1000 A, 4400 V silicon rectifier diode for railway traction

Technology development of a high-power large-area mesa rectifier diode is described. For achieving the high reverse blocking capability, a shallow gradient deep Ga/Al impurity diffusion profile has been used in conjunction with surface electric field control. A positively-bevelled Mo-Si alloyed edge-contoured structure passivated by a high dielectric strength rubber, helped in realising the 4.4 kV diode. The behaviour of the reverse voltage-current characteristics of the diode has been studied at room temperature (25/spl deg/C) and elevated temperature (150/spl deg/C). The leakage current was 10 /spl mu/A at 4.4 kV at 25/spl deg/C and increased to 50 mA (maximum) at 4 kV at 150/spl deg/C. The variation of leakage current with process stages has been monitored. Influence of high voltage surface passivation on leakage current has also been investigated.