JOURNAL OF MATERIALS SCIENCE LETTERS 18 (1 9 9 9 ) 1095 – 1097 Elaboration of (Bi 1-x Sb x ) 2 Te 3 thin films by metallorganic chemical vapor deposition B. ABOULFARAH, A. MZERD Universit ´ eM ed V Agdal, Facult ´ e des Sciences de Rabat, D ´ epartement de Physique, Laboratoire de Physique des Mat ´ eriaux, Rabat, Maroc A. GIANI, A. BOULOUZ, F. PASCAL-DELANNOY, A. FOUCARAN, A. BOYER Centre d’Electronique et de Micro-Opto ´ electronique de Montpellier, UM II, UMR 5507 CNRS, Place E. Bataillon, 34095 Montpellier C ´ edex 05, France Metallorganic chemical vapor deposition (MOCVD) of (Bi 1−x Sb x ) 2 Te 3 (0.25 ≤ x ≤ 0.9) using trimethylbis- muth, triethylantimony and diethyltellerium has been obtained on pyrex substrates. A polycrystalline struc- ture has been confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) observation. Energy dispersive X-ray spectroscopy (EDX) has been used to determine the chemical composition. We have studied the solid composition of antimony (x s ) as func- tion of its vapor composition (x v ). The electrical proper- ties of the alloys have been determined by using the Hall effect measurements. The measurement of the Seebeck coefficient revealed that p-type (Bi 1−x Sb x ) 2 Te 3 thin films are promising for thermoelectric applications. The alloys of bismuth telluride with antimony tel- luride are among the better p-type materials available for thermoelectric applications near room temperature. Many researchers have studied the electrical and trans- port properties of Bi 2 Te 3 [1–5] and Bi 2 Te 3 –Sb 2 Te 3 [6–10]. Mzerd et al. [11] studied the thermoelectrical properties of Bi 2 Te 3 and its alloy Bi 0.1 Sb 1.9 Te 3 pro- duced by molecular beam deposition and constructed thermal sensors based on [Bi 0.1 Sb 1.9 Te 3 (p)−Bi 2 Te 3 (n)] with a good sensitivity. Joraide [12] proved that the tem- perature affects the anisotropic properties of the elec- trical resistivity, and the Seebeck coefficient of a fine grain (Bi 2 Te 3 ) 25 –(Sb 2 Te 3 ) 75 p-type alloy. Some trans- port properties of flash-evaporation Bi 0.5 Sb 1.5 Te 3 films and their dependence on various annealing conditions were studied by V¨ olklein et al. [13]. (Bi 1−x Sb x ) 2 Te 3 thin films have been deposited using several techniques such as flash evaporation [13], sputtering [14] and molecular beam epitaxy [11]. In this letter we report for the first time the growth of (Bi 1−x Sb x ) 2 Te 3 (0.25 ≤ x v ≤ 0.9) by MOCVD. We have presented the optimal experimental conditions for the elaboration, and we have studied the morphological aspects and the composition of the thin films. The in- vestigation of the electrical and thermoelectrical prop- erties such as carrier concentration ( p), mobility (µ), resistivity (ρ ) and thermoelectric power (α) is also presented. The electrical resistivity and Hall effect measurements were performed by the Van Der Pauw method at room temperature. The thermoelectric power was measured from the variation of the Seebeck elec- tromotive force versus the temperature. Thin layers of (Bi 1−x Sb x ) 2 Te 3 were grown on pyrex substrates in a horizontal reactor at atmospheric pres- sure (7 ×10 2 Torr). Trimethylbismuth (TMBi), triethyl- antimony (TESb) and diethyltellerium (DETe) were used, respectively, as bismuth, antimony and tellerium organometallic sources. The TMBi, TESb and DETe sources were maintained at 5, 20 and 20 ◦ C, respec- tively. Hydrogen was used as a carrier gas with a flow rate equal to 6 slm to obtain a better cracking efficiency [5]. The growth temperature (T s ), the VI/V ratio ( R VI/V = P DETe /( P TMBi + P TESb )) and the group V partial pres- sure  P v = ( P TMBi + P TESb ) were, respectively, 450 ◦ C, 9 and 0.8 × 10 −4 atm. The x v = ( P TESb / P v ) ratio was varied in the range of 0.25–0.9. We observed that the stoichiometry of the result- ing thin films depended on the growth parameters. The compositions were measured by an EDX micro- analyzer. The variation of the solid composition x s at growth conditions, as a function of the x v ratio in the range of 0.25–0.9, is reported in Fig. 1. It is observed that the dependence of x s to x v is nearly linear and the ratio x s to x v is found to be approximately unity. The typical composition found for x v = 0.75 appears to be very close to stoichiometry having 11.55 at % Bi, 26.59 at % Sb and 61.85 at % Te. The film showed a small de- ficiency in Sb and an excess of Te, which is due to the high-pressure ratio R VI/V = 9. Figure 1 Antimony solid composition x s as a function of x v = P TESb / ( P TESb + P TMBi ) (T s = 450 ◦ C; R VI/V = 9; P TESb + P TMBi = 0.8 × 10 −4 atm). 0261–8028 C  1999 Kluwer Academic Publishers 1095