G.N. Pain

Use of MeMn(CO)5 in the low temperature MOCVD growth of Mn containing alloys

Abstract The new organometallic feedstock MeMn ( CO ) 5 has been used for the MOCVD growth of Cd 1− x Mn x Te (111B) epilayers on GaAs (100) substrates. The epitaxial relationship was established by HRTEM and X-ray diffraction (XRD). The quaternary alloy Hg 1−x−y Cd x Mn y Te was grown by in-situ annealing og HgTe overlayers on Cd 1−x Mn x Te epilayers. Adherent films of Hg 1−x Mn x Te on glass were grown by MOCVD. The electrical properties show semi-metal behaviour, and XRD and other properties indicate a zinc-blende structure.

Polarity determination of single‐crystal epitaxial layers by x‐ray diffraction

The anomalous scattering of x rays has been used to determine the polarity of single‐crystal epitaxial layers, as grown on the substrate material. The method relies on the breakdown of Friedel’s law in noncentrosymmetric structures and is particularly effective when there exists a large difference between the values of the imaginary anomalous dispersion correction, f‘, for the respective atomic species. The method is nondestructive and measurements are taken from only one side of the sample (the side with the epitaxial layer).

Selection of organometallics for MOCVD of Hg1−xCdxTe and doped semiconductors☆☆☆

Abstract Organometallic feedstocks of cadmium, mercury and tellurium, as well as dopants to create n-type, p-type or diluted magnetic semiconductors, can impose limits on the range of programmable parameters in the MOCVD reactor. The influence of the chosen organometallics on the crystal growth process is critically reviewed.

Structure and polarity of {111} CdTe on {100} GaAs

Ultramicrotome techniques are used to prepare thin cross sections of a {111} epilayer of CdTe deposited by metalorganic chemical vapor deposition onto a {100} GaAs substrate. The structure of these samples is investigated by transmission electron microscopy using high‐resolution (HRTEM) and diffraction contrast, and the polarity of the {111} layer by convergent beam electron diffraction (CBED) and characteristic x‐ray emission under various electron channelling conditions, or ALCHEMI. Rutherford backscattering and channelling experiments on the bulk film confirm the presence of a multiply twinned lamellar structure as observed by electron beam techniques. Strong channeling confirms that the crystallinity is good, and that no significant concentration of defects occurs. HRTEM images of the {111} epilayer from the interface across the lamellar twins show few dislocations or crystal defects. Diffraction contrast indicates the presence of a periodic strain in the GaAs and parallel to the interface. CBED and A...

Antimony sources for MOCVD. The use of Et4Sb2 as a p-type dopant for Hg1−xCdxTe and crystal structure of the adduct [Et4Sb2 · 2CdI2]n

Abstract Tetraethyldistibine, Et 4 Sb 2 , a new antimony source for MOCVD is evaluated. It is shown to be a useful and safe dopant feedstock for low temperature growth of p-type Hg 1- x Cd x Te. Attempted purification of Et 4 Sb 2 by adduct formation with CdI 2 resulted in isolation of a polymeric chain adduct [Et 4 Sb 2 · 2CdI 2 ] n ( 1 ). The structure of 1 has been determined by X-ray crystallography and consists of chains of iodide-bridged Et 4 Sb 2 · 2CdI 2 units which have CdI 2 bonded to each antimony atom. Antimony and two iodine atoms form a trigonal planar arrangement around cadmium, and two weak axial bonds to the iodine atoms of adjacent units give distorted trigonal bipyramidal coordination to cadmium. The distibine molecules display a skew configuration of the ethyl substituents. The Sb II -Sb II and Sb II -Cd II distances are 2.784(2) and 2.822(2) A respectively. Dropwise addition of Me 2 Cd to Et 4 Sb 2 in the absence of solvent gave an insoluble 1:1 adduct. Et 4 Sb 2 reacts with Te but not with Cd or Hg.

Low temperature MOCVD of Hg1−xCdxTe on 311, 511, 711 and shaped GaAs

Abstract The influence of six new GaAs substrate orientations on the surface morphology and defect hillocks of epitaxial Hg 1− x Cd x Te (MCT) layers, grown by low temperature MOCVD, is investigated using Nomarski interference contrast microscopy and SEM. Smoother epitaxial layers are obtained on (311), (511) and (711) substrates of A or B polarity compared with growth on (100) or (100) 2° off toward (110) substrates. The quality and orientation of the layers was monitored by X-ray techniques, Rutherford backscattering/channeling and selected area electron channeling patterns. Absolute polarity determination by X-ray diffraction confirmed that the epilayers adopted the polarity of the substrate. Conformal growth on contoured substrates revealed preferential facet formation and growth rate variation which leads to local composition changes in the interdiffused multilayer process. The growth hillocks commonly observed in epitaxy of MCT are related to the oval defects in III–V compounds, and dissolve on annealing.

