Raman characterization of GaAs/InGaP heterostructure bipolar transistor

Micro-Raman spectroscopy has been used to study GaAs/InGaP Heterostructure Bipolar Transistor (HBT) structure that has been fabricated into an operational device. Carrier concentration measurements from the exposed Tellurium-doped In_xGa_1-x As contact emitter and silicon doped GaAs sub-collector were estimated from the position of the high frequency coupled Plasmon-Longitudinal optical Phonon (PLP) mode. The frequency of the coupled PLP mode in In_0.6Ga_0.4As emitter contact layer was measured as 1811 cm^-1 with a corresponding carrier concentration of n=1.3×10¹⁹ cm^-1. The GaAs sub-collector carrier concentration was estimated to be n=4.510¹⁸ cm^-3. These carrier concentrations were in good agreement with that measured using other techniques and that expected from the growth conditions. The Raman technique was not sensitive to the hole concentration of the carbon doped GaAs base. While micro-Raman technique can be used studying the doping levels of fabricated HBT devices the inability to probe the carbon-doped base limits the usefulness of this technique for these devices