Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen OPUS4-4390 Wissenschaftlicher Artikel Becker, Charles R.; He, L.; Einfeldt, S.; Wu, Y. S.; Lérondel, G.; Heinke, H.; Oehling, S.; Bicknell-Tassius, R. N.; Landwehr, G. Molecular beam epitaxial growth and characterization of (100) HgSe on GaAs In this paper, we present results on the first MBE growth of HgSe. The influence of the GaAs substrate temperature as well as the Hg and Se fluxes on the growth and the electrical properties has been investigated. It has been found that the growth rate is very low at substrate temperatures above 120°C. At 120°C and at lower temperatures, the growth rate is appreciably higher. The sticking coefficient of Se seems to depend inversely on the Hg/Se flux ratio. Epitaxial growth could be maintained at 70°C with Hg/Se flux ratios between lOO and ISO, and at 160°C between 280 and 450. The electron mobilities of these HgSe epilayers at room temperature decrease from a maximum value of 8.2 x 10^3 cm2 /V' s with increasing electron concentration. The concentration was found to be between 6xlO^17 and 1.6x10^19 cm- 3 at room temperature. Rocking curves from X-ray diffraction measurements of the better epilayers have a full width at half maximum of 5S0 arc sec. 1993 urn:nbn:de:bvb:20-opus-50947 Physikalisches Institut OPUS4-4392 Wissenschaftlicher Artikel Becker, Charles, R.; Latussek, V.; Heinke, H.; Regnet, M. M.; Goschenhofer, F.; Einfeldt, S.; He, L.; Bangert, E.; Kraus, M. M.; Landwehr, G. Molecular beam epitaxial growth and characterization of (001) Hg\(_{1-x}\) Cd\(_x\) Te-HgTe superlattices The molecular beam epitaxially growth of (001) Hg\(_{1-x}\) Cd\(_z\) Te-HgTe superlattices has been systematically investigated. The well width as well as the period were determined directly by X-ray diffraction. This was accomphshed for the well width by exploiting the high reflectivity from HgTe and the low reflectivity from CdTe for the (002) Bragg reflection. Knowing the well and barrier thicknesses we have been able to set an upper limit on the aver~ge composition of the barriers, Xl, by annealing the superlattice and then measuring the composition of the. resultmg alloy. Xb was shown to decrease exponentially with decreasing barrier width. Xb is appreciably smaller m. narrow barriers due to the increased significance of interdiffusion in the Hg\(_{1-x}\)Cd\(_x\) Te/HgTe interface in narrow barriers. The experimentally determined optical absorption coefficient for these superlattices is compared WIth theoretical calculations. The absorption coefficient was determined from transmission and reflection spectra at 300, 77 and 5 K. Using the thickness and composition of the barriers and wells, and an interface width due to interdiffusion, the complex refractive index is calculated and compared with the experimental absorption coefficient. The envelope function method based on an 8 x 8 second order k . p band model was used to calculate the superlattice states. These results when inserted into Kubo's formula, yield the dynamic conductivity for interband transitions. The experimental and theoretical values for the absorption coefficient using no adjustable parameters are in good agreement for most of the investigated superlattices. Furthermore the agreement for the higher energetic interband transitions is much worse if values for the barrier composition, which are appreciably different than the experimentally determined values, are used. The infrared photoluminescence was investigated at temperatures from 4.2 to 300 K. Pronounced photoluminescence was observed for all superlattices in this temperature range. 1993 urn:nbn:de:bvb:20-opus-50959 Physikalisches Institut OPUS4-3182 Wissenschaftlicher Artikel Wu, Y. S.; Becker, Charles R.; Waag, A.; Schmiedl, R.; Einfeldt, S.; Landwehr, G. Oxygen on the (100) CdTe surface We have investigated oxygen on CdTe substrates by means of x-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). A Te oxide layer that was at least 15 A thick was found on the surface of as-delivered CdTe substrates that were mechanically polished. This oxide is not easily evaporated at temperatures lower than 350°C. Furthermore, heating in air, which further oxidizes the CdTe layer, should be avoided. Etching with HCI acid (15% HCl) for at least 20 s and then rinsing with de-ionized water reduces the Te oxide layer on the surface down to 4% of a monoatomic layer. However, according to XPS measurements of the 0 Is peak, 20%-30% of a monoatomic layer of oxygen remains on the surface, which can be eliminated by heating at temperatures ranging between 300 and 340 cC. The RHEED patterns for a molecular beam epitaxially (MBE)-grown CdTe film on a (lOO) CdTe substrate with approximately one monoatomic layer of oxidized Te on the surface lose the characteristics of the normal RHEED pattems for a MBE-grown CdTe film on an oxygen-free CdTe substrate. 1993 urn:nbn:de:bvb:20-opus-37869 Physikalisches Institut OPUS4-3168 Wissenschaftlicher Artikel Einfeldt, S.; Heinke, H.; Behringer, M.; Becker, Charles R.; Kurtz, E.; Hommel, D.; Landwehr, G. The growth of HgSe by molecular beam epitaxy for ohmic contacts to p-ZnSe The structural properties of HgSe grown by molecular beam epitaxy (MBE) are investigated for different lattice mismatches to the substrate and various growth conditions. The growth rate is shown to depend strongly on the growth temperature above lOO°C as well as on the Hg/Se flux ratio. It has been found that the crystalline perfection and the electrical properties are mainly determined by the layer thickness, especially for the growth on highly lattice mismatched substrates. Changes in the surface morphology are related to growth parameters. Differences between the electrical behavior of MBE-grown and bulk HgSe are discussed. The electrical properties of HgSe contacts on p-ZnSe are investigated as a function of different annealing procedures. 1994 urn:nbn:de:bvb:20-opus-38001 Physikalisches Institut OPUS4-3169 Wissenschaftlicher Artikel Schikora, D.; Hausleitner, H.; Einfeldt, S.; Becker, Charles R.; Widmer, T.; Giftige, C.; Lischka, K.; von Ortenburg, M.; Landwehr, G. Epitaxial overgrowth of II-VI compounds on patterned substrates The selected area epitaxial overgrowth of narrow gap HgTe as well as wide gap CdTe and ZnTe on CdTe/GaAs substrates, which had been structured by dry etching techniques, has been investigated. A plasma etching process using a barrel reactor with CH\(_4\)-CH\(_2\) gases has been employed to prepare stripes with a width of about 1 μm with anisotropic as well as isotropic etching profiles. It has been found, that the selected area HgTe overgrowth takes place with a high local selectivity to the low index planes of the patterned surface. In contrast, the selected area overgrowth of the wide gap CdTe and ZnTe is controlled by anisotropic growth kinetics provided that the substrate temperature is not lower than 220°C and the starting surface consists of well developed low index crystallographic planes. 1994 urn:nbn:de:bvb:20-opus-37985 Physikalisches Institut OPUS4-3187 Konferenzveröffentlichung Boege, P.; Schäfer, H.; Shanjia, Xu; Xinzhang, Wu; Einfeldt, S.; Becker, Charles R.; Hommel, D.; Geick, R. Improved conductivity-measurement of semiconductor epitaxial layers by means of the contactless microwave method Measurements and calculations of the scattering-characteristics of stratified lossy dielectric blocks completely filling a waveguide cross section are presented. The method is used for contactless conductivity measurements of MBE-grown II-VI semiconductor layers. 1994 urn:nbn:de:bvb:20-opus-37763 Physikalisches Institut