When a low forward voltage is required, choose a germanium diode.
When a high forward voltage is required, choose a silicon diode.
When a small reverse current is required, choose a silicon diode.
When a high reverse breakdown voltage is required, choose a silicon diode.
When high temperature resistance is required, choose a silicon diode.
When a large forward current is required, choose a surface-contact diode.
When a high operating frequency is required, choose a point-contact diode.