Gas source molecular epitaxy of Ge1−ySny materials and devices using high order Ge4H10 and Ge5H12 hydrides.

This paper describes the fabrication of Ge_1−ySn_y layers with 2%–13% Sn, utilizing a unique method that combines high-order Ge₄H₁₀ and Ge₅H₁₂ hydrides and gas source molecular epitaxy techniques. The latter operate at very low working pressures of 10⁻⁶–10⁻⁷ Torr leading to molecular flow regime conditions, promoting layer-by-layer epitaxy of crystalline materials at ultralow-temperatures (250–160 °C) that cannot be achieved by conventional thermal CVD. In both cases, a "direct injection" approach is employed, using the pure vapor of Ge₄H₁₀ and Ge₅H₁₂ as the source of the Ge flux, which is then reacted on the substrate surface with SnD₄ in the absence of gaseous carriers. Ge₄H₁₀ reactions were conducted at 215–190 °C, producing 6%–12% Sn samples. These were grown on both conductive, resistive, single-side, and double-side polished Si(100) with n-type Ge_1−xSi_x buffer layers (x = 2%–3%) to explore conditions and substrate formats that facilitate back-side illumination, enabling transparency and enhanced responsivity at 1550 nm in prototype p-i-n devices. Exploratory reactions of Ge₅H₁₂ with SnD₄ produced Ge_1−ySn_y with 2%–13% Sn at 250–160 °C for the first time. All samples were characterized by XRD, RBS, IR-ellipsometry, AFM, and TEM to investigate the structure, composition, strain state, and morphology. The samples grow partially relaxed (T > 180 °C) and their compressive strains gradually diminish in situ with increasing film thickness (up to 700 nm) without epitaxial breakdown and Sn segregation. Residual strains are further reduced by RTA processing. The experiments described here demonstrate the practicality of our chemistry-based method as an alternative to thermal CVD for the fabrication of high crystal quality samples on larger area wafers for potential applications in IR devices. [ABSTRACT FROM AUTHOR]