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Classified abstracts 6988-6996
33 6988. Reflection high-energy electron diffraction observations during growth of ZnS,~Sel x(0 ~< x ~< 1) by molecular-beam epitaxy Different surface reconstructions were observed during growth of ZnSxSe~ x(0 ~< x ~< 1) and the growth conditions under which these occur were determined. Zn-rich ZnSe growth shows a c(2 x 2) surface reconstruction, while under Se-rich growth a (2 x 1) surface is observed. On ZnSxSe~ x(X <<.0.16) and on ZnSe/ZnSxSel x superlattice structures a (5 × ) reconstruction is observed. Se desorption experiments suggest that Se is bound as a dimer to a Se stabilized ZnS~Se~ x surface. The intensity of the specular beam increases after switching from molecular-beam epitaxy growth of ZnSe to atomic layer epitaxy growth. Implications on the ZnSe growth mechanism are discussed. H J Cornelissen et al, J Vac Sci Technol, B6, 1988, 769 772. 33 6989. Improvements to and characterization of GalnAs/AllnAs heterointerfaces grown by molecular-beam epitaxy High-quality GalnAs/AllnAs quantum well samples have been grown by solid source molecular-beam epitaxy. Single quantum well samples have been characterized by photoluminescence spectroscopy and transmission electron microscopy. Emission from a 6.7 A. well was observed at 908.6 nm, which we believe is the shortest wavelength reported for a GaInAs quantum well. The full width at half-maximum of the luminescence lines from a range o f well .vidths are up to a factor of 5 narrower than previously reported for this materials system. From an analysis of the photoluminescence results comments are made on the GaInAs/AlInAs heterointerface quality. Flux stability, defect levels and flux transients are discussed. A simple set point ramping technique has significantly reduced flux transients caused by shutter operations. Raman spectroscopy and X-ray diffraction techniques have been used to determine the composition o f the constituent layers within multiquantum well samples. E G Scott et al, J Vac Sci Technol, B6, 1988, 603 606. 33 6990. Molecular-beam epitaxy growth of GaAs/InAs structures on (001)InP by alternating III/V fluxes Modified molecular-beam epitaxy in which group V flux is suspended during 1 monolayer (ML) deposition of group III elements, is employed for growth of strained GaAs/InAs superlattices on InP substrates with a GaInAs buffer layer. By the reflection electron diffraction intensity study and by X-ray photoelectron spectroscopy, the modification of growth procedure is shown to result in fast formation of a flat growth front without intermixing, which is necessary for superlattice growth. GaAs/InAs superlattice structures grown by the present method are characterized by X-ray diffraction and transmission electron microscopy. R Katsumi et al, J Vac Sci Technol, B6, 1988, 593 596. 33 6991. Molecular-beam epitaxial growth and characterization of ,seudomorphic InAs]ln0.s2Al0.4sAs quantum wells The evolution of the structural and optical quality of molecular-beam epitaxial (MBE) grown lnAs/In0 s2A10.4sAspseudomorphic quantum wells with increasing well thickness has been analyzed by transmission electron microscopy (TEM) and photoluminescence measurements. TEM was used to assess the commensurability of the samples as well as to confirm the build up of stress as the InAs layer is made thicker. Under our growth conditions, intense intrinsic photoluminescence is observed for InAs layers as thick as 30 /~. Beyond this thickness a deterioration of the photoluminescence characteristics occurs due to roughening of the interfaces rather than to relaxation of the lnAs lattice. J L de Miguei et al, J Vac Sci Technol, B6, 1988, 617 619. 33 6992. Influence of substrate misorientation on defect and impurity incorporation in GaAs/AIGaAs beterostructures grown by molecular-beam epitaxy GaAs/AIGaAs heterostructures have been grown by molecular-beam epitaxy on GaAs substrates intentionally oriented (tilted) a few degrees (0-6.5) off the (001) plane towards either (111)A, (111)B or (011). We observe that the 4-K photoluminescence and low-field electron transport properties of these structures may be functions of the substrate tilt angle and tilt direction depending on the concentration of impurities inco,porated during growth. A substrate tilt during molecular-beam epitaxy is observed to have the largest effect on these properties when the background impurity concentration in the molecular-beam epitaxial machine 990
