GeSn lasers enable monolithic integration of lasers on the Si platform using all-group-IV directbandgap materials. Although optically pumped GeSn lasers have made significant progress, the study of the electrically injected lasers has just begun only recently. In this work, we present explorative investigations of electrically injected GeSn heterostructure lasers with various layer thicknesses and material compositions. The cap layer total thickness was varied between 240 and 100 nm. At 10 K, a 240-nm-SiGeSn capped device had a threshold current density Jth = 0.6 kA/cm 2 compared to Jth = 1.4 kA/cm 2 of a device with 100-nm-SiGeSn cap due to an improved modal overlap with the GeSn gain region. Both devices had a maximum operating temperature Tmax = 100 K. Device with cap layers of Si0.03Ge0.89Sn0.08 and Ge0.95Sn0.05, respectively, were also compared. Due to less effective carrier (electron) confinement, the device with a 240-nm-GeSn cap had a higher threshold Jth = 2.4 kA/cm 2 and lower maximum operating temperature Tmax = 90 K, compared to those of the 240-nm-SiGeSn capped device with Jth = 0.6 kA/cm 2 and Tmax = 100 K. In the study of the active region material, the device with Ge0.85Sn0.15 active region had a 2.3 higher Jth and 10 K lower Tmax, compared to the device with Ge0.89Sn0.11 in its active region. This is likely due to higher defect density in Ge0.85Sn0.15 rather than an intrinsic issue. The longest lasing wavelength was measured as 2682 nm at 90 K. The investigations provide guidance to the future structure design of GeSn laser diodes to further improve the performance.

This paper reports the comprehensive characterization of a Ge0.92Sn0.08/Ge0.86Sn0.14/Ge0.92Sn0.08 single quantum well. By using a strain relaxed Ge0.92Sn0.08 buffer, the direct bandgap Ge0.86Sn0.14 QW was achieved, which is unattainable by using only a Ge buffer. Band structure calculations and optical transition analysis revealed that the quantum well features type-I band alignment. The photoluminescence spectra showed dramatically increased quantum well peak intensity at lower temperature, confirming that the Ge0.86Sn0.14 quantum well is a direct bandgap material.

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 of the active region material showed that device gain region using Ge 0.87 Sn 0.13 had a higher threshold and lower T max , compared to Ge 0.89 Sn 0.11 . The performance was affected by the metal absorption, free carrier absorption, and possibly defect density level. The maximum peak wavelength was measured as 2682 nm at 90 K by using Ge 0.87 Sn 0.13 in gain regions. The investigations provide directions to the future GeSn laser diode designs toward the full integration of group-IV photonics on a Si platform.

The persistent interest of the epitaxy of group IV alloy GeSn is mainly driven by the demand of efficient light source that could be monolithically integrated on Si for mid-infrared Si photonics. For chemical vapor deposition of GeSn, the exploration of parameter window is difficult from the beginning due to its non-equilibrium growth condition. In this work, we demonstrated the effective pathway to achieve the high quality GeSn with high Sn incorporation. The GeSn films were grown on Ge-buffered Si via ultra-high vacuum chemical vapor deposition using GeH4 and SnCl4 as precursor gasses. The influence of both SnCl4 flow fraction and growth temperature on the Sn incorporation and material quality were investigated. The key to achieve effective Sn incorporation and high material quality is to explore the proper parameter match between SnCl4 supply and growth temperature, which is also called optimized growth regime. The Sn precipitation is significantly suppressed in optimized growth regime, leading to more Sn incorporation into Ge and enhanced material quality. The prototype GeSn photoconductors were fabricated with typical samples, showing the promising devices applications towards mid-infrared optoelectronics.

In this work, all group-IV band-to-band lasers based on SiGeSn/GeSn/SiGeSn multi-quantum-well structures were demonstrated. Lasing performance was investigated via two 4-well samples. The thinner GeSn well sample exhibits a maximum lasing temperature of 20 K and a threshold of 55 kW/cm2 at 10 K, while the thicker well sample features a higher maximum operating temperature of 90 K and lower lasing thresholds of 25 and 62 kW/cm2 at 10 and 77 K, respectively. The distinct results were tentatively interpreted mainly by the difference of gain volume. This result provides guidance for the future GeSn quantum well laser optimization for higher performance.