(calculation: see slides 20+ in EC) NPN-BJT Collector Base Emitter Collector Base Emitter 𝐼 𝐶 𝐼 𝐸 𝑛 𝑝 𝑛 + 𝑛 p 𝑛 + 𝑉 𝐶𝐶 Out 𝑉 𝐶𝐵 𝐼 𝐵 𝑉 𝐵𝐸 𝑁 𝐷 + − 𝑁 𝐴 − 𝑅 𝐵2 𝑅 𝐵1 C E 𝑝 𝑛 𝑥 𝑝 𝑛0 𝑛 𝑝0 𝑛 𝑝 𝑥 Collector 𝑛 + 𝑝 𝑛 Base Emitter B-E space charge region C-B space E-field 𝑅 𝐿 𝐺𝑁𝐷 𝑁 𝐷 + − 𝑁 𝐴 − 𝑊 𝐶 𝑊 𝐵 𝑊 𝐸 B 𝑊 𝐶 𝑊 𝐵 𝑊 𝐸 𝑥 𝑊 𝑥 𝑁 𝐵 − 𝑋 𝐶 𝑋 𝐸 𝐼 𝐶 𝑁 𝐵 𝐸 𝑥 𝑉 𝐶𝐶 𝐼 𝐸 𝐸 𝑥 𝒆 − 𝑅 𝐿 𝑛 𝑝 𝑛 + 𝑥 C B E 𝐺𝑁𝐷 𝑥 holes 2) electrons get swept by the large E-field ⇒  𝑛 𝑝 0 ≈0 1) forward biased pn-junction: get concentrations by Shockley boundary conditions 3) Concentration gradient ⇒ diffusion current 𝐼 𝐵 𝐸 𝐹𝐸 𝐸 𝐹𝑖 𝑉 𝐸𝐵 𝒆 − 𝐸 𝐹0 𝐸 𝐶 𝑅 𝐵1 𝑅 𝐵2 𝐸 𝐹0 𝐸 𝐹𝑖 simple circuit 𝑉 𝐵𝐶 minority carrier concentrations (This graph explains the basics of the forward active mode. To determine the current amplification 𝛽, set 𝑉 𝐵𝐶 =0. This is just a convention everyone follows!) 𝐸 𝑉 𝐸 𝑉 Common-Emitter circuit (calculation: see slides 20+ in EC) 𝐸 𝐹𝐶 space charge distribution thermal equilibrium 𝐸 𝐶 Emitter Base Collector electric fields due to biasing Emitter Base Collector 𝐼 𝐸 𝐼 𝐶 𝑉 𝐶𝐶 𝑝 + 𝑛 𝑝 𝐺𝑁𝐷 𝑝 + 𝑛 𝑝 Out 𝑅 𝐵2 𝑅 𝐵1 E C 𝑉 𝐸𝐵 𝐼 𝐵 𝑉 𝐵𝐶 band diagram 𝑅 𝐿 B 𝑁 𝐷 + − 𝑁 𝐴 − 𝑁 𝐷 + − 𝑁 𝐴 − 𝑛 𝑝 𝑥 𝑛 𝑝0 𝑝 𝑛0 𝑝 𝑛 𝑥 Collector 𝑝 + 𝑛 p Base Emitter E-B space charge region B-C space E-field 𝑊 𝐸 𝑊 𝐵 𝑊 𝐶 𝑊 𝐸 𝑊 𝐵 𝑊 𝐶 𝑁 𝐵 𝑁 𝐵 𝑥 − 𝑋 𝐸 𝑋 𝐶 𝑥 𝑊 𝑉 𝐶𝐶 𝐼 𝐸 𝐼 𝐶 𝐺𝑁𝐷 holes 𝐸 𝑥 𝑝 + 𝑛 𝑝 𝑅 𝐿 𝐸 𝑥 E B C 𝒆 − 𝑥 𝐼 𝐵 𝑥 𝒆 − 𝐸 𝐶 𝑅 𝐵1 𝑅 𝐵2 𝐸 𝐹𝐶 based on the slides of the lecture „semiconductor devices“ by C. Bolognesi compilation by Stefan Rickli http://blogs.ethz.ch/ricklis Last major update: 20.09.2015 𝐸 𝐶 𝐸 𝑉 𝐸 𝐹𝑖 𝒆 − 𝒆 − 𝑉 𝐵𝐶 𝐸 𝐹𝑖 𝐸 𝑉 𝐸 𝐹0 PNP-BJT 𝐸 𝐹𝐸 𝐸 𝐹0 𝑉 𝐸𝐵

As always: If you have corrections or feedback/suggestions: write me an email to ricklis@student.ethz.ch I then try to incorporate your input and will re-upload the files.