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We report on the microscopic characteristics of polycrystalline CuIn1−xGaxSe2 thin films probed with Auger electron spectroscopy, cathodoluminescence spectroscopy, secondary ion mass spectrometry, and work function measurements. Confirming theory, we find a substantial reduction in Cu content from grain interior to boundary and a p-type potential barrier that acts to reduce hole recombination. Such compositional and electrostatic variations between grain boundaries and grain interiors in CuIn1−xGaxSe2 solar cell absorber layers may improve the overall photovoltaic efficiency. The high degree of intergranular inhomogeneity emphasizes the importance of detailed grain-by-grain analysis. These results show that careful specimen preparation and ultrahigh vacuum conditions, coupled with nanoscale instrumental resolution, are pivotal for such analysis.

Interfacial interdiffusion in quantum wells and superlattices could alter the interfacial strain, band alignment, and even the atomic symmetry at the interface, thus potentially changing the electronic and optical properties. We consider the InAs/GaSb system describing the interdiffused interfaces via a simple kinetic model of molecular beam epitaxy growth. The predicted atomic positions after interdiffusion are then used in a pseudopotential theory to describe the electronic and optical consequences of interdiffusion. We determine (i) the effects of different interfacial bonding compositions on the electronic and optical properties; (ii) the segregation profiles at the normal and inverted interfaces; and (iii) the effect of structural disorder on band gaps. The application of our method to the InAs/GaSb superlattices allows us to explain numerous observed results and trends.

The occurrence of spontaneous CuPt‐like ordering in epitaxial Ga1−xInxP alloys is examined by means of a thermodynamic theory. We treat both cation‐ and anion‐terminated surfaces. We find that the order parameter of the observed CuPtB variant is significant for reconstructed cation‐terminated surfaces even at preparation temperatures. A possible mechanism for the formation of the three‐dimensional CuPtB structure involves partial equilibration of the cation‐terminated reconstructed surface followed by freezing of the cations as the surface is buried by newly deposited layers.

The relationship between interfacial atomic structure and band offsets at semiconductor heterojunctions is explored through first‐principles local density functional calculations. In particular, the effects of variations in interfacial geometry are analyzed for (001) interfaces between III–V/III–V materials. For the AC/BC case of a common atom, isovalent A–B intermixing in the noncommon atomic planes near the interface does not affect the band offset, even in the case of large lattice‐mismatched systems. For quaternary AB/CD systems, there are two possible chemically abrupt interfaces (A–D or B–C); these can have offsets that differ by up to 80 meV. In those cases where the chemically abrupt AB/CD offset depends on the interfacial identity, intermixing leads to offset variations which are directly related to the offset difference between the chemically abrupt A–D and B–C interfaces. The differing behavior of common‐atom versus noncommon‐atom systems is analyzed in terms of the symmetry of the nearest‐neig...

Using the first‐principles pseudopotential method we have studied the fully covered cation‐terminated (001) surfaces of Ga0.5In0.5P alloys. We find that among several possible Ga and In surface patterns (within a 2×2 unit cell), the one corresponding to CuPt‐like bulk ordering is stabilized by ∼100 meV per surface atom. This structure has been observed experimentally in thick films, yet is known to be bulk unstable. The stability of a CuPt‐like surface layer is related to electronically driven surface reconstructions—dimerization, buckling, and tilting—which are discussed in detail.

Simple tests are presented that gauge the accuracy of some of the pseudopotentials currently used in the literature to calculate within the density–functional approach the electronic properties of molecules, solids and surfaces. These include the local ’’soft‐core’’ and ’’hard‐core’’ potentials as well as the nonlocal first principles (’’hard‐core’’) potentials. A discussion of common misconceptions regarding pseudopotentials is included.

It has been traditionally accepted in various theoretical approaches to II–VI semiconductors (e.g., tight binding, pseudopotentials) to neglect the effects of the cation d bands, hoping that in some sense they are ‘‘deep,’’ ‘‘localized,’’ and hence, unresponsive to many perturbations of chemical interest. There are, however, two qualitative reasons to think that this is not so: first, d bands in II–VI’s are only 7–11 eV below the valence‐band maximum (VBM) (i.e., inside the main valence band), and second, in tetrahedral (but not octahedral) symmetry, cation d orbitals have the same representation (Γ15) as the anion p orbitals, hence the two can interact. We have considered the effects of the cation d bands in II–VI’s on both the electronic and structural properties of the binary and ternary compounds, treating all electrons on the same footing, in a self‐consistent first‐principles manner. We find that the d orbitals: (i) reverse the direction of charge transfer in the alloy (e.g., relative to s–p tight b...

A re‐examination of the experimental data and previous electronic structure calculations on the prototype system Al/GaAs(110), together with new calculations and models, indicates that at low coverages and temperatures neither a covalent bond nor a metallic bond is formed between Al and the substrate. Instead, the predominant species is likely to be Al clusters which interact only weakly with the substrate.

Note: Solar energy res inst,golden,co 80401. univ colorado,dept phys,boulder,co 80309. Daniels, rr, univ wisconsin,dept phys,madison,wi 53706.ISI Document Delivery No.: QS531 Reference LSE-ARTICLE-1983-003 Record created on 2006-10-03, modified on 2016-08-08

The valence band offsets of the common‐anion CdTe–HgTe, CdTe–ZnTe, ZnTe–HgTe, and GaAs–AlAs semiconductor pairs are calculated from the core level energies. The good agreement obtained with experiment for lattice‐matched systems and a simple electrostatic model analysis suggest interface dipoles to have only a small effect. Furthermore, the microscopic origin of the failure of the common‐anion rule in lattice‐matched systems is identified: it is found that participation of cation d orbitals (neglected by tight‐binding and pseudopotential approaches alike) in the valence band maxima is responsible for much of the band offset in these systems.

We investigated the adatom states for different Al coverages of InP(110) by synchrotron‐radiation photoemission, including ultralow coverages below 0.2 monolayer. The adatom states below 0.1 monolayer and above ∼3 monolayer appear similar to the corresponding Al–adatom states on GaAs(110). In particular, the results for both systems appear consistent with the formation of Al clusters at 0.1–2 monolayer coverage, and the Fermi‐level pinning occurs when the cluster formation starts. However, the similarity between the two systems is limited at intermediate (0.1–2 monolayer) coverages. At those coverages we observe a new bonded state for Al on InP, which is not observed on GaAs. Our results emphasize, in general, the need to extend the experiments to ultralow coverages when studying the Schottky barrier formation process.