1290-D Reamwood Ave., Sunnyvale, CA 94089
When an analog lock-in is your only option ...
... there’s always
PAR124A (1960s design & unavailable)
· Low-noise, all analog design
· No digital noise — CPU stopping
· 0.2 Hz to 200 kHz range
· 2. 8 nV/√Hz input noise
· Fiber-coupled GPIB, Ethernet and
Inspired by the 1960s PAR124A, but using today’s low-noise
analog components and design methodologies, the new SR124 is a tour de force
in low-noise, high performance analog instrumentation. With its all-analog design, easy-to-use front panel,
and wide frequency range, the SR124 will be right at home in your low-noise experiment.
a-Si/MoS2 photodetector has faster photoresponse
Two engineers at the University of California, Berkeley (UC
Berkeley) have created an amorphous silicon (a-Si) metal-semi-conductor-metal heterojunction photodetector with added
molybdenum disulfide (MoS2) that they say could speed up
medical imaging at low cost. 1 Molybdenum disulfide is well-known as a dry lubricant.
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 cost of the imaging device.
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.
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 can be used to make
thin, novel electronic devices or to improve existing ones.
Mechanically peeled flake
The structure consists of a 60-nm-thick mechanically exfoliated (peeled) MoS2 flake on a silicon dioxide (SiO2) substrate,
with the flake covered by a 100-nm-thick a-Si film using
plasma-enhanced chemical vapor deposition (see figure).
Gold (Au) and titanium contacts were also added via electron-beam evaporation. A control device without the MoS2
flake was also fabricated.
The photoresponse of the devices was measured using
standard blue, green, and red LEDs as light sources at
an incident power of about 0.4 mW/cm2. The photoresponse to light from the three LEDs was much higher for the
MoS2-containing device. The response of the detectors to