Molecular Beam Epitaxial Growth of Cd l-x zn x Te Matched to HgCdTe Alloys
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MUI fGULAR BEAM EPITAXIAL GROWTH OF Cdl.x7nxTe MATCHED TO HgCdTe ALLOYS
N. MAGNEA',
F.
DAL'BO', J. L. PAUTRATa. A. MILLION+.
L. DI CIOCCIO4
G. FEUILLET' Centre a'Etudes Nucl~aires ce Grenoble. 85 X - 38041 Grenoble Cedex. France DOpartement de Recherche Fondamentale +Laooratoire d'Electronique et ce Technologie de
linformatique
ABSTRACT CDI-xZnxTe alloys of various composition have been grown by the Molecular Beam Epitaxy Technique and characterized by Transmission Electron Microscopy. C(V) measurements and photoluminescence spectroscopy techniques. rhe quality of the thick layers is comparable to that of bulk material. Thin strained layers have also been grown whose interfaces are structurally good. The recombination within a CdTe well confined between Cdp7x~nxTe barriers is dominated by intrinsic processes.
I. INTRODUCTION
The fabrication of efficient infrared detectors based on II VI semiconductors can be achieved with the help of epitaxy techniques if suitable substrates are available. A good substrate must be of high cristalline quality and lattice matched to the layer to be grown. If not matched a convenient buffer layer must be grown. I he present work was aimed to the growth by the Molecular Beam Epitaxy technique of Cdo
layers 96
of
CdxZnlxTe
matched
to
Cd 0
8 Hg 0
. 2 Te.
The
substrate
of
7n0 . 0 4 Te is also lattice matched.
After a description of the growth and characterization techniques (Part II). the part III deals with the growth of Cdl-x7nxTe buffer layers (0 ( x < 10 %) and the properties of these layers deduced by photoluminescence. C(V) analysis and Transmission Electron Microscopy. Some heterostructures have also been fabricated with a CdTe well (50 to 230 nm) sandwiched between barriers of Cdl-xZnxTe. The optical response of the well and the quality of the interfaces have been analysed (Part IV).
Mat. Res. Soc. Symp. Proc. Vol. 90. 1987 Materials Research Society
456
II. DESCRIPTION OF THE EXPERIMENTS The (100)
Cd 0 9 6 Zn0
04
Te substrates are carefully polished in a Bromine In situ
methanol solution and cleaned before introduction in the MBE system. cleaning is performed by heating to 3000 for 10-15 minutes.
This allows for the
desorption of the excess surface Tellurium and the formation of a good RHEED diagramm as described before C13. The growth technique uses two effusion cells loaded with CdTe and ZnTe. As these compounds evaporate congruently the ratio of the fluxes coming from both cells defines the composition x of the layer if Zn and Cd have similar sticking coefficients : 1ZnTe ZnTe +4CdTe
where 4PZnTe and *CdTe During the growth,
are the equivalent fluxes of undissociated
The layer thickness reaches 2 to 5 g.m.
deposition rate is close to 0. 2 nm s-1 During the growth on the (100) streaked
(2x1)
molecules.
the substrate temperature is held fixed at 30000 and the
pattern
and
face the RHEED dlagramm displays a well
Kikuchi lines and
bands.
The morphology
and
cristalline quality are good up to x=0.3 as checked by X-ray diffraction data. T
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