1. 1 Photo-Gate LED test Wieman/Bieser 10-Sept-04

2. 2 Background  DC Measurements of Photo-gate/Drain gave (Sector 5) uSlow response uFe55 x-ray signal showed large spread in amplitude  Problem blamed on surface states at the epi-oxide interface beneath the photo gate  Support of this notion by Janesick who observed similar photo-gate behavior using TSMC process, but made a good photo-gate using the JAZZ foundry with a buried channel

3. 3 New photo-gate test  Used a single pixel in sector 5 (simple structure with photo- gate and small drain on the edge) uPhoto-gate voltage 1 volt uDrain voltage set by full reset voltage  Test sequence uReset all pixels uClock row and column shift registers to select a single pixel uInject 2 red LED pulses uObserve output voltage with oscilloscope throughout sequence  Also did same test with sector 1 ( the standard diode) for comparison Sector 5 Photo-gate drain

4. 4 Measured output voltage Pulse 1 Pulse 2  Features to note uBoth sectors exposed to same LED pulses, but light attenuated for sector 1 uSector 5 response to 1 st LED pulse much smaller than to 2 nd uSector 5 leakage current ramp increases after 1 st LED pulse uResponse difference for the two pulses in sector 5 is directly related to gate, since sector 1 shows that readout structures are not affected differently by the two pulses uReducing the pulse separation did not change effect

5. 5 Photo-gate time response to two pulses the same, only amplitude difference Pulse 1 Pulse 2 Adjust amplitude and overlay Signal fits: + plus leakage slope   204  s

6. 6 What does it mean?  Don’t know yet  Is this what should happen if surface states are saturated by the first pulse? Would have expected time response to change  Need more tests varying the size of the two pulses to see what effects second signal size. Also explore over wider range the effects of pulse time separation