Photoreflectance characterization on the InAlAs-InGaAs heterojunction bipolar transistors

Characterization of InAlAs-InGaAs heterojunction bipolar transistors (HBT's) with different spacer thickness inserted between emitter and base grown by molecular beam epitaxy has been performed by photoreflectance (PR) measurement. Analysis of the PR spectra above the fundamental band edge of InAlAs has enabled us to deduce the built-in electric field at the emitter-base junction, so the energy spike at the emitter side can be obtained. The two-dimensional electron gas (2-DEG) accumulated in the spacer channel has also been characterized. Both parameters mentioned above are very important for the performance of HBT's electrical characteristics.