Gas source molecular epitaxy of Ge_1-ySn_ymaterials and devices using high order Ge₄H₁₀and Ge₅H₁₂hydrides

This paper describes the fabrication of Ge1-ySny 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 Ge1-xSix 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 Ge1-ySny 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.