Single Crystalline Germanium-Lead Formed by Laser-Induced Epitaxy

Single crystalline germanium-lead (GePb) is formed using pulsed laser anneal (PLA). The anneal was performed on an amorphous GePb layer (1.1 atomic percent of Pb) capped by SiO2, Si3N4, or Al2O3 to study the impact of different capping layers on GePb formation. Among various laser fluences (300, 350, 400, 450, and 500 mJ/cm2) used, the best GePb crystalline quality was achieved using 350 mJ/cm2. Secondary ion mass spectrometry (SIMS) results show a final Pb composition in the GePb film after laser anneal of between 0.2 and 0.4 atomic percent, indicating a significant loss of Pb. Among the different capping layers used, Al2O3-capped GePb shows the highest Pb content in the GePb layer with the lowest Pb loss after PLA. The incorporation of Pb atoms in the substitutional sites of Ge lattice was confirmed by high resolution X-ray diffractometry (HRXRD) and high resolution Rutherford back scattering spectrometry (HR-RBS). The substitutionality, i.e. percentage of Pb atoms incorporated into substitutional sites of Ge lattice, is more than 70%. The anneal process leads to the formation of cavities in the GePb layer and pin holes on the surface, suggesting an out-diffusion of Pb from the GePb thin-film during laser anneal. Increasing the laser anneal fluence above 400 mJ/cm2, however, reduces the number of cavities and pin holes but increases the surface roughness of the film.