Dennis Rioux

Enhanced structural and electronic properties of strained Ge(100) films grown by molecular‐beam epitaxy with a Sb surfactant layer

Reflection high‐energy electron diffraction and angle‐resolved photoemission spectroscopy with synchrotron radiation were used to investigate the effect of a Sb surfactant layer on the growth and electronic properties of strained Ge(100) films. The Ge epilayers were grown by molecular‐beam epitaxy on highly ordered InP(100) substrates. The Ge/InP interface was found to be nonreactive yet extensive with outdiffusion of In into the overlayer. With a Sb surfactant layer the critical thickness for a coherently strained Ge film was increased to 5 ML, which is 2.5 times larger than the critical thickness for Ge films grown without a surfactant. The experimental values for the valence‐band offsets for epilayers under 2.9% tensile strain were found to be ΔEv = −0.94 ± 0.1 eV and ΔEv = −0.97 ± 0.1 eV for films grown with and without a surfactant layer, respectively. These results are in agreement with the model‐solid theoretical prediction of ΔEv = −1.00 eV for this strained heterostructure.

Correlation of interface chemistry, barrier height, and step density for Al on vicinal GaAs(100) surfaces

We have used soft x‐ray photoemission spectroscopy to study the chemical and electronic properties of Al on molecular beam epitaxy GaAs(100) vicinal surfaces, specifically with orientations 1°, 2°, and 4° toward [111]B, 2° toward [111]A, as well as 2° and 4° toward [110] surfaces. Our results show that (1) the interface chemistry depends on both the bonding nature of the steps and the degree of misalignment, (2) a monotonic correspondence exists between Schottky barrier and the density of step‐related atomic sites, irrespective of the misorientation direction, and (3) a nearly one‐to‐one functional dependence exists between the density of electronic states and the density of step‐related atomic sites. Our results emphasize the key role of local atomic bonding upon interface electronic and chemical properties.

Valence band discontinuity at the ZnTe/CdTe interface: Making ohmic contact to P‐type CdTe

We studied the growth and electronic structure of the ZnTe/CdTe(100) interface with angle‐resolved synchrotron radiation photoemission (ARPES) and reflection high energy electron diffraction (RHEED). RHEED patterns during the growth of ZnTe layers on the CdTe(100) substrate showed that the initial ∼16 A grows in registry. After this pseudomorphic 16 A layer, the next 120 A grows with defects to relieve the 6.6% strain between ZnTe and CdTe. After ∼140 A, the ZnTe layers are relaxed. ARPES taken near the Brillouin zone center gave a valance band offset ΔEv=0.14 eV, with the ZnTe valence band maximum (VBM) higher than the CdTe VBM.

Au interfaces with epitaxially grown CdTe(111): Chemistry and barrier heights

We have used high‐resolution soft x‐ray photoemission spectroscopy (SXPS) to study chemistry, atomic distributions, and Fermi level (EF) movement caused by Au deposition on molecular beam epitaxy (MBE) ‐grown CdTe(111)‐B surfaces. Using etch‐and‐anneal cycles, we produce clean surfaces with characteristic valence‐band and core‐level photoemission spectra. Au atoms disrupt substrate bonds releasing both Cd and Te atoms into the overlayer. Anions segregate preferentially to the free surface, while cations are more interspersed in the Au matrix. These first SXPS studies of CdTe(111) surfaces indicate that the atom‐induced disruption is comparable or less than that for cleaved (110) substrates. After correcting for photovoltaic effects, we obtain an equilibrium Fermi‐level position 0.55 eV above the valence‐band maximum (Ev), intermediate between stabilization positions for Au on (i) cleaved, bulk‐grown CdTe(110) (Ev+0.8 to 1.1 eV), and (ii) cleaved, bulk‐grown CdTe(110) with a Yb interlayer (Ev+0.45 eV). Des...

The effect of In doping in CdS/CuInSe2 heterojunction formation: A photoemission investigation

Synchrotron radiation soft x‐ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe2 heterojunction interface. In‐doped CdS overlayers were deposited in steps on single‐crystal n‐type CuInSe2 at 250 °C. Results indicate that the CdS(In) grows in registry with the substrate, initially in a two dimensional growth mode followed by three dimensional island growth as is corroborated by RHEED analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In4d, Se3d, Cd4d, and S2p core lines. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS(In)/CuInSe2 heterojunction valence band discontinuity and the consequent heterojunction band diagram as a function of In dopant concentration. We measured a valence band offset ΔEv=0.3 eV, independent of In doping.