Monolayer transition metal dichalcogenides (ML-TMDCs) are a versatile platform to explore the transport dynamics of the tightly bound excitonic states. The diffusion of neutral excitons in various ML-TMDCs has been observed. However, the transport of charged excitons (trions), which can be driven by an in-plane electric field and facilitate the formation of an excitonic current, has yet been well investigated. Here, we report the direct observation of diffusion and drift of the trions in ML-WS 2 through spatially and time-resolved photoluminescence. An effective diffusion coefficient of 0.47 cm 2 /s was extracted from the broadening of spatial profiles of the trion emission. When an inplane electric field is applied, the spatial shift of the trion emission profiles indicated a drift velocity of 7400 cm/s. Both the diffusion caused broadening and the drift caused shift of the emission profiles saturate because of the Coulomb interactions between trions and the background charges.
An AlGaN/GaN metal-heterostructure-metal (MHM) ultraviolet (UV) photodetector employing lateral Schottky contacts was fabricated and characterized at different temperatures. As the temperature increased from 25 to 250 °C, the photoresponsivity of the MHM photodetector increased 3.5 times. This was attributed to the spontaneous-polarization-induced spatial separation of the photogenerated electrons and holes and the increased optical absorption at higher temperatures. Meanwhile, the decay time constant of the photocurrent became approximately three orders of magnitude smaller. With the enhanced photoresponsivity and the decreased response time constant, kilohertz optical switching of the MHM photodetector was recorded at 250 °C. The AlGaN/GaN MHM photodetector, sharing the same GaN-on-Si electronics platform, provides an applicable candidate for an all-GaN integrated UV sensing and amplifying system for high-temperature applications.
The effect of different growth interruption time on the surface morphology and optical properties of InGaN quantum dots (QDs) grown on 2-inch silicon substrates is investigated. The surface becomes rougher and the photoluminescence intensity has been enhanced significantly when employing the growth interruption method. Temperature-dependent photoluminescence and excitation powerdependent photoluminescence both present unchanged peak energy and line-width of QDs. The sharp increase of PL intensity in medium temperature regime is attributed to the fingerprint of the existence of InGaN QDs. The shape of the QDs are further confirmed by the transmission electron microscopy with a size of 3 nm by 4 nm. Among the samples, a growth interruption time of 30 s gives the best optical performance.
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