Ultralow Resistivity Ge:Sb heterostructures on Si Using Hydride Epitaxy of Deuterated Stibine and Trigermane

The nonconventional deuterated stibine (SbD₃) compound has been used for the first time in combination with trigermane (Ge₃H₈) to produce hyper-doped Ge-on-Si films with carrier concentrations n > 10²⁰ cm^-3 and record-low resistivities ρ = 1.8 × 10^-4 Ω cm. The growth takes place on Ge and Ge_1-xSi_x buffered Si(100) wafers at ultralow temperatures (∼330 °C) at which Sb diffusion is negligible, leading to extremely flat atomic profiles of the constituents. The Sb substitution in the Ge lattice is determined by RBS channeling and corroborated by high-resolution XRD, which also reveal a systematic increase in lattice constant vs concentration, as expected due to the incorporation of the larger Sb. High-resolution TEM illustrates defect-free monocrystalline structures with device-quality morphologies. The electrical characteristics of the samples are measured using Hall effect and resistivity measurements combined with contactless infrared ellipsometry and are found to be consistent with an extrapolation of the bulk Ge:Sb properties to the high carrier concentrations achieved in our films. The Sb/Ge ratio in the doped layers is approximately the same as that in the precursor reaction mixture, indicating a highly efficient Sb incorporation afforded by the compatible reactivity of the molecules employed in this study. The resultant films are attractive for next generation germanium technologies that require low-resistance n+ junctions or a Fermi level that approaches the direct gap minimum in the conduction band, which drastically enhances the optical emission efficiency of n-type Ge.