Investigation of the CuGa_xIn_1–xSe₂ solid solutions

Abstract

Investigation of the CuGaJn, -,Se, Solid SolutionsThe CuTnSe, and CuGaSe, semiconducting compounds refer to the ternary AIBIITCVr type compounds crystallizing in the chalcopyrite structure and are the electron analogues of the AI1BV1 ones. The interest aroused by them is due to the fact that they are promising materials for fabricating light emitting diodes (WAGNER et al.), solar cells based on heterotransitions with the ATIBV1 compounds (SHAY et al. ; ROMEO et al. as well as nonlinear materials (BOYD et al.) Of some interest are the solid solutions based on the CuInSe, and CuGaSe, compounds, making it possible to change smoothly different physical-chemical parameters. Up to now the literature data on the CuGa,Inl-,Se, solid solution properties is scarce (HORIG et al. ; PAORICI et al.). The aim of the present paper is to plot the phase diagram and to study the growth conditions of single crystals as well as their dislocation structure.Copper (99.999%), indium, sulphur, and selenium (99.9999%) were used as starting materials for obtaining the CuGaSe,, CuInSe, ternary compounds and the CuGa,Inl -&e, solid solutions. The synthesis of the above mentioned compounds and solid solutions was carried out in a vertical furnace in doubIe quartz ampoules. The total charge was 10-15 g. The synthesis was made in the following way : the temperature of the furnace was slowly raised up to 650-700 "C and the ampoule was kept a t this temperature for 2 hr, then up to 1050 -1100 "C, with the melt being kept vibrating for 2 -3 hr. Then the melt was quenched up to room temperature. To achieve homogeneity of the obtained ternary CuGaSe,, CuInSe compounds and the CuGa,Inl-,Se, solid solutions the annealing was carried out for 20 d.The composition of the CuGaSe, and CuInSe, ternary compounds and the CuGa,Inl-,Se, solid solutions was tested by chemical analysis. The Cu, Ga, In, and Se elements were determined using the methods given by SRARLO, and ISHCHENKO e t a l . The chemical analysis data given in Table 1 from which it is seen that the experimental data agree with the calculated ones.The homogeneity and structure of the investigated compounds and solid solutions were determined by an X-ray method. X-ray patterns were taken by a URS-50 IM apparatus (copper filtered radiation). The investigations showed that the CuGaSe,, CuInSe, ter nary compounds and their solid solutions crystallize in the chalcopyrite structure (the I42d space group). The lattice periods, calculated according to well resolved doublet lines (424), (2281, (512), and (336) are for CuGaSe, a = 5.616 5 0.002 A; c = 11.016 f 0.005 A and for CuInSe, a = 5.782 f 0.002 A ; c = 11.620 & 0.005 A. The change of the lattice periods a and c obeys Vegard's law.The temperature of phase transformations were determined by the DTA method on an apparatus described by BELEVICH et al. with an accuracy of &2". The DTA measurements

The CuInSe2–CuGaSe2–2CdSe system and crystal growth of the γ-solid solutions

“…Our powder XRD results confirm the data from [22,23] that all samples of the CuInSe 2 -CuGaSe 2 system are single-phase ones at 870 K. The variation of the lattice constants with the solid solution composition is in agreement with Vegard's law (Fig. 2).…”

“…The constructed phase diagram (Fig. 3) agrees well with the data of [22] in the range of low temperatures. However, there are two additional fields (2 and 3) at liquidus temperatures at the CuGaSe 2 -rich side, which are caused by the peritectic formation of copper selenogallate.…”

“…[22] is not consistent with the fact that CuGaSe 2 is formed after a peritectic reaction in the Cu 2 Se-Ga 2 Se 3 system [16][17][18]. Therefore, we have re-investigated the system.…”

“…The phase diagram of the CuInSe 2 -CuGaSe 2 system was established in [22]. A continuous range of solid solutions is formed between the components, so the phase diagram is referred to type I according to Rozeboom's classification.…”

The CuGaSe2–CuInSe2–2CdS system and single crystal growth of the γ-phase

“…This phase diagram in the CuGaSe 2 -rich part at liquidus temperatures contains several fields that correspond to the primary and secondary crystallization of the g 0 -phase, which takes part in the peritectic reaction yielding CuGaSe 2 in the system Cu 2 Se-Ga 2 Se 3 . A continuous range of the chalcopyrite solid solutions based on LT-modifications of CuInSe 2 and CuGaSe 2 exists in the system at 870 K [23][24][25]. Single crystals of the CuGa x In 1 À x Se 2 solid solutions have the chalcopyrite structure and are of the p-type [25].…”