Abstract
We have realized a simple method for patterning an M-π-n CdTe diode with a deeply diffused pn-junction, such as indium anode on CdTe. The method relies on removing the semiconductor material on the anode-side of the diode until the physical junction has been reached. The pixelization of the p-type CdTe diode with an indium anode has been demonstrated by patterning perpendicular trenches with a high precision diamond blade and pulsed laser. Pixelization or microstrip pattering can be done on both sides of the diode, also on the cathode-side to realize double sided detector configuration.The article compares the patterning quality of the diamond blade process, pulsed pico-second and femto-second lasers processes. Leakage currents and inter-strip resistance have been measured and are used as the basis of the comparison. Secondary ion mass spectrometry (SIMS) characterization has been done for a diode to define the pn-junction depth and to see the effect of the thermal loads of the flip-chip bonding process. The anode and cathode-sides of a 6 × 6 mm2 diodes were patterned with a diamond blade and flip-chip bonded to the Medipix2 readout chips. First imaging results with an X-ray source show reduced polarization effect and edgeless detector behavior for the anode-side patterned detector.
Highlights
The article compares the patterning quality of the diamond blade process, pulsed pico-second and femto-second lasers processes
The comparison was done by measures of leakage current and inter-strip resistance and the following numbers are given at 100 V reverse bias for the 6 mm long strips
The lowest leakage current levels of 2–5 nA/cm2 were measured with the PS-laser process but with a poor inter-strip isolation of 0.3–1 GΩ
Summary
This section describes the results of visual inspection and Secondary Ion Mass Spectrometry (SIMS) characterization of patterned M-π-n CdTe diodes. First attempts to pattern the CdTe diode with the diamond blade caused cracking of the crystal along the trenches. This cracking has been removed as figure 1 illustrates. With SIMS alone, one is not able to determine the pn-junction depth directly, but it can be used to give more knowledge about the structure. The thermal processes during the fabrication are well managed and the diffusion is in control resulting in the pn-junction depth below 5 μm
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