A new method for the preparation of crystalline Ga x Se 1-x P. Gupta, P.K. Bhatnagar * Department of Electronic Science, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi 110 021, India Received 10 February 1999; accepted 20 January 2000 Abstract X-ray powder data are presented and analysed for the semiconducting compound Ga x Se 1-x (x  0.2, 0.3, 0.4), which was prepared by the melt-quenching method. X-ray diffraction shows the crystalline nature of the compound. This behaviour is anomalous and contrary to the normal practice because amorphous materials are obtained by the melt-quenching technique; but in the case of GaSe it has been proved that one can obtain the crystalline material by using the melt-quenching technique (which of course is a quicker process). Such behaviour may be attributed to the very low equilibrium time of the GaSe compound.  2000 Elsevier Science Ltd. All rights reserved. Keywords: A. Chalcogenides; B. Crystal growth; C. X-ray diffraction 1. Introduction There are many different techniques for the preparation of amorphous as well as crystalline materials. Normally, the melt-quenching technique has been used to grow amorphous materials [1,2] and the slow-cooling technique has been used to grow crystalline materials [3]. A number of binary and ternary compounds have been made in our laboratory (Sb x Te 1-x , Bi x Se 1-x , Pb 40-x Bi x Se 60 , etc.), and it has been observed that, except for Ga x Se 1-x , for all other materials studied so far by us, we obtained amorphous compounds using the melt-quenching technique. However, in the present work we have observed a different phenomenon for Ga x Se 1-x materials which have been reported to be used in the preparation of a number of devices: MOSFET- type application, IR detector, Solar Cell, compound semi- conductor heterostructure, etc. in the crystalline form [4,5], while in the amorphous form it is a potential candidate for optical memory applications [6]. It has also attracted attention as a semiconductor material for optoelectronic devices applications [7]. We have been able to grow crystalline Ga x Se 1-x using the melt-quenching technique and the crystallinity has been verified by X-ray diffraction (XRD) for three samples with three different compositions. 2. Experimental 2.1. Sample preparation The alloys of Ga x Se 1-x (x  0.2, 0.3, 0.4) were prepared from 5N-purity constituent elements Ga and Se. The quartz ampoules were cleaned with acetone and filled with materi- als (according to their atomic percentage). They were then evacuated to 10 -5 Torr and sealed under vacuum. The ampoules were slowly heated in a rocking furnace to reac- tion temperature, melted and kept for 24 h (1050°C) [8]. During alloying, the material is continuously stirred to make the melt homogeneous. After alloying, the material is quenched in ice-chilled water. The quenched samples were removed from ampoules by dissolving it in a mixture of HF + H 2 O 2 for about 20 h. The samples prepared were of reddish brown colour. 2.2. X-ray diffraction The samples were checked for their nature (crystalline/ amorphous). For this purpose XRD was carried out on SIEMENS Model D-500, CuK a ! l  1:5418  A: XRD was carried out for three different samples with different compositions (x  0.2, 0.3, 0.4) in powder form. 3. Results and conclusions Fig. 1 shows the XRD patterns of Ga x Se 1-x (x  0.2, 0.3, Journal of Physics and Chemistry of Solids 61 (2000) 1703–1705 0022-3697/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S0022-3697(00)00033-0 www.elsevier.nl/locate/jpcs * Corresponding author.