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Notes: A natural monolayer {111} superlattice (the CuPt ordered structure) is formed spontaneously during organometallic vapor phase epitaxial (OMVPE) growth of Ga0.52In0.48P. The extent of this ordering process is found to be a strong function of the input partial pressure of the phosphorus precursor during growth due to the effect of this parameter on the surface reconstruction and step structure. Thus, heterostructures can be produced by simply changing the flow rate of the P precursor during growth. It is found, by examination of transmission electron microscope (TEM) and atomic force microscope (AFM) images, and the photoluminescence (PL) and PL excitation (PLE) spectra, that order/disorder (O/D) (really less ordered on more ordered) heterostructures formed by decreasing the partial pressure of the P precursor during the OMVPE growth cycle at a temperature of 620 °C are graded over several thousands of Å when PH3 is the precursor. The ordered structure from the lower layer persists into the upper layer. Similarly, D/O structures produced by increasing the PH3 flow rate yield PL spectra also indicative of a graded composition at the heterostructure. The grading is not reduced by a 1 h interruption in the growth cycle at the interface. Similar heterostructures produced at 670 °C using tertiarybutylphosphine (TBP) as the P precursor show a totally different behavior. Abrupt D/O and O/D heterostructures can be produced by abruptly changing the TBP flow rate during the growth cycle. PL and PLE studies show distinct peaks closely corresponding to those observed for the corresponding single layers. TEM dark field images also indicate that the interfaces in both for D/O and O/D heterostructures are abrupt. The cause of the difference in behavior for TBP and PH3 is not clear. It may be related to the difference in temperature. © 1997 American Institute of Physics.

Notes: Ga0.5In0.5P layers have been grown by organometallic vapor-phase epitaxy using various values of input V/III ratio for two phosphorus precursors, phosphine, the conventional precursor, and tertiarybutylphosphine (TBP), a newly developed, less-hazardous precursor. For growth on nominally (001) GaAs substrates misoriented by 3° (and in some cases by 0° or 6°) to produce [110] steps on the surface at a growth temperature of 620 °C, the Cu–Pt-type ordering is found to be strongly affected by the input flow rate of the phosphorus precursor (V/III ratio). For decreasing input partial pressures below 3 Torr for PH3 and 0.75 Torr for TBP the low-temperature photoluminescence (PL) peak energy increases indicating a lower degree of order. This is confirmed by transmission electron diffraction results. The decrease in the degree of order corresponds to a decrease in the concentration of [1¯10]-oriented P dimers on the surface, as indicated by surface photoabsorption spectroscopy results. These data indicate that the reduction in ordering is caused by the loss of the (2×4) reconstructed surface during growth. The difference in the behavior for PH3 and TBP is interpreted as due to the lower pyrolysis efficiency of PH3. The surface structure measured using high-resolution atomic force microscopy indicates that the [110] steps produced by the intentional misorientation of the substrate are bunched to produce supersteps approximately 30–40 A(ring) in height for the lowest V/III ratios. The step height decreases markedly as the input phosphorus partial pressure increases from 0.4 to 0.75 Torr for TBP and from 1 to 3 Torr for PH3. This corresponds to a change from mainly monolayer to predominantly bilayer steps in the vicinal regions between bunched supersteps. Stabilization of the bilayer steps is interpreted as due to formation of the (2×2) reconstruction on the (111)B step edges. The degree of order is an inverted U-shaped function of the flow rate of the phosphorus precursor. Thus, use of very high input V/III ratios is also found to reduce the degree of order in the Ga0.5In0.5P layers. These high input phosphorus flow rates are found to result in a monotonic increase in the density of [1¯10]-oriented P dimers on the surface. This decrease in order is believed to be related to a change in the structure of kinks on the [110] steps at high V/III ratios. © 1996 American Institute of Physics.

Notes: The step structure and CuPt ordering in GaInP layers grown by organometallic vapor phase epitaxy on singular GaAs substrates have been investigated as a function of Te (DETe) doping using atomic force microscopy, and electrical and optical properties measurements. The degree of order decreases for Te concentrations of 〉1018 cm−3. It is estimated from the photoluminescence peak energy to be approximately 0.5 for undoped layers and the layers are completely disordered at sufficiently high Te doping levels. The bandgap energy is changed by 110 meV as the Te doping level increases from 1017 to 1018 cm−3. The step structure also changes markedly over the range of doping that produces disordering, from a mixture of monolayer and bilayer steps for undoped layers to solely monolayer steps for electron concentrations exceeding 1018 cm−3. For growth at 670 °C, the spacing between [1¯10] steps increased by over an order of magnitude as the doping level was changed over the range investigated, while the step spacing between [110] steps increased only slightly. In general, Te doping significantly improves the surface morphology viewed using atomic force microscopy. The degree of order and surface structure are changed at exactly the same doping concentration. This suggests that the disordering may be controlled by the fast propagation of [1¯10] steps due to kinetic effects at the step edges. A qualitative model is presented to explain these effects. © 1998 American Institute of Physics.

