In this paper, we report on the formation of heavily n-doped Ge:Sb layers on Si(001) substrates by MBE with active dopant concentration exceeding 10 20 cm −3 and discuss their thermal stability. Rapid thermal annealing was applied to the samples with different doping densities being both below and above the equilibrium solubility limit of Sb in Ge. Experimentally obtained changes of the impurity atomic concentration and carrier density were attributed to Sb bulk diffusion, desorption and dopant clustering. The qualitatively different modifications of room-temperature photoluminescence (PL) due to annealing were obtained for the n-Ge layers with different doping levels. In particular, for the doping levels which were below or close to the equilibrium solid solubility the overall positive impact of annealing on the PL intensity was observed. However, for the n-Ge layers with higher doping levels a more complex behavior was obtained, namely, a significant drop followed by the subsequent partial restoration of the PL intensity with the increase of annealing temperature. Changes of the PL response were attributed to the two main processes which occur during thermal treatment-annealing of the point defects generated due to low-temperature growth of a doped layer and dopant cluster formation-which have the opposite impact on the PL intensity. The obtained results allowed us to formulate the recommendations on thermal treatment of the n-type doped Ge layers, which may be useful for Ge-based Si photonics applications.

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A high-performance light-trapping structure for Si was fabricated with an etching margin of only >1 µm using Ge islands grown by gas-source molecular beam epitaxy as etching masks. KOH solution containing isopropyl alcohol and HF + H 2 O 2 + CH 3 COOH mixed solution were used as etchants. The reflectance of the structure was shown to be comparable to that of a conventional pyramid texture, which requires a larger etching margin of >10 µm. In addition, a potential short-circuit current density (p-J sc ) of 42.3 mA/cm 2 was obtained for the sample after the deposition of indium tin oxide, which confirms that the light-trapping structure is applicable to crystalline Si solar cells with thinner wafers.

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