Physical characterization of OMVPE-grown AlxGa1-xAs multi-layer films by means of non-destructive optical reflectometry

A novel Fourier transform technique which was developed by us previously, is applied in this work for non-destructive determination of thickness and refractive index steps of experimental multilayer heteroepitaxial structures. No time consuming least-squares curve-fits are required and theoretically there is no limit on the number of layers which can be analyzed. In order to demonstrate the above method experimentally, multilayer structures of Al_xGa_1-xAs containing up to five layers on GaAs substrates, were grown by organometallic vapour phase epitaxy (OMVPE). For calibration purposes, initial experiments involved the growth of Al_xGa_1-xAs single epilayers on GaAs substrates by the same technique. Layers were grown at five different compositions from x = 0.1 to x = 0.5. Both photoluminescence (at 12 K) and double-crystal X-ray diffraction measurements were undertaken on the single layers in order to establish the composition of the material. The results show excellent correspondence with each other. These results were also compared to secondary ion mass spectrometry data. The agreement between the optical technique developed by us and the other analytical methods was excellent.