is high. This supports our contention that the observed changes in material characteristics are due to differences in the incorporation of defects and impurities. The incorporation of defects and impurities are reduced by using substrates tilted toward (111 )A in comparison to nominally flat (001) substrates or substrates tilted toward (111)B. D C Radulescu et al, J appl Phys, 63, 1988, 5115 5 120. 33 6993. Molecular stream epitaxy and the role of the boundary layer in chemical vapor deposition Molecular stream epitaxy (MSE) is a new growth technique that modifies the nature of the metal-organic chemical vapor deposition (MOCVD) process to take advantage of molecular-beam epitaxy (MBE) growth concepts, and was used for the growth of InGaAs, GaAsP and |nGaAs/ GaAsP strained-layer superlattices (SLSs). In this technique, the growth proceeds by rotating the substrate to cut into streams of reactant gases and thus eliminates gas-flow transients and provides a method to mechanically shear off the gaseous boundary layer above the substrate between successive exposures. In the growth of InGaAs and GaAsP, growth rate enhancement and compositional changes were observed in the faster rotation regime. These phenomena were attributed to the effective reduction of the diffusion boundary layer above the substrate. In the growth of InGaAs/GaAsP SLSs the individual layer thickness of these SLSs was controlled precisely down :o 8 ~ by simply changing the exposure time to the stream of reactant gases. The optical properties of these SLSs were comparable to those obtained for equivalent superlattices by gas source MBE. T Katsuyama and S M Bedair, Jappl Phys, 63, 1988, 5098 6103. 33 6994. Seed shape dependence of Si solid-phase epitaxy : preferential facet growth A new facet formation mode in Si lateral solid-phase epitaxy (L-SPE) of amorphous Si on SiOz is presented. This mode occurs in the case of L-SPE using a two-dimensional seed area. Depending on whether the seed shape is convex or concave, a {111} facet with a slow SPE rate or a {I 10} facet with a fast SPE rate dominates in the case of {100} Si substrate. This preferential facet growth is explained using a microscopic model of crystallization, and seems to be generalized to other crystal growth and etching processes. Similar results are obtained for seeds surrounded by an SiO2 layer and for seeds surrounding an SiO2 island. These results must be considered in practical device design. Eiichi Murakami et al, J appl Phys, 63, 1988, 4975~4978. 33 6995. Optical properties of molecular beam epitaxially grown GaAsl ,,Sbx (0 < x < 0.5) on GaAs and InP substrates Undoped and lightly Si doped GaAs t xSbx bulk layers have been grown on GaAs substrates with Sb composition as high as 0.5 by molecular beam epitaxy. Low temperature (4 K) photoluminescence (PL) and absorption measurements were carried out. For samples with x values smaller than 0.06, PL spectra were dominated by two bands, the emission associated with the bound excitons and with the electron (or donor) to aceeptor recombinations. However, the free exciton peak was clearly observable in absorption spectra. For higher Sb compositions (x > 0.06), only one peak associated with the impurity or defect related transitions dominates PL spectra. We found that the energy and the line shape of this main peak are closely related to the sample quality for the same x value. The lower peak energy than the band gap, the low signal intensity and the large line broadening are due to the emissions associated with the defect band below the ideal (perfect crystal) energy gap introduced by the lattice mismatch near the heterointerfaee of GaAsl xSbx and GaAs. As expected, higher quality epilayers provide a stronger PL intensity, smaller line width, as well as a higher peak energy. D Huang et al, J appl Phys, 63, 1988, 5859 5862. 33 6996. Ultrahigh vacuum in situ transmission electron microscopy observations of Julecular-beam epitaxiafly grown InSb(ll 1) Ultra',gn vacuum in situ transmission electron microscopy has been used to investigate homoepitaxial growth processes and a 2 x 2 surface reconstruction of I n S b ( l l l ) by molecular-beam epitaxy. When the incident fluxes (1 : 1) o f Sb4 and Inl are impinged onto the substrate, the respective molecules form homoepitaxially grown lnSb films, leaving an excess molecule Sb* which does not contribute to the formation of the InSb films. As a result, there exists a critical temperature (Th) for the
