Characterization of GaAs/AlGaAs heterojunction bipolar transistor devices using photoreflectance and photoluminescence

Photoreflectance (PR) and photoluminescence (PL) techniques were used to ch aracterize the AlGaAs/GaAs heterojunction bipolar transistor (HBT) wafers g rown by molecular beam epitaxy (MBE). The line shape of the PR GaAs signal is closely related to the cleanliness of the MBE system. The Franz-Keldysh oscillations of the GaAs signal become sharper, well defined, and the oscil lation amplitude increases slightly as the MBE system is cleaned up. The dc current gain of the HBT devices was observed to increase accordingly. The origin for this correlation is discussed. The PL spectra of the HBT device wafers indicate that the intensity of the free-to-bound transition correspo nding to the donor to valence band becomes strong in high gain device wafer s. (C) 1999 American Institute of Physics. [S0021-8979(99)05723-0].