L. C. Su

Effects of substrate misorientation and growth rate on ordering in GaInP

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 [110] direction by angles ϑm, 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 for layers grown with rg=4 μm/h and ϑm=0° to 2500 A for rg=1 μm/h and ϑm=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 ...

Order/disorder heterostructure in Ga0.5In0.5P with ΔEg = 160 meV

Ordering in Ga0.5In0.5P can be controlled by variations in the substrate temperature during organometallic vapor phase epitaxial (OMVPE) growth. Growth at 720°C at a rate of 0.5 μm/h is shown to produce completely disordered material, as evidenced by the transmission electron diffraction (TED) and the photoluminescence (PL) results. The ordering produced at a growth temperature of 620°C is found to depend strongly on the substrate misorientation. Transmission electron micrographs and TED patterns for misorientations of 0°, 3°, 6°, and 9° from (001) toward the [100] direction in the lattice show that increasing the misorientation from 0° to 3° leads to the elimination of one variant, the elimination of twin boundaries, and an overall increase in the degree of order. Further increases in the misorientation angle to 6° and 9° at this growth temperature lead to increasing disorder, although only one variant is formed and the distance between antiphase boundaries (APBs) increases monotonically with increasing θm. This wide variation in ordering behavior has allowed the growth of an order/disorder heterostructure for a substrate misorientation of 3°. The heterostructure consists of a Ga0.52In0.48P layer 0.5 μm thick grown at 740°C followed by an ordered layer 0.4 μm thick grown at 620°C. The X-ray diffraction results show that both layers are precisely lattice-matched to the GaAs substrate. TED patterns show that the first layer is completely disordered and the top layer is highly ordered, with only a single variant. High resolution images indicate that the interface is abrupt, with no dislocations or other defects. 10 K PL shows two sharp and distinct peaks at 1.995 and 1.830 eV for high excitation intensities. The peak separation is even larger at lower excitation intensities. The two peaks come from the disordered and ordered material, respectively. The peak separation represents the largest energy difference between ordered and disordered material reported to date. This large energy difference, 6.6kT at room temperature, may make such heterostructures useful for photonic devices such as light emitting diodes, lasers, and solar cells.

Surface photoabsorption study of the effects of growth temperature and V/III ratio on ordering in GaInP

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 [110]‐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 i...

Atomic ordering of GaInP studied by Kelvin probe force microscopy

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.

Control and characterization of ordering in GaInP

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 (111) and (111) 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 dir...

Kinetically controlled order/disorder structure in GaInP

A Ga0.52In0.48P order/disorder heterostructure having a band‐gap energy difference exceeding 160 meV has been grown by organometallic vapor phase epitaxy. The two layers were grown on a nominally (001)‐oriented GaAs substrate misoriented by 3° toward the [110] direction in the lattice. The disordered layer was grown first, at a temperature of 740 °C. The temperature was then reduced to 620 °C for the growth of the second, highly ordered, layer. X‐ray diffraction shows that the two layers have the same composition and are both lattice matched to the GaAs substrate. Transmission electron diffraction patterns indicate that the first layer is completely disordered and that the second layer is highly ordered with only one variant. A low density of antiphase boundaries is observed in the dark field transmission electron microscope image of the top (ordered) layer. High resolution images demonstrate that the interface is abrupt with no dislocations or other defects. Photoluminescence measured at 10 K shows two ...

Effects of V/III ratio on ordering in GaInP: Atomic scale mechanisms

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 [110]‐oriented P dimers on the surface, as indicated by surface photoabsorption spectroscopy results. These data indicate that the...

Control of ordering in GaInP and effect on bandgap energy

GaxIn1-x P layers with x ≈ 0.5 have been grown by atmospheric pressure organometallic vapor phase epitaxy on GaAs substrates with 10 micron wide, [110]-oriented grooves produced photolithographically on the surface. The [110] steps and the misorientation produced at the edges of the grooves have been found to have important effects on the formation of the Cu-Pt ordered structure (ordering on {111} planes) in the GaInP layers during growth. In this work, the groove shape is demonstrated to be critically important. For the optimum groove shape, with a maximum angle to the (001) surface of between 10 and 16°, single domains of the (-111) and (1-11) variants of the Cu-Pt ordered structure are formed on the two sides of the groove. Shallow (≤0.25 μm deep) grooves, with maximum angles of <10°, are less effective. Within the large domains on each side of the groove, small domains of the other variant are observed. The boundary between the two domains is seen to wander laterally by a micron or more during growth, due to the change in shape of the groove during growth. For deep (1.5 μm) grooves, with maximum angles to the (001) plane of 35°, only a single variant is formed on each side of the groove. However, the domains are small, dispersed in a disordered matrix. For substrates with deep grooves on a GaAs substrate misoriented by 9° toward the [-110] direction, an interesting and useful pattern is produced. One half of the groove is a single domain which shrinks in size as the growth proceeds. The other half of the groove, where the misorientation is larger, is disordered. Thus, every groove contains large (>1 μm2 cross-sectional area and several mm long) regions of highly ordered and completely disordered material separated by no more than a few microns. This allows a direct determination of the effect of ordering on the bandgap of the material using cathodoluminescence (CL) spectroscopy. The 10K photoluminescence (PL) consists of three distinct peaks at 1.94, 1.88, and 1.84 eV. High resolution CL images reveal that the peaks come from different regions of the sample. The high energy peak comes from the disordered material and the low energy peak comes from the large ordered domains. Electron microprobe measurements of the solid composition demonstrate that the shift in emission energy is not due to changes in solid composition. This is the firstdirect verification that ordering causes a reduction in bandgap of any III/V alloy. Decreasing the Ga0.5In0.5P growth rate from the normal 2.0 to 0.5 μ/h is found to enhance ordering in layers grown on planar GaAs substrates. Transmission electron diffraction results show that the domain size also increases significantly. For material grown on exactly (001)-oriented substrates, a pronounced [001] streaking of the superlattice spots is observed. This is correlated with the presence of a dense pattern of fine lines lying in the (001) plane in the transmission electron micrographs. The PL of this highly ordered material consists of a single peak that shifts to higher energy by > 110 meV as the excitation intensity is increased by several orders of magnitude.

Ordering in GaInP grown at low temperatures

Abstract Ordering has been studied in Ga x In 1 − x P with x ≈ 0.52 grown by organometallic vapor phase epitaxy at a rate of 0.5 μm/h. The GaAs substrates were misoriented from the (001) plane toward the [110] direction by angles of 0, 3, 6, and 9°. Growth temperature is a key factor in determining both the rate of the ordering process, occurring at the surface during growth, and the annealing process, occurring in the layer after growth. Results are reported for growth at temperatures as low as 520°C. The CuPt type ordering in the epitaxial layers was characterized mainly using photoluminescence (PL) spectroscopy. The PL peak energy decreases as the degree of order increases. For growth at 520°C the layers are not strongly ordered. The lowest 10 K PL peak energy of 1.936 eV, about 60 meV below that of highly disordered Ga 0.52 In 0.48 P, occurs for a misorientation angle of 9°. The degree of order, judged from the PL peak energy, generally increases with increasing misorientation angle. The results indicate that the annealing process is slow at 520°C, but so is the ordering process. Nevertheless, the layers are partially ordered and the presence of [110] steps accelerates the surface ordering process.

Control of ordering in Ga0.5In0.5P using growth temperature

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 [110] 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 th...