Divinylmercury as a Precursor in the Metalorganic Molecular Beam Epitaxy of Hg Containing II-VI Materials
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DIVINYLMERCURY AS A PRECURSOR IN THE METALORGANIC MOLECULAR BEAM EPITAXY OF Hg CONTAINING I-VI MATERIALS
J. J. Zinck and D. Rajavel Hughes Research Laboratories, Malibu, California
ABSTRACT We have used x-ray photoelectron spectroscopy, temperature programmed desorption, and epitaxial growth experiments to study the feasibility of using divinylmercury (DVHg) as a precursor for metalorganic molecular beam epitaxial (MOMBE) growth of Hg-containing II-VI materials. The surface chemistry associated with the interaction of DVHg and Te was investigated using polycrystalline Te (poly-Te) films as the substrates for DVHg adsorption. DVHg dissociatively adsorbed on a poly-Te surface at temperatures as low as -118 0 C. However, the DVHg dissociation probability was temperature dependent and substantially less than unity when extrapolated to typical Hgl 5 CdxTe growth temperatures of 150-200'C. Preliminary results from MOMBE growth experiments showed that successful MOMBE growth of HgTe on CdTe/ZnTe//GaAs using DVHg and thermally precracked diethyltellurium was only possible when the DVHg was also thermally precracked. Simultaneous exposure of atomic H and DVHg to a poly-Te surface significantly enhanced the dissociative adsorption of DVHg, indicating that the presence of atomic H in the growth environment may be an effective alternative to precracking DVHg for MOMBE growth. INTRODUCTION The current industry standard for infrared detector materials is Hgl 5 Cd5 Te because it has the advantageous features of a strong absorption coefficient, high mobility, and a bandgap which can be tuned from 0 to 1.6 eV by a suitable selection of x value. 1 However, growth of high quality Hgl. 5 Cd5 Te requires precise control of the constituent fluxes as small changes in x value produce significant changes in cutoff wavelength of the detector. In the case of elemental Hg, flux control is complicated by the low condensation coefficient and high vapor pressure of the element at typical molecular beam epitaxial (MBE) growth temperatures of 150-200'C. 2.3 These two factors necessitate a substantial elemental Hg overpressure to be used during conventional MBE growth which imposes a significant load on the pumping system and requires special handling facilities in the MBE chamber itself. In addition, the elemental Hg flux in conventional MBE systems is controlled by the temperature of the Hg reservoir. Consequently, when a change in Hg flux is desired the temperature of the reservoir must be varied and stabilized. Metalorganic sources offer the advantage of feedback pressure control, by which rapid and reproducible flux variations can be precisely implemented. Additionally, selection of a metalorganic mercury source which can be decomposed at the substrate surface may alter the incorporation kinetics of Hg, possibly leading to lower vacancy concentrations in the growing film, and also minimizing exposure of the growth system to elemental Hg. In this paper we report on investigations of divinylmercury (DVHg) as a precursor for metalorganic MBE (M
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