Budapest University of Technology and Economics Department of Electron Devices Microelectronics, BSc course Bipolar transistors 2
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Built-in field, efficiencies ► Calculation of the built-in field ► Injection and transport efficiencies
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Calculation of the built-in field The hole concentration in the base has a gradient The holes do not drift There must be an electrical field, which induces a drift current balancing this! n-type diffusion p-type diffusion base concentration emitterbase collector
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Calculation of the built-in field
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Calculation of the built-in field Problem Let us calculate the built-in potential of the base assuming the following data: N B (0) = /cm 3, N B (w B ) = /cm 3
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Injection and transport efficiency Injection efficiency: Transport efficiency: or emitter efficiency recombination
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Calculation of emitter efficiency We assume a transistor with homogeneous base
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Calculation of emitter efficiency In case of inhomogeneous doping: Gummel number
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Calculation of transport efficiency We assume a transistor with homogeneous base
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Emitter & transport efficiency Let us calculate the emitter and transport efficiencies of the homogeneous base transistor having the following parameters: N E = /cm 3, w E = 2 m, N B = 4 /cm 3, w B = 1,5 m, D n =0,0026 m 2 /s, D p = 0,0011 m 2 /s, n = s. Problem
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Operating modes of the transistor, Ebers-Moll model
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET Operating modes of the transistors Normal active Inverse active SaturationClosed EB: open CB: closed EB: closed CB: open EB: open CB: open EB: closed CB: closed
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET The Ebers - Moll model Equivalent circuit in normal active mode:
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET The Ebers - Moll model Equivalent circuit in inverse active mode:
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET The Ebers - Moll model In saturation the two models are superimposed:
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET The Ebers - Moll equations
Budapest University of Technology and Economics Department of Electron Devices Microelectronics BSc course, Bipolar transistors 2 © András Poppe & Vladimír Székely, BME-EET The Ebers - Moll equations