Solubilities of CdTe in the liquid III metals

Abstract

Recently, CdTe has been studied extensively because of its possible applications in radiation detectors, solar batteries and other opto-electronic devices [1]. Liquidus solubility data of various solutes in solvents are needed to grow crystals by a liquid-phase epitaxial growth method or to make ohmic or rectifying contact by an alloying method. For these reasons, the phase diagrams of the CdTe-Bi [2], CdTe-Sb [2], CdTe-Sn [3], CdTe-Pb [3], CdTe-In [4], CdTe-CdCI2 [5] and CdTe-CdBr2 [5] systems have been studied by the present authors. The column IIlb metals such as Ga, In and Yl may be expected to be solvent metals suitable for the liquid-phase epitaxial growth of CdTe, because they have a low melting point and do not form an intermediate compound with CdTe. The phase diagrams of CdTe-Ga [6], CdTe-In [4, 7] and CdTe-T1 [8] systems are already presented in the literatures, but precise liquidus solubilities of CdTe in the IIIb metals have not been presented. In this paper the liquidus solubilities of CdTe in Ga, In and T1 were measured by differential thermal analysis (DTA) and disolution methods, with particular attention being paid to the lowtemperature region where the solubility becomes quite small. The single crystals of CdTe were grown by the Bridgman method from Cd and Te, both of 99.999% purity. The purities of Ga and In were 99.999% and that of Tl was 99.9%. Details of the DTA apparatus have been described in a previous paper [2]. The specimen for DTA was sealed in an evacuated quartz ample. The DTA peak becomes more obscure with decreasing CdTe content in the specimen. At the same time, since supercooling phenomena are prone to occur, it becomes very difficult to determine the liquidus temperature by the DTA method. In such cases, the liquidus temperature was determined by the dissolution method. At each temperature, liquid III b metal was saturated with one or two pieces of CdTe crystal in the evacuated quartz ample for sufficient time and quenched. After equilibration, the Ga or In metal which had adhered to the CdTe crystals was amargamated with Hg and removed from the CdTe in dilute nitric acid. The solubility was calculated from the weight loss of the CdTe crystals. Identification of the phases in the systems and lattice parameter measurements were carried out using an X-ray diffractometer (Type cl-3F, from Rigaku Denki Co.,). The metal-rich side of the liquidus solubility curves of the CdTe-Ga, CdTe-In and CdTe-T1 systems are shown in Fig. 1. Solid marks and open marks indicate data points determined by the DTA method and the dissolution method, respectively. In the CdTe-Ga and CdTe-In systems, thermal effects which were assigned to liquidus and eutectic lines were detected by the DTA method, while in the CdTe-T1 system other thermal effects were detected near 653 and 498 K. The thermal effect at the 498K was assigned to the phase trans-