5 years ago

Photo-excited hot carrier dynamics in hydrogenated amorphous silicon imaged by 4D electron microscopy

Photo-excited hot carrier dynamics in hydrogenated amorphous silicon imaged by 4D electron microscopy
Ebrahim Najafi, Austin J. Minnich, Bolin Liao, Ahmed H. Zewail, Heng Li

Charge carrier dynamics in amorphous semiconductors has been a topic of intense research that has been propelled by modern applications in thin-film solar cells1, transistors and optical sensors2. Charge transport in these materials differs fundamentally from that in crystalline semiconductors3, 4 owing to the lack of long-range order and high defect density. Despite the existence of well-established experimental techniques such as photoconductivity time-of-flight5, 6, 7, 8 and ultrafast optical measurements9, 10, 11, 12, many aspects of the dynamics of photo-excited charge carriers in amorphous semiconductors remain poorly understood. Here, we demonstrate direct imaging of carrier dynamics in space and time after photo-excitation in hydrogenated amorphous silicon (a-Si:H) by scanning ultrafast electron microscopy (SUEM)13, 14. We observe an unexpected regime of fast diffusion immediately after photoexcitation, together with spontaneous electron–hole separation15 and charge trapping3 induced by the atomic disorder. Our findings demonstrate the rich dynamics of hot carrier transport in amorphous semiconductors that can be revealed by direct imaging based on SUEM.

Publisher URL: http://dx.doi.org/10.1038/nnano.2017.124

DOI: 10.1038/nnano.2017.124

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