Defect reduction by liquid phase epitaxy of germanium on single-crystalline-like germanium templates on flexible, low-cost metal substrates

Single-crystalline-like germanium (Ge) templates were demonstrated on low-cost, flexible metal substrates and have been used to fabricate III-V materials and devices for photovoltaics and flexible electronics applications. However, these Ge templates, fabricated by magnetron sputtering or plasma enhanced chemical vapor deposition, contain a high density of defects. In order to improve the performance of optoelectronic devices made using the Ge templates, a homo-epitaxial Ge layer has been additionally grown by a liquid phase epitaxy (LPE) method. The LPE Ge layer is composed of significantly larger grains (similar to 26 m) compared to that of the Ge template (similar to 200 nm). This large size of the LPE Ge grains effectively reduces the volume fraction of grain boundaries. The LPE Ge shows an out-of-plane texture of similar to 0.63 degrees and an in-plane texture Delta phi of similar to 1.26 degrees, which signify improvements of similar to 39.3% and similar to 76.6% compared to that of the vapor-deposited Ge template, respectively. Further, the LPE Ge is strain free, compared to the strained Ge template hetero-epitaxially grown on cerium oxide. Defects caused by low-angle grain boundaries, impurities and strain relaxation in the Ge template are found to be suppressed in the LPE Ge. The threading dislocation density is roughly estimated to be similar to 5 x 10(6) cm(-2) in the LPE Ge compared to similar to 1 x 10(10) cm(-2) in the Ge template.