PHOTOEMISSION-STUDY ON THE SNO2/P A-SICX-H INTERFACE

Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) have been employed to SnO2 and its interface with P-type a-SiCx:H. The HeI valence band spectra of SnO2 show that the valence band maximum (VBM) shifts from 4.7 eV to 3.6 eV below the Fermi level (E(F)), and the valence band tail (VBT) extends up to the E(F), as a consequence of H-plasma treatments. The work function difference between SnO2 and P a-SiCx:H is found to decrease from 0.98 eV to 0.15 eV, owing to the increase of the work function of the treated SnO2. The reduction of SnO2 to metallic Sn is also observed by XPS profiling, and it is found that this leads to a wider interfacial region between the treated SnO2 and the successive growth of P a-SiCx:H.

AN ANALYSIS OF CHARGE STATES FOR LOCAL VIBRATIONAL-MODES BY OXYGEN DEFECTS IN SEMI-INSULATING GAAS

The high-resolution spectral measurements for new local vibrational modes near 714 cm-1 due to the oxygen defect in semi-insulating GaAs are analyzed on the basis of a model calculation by self-consistent bond orbital approach. Two charge states of oxygen atom with 1 and 2 extra electrons are assigned to be responsible for these local modes. The observed frequencies are explained by the properties of Ga-O-1 and Ga-O-2 bonds and the calculated cohesive energy indicates that the O-2 state is stable. The results are in good agreement with the kinetic analysis.

Stoichiometric defects in semi-insulating GaAs

The influences of arsenic interstitials and dislocations on the lattice parameters of undoped semi-insulating (SI) GaAs single crystals were analyzed. It was shown that the dislocations in such crystals serve as effective gettering sites for arsenic interstitials due to the deformation energy of dislocations. The average excess arsenic in GaAs epilayers grown by molecular-beam epitaxy (MBE) at low temperatures (LT) is about 1%, and the lattice parameters of these epilayers are larger than those of liquid-encapsulated Czochralski-grown (LEG) SI-GaAs by about 0.1%. The atomic ratio, [As]/([Ga] + [As]), in SI-GaAs grown by low-pressure (LP) LEC is the nearest to the strict stoichiometry compared with those grown by high-pressure (HP) LEC and vertical gradient freeze (VGF). After multiple wafer annealing (MWA), the crystals grown by HPLEC become closer to be strictly stoichiometric.