For what value of voltage will the reverse current $I_0$ in a $p-n$ junction $Ge$ diode reach $90\%$ of its saturation value at room temperature?

For the following logic circuit, 

$Y=0$ for $A=1, B=1, C=1$
$Y=0$ for $A=0, B=0, C=0$
$Y=1$ for $A=1, B=0, C=0$

The logic gate in the question-marked box will be,