Theoretical Analysis of Threshold Characteristics in Electrically-Driven GeSn Lasers (original) (raw)
Related papers
Si-Based GeSn Lasers with Wavelength Coverage of 2–3 μm and Operating Temperatures up to 180 K
ACS Photonics, 2017
A Si-based monolithic laser is strongly desired for the full integration of Si-photonics. Lasing from the direct bandgap group-IV GeSn alloy has opened a new avenue, different from the hybrid III-V-on-Si integration approach. We demonstrated optically pumped GeSn lasers on Si with broad wavelength coverage from 2 to 3 µm. The GeSn alloys were grown using newly developed approaches with an industry standard chemical vapor deposition reactor and low-cost commercially available precursors. The achieved maximum Sn composition of 17.5% exceeded the generally acknowledged Sn incorporation limits found with similar deposition chemistries. The highest lasing temperature was measured as 180 K with the active layer thickness as thin as
arXiv (Cornell University), 2017
A Si-based monolithic laser is highly desirable for full integration of Si-photonics. Lasing from direct bandgap group-IV GeSn alloy has opened a completely new venue from the traditional III-V integration approach. We demonstrated optically pumped GeSn lasers on Si with broad wavelength coverage from 2 to 3 μm. The GeSn alloys were grown using newly developed approaches with an industry standard chemical vapor deposition reactor and low-cost commercially available precursors. The achieved maximum Sn composition of 17.5% exceeded the generally acknowledged Sn incorporation limits for using similar deposition chemistries. The highest lasing temperature was measured as 180 K with the active layer thickness as thin as 2 260 nm. The unprecedented lasing performance is mainly due to the unique growth approaches, which offer high-quality epitaxial materials. The results reported in this work show a major advance towards Si-based mid-infrared laser sources for integrated photonics.
Theoretical Analysis of GeSn Alloys as a Gain Medium for a Si-Compatible Laser
IEEE Journal of Selected Topics in Quantum Electronics, 2000
In this paper, a theoretical analysis of unstrained GeSn alloys as a laser gain medium was performed. Using the empirical pseudopotential method, the band structure of GeSn alloys was simulated and verified against experimental data. This model shows that GeSn becomes direct bandgap with 6.55% Sn concentration. The optical gain of GeSn alloys with 0-10% Sn concentration was calculated with different n-type doping concentrations and injection levels. It is shown theoretically that adding Sn greatly increases the differential gain owing to the reduction of energy between the direct and indirect conduction bands. For a double-heterostructure laser, the model shows that at a cavity loss of 50 cm −1 , the minimum threshold current density drops 60 times from Ge to Ge 0 .9 Sn 0 .1 , and the corresponding optimum n-doping concentration of the active layer drops by almost two orders of magnitude. These results indicate that GeSn alloys are good candidates for a Si-compatible laser.
Investigation of carrier confinement in direct bandgap GeSn/SiGeSn 2D and 0D heterostructures
Scientific Reports
Since the first demonstration of lasing in direct bandgap GeSn semiconductors, the research efforts for the realization of electrically pumped group IV lasers monolithically integrated on Si have significantly intensified. This led to epitaxial studies of GeSn/SiGeSn hetero-and nanostructures, where charge carrier confinement strongly improves the radiative emission properties. Based on recent experimental literature data, in this report we discuss the advantages of GeSn/SiGeSn multi quantum well and quantum dot structures, aiming to propose a roadmap for group IV epitaxy. Calculations based on 8-band k•p and effective mass method have been performed to determine band discontinuities, the energy difference between Γand L-valley conduction band edges, and optical properties such as material gain and optical cross section. The effects of these parameters are systematically analyzed for an experimentally achievable range of Sn (10 to 20 at.%) and Si (1 to 10 at.%) contents, as well as strain values (−1 to 1%). We show that charge carriers can be efficiently confined in the active region of optical devices for experimentally acceptable Sn contents in both multi quantum well and quantum dot configurations. A significant outcome of technological development is the widespread use of network communications and data centers. The amount of information that are processed in these data centers is constantly increasing, reaching the limits of present day electronic chips concerning bandwidth and power consumption. Fundamental changes in chip design and data communication are therefore necessary to meet increasing demands 1. Integration of photonic circuits with existing electronics is considered as one of these solutions, aiming to achieve on-chip or chip-to-chip communication via photons instead of electrons 2,3. State of the art chip technology uses Si-based materials, hence solutions based on group IV semiconductors are favored. Si, Ge and their alloys are indirect bandgap semiconductors, meaning that radiative processes in these materials are inefficient and slow. Therefore, finding suitable direct bandgap alloys based on group IV semiconductors is of primary importance. Ge is an indirect bandgap semiconductor with the lowest indirect conduction band valley (at the L point) only 150 meV below the direct valley at the Γ point. Since Sn has a negative bandgap at the Γ point, partial replacement of Ge by Sn atoms changes the electronic band structure of GeSn so that the Γ-valley energy E Γ decreases faster than the L-valley energy E L , increasing the directness ΔE L-Γ = E L − E Γ. Eventually, this results in a transition into a fundamental direct bandgap semiconductor at Sn concentrations around 8 at.