Voltage of a diode at which current increases?

In a Silcon diode no current flows in the forward direction (anode to positive voltage) until approximately 0.6 - 0.7Volts is reached. Above this voltage the current rises in line with Ohms Law. In the reverse direction only micro Amps flow (leakage current)

In a Germanium diode the threshold is about 0.2 volts and reverse leakage is higher.