Ge1-ySny (y = 0.01-0.10) alloys on Ge-buffered Si: Synthesis, microstructure, and optical properties

Abstract

Novel hydride chemistries are employed to deposit light-emitting Ge1-ySny alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge2H6 and deuterated stannane SnD4. For y ≥ 0.06, the Ge precursor was changed to trigermane Ge3H8, whose higher reactivity enabled the fabrication of supersaturated samples with the target film parameters. In all cases, the Ge wafers were produced using tetragermane Ge4H10 as the Ge source. The photoluminescence intensity from Ge1−ySny/Ge films is expected to increase relative to Ge1−ySny/Si due to the less defected interface with the virtual substrate. However, while Ge1−ySny/Si films are largely relaxed, a significant amount of compressive strain may be present in the Ge1−ySny/Ge case. This compressive strain can reduce the emission intensity by increasing the separation between the direct and indirect edges. In this context, it is shown here that the proposed CVD approach to Ge1−ySny/Ge makes it possible to approach film thicknesses of about 1 μm, for which the strain is mostly relaxed and the photoluminescence intensity increases by one order of magnitude relative to Ge1−ySny/Si films. The observed strain relaxation is shown to be consistent with predictions from strain-relaxation models first developed for the Si1−xGex/Si system. The defect structure and atomic distributions in the films are studied in detail using advanced electron-microscopy techniques, including aberration corrected STEM imaging and EELS mapping of the average diamond–cubic lattice.

Ion-beam synthesis and thermal stability of highly tin-concentrated germanium – tin alloys

“…%. This result is certainly encouraging as it is comparable to some of the best studies using molecular beam epitaxy 12,13 and chemical vapour deposition 14,15 . For the 4.0 × 10 16 −2 sample, the high scattering yield of the channelling spectrum (purple) represents a disordered layer, noting the two large bumps: one at the sample's surface and one at about the back edge of the amorphous layer.…”

Direct gap Ge1-ySny alloys: Fabrication and design of mid-IR photodiodes

“…A solution of this problem is the insertion of pure Ge buffer layers, which drastically reduce the starting lattice mismatch between the Si(100) substrate and the film. 21 This means that strain relaxation can be achieved with a much lower dislocation density, which facilitates the growth of thick films and reduces the non-radiative recombination velocities at the film-buffer interface. A number of groups have utilized this approach to fabricate n-Ge/i-Ge 1-y Sn y /p-Ge heterostructure light emitting diodes (LEDs) in which the GeSn active layers are ensconced by p-and n-type Ge electrodes.…”

Group IV Direct Band Gap Photonics: Methods, Challenges, and Opportunities

“…Regarding the epitaxial growth of direct band gap GeSn alloys, nearly strain relaxed or even tensilely strained layers are highly desired, since for compressively strained GeSn layers, i.e., GeSn coherently grown on Ge VS, higher Sn contents are necessary for the indirect to direct transition . Owing to an advantageous relaxation mechanism for GeSn layers on Ge VS, dislocations seem to mostly protrude into the Ge VS rather than into the GeSn layer, which is beneficial for optical properties as the density of non-radiative recombination centers is reduced (Takeuchi et al, 2006;Senaratne et al, 2014;Wirths et al, 2015). Although relaxation takes place, a certain level of compressive biaxial strain (typically between −0.6 to −0.8%) remains nevertheless, which, as already said in connection with Figure 2, shifts the indirect-to-direct band gap crossover to higher Sn concentrations with respect to fully relaxed GeSn.…”

“…Although relaxation takes place, a certain level of compressive biaxial strain (typically between −0.6 to −0.8%) remains nevertheless, which, as already said in connection with Figure 2, shifts the indirect-to-direct band gap crossover to higher Sn concentrations with respect to fully relaxed GeSn. Therefore, several approaches are being followed to reduce the compressive strain, such as growth on lattice-matched InGaAs VS (Chen et al, 2011a), which is not acceptable within a CMOS processing line, or deposition of ever thicker layers to enforce further strain relaxation (Senaratne et al, 2014;Wirths et al, 2015). Gupta et al (2013b) introduced a robust etching approach enabling to selectively dry etch the Ge VS underneath the epitaxial GeSn layers.…”