Rodney I. Pelzel

Formation of self‐assembled InP islands on a GaInP/GaAs(311)A surface

The coherent Stranski–Krastanov growth mode is used to create selfassembled InP islands on GaInP/GaAs(311)A surfaces. The resulting islands on (311)A surfaces have a base width distribution peaked in the range of 600–800 A in contrast to a distribution peaked at 1200 A for islands on (100) surfaces. In addition on the (311)A surfaces, there is a bimodal island height distribution peaked at 15 and 50 A. For the (311)A surfaces, the islands are significantly smaller and more dense (∼1010 islands/cm2) than the islands formed on (100) surfaces (∼109 islands/cm2). Despite these differences in the islands formed on the two surfaces, the growth occurs similarly for the two surfaces, with the formation of three different types of islands distinguished primarily by height.

Characteristics of metal-ferroelectric-insulator-semiconductor diodes composed of Pt electrodes and epitaxial Sr0.8Bi2.2Ta2O9(001)/SrTiO3(100)/Si(100) structures

Epitaxial metal-ferroelectric-insulator-semiconductor diodes were fabricated by depositing a chemical-solution-decomposed Sr0.8Bi2.2Ta2O9 (SBT) film on an SrTiO3-coated Si(100) wafer. X-ray diffraction analysis revealed that the SBT film was composed mostly of c-axis-oriented grains. In Pt/SBT(300 nm)/SrTiO3(23 nm)/Si diodes, a memory window as wide as 1.1 V was obtained for a voltage sweep of ±7 V in capacitance-voltage measurement. The capacitance change in per decade increase in the retention time was approximately 10% up to 24 h. The origin of the ferroelectricity in a c-axis-oriented SBT film is discussed.

Surface morphology in InAs/GaAs(111)A heteroepitaxy: Experimental measurements and computer simulations

The surface morphology of InAs films grown on GaAs(111)A has been studied by scanning tunneling microscopy. The vertical surface displacement on the InAs films has been found to depend on the underlying GaAs buffer layer thickness: specifically, thin GaAs layers are observed to behave mechanically similar to compliant substrates. Atomistic simulations within a valence force field model have been used to compare quantitatively how the InAs surface morphology depends on film thickness and the underlying GaAs layer thickness. The experimental and theoretical results are in excellent agreement over a range of film thicknesses where the misfit dislocation network at the semicoherent InAs/GaAs interface is fully developed.

Kinetics of strain relaxation through misfit dislocation formation in InAs/GaAs(111)A heteroepitaxy

The kinetics of strain relaxation through misfit dislocation formation is investigated in InAs/GaAs(111)A layer-by-layer heteroepitaxy. Experimental measurements are presented of strain relaxation as a function of InAs film thickness for epitaxial film growth on thin and thick GaAs buffer layers. The experimental measurements are described successfully through a phenomenological mean-field theoretical analysis. The analysis reveals that the mechanical behavior of our heteroepitaxial system with a thin buffer layer is similar to that of a system with a thin compliant substrate that is practically unconstrained at its base.

Mechanical behavior of thin buffer layers in InAs/GaAs(111)A heteroepitaxy

The mechanical behavior of thin buffer layers for InAs/GaAs(111)A heteroepitaxy has been investigated by x-ray diffraction (XRD). XRD θ–2θ spectra are presented for the (220) reflection for two monolayers (MLs) of InAs deposited on GaAs buffer layers of both 20 ML and 150 nm (≅ 460 ML) in thickness. For the thicker buffer layer, the XRD spectrum exhibits a single, symmetric peak at a reflected angle corresponding to the bulk GaAs lattice parameter, while for the thinner one it exhibits asymmetry around the GaAs substrate reflection with the spectrum tailing to lower angle. This indicates that the thin buffer layer possesses a distribution of interlayer distances in the [220] direction that are larger than that of the GaAs substrate. The XRD data agree very well with theoretical calculations in which the thin GaAs buffer layer is modeled as unconstrained at its base. Our results provide direct evidence that thin GaAs buffer layers behave mechanically similarly to compliant substrates.

Deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems: Theoretical calculations and experimental measurements

A comprehensive, quantitative analysis is presented of the deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems. The analysis combines a hierarchical theoretical approach with experimental measurements. Continuum linear elasticity theory is linked with atomic-scale calculations of structural relaxation for detailed theoretical studies of deformation in systems consisting of InAs thin films on thin GaAs(111)A substrates that are mechanically unconstrained at their bases. Molecular-beam epitaxy is used to grow very thin InAs films on both thick and thin GaAs buffer layers on epi-ready GaAs(111)A substrates. The deformation state of these samples is characterized by x-ray diffraction (XRD). The interplanar distances of thin GaAs buffer layers along the [220] and [111] crystallographic directions obtained from the corresponding XRD spectra indicate clearly that thin buffer layers deform parallel to the InAs/GaAs(111)A interfacial plane, thus aiding in the accommodation of the st...

Effects of buffer layer thickness and film compositional grading on strain relaxation kinetics in InAs/GaAs(111)A heteroepitaxy

Abstract The effects on the strain relaxation kinetics of a thin buffer layers mechanical response and of the epitaxial film compositional grading are investigated in the epitaxial growth of InAs on GaAs(111)A. Two heteroepitaxial systems are analyzed, consisting of thin and thick GaAs buffer layers grown on GaAs(111)A epi-ready substrates. In both cases, one monolayer of In0.50Ga0.50As is grown initially on the buffer layer followed by growth of several monolayers of InAs. In both systems, strain relaxation in the grown film is measured as a function of film thickness. The experimental measurements are described successfully by a phenomenological mean-field theoretical analysis. Our results support that the mechanical response of a thin buffer layer is similar to that of a thin compliant substrate that is unconstrained at its base. Furthermore, our results indicate that the mechanical behavior of a thin buffer layer can be used in conjunction with film compositional grading toward strain relaxation engineering in semiconductor heteroepitaxy.

Interfacial stability and structure in InAs/GaAs(111)A heteroepitaxy: Effects of buffer layer thickness and film compositional grading

Interfacial stability and the morphology of the epitaxial film surface have been studied in InAs/GaAs(111)A heteroepitaxy based on atomistic simulations and scanning tunneling microscopy. Effects of buffer layer thickness were examined by analyzing two heteroepitaxial systems consisting of thin and thick GaAs buffer layers. In both cases, one monolayer of In0.50Ga0.50As is grown initially on the buffer layer prior to InAs growth. Our results indicate that film compositional grading and the resulting segregation of In atoms at defects in the semicoherent interface can be used effectively in conjunction with the mechanical compliance of thin buffer layers to delay the completion of the coherent-to-semicoherent interfacial transition.

Effect of initial surface reconstruction on the GaS/GaAs(001) interface

We have used photoluminescence of a GaAs/Al0.3Ga0.7As near-surface quantum well structure to study the quality of the interface between GaAs and GaS deposited in ultrahigh vacuum (UHV) using [(tBu)GaS]4. In addition to the luminescence of the near-surface and the deep/reference quantum wells, luminescence was observed for the GaAs cap following the deposition of 100 A of GaS. This additional feature demonstrates the high quality GaS/GaAs interface achievable through the UHV deposition of this precursor. The ratios of the integrated luminescence intensity of both the GaAs cap and the near-surface GaAs quantum well to the deep/reference quantum well indicate that there are fewer GaS/GaAs interface states for deposition on the Ga-rich GaAs(001)-(4×2)/(2×6) surface compared to deposition on the As-rich GaAs(001)-(2×4) surface. Furthermore, GaS passivated samples exposed to ambient conditions for eight months exhibit no luminescence degradation for the near-surface quantum well confirming that these films prov...

Growth of GaS on GaAs(100)-(4 × 2) with the single-source precursor [(tBu)GaS]4

The growth of a GaS film on the GaAs(100)-(4×2) surface, using [(tBu)GaS]4, has been studied in ultra-high vacuum using high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and temperature-programmed desorption (TPD). Upon the adsorption of a monolayer of GaS, we observed the formation of a (2×1) superstructure, as evidenced by LEED. For multilayer growth at 650 K, a (1×1) LEED pattern was observed. For submonolayer coverages of the precursor adsorbed at 100 K, thermally induced β-hydrogen elimination of the tert-butyl ligands was observed at 650 K, as evidenced by concurrent desorption of isobutene and molecular hydrogen. An amorphous GaS film is formed after multilayer adsorption of [(tBu)GaS]4 at 100 K, followed by annealing to 650 K. However, isobutane, isobutene, and molecular hydrogen desorption is seen from such a surface, suggesting an additional tert-butyl ligand removal pathway. Finally, layer-by-layer growth of a GaS film was achieved by a cyclic process of monolayer adsorption of [(tBu)GaS]4 at 200 K, followed by annealing to 700 K.