% for unstrained GeSn 4,5. Breakthrough in epitaxial growth of GeSn alloys, mostly due to advances in low temperature chemical vapor deposition (CVD) methods and new precursors, enables alloy compositions that exceed the solubility limits of Sn in Ge by an order of magnitude 6-10. These advances led to the successful demonstration of lasing from thick bulk GeSn/Ge/Si layers with Sn contents of 12.5 at.% at temperatures up to 90 K 5. By incorporating even higher Sn concentrations, of up to 17.5 at.%, the lasing temperature limit reached 180 K 11,12. On the way towards an electrically pumped room temperature laser, GeSn research benefits from the previous development of III-V semiconductor lasers, where heterostructures have been introduced in the 60 s 13. To pursue this approach, a suitable barrier material for GeSn has to be found. Both the experiments and theoretical band alignment calculations
Characterization of GeSn for Si-based Optoelectronic Devices
2013
High-quality compressive-strained Ge 1Àx Sn x /Ge films have been deposited on Si(001) substrate using a mainstream commercial chemical vapor deposition reactor. The growth temperature was kept below 450°C to be compatible with Si complementary metal-oxide-semiconductor processes. Germanium tin (Ge 1Àx Sn x) layers were grown with different Sn composition ranging from 0.9% to 7%. Material characterizations, such as secondary-ion mass spectrometry, Rutherford backscattering spectrometry, and x-ray diffraction analysis, show stable Sn incorporation in the Ge lattice. Comparison of the Sn mole fractions obtained using these methods shows that the bowing factor of 0.166 nm (in Vegard's law) is in close agreement with other experimental data. High-resolution transmission electron microscopy and atomic force microscopy results show that the films have started to relax through the formation of misfit and threading dislocations. Raman spectroscopy, ellipsometry, and photoluminescence (PL) techniques are used to study the structural and optical properties of the films. Room-temperature PL of the films shows that 7% Sn incorporation in the Ge lattice results in a decrease in the direct bandgap of Ge from 0.8 eV to 0.56 eV.
Electrically injected GeSn lasers with peak wavelength up to 2.7 μm
Photonics Research, 2021
GeSn lasers enable the monolithic integration of lasers on the Si platform using all-group-IV direct-bandgap material. The GeSn laser study recently moved from optical pumping into electrical injection. In this work, we present explorative investigations of GeSn heterostructure laser diodes with various layer thicknesses and material compositions. Cap layer material was studied by using Si 0.03 Ge 0.89 Sn 0.08 and Ge 0.95 Sn 0.05 , and cap layer total thickness was also compared. The 190 nm SiGeSn-cap device had threshold of 0.6 kA / cm 2 at 10 K and a maximum operating temperature ( T max ) of 100 K, compared to 1.4 kA / cm 2 and 50 K from 150 nm SiGeSn-cap device, respectively. Furthermore, the 220 nm GeSn-cap device had 10 K threshold at 2.4 kA / cm 2 and T max at 90 K, i.e., higher threshold and lower maximal operation temperature compared to the SiGeSn cap layer, indicating that enhanced electron confinement using SiGeSn can reduce the threshold considerably. The study...
Direct Bandgap Group IV Epitaxy on Si for Laser Applications
Chemistry of Materials, 2015
The recent observation of a fundamental direct bandgap for GeSn group IV alloys and the demonstration of low temperature lasing provide new perspectives to the fabrication of Si photonic circuits. This work addresses the progress in GeSn alloy epitaxy aiming at room temperature GeSn lasing. Chemical vapor deposition of direct bandgap GeSn alloys with a high to L-valley energy separation and large thicknesses for efficient optical mode confinement is presented and discussed. Up to 1 µm thick GeSn layers with Sn contents up to 14 at.% were grown on thick relaxed Ge buffers, using Ge 2 H 6 and SnCl 4 precursors. Strong strain relaxation (up to 81 %) at 12.5 at.% Sn concentration, translating into an increased separation between-and L-valleys of about 60 meV, have been obtained without crystalline structure degradation, as revealed by Rutherford backscattering/ion channeling spectroscopy and Transmission Electron Microscopy. Room temperature transmission/reflection and photoluminescence measurements were performed to probe the optical properties of these alloys. The emission/absorption limit of GeSn alloys can be extended up to 3.5 µm (0.35 eV), making those alloys ideal candidates for optoelectronics in the mid-infrared region. Theoretical net gain calculations indicate that large room temperature laser gains should be reachable even without additional doping.