An alternative, combining two plots with Show
:
Show[
ParametricPlot3D[
{0, u, v}, {u, 0, 1}, {v, 0, 2 u},
Mesh -> None, PlotStyle -> Green
],
ParametricPlot3D[
v {Cos[u], Sin[u], 0}, {u, 0, \[Pi]/2}, {v, 0, 1},
Mesh -> None, PlotStyle -> Green
],
Boxed -> False, AxesOrigin -> {0, 0, 0},
ViewPoint -> 7 {0.2, 0.2, 0.1}
]