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 [1̄10] 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 Å for layers grown with rg=4 μm/h and ϑm=0° to 2500 Å 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 growth rate. From the superspot intensities in the TED patterns, the degree of order appears to be a maximum for ϑm≊5°. Judging from the reduction in photoluminescence peak energy caused by ordering, the maximum degree of order appears to occur at ϑm≊4°.

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.

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 [1̄10] 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 sharp and distinct peaks at 1.998 and 1.835 eV for high excitation intensities. The peak separation is even larger at lower excitation intensities. The two peaks come from the disordered and ordered materials, respectively. The peak separation represents the largest energy difference between ordered and disordered material reported to date. This large energy difference, much larger than kT at room temperature, may make such heterostructures useful for photonic devices such as light emitting diodes and lasers.

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 [1̄10]-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 [1̄10]-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 Å) 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.

No abstract