Effect of Substrate Misonrentation on Ordering in Ga0.5In0.5P

Abstract

ABSTRACTOrdering produced in Ga0.5ln0.5P epitaxial layers grown by OMVPE can be controlled by variations in the substrate misorientation as well as the growth temperature and the growth rate. The ordering produced at a growth temperature of 620°C and a relatively low growth rate of 0.5 μm/hr is found to depend strongly on both the direction and angle of substrate misorientation. Transmission electron microscope images and transmission electron diffraction (TED) patterns as well as electrostatic force microscopy (EFM) and photoluminescence (PL) has been studied for misorientation angles of 0, 3, 6, and 9° from (001) toward the (111)B, (111)A, and [010] directions in the lattice. Misorientation in the (111)B direction (to produce [110] steps) increases ordering for angles of up to approximately 4°. Increasing the misorientation angle in the (111)A direction actually leads to a decrease in the degree of order observed. Misorientation in the [010] direction also decreases the degree of order, although the effect is much less than observed for misorientation in the (111)A direction. The most highly ordered material produced under these growth conditions is for a misorientation angle of 3° in the (111)A direction. Increasing the growth temperature to 720°C produces completely disordered material. This wide variation in ordering behavior has allowed the growth of an order/disorder heterostructure for a substrate misorientation of 3° in the (111)A direction. The heterostructure consists of a Ga0.52In0.48P layer grown at 740°C followed by an ordered layer 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. EFM images of the order/disorder heterostructure show a pronounced contrast at the interface, attributed to the large difference in the nature of the surface states in the ordered and disordered materials. The 10 K PL spectrum consists of two sharp and distinct peaks at 1.995 and 1.830 eV from the disordered and ordered materials, respectively. The peak separation represents the largest energy difference between ordered and disordered materials reported to date. Such heterostructures may be useful for photonic devices.