Question

P2. Assume that the BJT (of P1) operates in the active mode and the applied voltages are: V 0.5V and V-2V. The Shockley assumptions apply (Uniform doping in the individual doping regions, abrupt junctions, low-level injection, no losses due to generation and recombination in the depletion regions). a) Schematically sketch the energy band diagram in the active mode. Indicate the quasi Fermi levels and the width of the space charge regions. b) The voltage Vis further increased. As a consequence of the increased emitter-base voltage more carriers are injected so that the assumption of low injection does not apply anymore. Calculate the emitter-base voltage V level which leads to a transition from low to high injection.

Answer 1

The idea of a bipolar transistor with a wide gap emitter was originally proposed by Shockley. We are familiar with a BJT Here we introduce HBT. Use of a wide gap material for the emitter in HBT creates and additional potential barrier for the holes being injected from the basis. This interims assures very high emitter injection efficiency impossible to achieve in a BJT. Energy band structure of BJT in the active mole \r\n Energy band structure of hetero junction Bipolar transistor based in active mode Single hetero junction devices base and collector are composed of the same narrow band gap materials \r\n emitter base collector Energy band diagram of an SHBT based in the active mode operated in the quasi saturation region. High injection effects occur in a bipolar junction transistor \r\n So for we have assumed low injection As VBE increase the injected minority carries concentration exceeds the majority carrier V_EB greaterthanorequalto 2 v_t ln N_E/ni