Trions, quasi‐particles consisting of two electrons combined with one hole or of two holes with one electron, have recently been observed in transition metal dichalcogenides (TMDCs) and drawn increasing attention due to potential applications of these materials in light‐emitting diodes, valleytronic devices as well as for being a testbed for understanding many‐body phenomena. Therefore, it is important to enhance the trion emission and its stability. In this study, a MoSe₂/FePS₃ van der Waals heterostructure (vdWH) with type‐I band alignment is constructed, which allows for carriers injection from FePS₃ to MoSe₂. At low temperatures, the neutral exciton (X⁰) emission in this vdWH is almost completely suppressed. The I_Trion/I_x0 intensity ratio increases from 0.44 in a single MoSe₂ monolayer to 20 in this heterostructure with the trion charging state changing from negative in the monolayer to positive in the heterostructure. The optical pumping with circularly polarized light shows a 14% polarization for the trion emission in MoSe₂/FePS₃. Moreover, forming such type‐I vdWH also gives rise to a 20‐fold enhancement of the room temperature photoluminescence from monolayer MoSe₂. These results demonstrate a novel approach to convert excitons to trions in monolayer 2D TMDCs via interlayer doping effect using type‐I band alignment in vdWH.

Controlled doping with an effective carrier concentration higher than 10²⁰ cm⁻³ is a key challenge for the full integration of Ge into silicon-based technology. Such a highly doped layer of both p- and n type is needed to provide ohmic contacts with low specific resistance. We have studied the effect of ion implantation parameters i.e., ion energy, fluence, ion type, and protective layer on the effective concentration of electrons. We have shown that the maximum electron concentration increases as the thickness of the doping layer decreases. The degradation of the implanted Ge surface can be minimized by performing ion implantation at temperatures that are below −100 °C with ion flux less than 60 nAcm⁻² and maximum ion energy less than 120 keV. The implanted layers are flash-lamp annealed for 20 ms in order to inhibit the diffusion of the implanted ions during the recrystallization process.

Ion implantation of S and Te followed by sub-second flash lamp annealing with peak temperature about 1100 °C is employed to obtain metallic n ⁺⁺-GaAs layers. The electron concentration in annealed GaAs is as high as 5 × 10¹⁹ cm⁻³, which is several times higher than the doping level achievable by alternative methods. We found that heavily doped n ⁺⁺-GaAs exhibits positive magnetoconductance in the temperature range of 3–80 K, which is attributed to the magnetic field suppressed weak localization. By fitting the magnetoconductance results with Hikami–Larkin–Nagaoka model, it is found that the phase coherence length increases with increasing carrier concentration at low temperature and is as large as 540 nm at 3 K. The temperature dependence of the phase coherence length follows l _∅ ∝ T ^η (η ∼ 0.3), indicating defect-related scattering as the dominant dephasing mechanism. In addition, the high doping level in n-type GaAs provides the possibility to use GaAs as a plasmonic material for chemical sensors operating in the infrared range.

N-type doping in GaAs is a self-limited process, rarely exceeding a carrier concentration level of 1019 cm−3. Here, we investigated the effect of intense pulsed light melting on defect distribution and activation efficiency in chalcogenide-implanted GaAs by means of positron annihilation spectroscopy and electrochemical capacitance–voltage techniques. In chalcogenide-doped GaAs, donor–vacancy clusters are mainly responsible for donor deactivation. Using positrons as a probe of atomic scale open volumes and DFT calculations, we have shown that after nanosecond pulsed light melting the main defects in heavily doped GaAs are gallium vacancies decorated with chalcogenide atoms substituting As, like VGa–nTeAs or VGa–nSAs. The distribution of defects and carriers in annealed GaAs follows the depth distribution of implanted elements before annealing and depends on the change in the solidification velocity during recrystallization.