A. Wall

New ternary semiconductors for infrared applications: Hg1−x MnxTe

Hg1−xMnxTe alloys have been proposed as a suitable alternate material to mercury–cadmium–telluride for infrared applications. We report synchrotron radiation photoemission studies of the electronic structure of such alloys for x≤0.15. Valence band resonant photoemission was exploited to probe the valence states, while high resolution core photoemission yielded information on bonding stability and ionicity. The results are compared with those obtained for Hg1−xCdxTe and for HgTe. The Mn bonding in Hg1−xMnxTe appears mostly due to the coupling of metal‐s states with Te p‐states, with limited evidence of d–p hybridization. The ionicity of the Hg–Te bond is not substantially modified in the ternary alloy relative to HgTe, while for Hg1−xCdxTe we directly observe dramatic destabilization of the Hg–Te bond. Correspondingly, Hg1−xMnxTe should exhibit lattice surface and interface stability similar to those of the binary parent compound and largely exceeding those of Hg1−xCdxTe.

Local stoichiometry and atomic interdiffusion during reactive metal/mercury–cadmium–telluride junction formation

Synchrotron-radiation photoemission studies of Ag, Ge, and Sm overlayers on Hg1-xCdxTe (110) surfaces are summarized. These metals exhibit widely different interface reactivity with Hg/sub 1-x/Cd/sub x/Te and yield a range of different interface morphologies. To assess the relative importance of the microscopic driving forces that determine the local composition at the interface and in the semiconductor near-surface region, the authors present a systematic comparison the data with calculated thermodynamic parameters such as the cation-metal heat of solution, the heat of alloying from Miedemas semi-empirical model, and the metal/telluride formation enthalpy.

Bonding and stability in narrow‐gap ternary semiconductors for infrared applications

The electronic properties of narrow‐gap ternary semimagnetic semiconductors Hg1−xFexSe and Hg1−xMnxSe have been studied using synchrotron radiation photoemission techniques. This work was undertaken to assess the character and stability of the Hg–chalcogenide bond. The results are compared to those of similar studies obtained for Hg1−xCdxTe and Hg1−xMnxTe alloys, and for the binary compounds HgSe and HgTe. Synchrotron radiation photoemission studies show that the addition of Mn or Fe to the binaries perturbs only slightly the Hg–chalcogenide bond, in contrast to the case of Cd where large destabilization is observed. A striking result of the present study is that the addition of Fe to HgSe greatly enhances the stability of the carrier concentration against standard processing techniques such as annealing in a Hg or Se atmosphere.

A photoemission survey of the electronic properties of ternary semimagnetic semiconductor alloys

We review the results of a number of recent synchrotron radiation photoemission studies of the electronic structure of concentrated ternary semimagnetic semiconducting alloys. The materials examined include Cd1−xMnxS, Cd1−xMnxSe, Cd1−xMnxTe , Zn1−xMnxSe, and the narrow‐gap Hg1−xMnxTe, Hg1−xMnxSe, and Hg1−xFexSe. Photon‐energy‐dependent photoemission methods are being used to probe the elemental and orbital contribution to the valence states. The new information is stimulating novel theoretical work on the electronic structure and lattice stability of these semiconductors.

Diffusion barriers at mercury–cadmium–telluride/metal interfaces: The case of Hg1−xCdxTe(110)/Yb/Al

The rare‐earth metals Yb and Sm show unique reactive behavior on mercury–cadmium–telluride (MCT) surfaces, due to the large rare‐earth affinity for both Hg and Te. Semiempirical calculations of thermodynamic parameters using Miedema’s model suggest that the rare earths should act as effective diffusion barriers at the interface between MCT and prototypical reactive metals such as Al, In, or Cr. We present here a synchrotron radiation photoemission investigation of the effect of Yb interlayers at the Hg1−xCdxTe(110)/Al junction. Our results indicate that layers of Yb are effective in preventing Al–Te reaction and reducing the Al‐induced mercury depletion of the substrate. Our data confirm that such a diffusion barrier effect is the result of the superior thermodynamic stability of the MCT/Yb reaction products at the interface.

Inverse photoemission and resonant photoemission characterization of semimagnetic semiconductors

The new magnetotransport and magneto‐optical properties of the semimagnetic Cd1−xMnxTe semiconductor alloy series depend critically on the nature of the Mn‐derived d states. We examine here the electronic structure of these alloys with a combination of inverse photoemission spectroscopy, core‐level photoemission line‐shape analysis, valence‐band resonant photoemission, and local density pseudofunction theory. The spectroscopic data reflect the local Mn–Te coordination and are in remarkable agreement with our one‐electron calculations. We see no evidence of Mn‐derived d states in the gap, and observe an experimental d↑–d↓ exchange splitting of 8.4±0.4 eV, i.e., almost twice as large as expected from earlier theoretical estimates. The ground‐state configuration of Mn in the solid is primarily (d↑)(s↑)(p↑), and the super‐exchange interaction has an important role in determining the stability of such a configuration relative to (d↑)5s2.

Nonmonotonic Evolution and Thermodynamic Trends at Metal/(Hg,Cd)Te Interfaces: Yb/Hg0.78Cd0.22Te.

The microscopic interaction of cleaved Hg0.78Cd0.22Te surfaces with the highly reactive rare earth Yb was studied by use of photoemission spectroscopy and synchrotron radiation. We compare the results of this study with our previous investigation of Sm/(Hg,Cd)Te interface formation. Yb and Sm are similar in their initial stage of interface formation: rapid attenuation and near loss of the Hg emission is followed by its dramatic recovery. However, differences in valency between Sm and Yb develop during metal deposition and subsequently lead to differences in interface morphology. Calculated heats of solution are shown to correlate with the different behaviors observed during rare earth/(Hg,Cd)Te interface formation.