Surface photovoltage spectroscopy and contactless electroreflectance characterization of a GaInP/GaAs heterojunction bipolar transistor structure

We have characterized a GaInP/GaAs HBT structure fabricated by MOCVD using SPS and CER, including the dependance of the CER signals on polarization to obtain the degree of ordering in the emitter. From the observed FKOs we have evaluated F^coll and F^emitter.The related doping levels were determined based on a SCPCE calculation (including the photovoltaic effect). There is good agreement between the calculated and nominal doping values for both emitter and collector regions. In addition, we estimated electrodhole coherence lengths in these portions. The ordering parameter η was deduced from both ΔE_EBS and ΔE_BGR. The correspondence of η between these determinations is an indication that the emitter is lattice matched to the GaAs. The properties of the base have been evaluated by means of SPS. A comparison of the SPS lineshape with a SCPCE calculation has enabled us to estimate 190<β<290. This value is higher than experimentally determined number, an effect that may be due to interface roughness.The large number of FKOs from both the collector and emitter are an indication of the high quality of the GaAs and GaInP materials. This experiment demonstrates that the combination of CER (or photoreflectance) and SPS can be used to nondestructively evaluate important parameters of the collector, emitter, and base of GaInP/GaAs HBTs.