Molecular beam epitaxial growth of the ZnSe1-xTex (x=0.44-0.47) alloy on vicinal (001) GaAs substrates tilted four, six, and nine degree-[111]A or B results in partial phase separation of the alloy with a vertical modulation between different compositions. Transmission electron microscopy images of samples grown on four degree-tilted substrates showed superlattice-like structures, with periods in the range 13.4-28.9Â. Lattice images reveal diffuse interfaces between light and dark bands. Period variations were detected in isolated regions of some samples. We present evidence that the modulation develops at the growth surface, and remains stable in the bulk at temperatures up to 450°C. Satellite spot pairs with approximate indices (h k 1 + δ) were present near the zinc-blende spots in electron diffraction patterns and x-ray diffraction data, as expected from material with a sinusoidal composition profile. The orientation of the spots reveals that the modulation vector is parallel to the growth direction, rather than to [001]. The [111]A- and B-tilted samples showed significant modulation, while the five degree-[110] and on-axis material showed no detectable modulation. The modulation wavelength did not strongly depend on growth temperature in the range examined (285–335°C). Samples showing composition modulation did not exhibit significantly altered low-temperature luminescence spectra from material with no modulation.

The formation chemistry and growth dynamics of thin-film CuInSe2 grown by physical vapor deposition have been considered along the reaction path leading from the CuxSe:CuInSe2 two-phase region to single-phase CuInSe2. The (Cu2Se)β(CuInSe2)1−β (0<β≤1) mixed-phase precursor is created in a manner consistent with a liquid-phase assisted growth process. At substrate temperatures above 500 °C and in the presence of excess Se, the film structure is columnar through the film thickness with column diameters in the range of 2.0–5.0 μm. Films deposited on glass are described as highly oriented with nearly exclusive (112) crystalline orientation. CuInSe2:CuxSe phase separation is identified and occurs primarily normal to the substrate plane at free surfaces. Single-phase CuInSe2 is created by the conversion of the CuxSe into CuInSe2 upon exposure to In and Se activity. Noninterrupted columnar growth continues at substrate temperatures above 500 °C. The addition of In in excess of that required for conversion produces an In-rich near-surface region with a CuIn3Se5 surface chemistry. A model is developed that describes the growth process. The model provides a vision for the production of thin-film CuInSe2 in industrial scale systems. Photovoltaic devices incorporating Ga with total-area efficiencies of 14.4%–16.4% have been produced by this process and variations on this process.

We describe our study of II–VI alloy ZnSe0.5Te0.5 in search of spontaneous ordering. Samples were prepared by molecular beam epitaxy in a variety of structure configurations and growth temperatures, in order to scan a wide range of parameters and identify a favorable condition for ordering. Transmission electron microscopy was carried out on these samples and revealed indications of spontaneous ordering in several samples, where regions with stacking of atoms that appear to be different from the zinc-blende structure were observed. Preliminary study shows that such regions have the CuAu [i.e., the (100) superlattice] structure.

Long-range order of the CuPt type has been observed in the I-III-VI2 material CuInSe2. The ordering was observed by transmission electron diffraction and by high resolution transmission electron microscopy. Comparison with simulated images confirms the CuPt-type ordering and shows the high degree of ordering. Extrinsic stacking faults were found near domain boundaries of the CuPt-type ordered material. During irradiation with the electron beam, the transformation from CuPt ordered to the sphalerite or chalcopyrite phase of CuInSe2 was observed.

Two different ordered phases of CuInSe2 have been investigated by transmission electron microscopy (TEM) methods: the so‐called ‘‘ordered vacancy compound,’’ found in Cu‐poor material, and a new structure, CuPt‐ordered material, which has been found only in Cu‐rich material so far. Both phases may have a strong influence on the performance of solar cells—the ordered vacancy compound by forming the actual heterointerface in a solar cell—the CuPt‐ordered material through effects on the band structure of the material. Here, we present first TEM experiments to identify the ‘‘ordered vacancy compound,’’ and we show the existence of the CuPt‐ordered phase.

Epitaxial growth of the ordered vacancy compound CuIn3Se5 has been achieved on GaAs (100) by molecular beam epitaxy from Cu2Se and In2Se3 sources. Electron probe microanalysis and x-ray diffraction have confirmed the composition for the 1-3-5 phase and that the films are single-crystal CuIn3Se5 (100). Transmission electron microscopy characterization of the material also showed it to be single crystalline. Structural defects in the layer consisted mainly of stacking faults. Photoluminescence measurements performed at 7.5 K indicate that the band gap is 1.28 eV. Raman spectra reveal a strong polarized peak at 152 cm−1, which is believed to arise from the totally symmetric vibration of the Se atoms in the lattice.

