We demonstrate a low threading dislocation density (TDD) and smooth surface InAs layer epitaxially grown on Si by suppressing phase separation of InxAl1−xAs (x = 0 to 1) graded buffer and by inserting a tensile-strained In0.95Al0.05As dislocation filter layer. While keeping the total III–V layer below 2.7 μm to avoid thermal cracks, we have achieved a sixfold reduction of TDD in InAs on Si compared to the unoptimized structure. We found a strong correlation between the metamorphic InAs surface roughness and TDD as a function of InxAl1−xAs buffer thickness. An optimal thickness of 175 nm was obtained where both phase separation and 3D islanding growth were suppressed. Moreover, a tensile-strained In0.95Al0.05As dislocation filter layer and high growth temperature of the InAs cap layer further assisted the dislocation reduction process, which led to a TDD to 1.37 × 108 cm−2. Finally, an InAs p-i-n photodetector grown on the optimized InAs/Si template confirmed its high quality by showing an improved responsivity from 0.16 to 0.32 A/W at a 2 μm wavelength.

We report on the photoluminescence enhancement of 1.3 μm InAs quantum dots (QDs) epitaxially grown on an ultrathin 250 nm GaAs buffer on a Si substrate. Decreasing the GaAs buffer thickness from 1000 to 250 nm was found to not only increase the coalesced QD density from 6.5 × 10 8 to 1.9 × 10 9 cm −2 but also decrease the QD photoluminescence emission intensity dramatically. Inserting an Al 0.4 Ga 0.6 As potential barrier layer maintained strong photoluminescence from the QDs by effectively suppressing carrier leakage to the GaAs/Si interfacial region even when the GaAs buffer was thinned to 250 nm. We then fabricated a light-emitting diode using the ultrathin 250 nm GaAs buffer on Si and confirmed strong electroluminescence peaking at 1.28 μm without interfacial defect emission at room temperature. We believe that this work is promising for monolithically integrated evanescent Si lasers using InAs/GaAs QDs.

Current infrared thermal image sensors are mainly based on planar firm substrates, but the rigid form factor appears to restrain the versatility of their applications. For wearable health monitoring and implanted biomedical sensing, transfer of active device layers onto a flexible substrate is required while controlling the high-quality crystalline interface. Here, we demonstrate highdetectivity flexible InAs thin-film mid-infrared photodetector arrays through high-yield wafer bonding and a heteroepitaxial lift-off process. An abruptly graded In x Al 1−x As (0.5 < x < 1) buffer was found to drastically improve the lift-off interface morphology and reduce the threading dislocation density twice, compared to the conventional linear grading method. Also, our flexible InAs photodetectors showed excellent optical performance with high mechanical robustness, a peak room-temperature specific detectivity of 1.21 × 10 9 cm-Hz 1/2 /W at 3.4 μm, and excellent device reliability. This flexible InAs photodetector enabled by the heteroepitaxial lift-off method shows promise for next-generation thermal image sensors.