Sattar Al-Kabi

An optically pumped 2.5 μm GeSn laser on Si operating at 110 K

This paper reports the demonstration of optically pumped GeSn edge-emitting lasers grown on Si substrates. The whole device structures were grown by an industry standard chemical vapor deposition reactor using the low cost commercially available precursors SnCl4 and GeH4 in a single run epitaxy process. Temperature-dependent characteristics of laser-output versus pumping-laser-input showed lasing operation up to 110 K. The 10 K lasing threshold and wavelength were measured as 68 kW/cm2 and 2476 nm, respectively. Lasing characteristic temperature (T0) was extracted as 65 K.

Systematic study of GeSn heterostructure-based light-emitting diodes towards mid-infrared applications

Temperature-dependent characteristics of GeSn light-emitting diodes with Sn composition up to 9.2% have been systematically studied. Such diodes were based on Ge/GeSn/Ge double heterostructures (DHS) that were grown directly on a Si substrate via a chemical vapor deposition system. Both photoluminescence and electroluminescence spectra have been characterized at temperatures from 300 to 77 K. Based on our theoretical calculation, all GeSn alloys in this study are indirect bandgap materials. However, due to the small energy separation between direct and indirect bandgap, and the fact that radiative recombination rate greater than non-radiative, the emissions are mainly from the direct Γ-valley to valence band transitions. The electroluminescence emissions under current injection levels from 102 to 357 A/cm2 were investigated at 300 K. The monotonic increase of the integrated electroluminescence intensity was observed for each sample. Moreover, the electronic band structures of the DHS were discussed. Despite the indirect GeSn bandgap owing to the compressive strain, type-I band alignment was achieved with the barrier heights ranging from 11 to 47 meV.

Optical Characterization of Si-Based Ge1−x Sn x Alloys with Sn Compositions up to 12%

Optical properties of germanium tin (Ge1−xSnx) alloys have been comprehensively studied with Sn compositions from 0 (Ge) to 12%. Raman spectra of the GeSn samples with various Sn compositions were measured. The room temperature photoluminescence (PL) spectra show a gradual shift of emission peaks towards longer wavelength as Sn composition increases. Temperature dependent PL shows the PL intensity variation along with the temperature change, which reveals the indirectness or directness of the bandgap of the material. As temperature decreases, the PL intensity decreases with Sn composition less than 8%, indicating the indirect bandgap Ge1−xSnx; while the PL intensity increases with Sn composition higher than 10%, implying the direct bandgap Ge1−xSnx. Moreover, the PL study of n-doped samples shows bandgap narrowing compared to the unintentionally (Boron) doped thin film with similar Sn compositions due to the doping.

Study of a SiGeSn/GeSn/SiGeSn structure toward direct bandgap type-I quantum well for all group-IV optoelectronics

A SiGeSn/GeSn/SiGeSn single quantum well structure was grown using an industry standard chemical vapor deposition reactor with low-cost commercially available precursors. The material characterization revealed the precisely controlled material growth process. Temperature-dependent photoluminescence spectra were correlated with band structure calculation for a structure accurately determined by high-resolution x-ray diffraction and transmission electron microscopy. Based on the result, a systematic study of SiGeSn and GeSn bandgap energy separation and barrier heights versus material compositions and strain was conducted, leading to a practical design of a type-I direct bandgap quantum well.

Si based GeSn light emitter: mid-infrared devices in Si photonics

Ge1-xSnx/Ge thin films and Ge/Ge1-xSnx/Ge n-i-p double heterostructure (DHS) have been grown using commercially available reduced pressure chemical vapor deposition (RPCVD) reactor. The Sn compositional material and optical characteristics have been investigated. A direct bandgap GeSn material has been identified with Sn composition of 10%. The GeSn DHS samples were fabricated into LED devices. Room temperature electroluminescence spectra were studied. A maximum emission power of 28mW was obtained with 10% Sn LED under the injection current density of 800 A/cm2.

