Transcript Slide 1

Detectors (UV-Vis)
1.
2.
3.
4.
5.
6.
Phototube
Photomultiplier Tube (PMT)
Si Photodiode
Photodiode Array (PDA)
Charge Coupled Device (CCD)
Charge Injection Device (CID)
1. Phototube
200 – 1000 nm
1-10 ns response time
0.01 A/W
2. Photomultiplier Tube (PMT)
110 – 1000 nm
1-10 ns response time
10,000 A/W
2. Photomultiplier Tube (PMT)
3. Si Photodiode
Si: 3s23p2
Covalent Bonds in Solid
Therefore 1/2–filled
sp3
ΔE ≤ 2.5 eV
(semiconductor)
4 electrons fill a valence band at 0K
At higher T an electron can move to conduction band
Leaving a positive hole behind (both are mobile)
3. Si Photodiode
Doping Si with a group 5
element (As or Sb) results
in extra electrons (n-type).
Doping with a group 3
element (In, Ga) results
in extra holes (p-type)
3. Si Photodiode
3. Si Photodiode
Forward bias (not very useful for spectroscopy)
3. Si Photodiode
Reversed Bias:
Depletion zone at the
junction.
Photons may eject
electrons and form
holes
Current proportional
to number of photons
3. Si Photodiode
200 – 1000 nm
1-10 ns response time
0.05 A/W
4. Linear Photodiode Array
200 – 1000 nm
1-10 ns response time
0.05 A/W
4. Linear Photodiode Array
5. Charge Coupled Device (CCD)
200 – 950 nm
1-10 ns response time
0.05 - 1000 A/W
5. Charge Coupled Device
6. Charge Injection Device (CID)
Detector Responsivity
R(λ) =
Current Output (A)
Incident Power (W)
Gain of the Signal Modifier
G = Output Potential (V)
Input Current (A)