Nanometer-scale compositional structure in InAs x P 1Ϫx /InN y As x P 1ϪxϪy //InP heterostructures grown by gas-source molecular beam epitaxy and in InAs 1Ϫx P x /InAs 1Ϫy Sb y /InAs heterostructures grown by metalorganic chemical vapor deposition has been characterized using cross-sectional scanning tunneling microscopy. InAs x P 1Ϫx alloy layers are found to contain As-rich and P-rich clusters with boundaries formed preferentially within ͑111͒ and ͑111͒ crystal planes. Similar compositional clustering is observed within InN y As x P 1ϪxϪy alloy layers. Imaging of InAs 1Ϫx P x /InAs 1Ϫy Sb y superlattices reveals nanometer-scale clustering within both the InAs 1Ϫx P x and InAs 1Ϫy Sb y alloy layers, with preferential alignment of compositional features in the ͓112͔ direction. Instances are observed of compositional features correlated across a heterojunction interface, with regions whose composition corresponds to a smaller unstrained lattice constant relative to the surrounding alloy material appearing to propagate across the interface.
We report on the transport properties of low-temperature ͑LT͒ InP/In x Ga 1Ϫx As/InP heterostructures and LT InP thin films. Hall effect measurements performed at hydrostatic pressure up to 1.5 GPa and temperatures ranging from 4.2 K to 250 K on both types of samples as well as Shubnikov-de Haas experiments made on heterostructures clearly reveal the metastable character of phosphorus antisite defects present in LT InP layers.
We report a study of the effect of source switching sequences on the interface abruptness of InGaAs/InGaAsP quantum wells ͑QWs͒ grown by gas-source molecular beam epitaxy. Four methods were investigated: i.e., at each interface during growth interruption, ͑1͒ introducing a residual group-V source evacuation time ͑RSE͒ t where all sources are shut off; ͑2͒ no RSE; ͑3͒ no RSE but adding a group-III InϩGa prelayer of m monolayers; or ͑4͒ using RSE plus the InϩGa prelayer. InGaAs/InGaAsP QWs grown by the different methods were characterized by low-temperature photoluminescence ͑PL͒. The results show that by optimizing t or m, both RSE and prelayer methods can improve the heterostructure interface abruptness, which is evidenced by the stronger PL intensity and narrower PL linewidth, and that combining the two with optimized t and m gives the best result. This is due to the minimization of the memory effect by using RSE and of the As/P exchange by using the group-III prelayer.
We report the effects of growth conditions on the strain and crystalline quality of lowtemperature (LT) grown GaP films by gas-source molecular beam epitaxy. At temperatures below 160 °C, poly-crystalline GaP films are always obtained, regardless of the PH3 low rate used, while at temperatures above 160 °C, the material quality is affected by the PH3 flow rate. Contrary to compressively strained LT GaAs, high-resolution X-ray rocking curve measurement indicates a tensile strain of the LT GaP films, which is considered to be due to PGa antisite defects. The strain is found to be affected by the PH3 flow rate, the growth temperature, and post-growth annealing. Contrary to LT GaAs, no P precipitates are observed in cross-sectional transmission electron microscopy.
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