Notes: Heterostructures and quantum wells can be produced in GaInP without changing the solid composition by simply varying the order parameter. Since CuPt ordering reduces the band-gap energy, changes in the order parameter induced by changes in growth conditions result in heterostructures with band-gap energy discontinuities as large as 160 meV. The most convenient growth parameter to change is the flow rate of the P precursor. However, previous work has shown that under some conditions the change in order parameter is sluggish, giving rise to graded heterostructures. The cause of the slow change in order parameter is the topic of this article. CuPt ordering has been shown to be driven by the formation of [1¯10] P dimers, characteristic of the (2×4) surface reconstruction. Thus, this study of the transient in the degree of order induced by changing the flow rate of the P precursor has relied on the use of surface photoabsorption (SPA) to monitor the surface reconstruction during the period after the partial pressure of the P precursor was reduced. The SPA transient has then been correlated with the abruptness of the heterostructure interface, determined from the transmission electron microscopy images and the photoluminescence spectra, for organometallic vapor phase epitaxial (OMVPE) growth at temperatures of 620 and 670 °C using the P precursors phosphine (PH3) and tertiarybutylphosphine (TBP). For TBP at both 620 and 670 °C, the SPA reflectance transient is extremely short, with a time constant of less than 10 s, corresponding to the time response of the OMVPE growth system. Abrupt interfaces are produced using these conditions. For PH3, the SPA reflectance transient is abrupt at 670 °C; however, at 620 °C the SPA response is extremely sluggish, with a time constant of approximately 6.5 min. The effect is tentatively attributed to a surfactant effect due to H on the surface. Corresponding heterostructures were abrupt at 670 °C and graded at 620 °C. © 1998 American Institute of Physics.

Notes: Cu–Pt ordering is widely observed in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. The degree of order is a strong function of the input partial pressure of the phosphorus precursor, i.e., the V/III ratio, during growth. By observing the surface structure using in situ surface photoabsorption (SPA) measurements, the concentration of [1¯10]-oriented P dimers, characteristic of the (2×4) reconstructed surface, has been measured as a function of the growth conditions. For growth at 670 °C, the P-dimer concentration is found to increase systematically as the input tertiarybutylphosphine pressure is increased from 10 to 200 Pa. This corresponds directly to a monotonic increase in the degree of order, measured using transmission electron microscopy and low-temperature photoluminescence. These data strongly suggest that the (2×4) surface reconstruction is necessary for formation of the Cu–Pt structure. The step structure at the surface was also observed for these layers using atomic force microscopy. For high V/III ratios the structure of the layers grown on exactly (001) oriented GaAs substrates consists of islands surrounded mainly by bilayer (5.7 A(ring)) steps. As the V/III ratio is reduced, the step height transforms to 2.8 A(ring) (one monolayer). © 1996 American Institute of Physics.

Notes: The surface structure of Ga0.52In0.48P was studied by surface photoabsorption. An absorption peak due to P dimers on Ga0.52In0.48P was observed at ∼400 nm, shorter than for InP (430 nm). From comparison with results for GaAs and InP, the data are interpreted to indicate that at a tertiarybutylphosphine (TBP) pressure of 50 Pa for temperatures below 670 °C, the P-stabilized surface has P dimers aligned along the [1¯10] direction, i.e., it has a (2×4)-like structure. Above 670 °C, the 400 nm peak due to the P-dimer structure disappears because of P desorption from the surface at this TBP partial pressure. Epitaxial Ga0.52In0.48P layers grown using TBP, trimethylgallium and ethyldimethylindium are nearly disordered at 670 °C and highly ordered at 620 °C. These data suggest a correlation between surface structure and ordering. © 1995 American Institute of Physics.

Notes: Photodissociation of trifluoroethylene (F2CCFH) at 157 nm has been investigated using photofragment translational spectroscopy. Four dissociation channels have been experimentally observed: molecular HF elimination, H atom elimination, F atom elimination, and double bond breaking. Double bond breaking is found to be the most important channel, while molecular HF elimination and H atom elimination are found to be significant. Contribution from F atom elimination is minor. Product translational energy distributions for all dissociation channels have been determined. The translational energy distributions for all four dissociation channels are peaked away from zero energy. This is quite similar to that of 1,1-difluoroethylene. Branching ratios and averaged energy partitions for all dissociation channels have also been estimated. © 1998 American Institute of Physics.