Monolithic multijunction power converter

A method of making a multijunction power converter, comprising:

• growing a first semiconductor layer overlying a GaAs or Ge substrate, wherein the first semiconductor layer does not absorb at a monochromatic wavelength, wherein the monochromatic wavelength is within a range from 1.3 micron to 1.55 micron;
• growing a first GaInNAsSb junction on the first semiconductor layer, wherein the first GaInNAsSb junction has a bandgap configured to absorb at the monochromatic wavelength;
• growing a first tunnel junction on the first GaInNAsSb junction;
• growing a second GaInNAsSb junction on the first tunnel junction, wherein the second GaInNAsSb junction has the bandgap configured to absorb at the monochromatic wavelength;
• growing a second semiconductor layer overlying the second GaInNAsSb junction, wherein the second semiconductor layer does not absorb at the monochromatic wavelength;
• growing a distributed bragg reflector overlying the GaAs or Ge substrate, wherein the first semiconductor layer overlies the distributed bragg reflector, wherein the distributed bragg reflector comprises layers of GaAs and AlGaAs;
• and
• thinning the GaAs or Ge substrate wherein incoming radiation is first incident on the GaAs or Ge substrate before being incident on the first and second GaInNAsSb junctions.