1. Detecting elements for the CALICE MAPS design
Questions
Detecting elements for the CALICE MAPS design
How does the collected charge depend on
Diode size?
Diode position with respect to the NWELL?
Diode bias voltage?

2. Setup The NWELL is 3 μm wide Diode size and position are variable
The location of the MIP track is also variable
* The finite length of this structure does not allow full charge collection – some error is introduced Dx Dw
NWELL +3.3V
Diodes VD
reflected charge
MIP track
substrate (p+)
25 m
50 m X

3. Question 1 - Diode size The MIP hits at X from the NWELL centre
Diode size Dw is variable, Dx = 12 μm

4. Question 2 - Diode position with respect to the NWELL
The MIP hits the centre of the NWELL (X=0)
Diode size Dw and their distance from the NWELL Dx are variable

5. Question 3 - Diode bias voltage
The MIP hits at distance 8 μm from centre of the NWELL
Diode size Dw and bias are variable, distance from the NWELL Dx is fixed to 12 μm

6. A movie speaks more than 1000 words
The MIP hits at distance 8 μm from the NWELL centre
Diode size Dw = 4 μm, 12 μm from the NWELL centre
Click to start/stop
Depletion regions under the diodes are 3 μm deep.
This is clearly visible as the electron density in the depleted regions is small (charge is transported very quickly there – seen as “liquid flow”)

7. Conclusions
Surprisingly, increasing the diode size does not proportionally improve the collection efficiency
Should the effect be much stronger in 3D ( ~(Dw)2 rather than ~Dw)?
Very important to verify in 3D
Placing the diodes next to the NWELL has some effect on reducing the charge loss
Diode bias voltage is minor effect
This is not a substitute for proper 3D simulation similar to Giulio’s