Deodatta Vinayak Shenai-Khatkhate

The growth of CdHgTe by MOCVD at reduced temperatures

Abstract CdHgTe has been grown by MOCVD at 350°C using IMP. The material was superior to that grown at 410°C in terms of surface morphology, decreased acceptor concentration and better interface control. The compositional uniformity was also greatly improved, and at 1% in x over 1 cm 2 in the best ever reported for MOCVD grown CMT.

Preparation and purification of metal alkyls for use in the MOCVD growth of II/VI compound semiconductors

Abstract The preparation of adducts of Me 2 Cd and Me 2 Zn with a range of nitrogen donor ligands has been investigated. Those with two nitrogen atoms, which cannot for geometrical reasons bind to the same metal atom, are shown to give involatile polymeric adducts, which dissociate on heating at one atmosphere or in vacuo below the sublimation temperature of the adduct or the Lewis Base. These adducts may be suitable for the purification of Me 2 Cd or Me 2 Zn. Those that dissociate Me 2 Zn or Me 2 Cd below the melting point of the adduct may be suitable precursors for the delivery of these alkyls by the MEM method. A new preparation of Et 2 Te based on the two phase reactions of aqueous Na 2 Te with EtBr is also reported. This gives high yields of Et 2 Te which is polytellurium-free.

Homolytic reactions of diorganotellurium and diorganoditellurium compounds in solution; an EPR study

Abstract The thermal and photochemical decompositions of dialkyltelluriums and dialkylditelluriums in t-butylbenzene solvent have been studied by, EPR spectroscopy. On photolysis, di-t-butyl, diallyl, allyl methyl, and dibenzyl tellurium showed EPR spectra of t-butyl, allyl, allyl, and benzyl radicals respectively. Alkyl radicals were not detected directly on thermolysis in the range 300–370 K but, primary, secondary, and tertiary alkyl, benzyl and allyl telluriums gave spin adducts of the corresponding alkyl radical with nitrosodurene. Dimethyl tellurium was unreactive in the same temperature range. The rates of thermal decomposition of the diorgano telluriums at 315 K were found to be in the following order, as judged by the intensity of the spin adduct spectra: t Bu 2 Te ∼ t BuTeMe > (allyl) 2 Te ∼ allylTeMe > s Bu 2 Te > (benzyl) 2 Te > i Pr 2 Te > Et 2 Te > Me 2 Te. For dihex-5-enyltellurium the results were consistent with formation and cyclisation of hex-5-enyl and hex-5-enetelluryl radicals. In the case of dipent-4-enyltellurium, the results suggested that both exo - and endo -cyclisation of the pentene telluryl radicals were important. Di-isopropyl- and di-t-butyl-ditelluriums gave spin adducts of the corresponding alkyl radicals on thermolysis in the same temperature range as the monoalkyltelluriums.

Synthesis and decomposition studies of dialkyltellurides of type RTeR

Unsymmetrical dialkyltellurides of type RTeR′ suitable for use as precursors in the metalorganic vapour phase epitaxy (MOVPE) of cadmium mercury telluride (CMT) can be prepared by an alkyl exchange process. For certain organotellurium compounds, reaction of R2Te (R = alkyl, allyl) with R′2Te2 (R′ = alkyl) produces an equilibrium mixture containing RTeR′ and RTe2R′. Suitable selection of R and R′ allows good yields of RTeR′ to be prepared in high purity. ESR studies show that free radicals are formed on thermal or photochemical decomposition of R2Te and that the stability of (allyl)TeMe is very similar to that of (allyl)2Te but quite different from that of Me2Te.

Ultra-pure organotellurium precursors for the low temperature MOVPE growth of II/VI compound semiconductors

Abstract The preparation of a wide range of dialkyltellurium compounds of potential use as the precursors for the epitaxial growth of materials in the CdHgTe system is described. In general these are synthesised by a previously reported route. Methods for the purification of dialkyltelluriums by the formation and dissociation of adducts with Lewis acids are discussed together with the criteria necessary for their successful purification by this method. Finally, an assessment of purity of the alkyls is derived from the spectroscopic analysis of the metal alkyls and by SIMS analysis of layers of cadmium mercury telluride grown from the alkyls.

Assessment of Organotellurium Compounds for Use as Movpe Precursors

In order to reduce the growth temperature of (Hg,Cd)Te by MOVPE below 350–400°C, alternative organometallic precursors will be required which either decompose at a lower temperature than existing precursors or which absorb strongly at a suitable wavelength in the ultraviolet. The features required for a programme of assessment of organometallics are discussed. UV absorption spectra for dimethyltelluride, dimethylditelluride, diethyltelluride, di-iso-propyltelluride and diallyltelluride are presented and their usefulness as photolytic MOVPE precursors discussed.

Laser-induced epitaxial growth of CdTe

Abstract Laser-induced epitaxial growth of CdTe and laser patterning of substrates with epitaxial films is reported. Laser-induced deposition rates and photo-enhancement factors have been determined, using a 257 nm frequency-doubled argon-ion laser, to photolytically decompose diethyltelluride or dimethylditelluride combined with dimethylcadmium. These parameters and the UV absorption spectra have been used to anticipate photo-deposition conditions for selective-area epitaxy.