Modulated Structures and Atomic Ordering in InP y Sb 1Ày Layers Grown by Organometallic Vapor Phase Epitaxy Tae-Yeon SEONG  , G. Roger BOOKER 1 , Andrew G. NORMAN 2 , and Gerald B. STRINGFELLOW 3 Department of Materials Science and Engineering, Korea University, Seoul 136-713, Korea 1 Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K. 2 National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393, U.S.A. 3 Department of Materials Science and Engineering, University of Utah, Salt Lake City, UT 84112, U.S.A. (Received December 5, 2007; accepted January 5, 2008; published online April 18, 2008) Modulated structure in organometallic vapour phase epitaxially grown InPSb(001) layers has been investigated using transmission electron microscopy (TEM) and transmission electron diffraction (TED). TEM results show that a fine scale modulated contrast (15 – 20 nm) and a fine scale speckled contrast (5 nm) are simultaneously present. In addition, a fine needle-like contrast (1:5–2.1 nm) is present. TED patterns show that ð  111Þ and ð1  11Þ CuPt-type ordered variants are present. Diffuse streaks along the [110] direction are also observed in the ½  110 TED pattern and found to be associated with the needle-like contrast. A possible model involving segregation of atoms associated with rows of missing dimers in the surface reconstruction or the presence of antiphase boundaries (APBs) and domain boundaries in CuPt-type ordered regions present in the layers is suggested to explain the origin of the needle-like contrast. [DOI: 10.1143/JJAP.47.2209] KEYWORDS: transmission electron microscopy, fine scale modulated contrast, speckled contrast, needle-like contrast, atomic ordering, InPSb, organometallic vapor phase epitaxy, spinodal decomposition, III–V compound semiconductors 1. Introduction Transmission electron microscopy (TEM) studies of ternary III–V semiconductor layers revealed the presence of atomically ordered CuPt-type structure, which is com- prised of alternating {111}B monolayers of two binary components. 1–4) It was known that the formation of CuPt- type ordering is directly related to surface processes. 5) It was experimentally shown that CuPt-type ordering causes reduction of band-gap of InGaAs layers. 6) Such ordering- induced band-gap modification is advantageous for devices, such as high-efficiency solar cells. 4) It was further shown that ordering could provide the attractive opportunities of producing heterostructures 3) by changing the band gap energy without altering solid compositions. Atomically ordered structure was also observed in InGaN 7) and CdZnTe 8) alloy layers. In addition, TEM results also showed the presence of modulated contrast attributed to alloy clustering possibly occurring as a result of spinodal decom- position in III–V compound semiconductor layers. 9,10) It was argued that alloy clustering may have an adverse effect on both the electrical and optical properties of semiconductor layers. 11) The ternary alloy InP y Sb 1y is of interest for application in devices, e.g., two-dimensional electron gas devices. 12) InP y Sb 1y alloys have been calculated to have a very large enthalpy of mixing due to the large difference in lattice constant between the InP and InSb binary components. Theoretical calculations indicated a critical temperature of 1046  C and a miscibility gap extending from y ¼ 0:03 to 0.98 at 480  C. 13) The presence of miscibility gap could cause the occurrence of superlattice structures or alloy clustering, which may affect the electrical and optical properties of InPSb layers. However, detailed structural investigations have not been widely performed on InPSb layers to date. In this work, we present detailed TEM and transmission electron diffraction (TED) examinations of InPSb layers grown by organometallic vapor phase epitaxy (OMVPE). It is shown that there are fine scale modulated contrast (15 – 20 nm), fine scale speckled contrast (5 nm), and fine needle-like contrast (1:5–2.1 nm) in the layers. In addition, CuPt-type ordering is observed in the InPSb layers. 2. Experimental Procedure OMVPE growth experiments were performed in an atmospheric pressure, horizontal, infrared heated reactor. The reactants were trimethylindium (TMIn) and trimethyl- antimony (TMSb), kept in temperature controlled baths at 11 and 15  C, respectively, and phosphine, 10% balanced in H 2 . The layers were grown on (001) InAs substrates at growth temperatures in the range 460 – 500  C and growth rates of 0.55 and 0.83 nm/s. (001) plan-view and {110} cross-section TEM specimens were prepared using standard techniques and the thinned materials were examined using a JEOL 4000EX electron microscopes operated at 400 kV. It should be stressed that the TEM specimens were carefully controlled not to induce ion-milling damages during a TEM specimen preparation process. 3. Results and Discussion TEM dark field (DF) images obtained from the [110] and ½  110 cross-section specimens of an InP 0:59 Sb 0:41 layer grown at 470  C and 0.56 nm/s are shown in Fig. 1. The results show that a fine scale modulated contrast (indicated by the dotted circles) and a fine scale speckled contrast (marked by the small arrows) are simultaneously present, and that in addition a fine needle-like contrast (marked by the larger arrows) is also present. The main characteristic features found are as follows: i) the modulated contrast consisted of dark and bright blobs elongated approximately along either [100] or [010] directions with the blobs of width of 15 – 20 nm in the h110i directions visible in both ð2  20Þ and (220) DF images, Figs. 1(a) and 1(b), respectively; ii) the speckled contrast consisted of dark and bright blobs without any specific orientation and of size 5 nm visible in both ð2  20Þ and (220) DF images;  E-mail address: tyseong@korea.ac.kr Japanese Journal of Applied Physics Vol. 47, No. 4, 2008, pp. 2209–2212 #2008 The Japan Society of Applied Physics 2209