It comes up as a gold-bonded germanium diode here. However, **broken link removed** brings up a replacement as the 1N4148 (bottom-right, page 3).
Anyway, if it's a germanium diode and having a datasheet to refer to the characteristics, a little research on the Internet will bring up a suitable part with similar parameters.
Seems like an unlikely part to use in a switcher power supply. Can you show us the board please Rakshitarya or tell us how it is connected in the circuit. For most applications using LNK30x devices, the diodes should be fast switching power types, not ordinary silicon or germanium diodes.