33 6988. Reflection high-energy electron diffraction observations during growth of ZnS,~Sel x(0 ~< x ~< 1) by molecular-beam epitaxy Different surface reconstructions were observed during growth of ZnSxSe~ x(0 ~< x ~< 1) and the growth conditions under which these occur were determined. Zn-rich ZnSe growth shows a c(2 x 2) surface reconstruction, while under Se-rich growth a (2 x 1) surface is observed. On ZnSxSe~ x(X <<.0.16) and on ZnSe/ZnSxSel x superlattice structures a (5 × ) reconstruction is observed. Se desorption experiments suggest that Se is bound as a dimer to a Se stabilized ZnS~Se~ x surface. The intensity of the specular beam increases after switching from molecular-beam epitaxy growth of ZnSe to atomic layer epitaxy growth. Implications on the ZnSe growth mechanism are discussed. H J Cornelissen et al, J Vac Sci Technol, B6, 1988, 769 772. 33 6989. Improvements to and characterization of GalnAs/AllnAs heterointerfaces grown by molecular-beam epitaxy High-quality GalnAs/AllnAs quantum well samples have been grown by solid source molecular-beam epitaxy. Single quantum well samples have been characterized by photoluminescence spectroscopy and transmission electron microscopy. Emission from a 6.7 A. well was observed at 908.6 nm, which we believe is the shortest wavelength reported for a GaInAs quantum well. The full width at half-maximum of the luminescence lines from a range o f well .vidths are up to a factor of 5 narrower than previously reported for this materials system. From an analysis of the photoluminescence results comments are made on the GaInAs/AlInAs heterointerface quality. Flux stability, defect levels and flux transients are discussed. A simple set point ramping technique has significantly reduced flux transients caused by shutter operations. Raman spectroscopy and X-ray diffraction techniques have been used to determine the composition o f the constituent layers within multiquantum well samples. E G Scott et al, J Vac Sci Technol, B6, 1988, 603 606. 33 6990. Molecular-beam epitaxy growth of GaAs/InAs structures on (001)InP by alternating III/V fluxes Modified molecular-beam epitaxy in which group V flux is suspended during 1 monolayer (ML) deposition of group III elements, is employed for growth of strained GaAs/InAs superlattices on InP substrates with a GaInAs buffer layer. By the reflection electron diffraction intensity study and by X-ray photoelectron spectroscopy, the modification of growth procedure is shown to result in fast formation of a flat growth front without intermixing, which is necessary for superlattice growth. GaAs/InAs superlattice structures grown by the present method are characterized by X-ray diffraction and transmission electron microscopy. R Katsumi et al, J Vac Sci Technol, B6, 1988, 593 596. 33 6991. Molecular-beam epitaxial growth and characterization of ,seudomorphic InAs]ln0.s2Al0.4sAs quantum wells The evolution of the structural and optical quality of molecular-beam epitaxial (MBE) grown lnAs/In0 s2A10.4sAspseudomorphic quantum wells with increasing well thickness has been analyzed by transmission electron microscopy (TEM) and photoluminescence measurements. TEM was used to assess the commensurability of the samples as well as to confirm the build up of stress as the InAs layer is made thicker. Under our growth conditions, intense intrinsic photoluminescence is observed for InAs layers as thick as 30 /~. Beyond this thickness a deterioration of the photoluminescence characteristics occurs due to roughening of the interfaces rather than to relaxation of the lnAs lattice. J L de Miguei et al, J Vac Sci Technol, B6, 1988, 617 619. 33 6992. Influence of substrate misorientation on defect and impurity incorporation in GaAs/AIGaAs beterostructures grown by molecular-beam epitaxy GaAs/AIGaAs heterostructures have been grown by molecular-beam epitaxy on GaAs substrates intentionally oriented (tilted) a few degrees (0-6.5) off the (001) plane towards either (111)A, (111)B or (011). We observe that the 4-K photoluminescence and low-field electron transport properties of these structures may be functions of the substrate tilt angle and tilt direction depending on the concentration of impurities inco,porated during growth. A substrate tilt during molecular-beam epitaxy is observed to have the largest effect on these properties when the background impurity concentration in the molecular-beam epitaxial machine 990