Investigation of GeSn Strain Relaxation and Spontaneous Composition Gradient for Low-Defect and High-Sn Alloy Growth

Recent development of group-IV alloy GeSn indicates its bright future for the application of mid-infrared Si photonics. Relaxed GeSn with high material quality and high Sn composition is highly desirable to cover mid-infrared wavelength. However, its crystal growth remains a great challenge. In this work, a systematic study of GeSn strain relaxation mechanism and its effects on Sn incorporation during the material growth via chemical vapor deposition was conducted. It was discovered that Sn incorporation into Ge lattice sites is limited by high compressive strain rather than historically acknowledged chemical reaction dynamics, which was also confirmed by Gibbs free energy calculation. In-depth material characterizations revealed that: (i) the generation of dislocations at Ge/GeSn interface eases the compressive strain, which offers a favorably increased Sn incorporation; (ii) the formation of dislocation loop near Ge/GeSn interface effectively localizes defects, leading to the subsequent low-defect grown GeSn. Following the discovered growth mechanism, a world-record Sn content of 22.3% was achieved. The experiment result shows that even higher Sn content could be obtained if further continuous growth with the same recipe is conducted. This report offers an essential guidance for the growth of high quality high Sn composition GeSn for future GeSn based optoelectronics.

SiyGe1−x−ySnx films grown on Si using a cold-wall ultrahigh-vacuum chemical vapor deposition system

Silicon germanium tin alloys were grown directly on Si substrates using a cold-wall ultrahigh-vacuum chemical vapor deposition system at 300 °C, where commercially available precursors of silane, germane, and stannic chloride were used to grow the epitaxial layers. The crystallinity and growth quality of the SiyGe1−x−ySnx films were investigated through material characterization methods including x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and transmission electron microscopy. Rutherford backscattering measurements show that 2%–5% of the Sn and 3%–5% of the Si were successfully incorporated. Investigation of the material growth parameters shows that a flow rate of stannic chloride higher than 1 sccm results in etching of the film, while an increase in the silane flow rate results in amorphous film growth. The photoluminescence study shows clear emission peaks ascribed to direct and indirect bandgap transitions, which are in agreement with theoretical calculations.

Investigation of optical transitions in a SiGeSn/GeSn/SiGeSn single quantum well structure

A SiGeSn/GeSn/SiGeSn single quantum well structure featuring type-I band alignment was comprehensively characterized. Three pump lasers with different penetration depths and photon energies were used to pinpoint the optical transition characteristics of the sample. The carrier generation, redistribution, and recombination under each pumping condition were analyzed in detail. By comparing the temperature-dependent photoluminescence spectra of the GeSn quantum well with that of SiGeSn and GeSn thin film samples possessing similar Si and Sn compositions, the optical transition mechanism was clearly identified.

Buffer-Free GeSn and SiGeSn Growth on Si Substrate Using In Situ SnD4 Gas Mixing

Buffer-free GeSn and SiGeSn films have been deposited on Si via a cold-wall, ultra-high vacuum chemical vapor deposition reactor using in situ gas mixing of deuterated stannane, silane and germane. Material characterization of the films using x-ray diffraction and transmission electron microscopy shows crystalline growth with an array of misfit dislocation formed at the Si substrate interface. Energy dispersive x-ray maps attained from the samples show uniform incorporation of the elements. The Z-contrast map of the high-angle annular dark-field of the film cross section shows uniform incorporation along the growth as well. Optical characterization of the GeSn films through photoluminescence technique shows reduction in the bandgap edge of the materials.

GeSn-based light sources and photoconductors towards integrated photonics for the mid-infrared

GeSn-based optically pumped lasers and photoconductors have been systematically investigated. The operation wavelength of these devices covers 2–3 μm. Since GeSn technique is fully compatible with current CMOS process, the GeSn-based devices can be widely used in the area of Si integrated photonics.