Electric field distributions in a molecular-beam epitaxy GaO•83 Alo.17 As/ GaAs/ GaAs structure using photoreflectance

We have studied the photorefiectance (PR) spectra from a molecular-beam epitaxially (MBE) grown heterostructure consisting of 200 nm of G!lo83 Alo 17 As, a 800-nm GaAs buffer layer on a semi-insulating (81) (100) (LEC) GaAs substrate. By varying both the pump beam wavelength and modulation frequency we are able to identify the component layers, their quality, and the quality of the various interfaces. In this study we find evidence for a low density of interface states between the GaAs buffer layer and the GaAIAs layer, and a relatively large density of interface states, between the substrate and buffer layers. These states, previously observed by deep-level transient spectroscopy (DL TS) of doped structures, are presumably associated with the interface produced by MBE growth on etched and air exposed substrates. However, in our experiment since the substrate is semi-insulating and the buffer layer is undoped, it is difficult to resolve these states spatially by CV techniques. Our results show that the PR technique can be used to characterize low conductivity or semi-insulating structures such as enhancement mode metalsemiconductor field effect transistor (ME8FET) and high electron mobility transistor (HEMT) type devices and it may be useful for the in situ characterization of epigrown surfaces and interfaces.