Abstract:The optical emission spectra from Ge films on Si are markedly different from their bulk Ge counterparts. Whereas bulk Ge emission is dominated by the material's indirect gap, the photoluminescence signal from Ge films is mainly associated with its direct band gap. Using a new class of Ge-on-Si films grown by a recently introduced CVD approach, we study the direct and indirect photoluminescence from intrinsic and doped samples and we conclude that the origin of the discrepancy is the lack of self-absorption in thin Ge films combined with a deviation from quasi-equilibrium conditions in the conduction band of undoped films. The latter is confirmed by a simple model suggesting that the deviation from quasi-equilibrium is caused by the much shorter recombination lifetime in the films relative to bulk Ge.

We introduce a synthetic strategy to access functional semiconductors with general formula A(3)XY (A = IV, X-Y = III-V) representing a new class within the long-sought family of group IV/III-V hybrid compounds. The method is based on molecular precursors that combine purposely designed polar/nonpolar bonding at the nanoscale, potentially allowing precise engineering of structural and optical properties, including lattice dimensions and band structure. In this Article, we demonstrate the feasibility of the proposed strategy by growing a new monocrystalline AlPSi(3) phase on Si substrates via tailored interactions of P(SiH(3))(3) and Al atoms using gas source (GS) MBE. In this case, the high affinity of Al for the P ligands leads to Si(3)AlP bonding arrangements, which then confer their structure and composition to form the corresponding Si(3)AlP target solid via complete elimination of H(2) at ∼500 °C. First principle simulations at the molecular and solid-state level confirm that the Si(3)AlP building blocks can readily interlink with minimal distortion to produce diamond-like structures in which the P atoms are arranged on a common sublattice as third-nearest neighbors in a manner that excludes the formation of unfavorable Al-Al bonds. High-resolution XRD, XTEM, and RBS indicate that all films grown on Si(100) are tetragonally strained and fully coherent with the substrate and possess near-cubic symmetry. The Raman spectra are consistent with a growth mechanism that proceeds via full incorporation of preformed Si(3)AlP tetrahedra with residual orientational disorder. Collectively, the characterization data show that the structuro-chemical compatibility between the epilayer and substrate leads to flawless integration, as expected for pseudohomoepitaxy of an Si-like material grown on a bulk Si platform.

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This paper reports the development and optimization of an enhanced process to produce viable quantities of trigermane, and controlled smaller quantities tetragermane, which are isolated as a mixture of perfectly stable isomers. The identity and fundamental structural properties of these higher order germanes (Ge3H8, and Ge4H10 isomers) are thoroughly characterized using spectroscopic methods and quantum chemical simulations. These hydride products are found to exhibit a remarkably good stability and “ease of use”, making them compatible with current industry standards. As a proof-of-concept, we demonstrate that Ge3H8 and Ge4H10 both represent efficient and cost-effective precursors for ultra-low-temperature chemical vapor deposition of pure Ge and GeSn alloy films directly on Si(100) wafers, at conditions compatible with processes currently employed in next-generation group IV device designs. In the case of Ge the crystallinity of the resultant films is found of optical quality, in spite of the extremely low temperature processing, suggesting the potential for rapid adoption of the new processes into the device application arena. In the case of GeSn alloys, the high growth rates achieved at low temperatures (∼ 300 °C) allow the formation of highly concentrated bulk-like layers with unprecedented thicknesses compatible with Si-based photonic applications such as infrared (IR) emitters and detectors directly on Si wafers.

We introduce a practical chemical vapor deposition strategy for next-generation Ge-on-Si epitaxy utilizing recently introduced Ge 4 H 10 hydride sources that confer unprecedented deposition efficiencies at very low-temperatures (<400 • C). The corresponding high growth rates produce thick bulk-like Ge films with structural and electrical properties significantly improved relative to state-of-the-art results obtained using conventional approaches. The use of a pure, single-source compound facilitates the control of residual doping, and enables p-i-n devices whose dark currents are not entirely determined by defects and whose zero-bias optical collection efficiencies are higher than obtained from samples fabricated using alternative Ge-on-Si approaches. The reaction pathways leading to the high-yield synthesis of Ge 4 H 10 are identified on the basis of quantum thermochemistry simulations. The results suggest a simple approach to routine synthesis of tetragermane as the main product in quantities sufficient to be deployed as a commercial source.