into proximity with the base collector junction the fundamental operation of the heterojunction bipolar transistor is the same as the simpler bipolar transistor although the heterojunction bipolar transistor emitter is of a higher band gap material means that no photons from the surface plasmon mode will be absorbed in that material this lack of absorption will contribute to higher efficiency in absorption of the surface plasmon photons in the base and collector base regions this configuration is also preferable because the charge carrier transport is in the vertical direction which generally results in a faster transistor the base of the transistor can be biased in the switching mode and in the linear mode in the switching mode when the device is nearly conducting the device is in the off state with the addition of absorbed electromagnetic energy in the base and collector base regions from the evanescent surface plasmon field the transistor can be switched on removing the surface plasmon field will switch the transistor off again in the linear mode the transistor is biased in the linearly conducting active region with a fixed quiescent device collector current such that with the addition of absorbed electromagnetic energy from the evanescent surface plasmon field the transistor can be switched.