Resistance to Pressure in Laser-doped p–n and Schottky-type Barrier Junctions

Abstract

Cadmium telluride (CdTe) is used as an X-ray image detector for dental applications. However, it is difficult to fabricate the large CdTe chips for such applications. Therefore, it is necessary to increase the detection area by tiling. In this study, to minimize the dead space caused by bonding CdTe and application-specific integrated circuits (ASICs), the detector was three-dimensionally stacked by flip-chip bonding. Furthermore, to achieve a high spatial resolution, a diode-type detector that can apply a high electric field was used. However, in flipchip bonding, layers were stacked while applying pressure and heat; therefore, Schottky-type detectors, which are diode-type detectors, were expected to have a low breakdown voltage because the Schottky junction was located at the interface between the CdTe layer and the electrode. However, the p-n junction was expected to have a high voltage resistance because it was located inside the CdTe layer. Therefore, we performed pressure tests on Schottky-type and p-n junction CdTe detectors, and the I-V and gamma-ray spectral characteristics before and after the tests were evaluated. As expected, the Schottky-type detector stopped exhibiting diode characteristics after pressurization, the reverse current increased, and gamma rays could hardly be detected; however, the p-n junction detector maintained its diode characteristics even after pressurization, and the I-V characteristics indicated a high voltage resistance with almost no change in both the I-V and the gamma-ray spectral characteristics.