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Abstract: The global in-time semiclassical and relaxation limits of the bipolar quantum hydrodynamic model for semiconductors are investigated in . We prove that the unique strong solution exists and converges globally in time to the strong solution of classical bipolar hydrodynamical equation in the process of semiclassical limit and that of the classical drift–diffusion system under the combined relaxation and semiclassical limits. [Copyright &y& Elsevier]

This paper concerns the stationary subsonic or sonic–subsonic solution of the electric potential driven problem to the isentropic hydrodynamic model for semiconductors. We give a necessary and sufficient condition to ensure the existence of this kind of solution. Specifically, there exists a subsonic or sonic–subsonic solution to this problem if and only if 0 ≤ ϕ r ≤ ϕ ̄ , with the number ϕ ̄ = O 1 τ . Here, ϕ r is the right side electric potential and τ is the relaxation time. Moreover, there is a number ϕ ̃ ∈ (0 , ϕ ̄ ] such that when ϕ r = ϕ ̃ , there exists a sonic–subsonic solution. In this way, we show the influence of the relationship between the boundary value of the electric potential and the semiconductor effect on the existence of this kind of solution. Finally, we prove the uniqueness of subsonic solution by the energy method under the assumption that ϕ r and ϕ r τ are both small enough. [ABSTRACT FROM AUTHOR]