Díaz Díaz, Jesús IldefonsoGaliano, GonzaloJungel, Ansgar2023-06-202023-06-201999-06-010362-546X10.1016/S0362-546X(98)00105-9https://hdl.handle.net/20.500.14352/57367The temporal and spatial localization of vacuum sets of the solutions to the drift-diffusion equations for semiconductors is studied in this paper. It is shown that if there are vacuum sets initially then there are vacuum sets for a small time, which shows the finite propagation speed of the support of the densities. It is also shown that for a certain recombination-generation rate there is no dilation of the initial support, and under some condition on the recombination-generation rate the vacuum will develop after a certain time even if there is no vacuum initially. These results are proved based on a local energy method for free boundary problems.engjournal articlehttp://www.sciencedirect.com/science/article/pii/S0362546X98001059http://www.sciencedirect.com/restricted access517.95isentropic drift-diffusion modeldegenerate parabolic equationsfree boundary problemlocal energy methodssemiconductorsdrift-diffusion modeluniquenessequationssupportspaceEcuaciones diferenciales1202.07 Ecuaciones en Diferencias