MBE Growth and Characterization of Small Band Gap HgTe-HgCdTe Superlattices.
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MBE GROWTH AND CHARACTERIZATION OF SMALL HgTe-HgCdTe SUPERLATTICES.
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Y. LANSARI, Z. YANG, S. HWANG, J.W. COOK, Jr, and J.F. SCHETZINA, Department of Physics, North Carolina State University, Raleigh, NC 27695-8202. ABSTRACT A series of modulation-doped small-band-gap HgTe-Hgl-xCdxTe N-type superlattices (SLs) have been grown by photoassisted MBE. or p-type conductivity was obtained in the modulation-doped samples by incorporating either In or As dopant atoms in the The electrical and optical properbarrier layers, respectively. ties that these new multilayered quantum well structures display will be discussed. INTRODUCTION In recent years, important advances in the growth and characterization of undoped HgTe-CdTe SLs have been achieved [1,2,3]. However, the problem of in-situ doping of these SLs has Since the well layers consist only recently been addressed [4]. of HgTe, a negative-band-gap semimetallic material, it is possible to engineer a semiconducting structure having a band gap in the long wavelength infrared (LWIR) region of the wavelength spectrum. In fact, by choosing appropriate barrier layer Lb and well layer Lz thicknesses, superlattices can now be prepared reproducibly that exhibit either semiconducting or semimetallic properties. Here, we report the properties of a series of modulation-doped HgTe-Hgl.xCdxTe superlattices grown by photoassisted MBE in which the Hgl-xCdxTe barrier layers were doped either p-type or n-type by
using In or As as the dopant species, EXPERIMENTAL
respectively.
DETAILS
All of the modulation-doped superlattices (SLs) were grown in a Hg-compatible MBE system, designed and built at North Carolina State University that is described in an earlier publication [5]. The modulation-doped SLs were deposited onto high structural quality, chemimechanically polished (100) CdZnTe (4% Zn) subPrior to their loading into the MBE system, the substrates. strates were degreased and etched in a 1:1 HCl and DI water solution to remove the native oxide. 0 The substrates were then preheated at a temperature of 300 C while in the MBE growth chamber. All of the modulation-doped SLs were grown at 140 *C In the photoassisted MBE process, the using photoassisted MBE. beam-expanded, broad-band output (458-514 nm) from a SpectraPhysics model 2016-05 argon-ion laser was used to uniformly Power densities of illuminate the substrates during film growth. 40 mW/cm2 were employed, resulting in negligible substrate heating The Hg flux, with equivalent beam pressure from the laser beam. of -1.5x10- 4 Torr, was maintained constant throughout each growth. The CdTe barrier layers, therefore, are grown under a Hg flux. Because of this overpressure of Hg, the barrier layers are actually Hgl-xCdTe, where the x-value depends on the growth Mat. Res. Soc. Symp. Proc. Vol. 161. @1990 Materials Research Society
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conditions. The CdTe and Te fluxes were such that the growth rates obtained for HgCdTe and HgTe were in the range of 1 A/s and 3 A/s, respectively. In the modulation doped samples, In and As were
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