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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: Surface photoabsorption (SPA) measurements were used to clarify the Cu–Pt ordering mechanism in Ga0.5In0.5P layers grown by organometallic vapor phase epitaxy. The Cu–Pt ordering is strongly affected by the growth temperature and the input partial pressure of the phosphorus precursor, i.e., the V/III ratio. SPA was used to measure the concentration of [1¯10]-oriented phosphorus dimers on the surface, which are characteristics of the (2×4) reconstruction, as a function of the growth temperature and V/III ratio. The degree of order decreases markedly with increasing growth temperature above 620 °C at a constant V/III ratio of 40 [tertiarybutylphosphine (TBP) partial pressure of 50 Pa]. This corresponds directly to a decrease of the P-dimer concentration on the surface. Below 620 °C, the degree of order decreases as the growth temperature decreases, even though the concentration of P dimers increases. This is most likely due to the slow migration of adatoms on the surface during growth. The degree of order is found to decrease monotonically with decreasing V/III ratio in the range from 160 to 8 at 670 °C. This corresponds directly to the decrease of the P-dimer concentration on the surface. The direct correlation of the [1¯10]-oriented phosphorus dimer concentration and the degree of order with changes in both temperature (≥620 °C) and V/III ratio suggests that the (2×4) surface reconstruction is necessary to form the Cu–Pt structure, in agreement with published theoretical studies. The physical structure of the surface of these Ga0.5In0.5P layers was also characterized, using atomic force microscopy. For growth at 670 °C and a V/III ratio of 160, the structure of the layers growth on exactly (001) oriented GaAs substrates consists of islands surrounded mainly by bilayer (approximately 6 A(ring)) steps. As the V/III ratio is reduced, the step height transforms to one monolayer. Exclusively monolayer steps are formed at a V/III ratio of 8. This is interpreted in terms of the stabilization of the bilayers by formation of the (2×2) reconstruction on the (111)B step face at high V/III ratios. © 1996 American Institute of Physics.

Notes: Ga0.5In0.5P layers grown by organometallic vapor-phase epitaxy on GaAs substrates misoriented by angles of 3°, 6°, and 9° from (001) toward the [1¯10] direction in the lattice have been studied using atomic force microscopy. The [110] steps are found to bunch in places to produce supersteps ranging in height from a few monolayers to as large as 30–70 A(ring). The supersteps, consisting of a (11n) facet adjacent to an (001) facet, are separated by an apparently vicinal surface. Both the height of the largest supersteps and the value of n depend on the growth conditions. The (001) facet length depends only slightly on misorientation angle and declines as (growth rate)−1/2, consistent with a diffusion limitation of the facet size. The distance between supersteps increases rapidly with decreasing growth rate and increasing substrate misorientation. A comparison of the superstep spacing and the distance between antiphase boundaries in the Cu–Pt-ordered structure formed during growth indicates a one-to-one correspondence. This leads to the hypothesis that the supersteps lead to loss of phase in the ordered structure during growth. © 1995 American Institute of Physics.

Notes: The kinetic processes leading to ordering in Ga0.52In0.48P have been studied by observing the effects of substrate misorientation (0°–9°), growth rate (0.1–0.5 μm/h), and substrate temperature (570–670 °C) during growth. The ordered structure and degree of ordering are determined using transmission electron microscopy and photoluminescence (PL) spectroscopy. Low growth rates were used for samples with misorientations of 0°–9° toward the [1¯10] lattice direction to elucidate the ordering mechanism; however, due to the long times required to grow layers thick enough for PL characterization (≈1 μm), at a temperature of 670 °C the samples became less ordered with increasing misorientation angle. This was attributed to a disordering annealing process occurring during growth which leads to disorder. In order to reduce the rate of this annealing process, the growth temperature was reduced from 670 to 570 °C. At this temperature, a growth rate of 0.5 μm/h produces material with an increasing degree of order as the angle of substrate misorientation is increased from 0° to 9°. This shows that the kinetics of the ordering process are assisted by an increasing density of [110] steps on the surface.

