Two-dimensional molybdenum disulfide (MoS 2 ) is an emergent semiconductor with great potential in next-generation scaled-up electronics, but the production of high-quality monolayer MoS 2 wafers still remains a challenge. Here, we report an epitaxy route toward 4 in. monolayer MoS 2 wafers with highly oriented and large domains on sapphire. Benefiting from a multisource design for our chemical vapor deposition setup and the optimization of the growth process, we successfully realized material uniformity across the entire 4 in. wafer and greater than 100 μm domain size on average. These monolayers exhibit the best electronic quality ever reported, as evidenced from our spectroscopic and transport characterizations. Our work moves a step closer to practical applications of monolayer MoS 2 .
Realizing an NbN superconducting nanowire single-photon detector (SNSPD) with a 100% intrinsic detection efficiency (IDE) at the near-infrared wavelengths is still challenging. Herein, we developed a post-processing method to increase the IDE of NbN SNSPDs to near unity using a 20 keV helium ion irradiation. The IDE enhancement was achieved owing to the ion-induced reduction of the superconducting energy gap and the electron density of states at the Fermi level, determined with the electrical and magnetic transport measurements. The change in optical absorptance of the irradiated SNSPD was negligible as confirmed by the measured optical reflectance and system detection efficiency (SDE). Benefited with the IDE enhancement, the SDE of an irradiated device was significantly increased from 49% to 92% at 2.2 K for a 1550 nm wavelength.Controllable modification of the physical properties of thin films is crucial for their application in different devices. Ion irradiation, which creates defects with wellcontrolled density and topology is one of the powerful tools for tuning the properties of semiconductors 1,2 and superconductors 3-5 . Studies on the ion irradiation effects have attracted great interest from both science and application, especially for superconductors. Because they can be used as a phase-sensitive method to both understand the superconductivity 6 and tune the performance of superconducting devices 7 . The ion irradiation effects depend on the mass and energy of the irradiating ions as well as the type of superconductors 3-5,8 . Previously, the He ion irradiation on NbN films which induced increasing of vacancies in both the Nb and N sublattices and then reduced the electron density of states ( N 0 ) at the Fermi level has been reported 3 .Superconducting nanowire single-photon detectors (SNSPDs), which have demonstrated unparalleled performance in near-infrared photon detection with high system detection efficiency (SDE, >90%) 9,10 , low dark count rate (DCR, <1 Hz) 11 , and high temporal resolution (<15 ps) 12 , are successfully employed in quantum information processing 13,14 , and high-speed optical communication 15 . To date, SNSPDs are often fabricated from 5-8 nm thick NbN films, forming 50-100 nm wide nanowires. The NbN SNSPD operates at a temperature range of 2-4 K with a commercial Gifford-McMahon (GM) cryocooler 10,16 . However, achieving a saturated intrinsic detection efficiency (IDE) for the near-infrared photons with an NbN SNSPD is difficult because of its relatively high critical temperature (T c ) or superconducting energy gap (∆) with respect to those of low gap materials 18-21 . Attempts to tune the performance of superconducting devices by varying their chemical components have been made by several groups 22 . However, there are few reports on the post-processing that could directly control and compare the performance of SNSPDs.The IDE indicates the probability of a pulse generation in the nanowire when a photon is absorbed. The detection mechanism of SNSPD relies on the conversion o...
Integration of high quality single crystalline InP thin film on Si substrate has potential applications in Si-based photonics and high-speed electronics. In this work, the exfoliation of a 634 nm crystalline InP layer from the bulk substrate was achieved by sequential implantation of He ions and H ions at room temperature. It was found that the sequence of He and H ion implantations has a decisive influence on the InP surface blistering and exfoliation, which only occur in the InP pre-implanted with He ions. The exfoliation efficiency first increases and then decreases as a function of H ion implantation fluence. A kinetics analysis of the thermally activated blistering process suggests that the sequential implantation of He and H ions can reduce the InP thin film splitting thermal budget dramatically. Finally, a high quality 2 inch InP-on-Si(100) hetero-integration wafer was fabricated by He and H ion sequential implantation at room temperature in combination with direct wafer bonding.
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