Method for forming ohmic N-contacts at low temperature in inverted metamorphic multijunction solar cells with contaminant isolation

A method of manufacturing a solar cell comprising:

• providing a first semiconductor substrate;
• operating an MOCVD reactor to deposit on the first substrate an epitaxial sequence of layers of semiconductor material forming a solar cell;
• bonding a surrogate substrate on top of the sequence of layers with a bonding material to form a processing assembly;
• removing the first substrate;
• depositing a contact layer including germanium and palladium on a top surface of the solar cell, said contact layer having a resistance of less than 5×10−4 ohms-cm2;
• lithographically patterning the contact layer to form a plurality of metal grid lines disposed on the top surface of the solar cell, said contact layer having at least one metal contact pad electrically connected to said grid lines and disposed adjacent to a first peripheral edge of said solar cell;
• supporting the processing assembly on a contaminant isolation envelope so that during a subsequent annealing process at a temperature sufficient to liquefy the bonding material, the surrogate substrate and the sequence of layers forming the solar cell do not become detached;
• and
• annealing the processing assembly at a temperature of at least 205 degrees C. wherein the surrogate substrate and the sequence of layers forming the solar cell do not become detached.