Notes: Epitaxial layers of GaxIn1−xP with x≈0.52 have been grown by organometallic vapor-phase epitaxy on GaAs substrates misoriented from the (001) plane in the [1¯10] direction by angles cursive-thetam, of 0°, 3°, 6°, and 9°. For each substrate orientation growth rates rg of 1, 2, and 4 μm/h have been used. The ordering was characterized using transmission electron diffraction (TED), dark-field imaging, and photoluminescence. The (110) cross-sectional images show domains of the Cu-Pt structure separated by antiphase boundaries (APBs). The domain size and shape and the degree of order are found to be strongly affected by both the substrate misorientation and the growth rate. For example, lateral domain dimensions range from 50 A(ring) for layers grown with rg=4 μm/h and cursive-thetam=0° to 2500 A(ring) for rg=1 μm/h and cursive-thetam=9°. The APBs generally propagate from the substrate/epilayer interface to the top surface at an angle to the (001) plane that increases dramatically as the angle of misorientation increases. The angle is nearly independent of growth rate. From the superspot intensities in the TED patterns, the degree of order appears to be a maximum for cursive-thetam≈5°. Judging from the reduction in photoluminescence peak energy caused by ordering, the maximum degree of order appears to occur at cursive-thetam≈4°.

Notes: Ga0.5ln0.5P layers grown by organometallic vapor phase epitaxy at rates of between 0.1 and 4.0 μm/h on exactly (001)-oriented GaAs substrates have been studied using atomic force microscopy. The surface is found to be covered by islands several monolayers in height that are elongated in the [110] direction. The edges of the islands are formed of clearly resolved bilayer (5.9 A(ring)) steps. Monolayer steps are rare and no steps larger than 6 A(ring) were observed. These observations explain the nature of the order twin boundaries in ordered GaInP grown on exactly (001)-oriented substrates. The (001) domain laminae are always found to consist of an even number of monolayers. For bilayer steps, the domain thickness will be twice the number of steps moving across the surface before the direction of step motion switches due to the undulating nature of the surface. This switch in the direction of step motion at a particular location on the surface produces the order twin boundaries observed. © 1995 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: This letter presents an experimental study, using high-resolution atomic force microscopy, of the nature of the steps on the surface of GaInP layers lattice matched to GaAs substrates. The substrates were intentionally misoriented from the (001) plane by angles of 3°, 6°, and 9° toward [1¯10] and the layers were grown by organometallic vapor phase epitaxy at temperatures of 570, 620, and 720 °C. The surfaces consist of a mixture of monatomic (2.9 A(ring)) [110] steps and [110] oriented supersteps with a distribution of heights from 2 to approximately 17 monolayers. The height of the largest steps increases monotonically with increasing misorientation angle. The supersteps are apparently formed by bunching of monatomic steps producing high index (11n) surfaces (n=4 to 7). This leaves relatively large (several hundred A(ring)) (001) facets adjacent to the supersteps. The superstep height increases and the density decreases with increasing growth temperature. An attempt is made to correlate the supersteps to the degree of order and the microstructure of the ordered domains. © 1995 American Institute of Physics.

Notes: The atomic ordering of GaInP has been established and studied by a variety of methods, including transmission electron microscopy, cathodoluminescence, and photoluminescence. In this work, a Kelvin probe force microscope (KPFM) has been employed to image several GaInP samples previously characterized by these established techniques. The results of our study clearly show that the KPFM is capable of distinguishing between ordered and disordered regions in GaInP, and that the KPFM contrast strongly depends on the amplitude of the applied ac bias voltage of the KPFM. The measurements indicate that ordering in GaInP modifies the density and/or lifetime of the surface states. © 1995 American Institute of Physics.

Notes: Ga0.51In0.49P layers have been grown by organometallic vapor phase epitaxy on GaAs substrates with [110]-oriented grooves on the surface that have an important effect on the formation of Cu-Pt ordered structures during growth. In this work, the groove shape is demonstrated to be critically important. For the optimum groove shape, single domains of the (1¯11) and (11¯1) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow grooves produce large domains on each side of the groove containing small domains of the other variant. For deep grooves, only a single variant is formed on each side of the groove, but the domains are small. For substrates with deep grooves on a GaAs substrate misoriented by 9°, every groove contains large regions of highly ordered and completely disordered material separated by a few micrometers. This allows a direct determination of the effect of ordering on the band gap of the material using cathodoluminescence spectroscopy, allowing the first direct demonstration that ordering reduces the energy band gap of a III/V alloy.