Epitaxy-Driven Synthesis of Elemental Ge/Si Strain-Engineered Materials and Device Structures via Designer Molecular Chemistry

Abstract

We describe the systematic epitaxial engineering of device-quality elemental structures in the Ge/Si system. By introducing small concentrations of (GeH 3 ) 2 CH 2 or GeH 3 CH 3 organometallic additives into conventional Ge 2 H 6 , we have developed several new low-temperature CVD growth strategies that permit heteroepitaxy of highly dissimilar materials and provide unprecedented control of film microstructure, morphology, composition, and tuning of optical properties. Optimized molecular mixtures of these compounds have enabled layer-by-layer growth via facile elimination of extremely stable CH 4 and H 2 byproducts, consistent with calculated chemisorption energies and surface reactivities. Collectively, our experiments indicate that the additives confer unique pseudosurfactant behavior that profoundly alters the classic Stranski-Krastanov growth mechanism of epitaxial Ge on Si surfaces. Using this approach, we have produced atomically smooth, carbon-free Ge layers directly on Si with dislocations densities less than 1 × 10 5 cm -2 (significantly less than those attainable from the best competing processes) at unprecedented low temperatures (350-420 °C) compatible with selective area growth applications. Full relaxation of the film is readily achieved via formation of Lomer dislocations confined to the Ge/Si interface, which should, in principle, allow film dimensions approaching bulk values to be achieved on a Si substrate. Here, films with thicknesses up to several micrometers have been grown for use as passive/ active heterostructure components. The practical utility of the approach is demonstrated for the first time by growing pure Ge seamlessly, conformally, and selectively in the "source/drain" regions of prototypical device structures. This innovation represents an ultimate extension of uniaxial strain techniques using group IV materials and is likely to have applications in the integration of microelectronics with optical components (photodiodes) into a single chip. As an additional example for high-mobility device template application, we have grown tensile Si films on the Ge buffers via decomposition of SiH 3 SiH 2 SiH 3 . The new Ge growth processes also provide a unique route to extend the utility of elemental Ge into the wider IR optoelectronic domain by tuning its fundamental optical properties using tensile strain as a main parameter. In this study, we use the metal-organic additives to circumvent traditional surface-energy limitations and produce for the first time high-quality, thermally stable, tensile strained Ge layers at low temperature (350-380 °C) on Ge 1-y Sn y -buffered Si(100). The precise strain state of the epilayers is controlled by varying the Sn content of the buffer, yielding tunable record-high tensile strains as high as 0.43%. This strain-tuning strategy may offer the prospect of producing direct optical gaps in elemental Ge.

Germanium epitaxy on silicon

“…Ge growth on a large lattice-parameter substrate such as InGaAs or GeSn buffer layers may cause tensile strain in the upper films. Fang et al [36, 37] reported that up to 0.25% tunable tensile strained Ge epitaxial films had been realized using a fully relaxed Ge 1− y Sn y ( y = 0.015–0.025) layer as a buffer. As the Sn incorporation into Ge was facilitated by a quite low temperature growth step to suppress Sn surface segregation, the GeSn alloys were therefore deposited on Si at a temperature around 350–380 °C.…”

Change in the interfacial reaction of Hf-silicate film as a function of thickness and stoichiometry

“…The strain value is very high compared to that of the strained Si film for mobility enhancement in CMOS technology; the reported compressive strain is less than 1%. 14,15 Moreover, the strain in the metal-oxide-semiconductor field effect transistor device is enhanced because the lateral strained region is limited in the device size. However, in infinite films such as our samples, the high strain implies the presence of defects: i.e., the deep blocking dips in the bulk Si changes to shallow dips in the transition layer, as shown in the inset of Fig.…”

Gas Source Techniques for Molecular Beam Epitaxy of Highly Mismatched Ge Alloys

“…Fractional distillation was used to separate the products, keeping 2 and 3 as these have been shown to dramatically improve the growth of germanium on silicon wafers [31,[48][49][50]. Thus, a four trap-to-trap distillation apparatus connected via high vacuum tubing collected the distillates from the reaction vessel at various temperatures: (i) −45 °C for the least volatile 4GeMe; (ii) −78 °C for 3; In Figure 4B, 2D HMBC correlates the resonance signal of the central carbon atom core with the resonance of the proton through C-Ge-H bonding.…”