is high. This supports our contention that the observed changes in material characteristics are due to differences in the incorporation of defects and impurities. The incorporation of defects and impurities are reduced by using substrates tilted toward (111 )A in comparison to nominally flat (001) substrates or substrates tilted toward (111)B. D C Radulescu et al, J appl Phys, 63, 1988, 5115 5 120. 33 6993. Molecular stream epitaxy and the role of the boundary layer in chemical vapor deposition Molecular stream epitaxy (MSE) is a new growth technique that modifies the nature of the metal-organic chemical vapor deposition (MOCVD) process to take advantage of molecular-beam epitaxy (MBE) growth concepts, and was used for the growth of InGaAs, GaAsP and |nGaAs/ GaAsP strained-layer superlattices (SLSs). In this technique, the growth proceeds by rotating the substrate to cut into streams of reactant gases and thus eliminates gas-flow transients and provides a method to mechanically shear off the gaseous boundary layer above the substrate between successive exposures. In the growth of InGaAs and GaAsP, growth rate enhancement and compositional changes were observed in the faster rotation regime. These phenomena were attributed to the effective reduction of the diffusion boundary layer above the substrate. In the growth of InGaAs/GaAsP SLSs the individual layer thickness of these SLSs was controlled precisely down :o 8 ~ by simply changing the exposure time to the stream of reactant gases. The optical properties of these SLSs were comparable to those obtained for equivalent superlattices by gas source MBE. T Katsuyama and S M Bedair, Jappl Phys, 63, 1988, 5098 6103. 33 6994. Seed shape dependence of Si solid-phase epitaxy : preferential facet growth A new facet formation mode in Si lateral solid-phase epitaxy (L-SPE) of amorphous Si on SiOz is presented. This mode occurs in the case of L-SPE using a two-dimensional seed area. Depending on whether the seed shape is convex or concave, a {111} facet with a slow SPE rate or a {I 10} facet with a fast SPE rate dominates in the case of {100} Si substrate. This preferential facet growth is explained using a microscopic model of crystallization, and seems to be generalized to other crystal growth and etching processes. Similar results are obtained for seeds surrounded by an SiO2 layer and for seeds surrounding an SiO2 island. These results must be considered in practical device design. Eiichi Murakami et al, J appl Phys, 63, 1988, 4975~4978. 33 6995. Optical properties of molecular beam epitaxially grown GaAsl ,,Sbx (0 < x < 0.5) on GaAs and InP substrates Undoped and lightly Si doped GaAs t xSbx bulk layers have been grown on GaAs substrates with Sb composition as high as 0.5 by molecular beam epitaxy. Low temperature (4 K) photoluminescence (PL) and absorption measurements were carried out. For samples with x values smaller than 0.06, PL spectra were dominated by two bands, the emission associated with the bound excitons and with the electron (or donor) to aceeptor recombinations. However, the free exciton peak was clearly observable in absorption spectra. For higher Sb compositions (x > 0.06), only one peak associated with the impurity or defect related transitions dominates PL spectra. We found that the energy and the line shape of this main peak are closely related to the sample quality for the same x value. The lower peak energy than the band gap, the low signal intensity and the large line broadening are due to the emissions associated with the defect band below the ideal (perfect crystal) energy gap introduced by the lattice mismatch near the heterointerfaee of GaAsl xSbx and GaAs. As expected, higher quality epilayers provide a stronger PL intensity, smaller line width, as well as a higher peak energy. D Huang et al, J appl Phys, 63, 1988, 5859 5862. 33 6996. Ultrahigh vacuum in situ transmission electron microscopy observations of Julecular-beam epitaxiafly grown InSb(ll 1) Ultra',gn vacuum in situ transmission electron microscopy has been used to investigate homoepitaxial growth processes and a 2 x 2 surface reconstruction of I n S b ( l l l ) by molecular-beam epitaxy. When the incident fluxes (1 : 1) o f Sb4 and Inl are impinged onto the substrate, the respective molecules form homoepitaxially grown lnSb films, leaving an excess molecule Sb* which does not contribute to the formation of the InSb films. As a result, there exists a critical temperature (Th) for the