1. Dark Current Analysis of
the ST-10XE CCD Camera
Scott Robbins
Ithaca College Department of Physics and Astronomy
2. What’s a CCD?
By mapping these counts to a
brightness scale, a black and white
image is created.
A Charge Coupled Device captures
freed photoelectric charges.
Photo Credit to Michael W. Davidson from
Florida State University
3. What’s with those
white spots?
Dark Frame taken at the Astronomy Camp at the
University of Nebraska-Lincoln
Even with the lens closed,
many pixels appear to
detect light. These are
called “dark frames”.
4. Can we measure this
Dark Current?
The slope of each line is the dark current at that temperature.
5. Can we predict Dark
Current behavior?
We expect the Dark Current to
follow the Arrhenius Law:
Linearize Dark Current vs. Temp. to create an Equation for the Dark Current!
6. What were the results?
Found a Band Gap Energy
of 0.795eV which differs
from the Band Gap energy
of Silicon (1.1eV).
From this plot we found
Dc (T) with an error of
0.56%
7. What can we learn?
Our experimental value of 0.795eV may indicate that the
Band Gap energy is subject to change with temperature.
Photo: http://what-when-how.com/remote-sensing-from-air-and-space/detectors-visible-imagery-remote-sensing/
This energy is 0.55eV at cold temperatures, and 1.1eV at room temperature.
8. A More Detailed model of
Dark Current
Arrhenius’ Law gives a good fit, but it may not give
the whole picture.
Meyer-Neldel Theoretical Model says:
Depletion term dominates at low temp.
Diffusion term grows at temperature increases
9. Overall
Characterized the Dark Current in the ST-10XE CCD
Camera.
Found the Band Gap Energy within the CCD.
Shed some light on the mystery of “Dark Current”.
Results should help future astronomers at IC know
which temperature regions will provide best images.
Full bucket white, empty bucket black. Charge in voltage, held by cap to send to comp for matrix of numbers.
Matrix of numbers
State that you took exposures at increasing time intervals and that these are fitted lines.
Remember that light hitting surface needs same bandgap kick as thermal energy! That’s why Arrhenius!
Should pass through origin, and instead has y intercept 1.0176 ± 0.0158. This relates to the bias being different at different temperatures because Neyer and D0!
Dark current needs same kick as photoelec, just because of thermal. Don’t even state directions of charge movement, just energy.
The reason our lines didn’t converge to same offset/intercept is because D0 has a temperature dependence! Diffusion is kinetic energy of atoms in the solid.
