Room-Temperature Photoreflectance Characterization of InAlAs/InGaAs Heterojunction Bipolar Transistor Structure Including Two-Dimensional Electron Gas

Using contactless photoreflectance at 300 K we have characterized two InAlAs/InGaAs heterojunction bipolar transistor structures grown by molecular beam epitaxy. The spectra from the InAlAs and InGaAs interface can be accounted for on the basis of a triangular potential well which confined two-dimensional electron gas. A detailed lineshape fit makes it possible to evaluate the Fermi energy, and hence the two-dimensional electron gas concentration. Furthermore, other important parameters of the system, such as built-in electric fields and In composition, can be evaluated.