The invention provides for a junction diode including a heavily doped first region having a first conductivity type, a second lightly doped or intrinsic region having a second conductivity type, and a third heavily doped region having a second conductivity type. The junction diode comprises more than one semiconductor or semiconductor alloy. In preferred embodiments, the lightly doped or intrinsic region has a higher proportion of germanium than on or the other or both of the heavily doped regions. In preferred embodiments, the junction diode is vertically oriented, and the top region has a higher proportion of silicon than the other regions.