Combination of layer deposition and pulsed UV laser annealing for thin GeSn:Sb layers hyperdoping.

GeSn has been attracting a lot of attention lately due to its potential uses in SWIR and MWIR photonics. Adding Sn to Ge at high substitutional concentrations (6-8% Sn) reduces the energy bandgap and changes its type from indirect to direct [1,2]. However, the low equilibrium solubility of Sn in Ge (<1 at.%) makes producing thick (1 um) GeSn layers with high Sn concentrations difficult. Recent research has shown that, by coupling Sn deposition on Ge substrates with pulsed UV laser annealing in the melt regime, it is possible to exceed this solid solubility and fabricate 200 nm-thick GeSn layers with Sn% > 6 at.% [3-5]. To facilitate the current flow across the final structure, GeSn integration requires the introduction of high dopant concentrations (>10^20 cm-3) within a shallow junction (<100 nm) close to the surface. In this study, we describe a process that combines an ultra-thin (< 2 nm) Sb layer deposition on previously fabricated GeSn and a laser annealing to achieve surface melting (< 200 nm). This allows for the incorporation of high levels of antimony concentration (n-type doping). After fabricating a GeSn layer as previously describes, a 2-nm-thick Sb layer was deposited and the Sb/GeSn stack is then laser-annealed under various conditions to finally obtain a 100 nm-thick hyperdoped GeSn:Sb layer with an active Sb concentration around 3x10^20 cm-3. Different investigations were also conducted on the melt depth evolution as a function of energy density for GeSn layers and on the impact of HF cleaning prior to the Sb layer deposition. Morphological and structural characterizations were performed to study the impact of Sb inclusion in GeSn by AFM (Fig. 1.a) and Raman spectroscopy (Fig. 1.b). Hall effect measurements (Fig. 1.c) and SIMS (Fig. 1.d) were used to analyze the electrical activation. [1] E. Talamas Simola et al., "CMOS-Compatible Bias-Yunable Dual-Band Detector Based on GeSn/Ge/Si Coupled Photodiodes," ACS Photonics, 2021, vol. 8, pp. 2166-2173. [2] Y. Miao et al., "Review of Si-Based GeSn CVD Growth and Optoelectronic Applications," Nanomaterials, 2021, vol. 11, p. 2556. [3] D. Fontana et al., "Ex-situ n-type heavy doping of Ge1-xSnx epilayers by surface Sb deposition and pulsed laser melting," Applied Surface Science, 2022, vol. 600, p. 154112. [4] E. Di Russo et al., "Synthesis of relaxed Ge0.9Sn0.1/Ge by nanosecond pulsed laser melting," Applied Surface Science, 2023, vol. 612, p. 155817. [5] D. Fontana et al., "Synthesis of supersaturated GeSn alloys on Ge and Ge-on-Si by nanosecond pulsed laser melting," EMRS Fall 2024, Warsaw, Poland, 16 - 19 September 2024.