Needs["Graphics`PlotField`"];
a = 0.04; b = 0.003; c = 0.0015; i0 = 0.06;
f = 
        Expand[v (a - v) (v - 1) - b/c v + 
            i0];
Solve[f ==  0];
bild1 = 
        Plot[{b/c v,  v (a - v) (v - 1) + i0}, {v, -0.3, 1}, 
          PlotRange -> {-0.1, 0.2}, 
          ImageSize -> {400, 
              300}, 
DisplayFunction -> Identity, 
          AxesLabel -> {"u", "v"}];
bild2 = 
        PlotVectorField[{v (a - v) (v - 1) - w + i0, 
            b v  -  c w}, {v, -0.25, 1, 0.2}, {w, -0.1, 0.2, 
            0.04}, 
ScaleFactor -> 0.15, 
          DisplayFunction -> Identity];
bild = 
        Show[Evaluate[{bild1, bild2}], 
          DisplayFunction -> $DisplayFunction, 
          ImageSize -> {400, 300}];