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5 October 2015 Optoelectronics in two-dimensional semiconductor alloys (Presentation Recording)
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Two -dimensional transition-metal dichalcogenides (2D-TMDs) have attracted attention for applications in electronics and photonics, as well as for the wealth of new scientific phenomena that arise at low dimensionality. Recently, the ability to grow 2D-TMDs by chemical vapor deposition has opened the path to large area devices, but also to the synthesis of semiconductor alloys with tunable bandgaps. In this presentation, I will discuss our recent experimental work in exploring the optoelectronic properties of 2D MoS_2(1-x)Se_2x alloys spanning the compositional range. In particular, we report the observation of a new regime of operation where the photocurrent depends superlinearly on light intensity. We use spatially-resolved photocurrent measurements on devices consisting of CVD-grown monolayers to show the photoconductive nature of the photoresponse, with the photocurrent dominated by recombination and field-induced carrier separation in the channel. Time-dependent photoconductivity measurements show the presence of persistent photoconductivity for the S-rich alloys, while photocurrent measurements at fixed wavelength for devices of different alloy compositions show a systematic decrease of the responsivity with increasing Se content associated with increased linearity of the current-voltage characteristics. A model based on the presence of different types of recombination centers is presented to explain the origin of the superlinear dependence on light intensity, which emerges when the non-equilibrium occupancy of initially empty fast recombination centers becomes comparable to that of slow recombination centers.
Conference Presentation
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François Léonard "Optoelectronics in two-dimensional semiconductor alloys (Presentation Recording)", Proc. SPIE 9553, Low-Dimensional Materials and Devices, 955310 (5 October 2015);

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