Method for improving low temperature current gain of bipolar transistors
AssigneeInternational Business Machines Corporation
InventorsTze-Chiang Chen, John D. Cressler
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Abstract
A method for improving the low temperature current gain of silicon bipolar transistors by implanting a first and a second impurity of the same conductivity type into the base region to provide a high doping level base that increases bandgap narrowing without decreasing freeze-out activation energy. The second impurity is selected to have a higher ionization energy that that of the first impurity. The second impurity thereby freezes out sooner than the first impurity resulting in the freeze-out activation energy being equal to or greater than the energy with only the first impurity.
Claims18
A method of improving the gain at a temperature of below about 80K of a bipolar transistor having an emitter region and a collector region of a first conductivity type and a base region of a second conductivity type opposite to said first type sandwiched between said emitter and collector regions, said base region having an intrinsic and an extrinsic region, comprising the step of:
- introducing a first and second impurity of said second conductivity type into said intrinsic base region, said second impurity having an ionization energy of at least approximately 0.010 eV greater than said first impurity such that the base region has an activation energy at said low temperature at least approximately equal to the activation energy of the base region doped with only the first impurity.
A method of improving the gain at a low temperature of below about 80K of a bipolar transistor having an emitter region and a collector region of a first conductivity type and a base region doped with a first impurity of a second conductivity type opposite to said first type sandwiched between said emitter and collector regions, comprising the step of:
- introducing a second impurity of said second conductivity type into said base region, said second impurity having an ionization energy of at least approximately 0.010 eV greater than said first impurity and being of a concentration to provide a gain at said lower temperature in the range of 20 to 100.
The method of claim 26 wherein the difference in ionization energy between said first and second impurities of said second conductivity type is in the range of between about 0.010 eV and 0.20 eV.
Dependencies are inferred from the claim text.