Built-in electric fields in GaAs/GaAs structures with different in situ substrate treatments

We have prepared GaAs substrates prior to molecular beam epitaxial growth b y the following in situ treatments: (1) The usual thermal cleaning under an arsenic flux, (2) cleaning by hydrogen radicals (H*), and (3) exposure to trisdimethylaminoarsine (TDMAAs). The effects of these treatments on the op tical properties and built-in electric fields in GaAs/GaAs structures were studied. In order to investigate the effects of the substrate type on the p roperties of the GaAs epilayers, undoped semi-insulating (SI) GaAs (100) an d Si-doped n(+)-GaAs(100) substrates were used. Reflection high-energy elec tron diffraction during the growth, and atomic force microscopy in air show ed that the smoothest surface morphology was obtained for the layer grown o n a H*-cleaned SI substrate at 570 degreesC. For Si-doped substrates the sm oothest layer was obtained on a TDMAAs-treated substrate. The concentration s of interfacial residual impurities of C and O were measured by secondary ion mass spectroscopy (SIMS). For SI substrates, the usual thermal cleaning process resulted in very high concentrations of C (2X10(19) atoms/cm(3)) a nd O (1.3x10(18) atoms/cm(3)) at the interface. The impurities were drastic ally diminished to below the SIMS detection limit by using H*-cleaning. We observed higher concentrations of impurities on Si-doped substrates. Intern al electric fields due to the interfacial impurities were detected by the p resence of Franz-Keldysh oscillations in the room temperature photoreflecta nce spectra. The samples with the highest amount of interfacial impurities presented the strongest internal electric fields. Photoluminescence results showed a clear correlation between the amount of interfacial impurities an d signal intensity, the lower the impurity content the stronger the photolu minescence intensity. The signal associated with carbon impurities dominate s the photoluminescence spectra for GaAs layers grown on SI substrates, whi le for samples grown on Si-doped substrates the signal coming from the subs trate is the dominant one. (C) 2001 American Vacuum Society.