Advances in light emission from group-IV alloys via lattice engineering and n-type doping based on custom-designed chemistries

Intrinsic and n-type Ge_1-ySn_y alloys with y = 0.003-0.11 have been grown on Ge-buffered Si via reactions of Ge₃H₈ and SnD₄ hydrides using UHV-CVD techniques. The films exhibit large thicknesses (t > 600 nm), low dislocation densities (10⁷/cm²), planar surfaces (AFM RMS ≈ 2 for intrinsic films) and mostly relaxed microstructures, making them suitable for subsequent characterization of the emission properties using photoluminescence (PL) spectroscopy. The PL spectra are acquired at room temperature and show tunable and distinct direct and indirect gap emission peaks versus composition. The peak intensity in a given sample is found to increase by exposing the layers to hydrogen plasma, indicating that surface passivation plays an important role in eliminating carrier recombination traps. The PL intensity is further increased by n-type doping with P/As atoms at levels 0.8-7 × 10¹⁹ cm^-3using P(GeH₃)₃, P(SiH₃)₃, and As(SiH₃)₃ precursors, indicating that desirable direct gap conditions can be approached even at relatively modest 6-8% Sn contents. The indirect and direct gap energies of the samples are then used to determine the direct gap cross over point at ∼9% Sn. Collectively the results in this paper show that strong light emission can be generated in this class of narrow gap alloys by adjusting the Sn content, subjecting the samples to post growth passivation treatments or doping the system n-type. The influence of precursor chemistry on the activation properties and optical behavior of the materials is explored with the objective to optimize the PL response near the indirect-direct gap threshold. New methods embodying environmentally safe conditions are designed to produce the dopant compounds in high purity for application in future generation working devices requiring enhanced IR optical performance.