Optoelectronic devices manufactured using different growth substrates
A growth structure having a lattice transition (or graded buffer) or an engineered growth structure with a desired lattice constant, different from a lattice constant of conventional substrates like GaAs, Si, Ge, InP, under a release layer or an etch stop layer is used as a seed crystal for growing optoelectronic devices. The optoelectronic device can be a photovoltaic device having one or more subcells (e.g., lattice-matched or lattice-mismatched subcells). The release layer can be removed using different processes to separate the optoelectronic device from the growth structure, which may be reused, or from the engineered growth structure. When using the etch stop layer, the growth structure or the engineered growth structure may be grinded or etched away. The engineered growth structure may be made from a layer transfer process between two wafers or from a ternary and/or a quaternary material. Methods for making the optoelectronic device are also described.
1. An optoelectronic device, comprising:
an epitaxial layer, comprising a plurality of stacked subcells that are lattice matched at a lattice constant different than a lattice constant of conventional single and binary element substrates, each subcell of the plurality of stacked subcells being configured to capture a different portion of a spectrum of light on the optoelectronic device or emit a different portion of a spectrum of light by the optoelectronic device, each subcell including at least one pn junction, a lattice constant of the plurality of stacked subcells not matching a lattice constant of a growth wafer on which the epitaxial layer was formed or matching a lattice constant of an engineered growth structure on which the epitaxial layer was formed, and the epitaxial layer being configured for further processing in which one or more additional layers are added to the optoelectronic device;
a reflector disposed below the epitaxial layer; and
a textured layer disposed between the reflector and the epitaxial layer, and configured to scatter light within the optoelectronic device,
wherein the conventional single and binary element substrates include Si, Ge, InP, and GaAs substrates, and
wherein the engineered growth structure is an unconventional substrate different from the conventional single and binary element substrates that include Si, Ge, InP, and GaAs substrates.
2. The optoelectronic device of claim 1 , wherein:
the lattice constant of the plurality of stacked subcells ranges from a lattice constant of GaAs (5.65 Å) to a lattice constant of InP (5.87 Å), or
the lattice constant of the plurality of stacked subcells ranges from a lattice constant of GaP (5.45 Å) to a lattice constant of GaAs (5.65 Å).
3. The optoelectronic device of claim 1 , wherein being lattice matched includes bulk epitaxial layers with thickness greater than 300 nanometers and with a lattice mismatch that is less than 500 arc-seconds.
4. The optoelectronic device of claim 1 , wherein:
the at least one pn junction in each subcell is a homojunction, or
the at least one pn junction in each subcell is a heterojunction.
5. The optoelectronic device of claim 1 , wherein:
the at least one pn junction in each subcell is a front junction positioned within a subcell of the plurality of stacked subcells closest to a side of a subcell of the plurality of stacked subcells that faces light incident on the optoelectronic device, or
the at least one pn junction in each subcell is a rear junction positioned within a subcell of the plurality of stacked subcells closest to a side of a subcell of the plurality of stacked subcells opposite a side that faces the light incident on the optoelectronic device.
6. The optoelectronic device of claim 1 , wherein the at least one pn junction in each subcell includes a p-n junction, an n-p junction, or a p-i-n junction.
7. The optoelectronic device of claim 1 , wherein the epitaxial layer includes a plurality of tunnel junctions, wherein each of the plurality of tunnel junctions are positioned between adjacent subcells of the plurality of stacked subcells.
8. The optoelectronic device of claim 1 , wherein:
the optoelectronic device is a photovoltaic device with more than three junctions, and
the plurality of stacked subcells include more than three subcells.
9. The optoelectronic device of claim 1 , further comprising:
a front window layer disposed over the epitaxial layer;
a contact layer disposed over at least portions of the front window layer;
an emitter layer and an absorber layer; and
one or both of a back-surface field (BSF) or a back-surface reflector (BSR).