PHOTOREFLECTANCE CHARACTERIZATION OF AN INALAS INGAAS HETEROSTRUCTUREBIPOLAR-TRANSISTOR/

We have measured the photoreflectance spectrum at 300 K from a lattice -matched InAlAs/InGaAs heterostructure bipolar transistor grown by mol ecular beam epitaxy. The energy features of photoreflectance spectra h ave been identified and the built-in dc electric fields and associated doping profiles have been evaluated in the n-InAlAs emitter from the observed Franz-Keldysh oscillations. The undoped InGaAs spacer between emitter and base was added on to change the built-in electric field. The results showed that the energy features above the InGaAs band gap are the transitions from the valence band to the quantized state of th e conduction band. The quantum well of the conduction band is in the i nterface of the InAlAs and InGaAs heterojunction. The interface charge densities in the spacer channel are determined to be 3.54x10(11) cm-2 and 4.22x10(11) cm-2, corresponding to the samples with spacer thickn esses of 300 and 500 angstrom, respectively. A triangular potential pr ofile model was used to calculate the Microstructure in the potential well and electron energy transition. The theoretical and experimental results were compared and good agreements were also found.