INFLUENCE DE LA TEMPERATURE D'EPITAXIE SUR LA QUALITE CRISTALLINE, LES PERFORMANCES ELECTRIQUES ET LE TYPE DE CONDUCTION DES COUCHES DE CdxHg1-xTe PREPAREES EN EPITAXIE PAR JETS MOLECULAIRES

L'épitaxie par jets moléculaires (EJM) du CdxHg1-x Te a été réalisée sur un substrat de CdTe orienté (111) à l'aide de trois cellules d'éffusion indépendantes : Cd, Te et Hg. Nous montrons que lorsque la température d'épitaxie augmente de 110°C à 180°C et que les paramètres de croissance sont maitrisés, la qualité cristalline s'améliore considérablement. Les performances éléctriques alors obtenues, sont comparables à celles des meilleurs matériaux Cdx Hg1-x Te. Nous montrons également que les couches préparées peuvent être de type n ou p. L'ensemble des résultats indique que les couches EJM de CdxHg1-xTe ont actuellement atteint des caractéristiques qui les rendent utilisables pour des dispositifs de détection infra-rouge.Molecular beam epitaxy (MBE) of Cdx Hg1-x Te has been achieved on (111) oriented CdTe substrate with three independant effusion cells Cd, Te and Hg. We report here, that when the temperature of the epitaxy is raised from 110°C to 180°C and when the growth parameters are controled, the cristallinity is hightly improved. The electrical properties obtained, are within the range of the best value reported previously for this material. The layers can be grown n - type or p - type. All these results indicate that Cdx Hg1-x Te layers grown by MBE are now suitable for infrared detection devices

Shubnikov-de Haas oscillations on molecular-beam-epitaxy-grown Hg 1-xCdxTe alloy doped with indium

Shubnikov-de Haas oscillations on the transverse resistivity ρxx and longitudinal resistivity ρzz of as-grown indium-doped alloys of Hg1-xCdxTe (0.24<x<0.34) grown by molecular-beam epitaxy on (111)B and (100) growth directions are observed in the temperature range from 1.2 to 25 K and in fields up to 12 T. The n-type density from the periodicity, the effective mass m* from the temperature dependence of the amplitude, and the Dingle temperature T D are determined from ρxx and ρzz oscillations. The oscillations establish the high Hall density which is found at low fields. The TD in ρxx is found to be higher in comparison to TD in ρzz. However, this difference decreases as the Hall density increases. The TD discrepancy is probably due to greater inhomogeneity in the plane of the layer. The T D is higher than the temperature calculated from the weak-field Hall mobility. The density and effective mass are used to calculate the energy band gap, Fermi energy, and the band-edge effective mass. The calculated energy band gaps are in good agreement with the reported results

VALENCE BAND DISCONTINUITIES IN THE Hg1-xCdxTe-Hg1-yCdyTe(111)B SYSTEM - XPS STUDY

XPS investigations on the Hg1-xCdxTe(111)B alloys show a small change in the binding energy difference between the two cations Cd and Hg for the whole range of alloy compositions. This confirms that the charge transfer between the two cations is very small in Hg1-xCdxTe-Hg1-yCdyTe(111)B heterojunctions. From this study it is concluded that the value of the nutural band discontinuity in HgTe-CdTe heterojunction (0.35eV) is identical to the value of the valence band discontinuity measured in that heterojunction (ƊEv=0.36eV) implying a negligible dipole contribution at the interface. We have also confirmed the validity of the linear model of the ƊEv in the Hg1-xCdxTe-Hg1-yCdyTe heterojunction system.L'étude conduite en XPS sur les alliages Hg1-x CdxTe(111)B montre que la différence entre les energies de liaison des deux cations Cd et Hg est pratiquement constante dans tout l'intervalle de composition de l'alliage. Ceci confirme que le transfert de charge entre les deux cations est faible dans les hétérojonctions Hg1-xCdxTe- Hg1-yCdyTe(111)B. De cette étude il est conclut que la valeur naturelle de la discontinuité de bandes dans l'hétérojonction HgTe-CdTe (0.35eV) est identique à la valeur de la discontinuité de bandes mesurée dans cette hétérojonction (ƊEv=0.36eV). Ceci implique que la contribution des dipoles à l'interface soit negligeable. Nous avons aussi confirmé la validité du modèle lineaire pour ƊEv dans le système d'hétérojonctions Hg1-xCdxTe-Hg1-yCdyTe

Role of the crystallographic orientation on the incorporation of indium in HgCdTe epilayers grown by molecular beam epitaxy

In-doped HgCdTe films have been grown by molecular beam epitaxy (MBE) on CdTe substrates in the (100) crystallographic orientation. They were characterized by Hall and secondary-ion mass spectroscopy measurements. The results are compared with those of In-doped HgCdTe layers grown in the (111)B orientation. In the (111)B orientation indium is incorporated in the metal site whereas in the (100) orientation it appears that indium is mainly incorporated interstitially. The results agree with a Te antisite model as a possibility for explaining the electrical behavior of (100) HgCdTe grown by MBE