Order/disorder heterostructure in Ga 0.5In 0.5P with ΔEg = 160 meV

Abstract

Ordering in Ga 0.5In 0.5P 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 [ 1 00] 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 θ m. 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 Ga 0.52In 0.48P 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, 6.6 kT at room temperature, may make such heterostructures useful for photonic devices such as light emitting diodes, lasers, and solar cells.