Jin Onuki1 and Masateru Suwa1
1Hitachi Research Laboratory, Hitachi Ltd., Hitachi
When a n+-type surface of a diode is bonded to an electrode using aluminum solder, a thin p-type silicon layer, i.e. a regrowth layer is formed on the n+-type silicon after bonding. Because of the layer formation, a considerably high forward voltage drop (FVD) is observed in the regrowth layer.
In the present investigation, molybdenum and tungsten were used for electrode. The phosphorous concentration in the diodes used were 2×1020 cm-3, 4×1020 cm-3 and 1.6×1021 cm-3. Effects of both electrode material and P concentration in diodes on FVD have been investigated. In the case of diodes with high P concentration (1.6×1021 cm-3), FVD was lowered by the use of molybdenum electrode in comparison with the case of tungsten electrode. However, in the case of low P concentration (2×1020 cm-3, 4×1020 cm-3) diodes, the reverse was true. These results are explained by the fact that in the case of molybdenum electrode, the dissolution of n+-type silicon into molten aluminum was increased and the thickness of regrowth layer was reduced in comparison with the case of tungsten electrode.
forward voltage drop, molybdenum electrode, tungsten electrode, phosphorous concentration, thickness of regrowth layer, brazing, aluminum, n+-type silicon, dissolution depth, diode
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