We have investigated the properties of individual grains in polycrystalline thin films of CuInSe2 and CdTe by transmission electron microscopy (TEM), transmission electron diffraction (TED), scanning electron microscopy (SEM), and energy dispersive x‐ray spectroscopy (EDS) in a Scanning Transmission Microscope (STEM). TED experiments showed that most grains possess the chalcopyrite structure, which is expected for CuInSe2. In some cases, however, a complex arrangement of different phases was found within a single grain, allowing a glimpse at the kinetics of the grain boundaries, EDS spectra were recorded in a SEM. The spectra show unambiguously the presence of grains with disparate composition. To assess the compositional changes within single grains, EDS spectra were taken at various locations on the grains in a STEM. Using the total photon count as a measure of the local grain thickness and the ratio of SeKα/SeLα intensities to correct for absorption losses, we can analyze the relative concentrations of Se, In, and Cu independently of grain thickness. CdTe films, grown on a CdS/SnO2/glass and examined by SEM showed that the grain size depends primarily on the film thickness. TEM experiments revealed the type, density, and distribution of the structural defects in this material. Threading dislocations, stacking faults, and twinned grains were frequently observed. However, their densities differed markedly from one grain to the next. Some grains exhibited defect densities in excess of 109 cm−2, while adjacent grains were virtually defect free. Cathodoluminescence experiments in the SEM showed a similar difference in the density of nonradiative recombination centers. The grain boundaries were found to be sites of enhanced nonradiative recombination.

This article presents a short review of our present understanding of the structure of semiconductor interfaces and the way they may be used to investigate solid state processes at the atomic level. Until recently it was customary to claim the fabrication of atomically perfect interfaces, based on the results of photoluminescence (PL) experiments. This was based on the splitting of PL lines into closely spaced satellites, thought to stem from the recombination of excitons within large, atomically perfect terraces. However, quantitative microscopic data, obtained by chemical mapping [A. Ourmazd, F. Baumann, M. Bode, and Y. Kim, Ultramicroscopy 34, 237 (1990)], clearly indicate the presence of significant atomic scale roughness [A. Ourmazd, D. W. Taylor, J. Cunningham, and C. W. Tu, Phys. Rev. Lett. 62, 933 (1989)]. This has been confirmed more recently by high resolution PL and photoluminescence excitation experiments [C. A. Warwick, W. Y. Jan, A. Ourmazd, and T. D. Harris, Appl. Phys. Lett. 56, 2666 (1990)], by Raman scattering [D. Gammon, B. V. Shannabrook, and D. S. Katzer, Phys. Rev. Lett. 67, 1547 (1991)] and by high resolution x-ray measurements [M. Lagally, presented at the MRS Fall Meeting in Boston, 1991, Ca5.2]. All these experiments reveal a more complex interfacial configuration, produced by the interplay of roughness at different length scales. The quantitative microscopic techniques developed for the study of interfacial structure also makes possible a class of experiments, where the interface is used as a "photographic emulsion" layer, capable of recording the passage of defects. This allows one to investigate solid state processes at the atomic level. For example, the intermixing caused by the passage of an implanted ion through a GaAs/AlAs interface of a multilayer may be used to track the ion and investigate the microscopics of its interaction with the host material [M. Bode, A. Ourmazd, J. A. Rentschler, M. Hong, L. C. Feldman, and J. P. Mannaerts, Mater. Res. Soc. Symp. Proc. 1989 157, 197 (1990)]. From this type of experiments it is possible to deduce the microscopic damage signature produced by individual implanted Ga+ ions [M. Bode, A. Ourmazd, J. Cunningham, and M. Hong, Phys. Rev. Lett. 67, 843 (1991)]. Intriguingly, the damage is charged, and thus strongly influenced by internal electric fields in the solid. This may be exploited to microscopically steer ion implantation damage in solids.

Thin films of CuInSe2, grown by coevaporation or by selenization of a Cu-In precursor, were analyzed in a scanning transmission electron microscope. While the coevaporated film shows clear evidence of second phases (Cu2Se) around the individual grains, no second phases could be found in the selenized material. Structural characterization also showed the presence of two ordered phases in the coevaporated films, the ordered-vacancy compound CuIn2Se3.5, and a CuPt-ordered phase of CuInSe2.