There is provided a method of bonding a first substrate and a second substrate, the method comprising: providing an aluminium (Al) connection having a first width on one side of a first substrate; providing a germanium (Ge) connection having a second width on one side of a second substrate, wherein the second width is larger than the first width; and bonding the Al connection on the first substrate and the Ge connection on the second substrate by eutectic bonding of at least a portion of the Al connection and at least a portion of the Ge connection to form an Al-Ge eutectic melt, wherein the Al-Ge eutectic melt is confined within the second width of the Ge connection.