Two engineers at the University of California, Berkeley (UC Berkeley) have built a device that is an amorphous silicon (a-Si) metal-semiconductor-metal heterojunction photodetector with added molybdenum disulfide (MoS2). The key ingredient in the device has been sold in auto parts shops for decades and could speed up medical imaging at a low cost.

Many photodetectors in large-area imaging devices use a-Si because it absorbs light well and is relatively inexpensive to process. But a-Si has defects that prevent the fast, ordered movement of electrons, leading to slower operating speeds and more exposure to radiation. Getting better performance requires more expensive, high-temperature processing, adding to the price tag of the imaging device. cemented carbide blade

Sayeef Salahuddin and Mohammad Esmaeili-Rad solved this problem by pairing a thin film of MoS2 with a sheet of a-Si. By forming a diode with the a-Si, the MoS2 allows the photogenerated electrons it collects to travel ten times faster through the a-Si. The detector has a photoresponsivity of 210 mA/W for green light -- two to four times higher than usual for a-Si devices.

Together, the MoS2 and amorphous silicon formed a diode that resulted in a photoresponse rate that was 10 times faster than conventional amorphous silicon alone.

“Our discovery could bring transformational changes in applications from biomedical imaging to solar cells to energy-efficient transistors,” said Salahuddin.

The researchers say that because these materials are easy and inexpensive to handle, the cost of speeding up photodetectors would be minimal. Unlike conventional semiconductors like Si, MoS2 consists of individual nanosheets that can be torn off like pages in a book. These sheets tungsten carbide tips can be used to make thin, novel electronic devices or to improve existing ones.

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