Study On TIBr Detector Wafer Surface Treatment And Secondary Annealing

As a promising material used for room-temperature semiconductor nuclear radiationdetector，TlBr has been widely studied at home and abroad in recent years. TlBr materialhas its unique features, the high atomic number (Tl:81, Br:35) and density (7.56g/cm3)make it have high stopping power for high energy rays, and its large band gap (2.68eV)capacitates the device to work steadily at room temperature with low noise signal. Due toits high detecting efficiency and energy resolution, TlBr detector has been widely used inspace astrophysics, medical and military fields. However, during the fabrication process ofthe detector, the damage layer, structure defaults on the wafer surface and the poorelectrode contact seriously affected the performance of the device. Therefore, the wafersurface treatments and electrode fabrication play an important role in the fabricationprocess. But there is no detailed report about the TlBr wafer surface treatments and theelectrode fabrication. So we carried out in-depth research on TlBr wafer surfacetreatments and the wafer re-annealing.In this paper, the TlBr crystals grown by electro dynamic gradient method (EDG)were cut into slices about2mm, the prepared wafers were used to study the influence ofdifferent polishing treatments on the quality of wafer surface. For the first time, weintroduced chemical mechanical polishing (CMP) technology into TlBr wafer surfacetreatment process and compare the effect of standard treatments (mechanical polishing,chemical etching) and CMP treatments on the remove of wafer surface rough. Theperformance of the wafers polished by different surface treatments were measured and theresult showed that the wafers polished by CMP treatments have a best surface quality, theas-fabricated device has a leakage current of6.16×10-8A for a bias of200V, and theresolution for241Am at room temperature is27.92%.In addition, we also studied the effect of the wafer re-annealing on the ohmic contactof the wafer. First, we studied the influence of annealing atmosphere on waferperformance. Wafers were annealed at100oC under different atmosphere (air and nitrogen)for90minutes. It turned out that the leakage current of the annealed wafers was reducedand the electrode contact was improved. And the wafers annealed under nitrogen got a better value. On this basis, the influence of the annealing temperature under a nitrogenatmosphere on wafer performance was studied. Wafers were annealed under nitrogen atdifferent temperature (80oC,100oC,120oC,150oC,200oC,250oC) for90minutes. Theleakage current of the wafers annealed under150oC reduced most significantly, and thevoltage-current characteristic curve of the wafers have the best linearity and symmetry.