Z. Dardas

Bio: Z. Dardas is an academic researcher from Purdue University. The author has contributed to research in topics: X-ray photoelectron spectroscopy & Ammonium sulfide. The author has an hindex of 3, co-authored 3 publications receiving 175 citations.

Investigations of ammonium sulfide surface treatments on GaAs

Abstract: X‐ray photoelectron spectroscopy (XPS) and reflection high‐energy electron diffraction (RHEED) results are presented for ammonium sulfide treated (100)GaAs surfaces. XPS shows that the sulfur coverage is independent of the ammonium sulfide concentration, although the relative amount of arsenic decreases as the sulfide concentration increases. RHEED patterns show that higher temperatures are required for the surface to restructure following treatment with higher sulfide concentration. In addition to the order of magnitude changes in the diode saturation current densities following ammonium sulfide treatment, we observe that the characteristics of gold and aluminum Schottky barriers on sulfide‐treated GaAs surfaces also vary with the substrate temperature during metal deposition.

X‐ray photoelectron spectroscopy of ammonium sulfide treated GaAs (100) surfaces

Abstract: The effect of an ammonium sulfide treatment on the GaAs (100) surface has been investigated by x‐ray photoelectron spectroscopy. The treatment produces a slight Ga enrichment on the surface and leaves roughly 0.6 of a monolayer of sulfide which inhibits initial oxidation of the surface. The sulfide is not lost as the surface becomes oxidized but appears to remain near the GaAs/oxide interface. Furthermore, in the oxidized layer, As oxide is preferentially drawn to the surface relative to Ga oxide.

Dual-wavelength radiation thermometry: Emissivity compensation algorithms

Abstract: The traditional contact methods of temperature measurement for metal processing applications provide accuracies of ±10 K. Noncontact methods based upon emissivity compensation techniques have the potential for improved accuracy with greater ease of use but require prior knowledge of the target emissivity behavior. The features of the basie spectral and ratio methods and five dualwavelength methods are reviewed. Experiments were conducted on a series of aluminum alloys with different surface treatments characterized by x-ray photoelectron spectroscopy in the temperature range 600 to 750 K. Compensation algorithms that account for surface characteristics are required to achieve improved accuracy.

Effects of low work function metals on the barrier height of sulfide‐treated n‐type GaAs(100)

Abstract: A comparative study of the Schottky barrier height variation on sulfide‐treated GaAs(100) surfaces with low work function metal contacts was made using current‐voltage and capacitance‐voltage measurements. Five different wet chemical sulfide treatments were found to cause little variation in the Sm (0.72 eV) and Mg (0.59 eV) Schottky barrier heights, but caused significant variation in the Al (0.58–0.75 eV) barrier heights when compared to the untreated control diodes. A low temperature (160 °C) anneal was found to cause variation in all of these, uniformly raising the barrier heights of the Sm (+0.07 eV) and Al (+0.04 eV) contacts, and degrading the Mg contacts. These results demonstrate the critical importance of both the reaction specifics and the stability of the interface on the Schottky barrier height.

Chalcogenide passivation of III–V semiconductor surfaces

Abstract: Experimental studies of chalcogenide passivation (by sulfur and selenium atoms) of III–V semiconductor surfaces are analyzed. The characteristic features of chemical-bond formation, the atomic structure, and the electronic properties of III–V semiconductor surfaces coated with chalcogenide atoms are examined. Advances in recent years in the application of chalcogenide passivation in semiconductor technology and trends and prospects for further development of this direction are discussed.

Chemical studies of the passivation of GaAs surface recombination using sulfides and thiols

Abstract: Steady-state photoluminescence, time-resolved photoluminescence, and x-ray photoelectron spectroscopy have been used to study the electrical and chemical properties of GaAs surfaces exposed to inorganic and organic sulfur donors. Despite a wide variation in S2–(aq) concentration, variation of the pH of aqueous HS–solutions had a small effect on the steady-state n-type GaAs photoluminescence intensity, with surfaces exposed to pH=8, 0.1-M HS–(aq) solutions displaying comparable luminescence intensity relative to those treated with pH=14, 1.0-M Na2S·9H2O(aq). Organic thiols (R-SH, where R=–CH2CH2SH or –C6H4Cl) dissolved in nonaqueous solvents were found to effect increases in steady-state luminescence yields and in time-resolved luminescence decay lifetimes of (100)-oriented GaAs. X-ray photoelectron spectroscopy showed that exposure of GaAs surfaces to these organic systems yielded thiols bound to the GaAs surface, but such exposure did not remove excess elemental As and did not form a detectable As2S3 overlayer on the GaAs. These results imply that complete removal of As0 or formation of monolayers of As2S3 is not necessary to effect a reduction in the recombination rate at etched GaAs surfaces. Other compounds that do not contain sulfur but that are strong Lewis bases, such as methoxide ion, also improved the GaAs steady-state photoluminescence intensity. These results demonstrate that a general class of electron-donating reagents can be used to reduce nonradiative recombination at GaAs surfaces, and also imply that prior models focusing on the formation of monolayer coverages of As2S3 and Ga2S3 are not adequate to describe the passivating behavior of this class of reagents. The time-resolved, high level injection experiments clearly demonstrate that a shift in the equilibrium surface Fermi-level energy is not sufficient to explain the luminescence intensity changes, and confirm that HS– and thiol-based reagents induce substantial reductions in the surface recombination velocity through a change in the GaAs surface state recombination rate.

Epitaxial film crystallography by high-energy Auger and X-ray photoelectron diffraction

Abstract: We review recent work in the application of Auger and X-ray photoelectron diffraction at high electron kinetic energies to the problem of structure determination in ultrathin epitaxial overlayers. These closely-related techniques are based on the fact that outgoing Auger and photoelectrons from single-crystal specimens undergo elastic scattering and interference from near-neighbour atoms in the vicinity of the emitter. Such coherent diffraction leads to large intensity modulations as the detected emission direction is varied with respect to the crystal axes of the specimen. The measured modulations are readily interpreted by means of model quantum mechanical scattering calculation in which atomic coordinates in the epitaxial film are systematically varied. Such analyses provide several kinds of useful information, including growth modes accompanying heteroepitaxy, structural details of alloy and compound formation, and quantitative determination of tetragonal distortion at lattice-mismatched hete...