An epitaxially grown layer III-V
solar cell is separated from the growth substrate by propagating a crack close to the epi /
wafer interface. The crack is driven by the elastic
strain energy built up due to thermal stresses between GaAs and
polyimide by cooling below
room temperature. A GaAs
wafer is bonded to a
polyimide substrate on the epi-side and scribed on the opposite side. The crack is initiated from the scratch and guided along the interface using an epitaxially grown sacrificial layer with lower
fracture toughness under the
solar cell. No expensive
ion implantation or lateral chemical
etching of a sacrificial layer is needed. The
active layer is transferred
wafer-scale to inexpensive, flexible, organic substrate. The process allows re-using of the wafer to grow new cells, resulting in savings in raw materials and
grinding and
etching costs amounting to up to 30% of the cost of the
cell. Several cells are integrated on a common
blanket polyimide sheet and interconnected by
copper plating. The
blanket is covered with a transparent spray-on polyimide that replaces the
cover glass. The
solar cell is stress-balanced to remain flat on
orbit.Wide bandgap materials, such as
Gallium Nitride (GaN) and
Silicon Carbide (SiC) are very promising for light-emitting diodes (LEDs) and
power electronics. These materials are
extremely hard and difficult to
machine and very expensive. The lack of good quality bulk GaN substrates with a
smooth surface at a reasonable price is hampering the development of vertical devices.A rapid
thinning technique is presented by lifting-off a 20-70 μm thick layer from the surface within a fraction of a second, which leaves the surface shiny and smooth. The savings in lapping and
polishing add up to 60%, when this technique is incorporated in the
crystal manufacturing process. This technology also has application for backside
thinning where the savings are even larger.