-h) drop state. Therefore the transition from a tenuous e-h gas to a dense e-h liquid can be treated either as a first-order transition or as two successive second-order transitions. With allowance for the correlation corrections the thermodynamic properties of the excitonic phase become slightly different from those of the drop state.