Evaluation of some manganese feedstocks for MOCVD

Abstract Devices applicable to the telecommunication and information industries can be fabricated from II–VI semiconductors incorporating manganese at doping or more substantial concentrations. It is desirable to grow thin films of these materials at low temperature by MOCVD in order to improve crystallinity and reduce solid state diffusion effects. Previously reported manganese MOCVD feedstocks have too high a decomposition temperature to be used directly in low temperature growth without precracking or plasma assistance. This paper reviews properties and preparation of some manganese compounds which might find application in low temperature MOCVD. Thermal analysis data for three manganese compounds is presented. The most promising compound is MeMn(CO) 5 , and details of its preparation and purification are given.

Interfacial structures and composition of ultramicrotomed MOCVD formed HgCdTe on GaAs

Abstract We demonstrate the application of ultramicrotome techniques for the preparation of thin semiconductor interfaces in cross-section, for analysis by electron beam techniques. This is of significance for semiconductor device technology, since a specific area on a particular device may be examined in cross-section. High-resolution transmission electron microscopy studies of twinned structures at the interface of a 1.2 μm metal-organic chemical vapour deposited HgCdTe epilayer on {100} GaAs are reported. {100} epitaxial growth starts to dominate about 40 nm from the interface, and continues to the top surface of the epilayer. Energy-dispersive X-ray analysis shows that the mercury concentration within the epilayer increases as the interface is approached. No evidence of diffusion into the GaAs substrate was obtained.

Interdiffusion profiles in MOCVD CdTe/HgTe superlattices and Hg1−xCdxTe multilayers

Composition profiles of ultramicrotomed cross sectional samples of epilayers of Hg1-xCdxTe and superlattices grown by MOCVD are measured on a 10 nm scale using an analytical electron microscope. Results compare well with a numerical model for interdiffusion, making use of analytical expressions for the diffusion coefficient available in the literature. Absorption contrast in electron micrographs yield changes in apparent layer thicknesses that are in excellent agreement with the theoretical model. Computer simulations of interdiffused composition profiles, where temperature, deposition rate, and thickness of each individual layer are specified, together with annealing conditions and cooling rate to ambient temperature, have been successful in modeling the layer are specified, together with annealing conditions and cooling rate to ambient temperature, have been successful in modeling the interdiffused composition across various MCT superlattice boundaries.

HRTEM studies of defects and interdiffusion in Hg1-x-yMnyCdxTe (O≤x,y≤1) grown by low temperature MOCVD

Specular Cd1−yMnyTe epilayers of (100) and (111)B orientation have been grown on 5 cm GaAs (100) and GaAs/Si (100) substrates using dimethyl cadmium, diethyl tellurium and the new organomanganese sources RMn(CO)5 (R = C6H5CH2 or CH3). The manganese compounds are volatile, air and water stable solids which are prepared in high yield and are readily purified by sublimation. Growth was performed at 320–350°C in a horizontal reactor at atmospheric pressure. The feasibility of low temperature interdiffused multilayer process (IMP) MOCVD of the quaternary alloy Hg1−x−yMnyCdxTe is demonstrated. Cati on interdiffusion profiles, including the first reported for Mn in II–VI compounds, are obtained by analytical electron microscopy of ultramicrotomed cross sectional samples using a fine 10 nm electron beam probe. Interdiffusion of Mn is comparable to that of Cd. The Cd1−yMnyTe (111)B layers exhibit fine scale 180°C rotational twinning. Growth of untwinned HgTe on Cd1−yMnyTe (111)B buffer layers is observed, with the HgTe layer adopting the orientation of the surface of the buffer layer. Interdiffusion during growth and subsequent annealing yields untwinned (111)B quaternary alloy on the HgTe side of the interface. The structural quality of (111)B and (100) epilayers is compared by lattice imaging and selected area electron diffraction patterns. No voids or precipitates are observed, in contrast to material grown by techniques employing higher temperatures.