Journal of Crystal Growth 113 (1991) 53—60 53 North-Holland Structural characterization of Hg 0 78Cd022Te/CdTe LPE heterostructures grown from Te solutions S. Bernardi CSELT, Via Reiss Romoli 274, 1-10148 Torino, Italy C. Bocchi, C. Ferrari, P. Franzosi and L. Lazzarini MA SPEC — CNR, Via Chiavari 18/A, 1-43100 Parma, Italy Received 30 November 1990; manuscript received in final form 26 February 1991 Hg0 78Cd022Te epilayers have been grown on CdTe substrates by slider liquid phase epitaxy. The crystal quality of the epitaxial material has been studied in as-grown structures and chemically or mechano-chemically prepared bevels using X-ray topography, double crystal diffractometry and transmission electron microscopy. It has been found that the bulk epilayers exhibit a very high crystal quality, as evidenced by the relatively low density of dislocations and the very narrow Bragg peaks. In contrast, a high dislocation and precipitate density and a broadening of the Bragg peak have been detected in the epilayer near the interface. Finally, a Hg decrease in the layer and a corresponding Hg increase in the substrate close to the interface have been observed. 1. Introduction them in bulk crystals. Moreover, the major ad- vantage of the epitaxial techniques is making the It is well known that Hg1 ~Cd~Te is the most advanced photovoltaic devices more practicable; important semiconducting material for infrared for this reason, Hg1 - ~Cd~Teis now appearing as a detectors and imaging arrays. Nowadays, there is promising material for optical telecommunication a strong interest in fabricating linear or two-di- systems too. mensional arrays with increasing number of ele- It is a common opinion that the properties of ments, which require large Hg1 — ~Cd~Teareas. De- the heterostructure are strongly dependent on the spite the progress indoubtedly made in the bulk crystal quality of the bulk epilayer as well as of crystal growth technology, Hg1 _~Cd~Te large di- the epilayer—substrate interface. From the point of ameter bulk ingots cannot be obtained since the view of the extended defects, threading disloca- quartz-tube cross-section area must be limited to tions propagating from the substrate into the layer, only a few square centimeters to withstand the misfit dislocations which are formed to accom- high pressure at the typical growth temperature of modate the lattice mismatch, precipitates and other 1100 K. defects originating during the epitaxial deposition On the contrary, large area Hg1 _~Cd~Te layers or the post-growth cooling are all able to affect can be epitaxially grown on suitable substrates by negatively the electro-optical properties of the a variety of deposition techniques [1]. In addition layer. to the larger area, Hg1 ~Cd~Te layers usually ex- In spite of the relevance of the structural char- hibit a better crystal quality than bulk crystals do; acterization, to date only a few papers dealing for example, no subgrain boundaries are formed with such studies in Hg1 ~Cd~Te layered struc- in the epitaxial material grown on single crystal tures have been published [2—7]. The present paper substrates, while it is quite common to observe reports the results of an investigation of the struc- 0022-0248/91/$03.50 © 1991 — Elsevier Science Publishers B.V. (North-Holland)