Chemische Transportreaktionen. IX. Der Transport von TiN mit HCl im Molybdänröhrchen

Abstract

Die Umsetzung von TiN mit HCl, bei der H2, N2 und die gasförmigen Chloride TiCl4, TiCl3 und TiCl2 nebeneinander entstehen, verläuft oberhalb 1300°C hinreichend schnell und reversibel, so daß sie den chemischen Transport von TiN im Temperaturgefälle ermöglicht. Im Zusammenhang hiermit wurde eine Arbeitstechnik für hohe Temperaturen entwickelt, bei der ein aus Molybdänfolie zusammengerolltes, elektrisch beheiztes Röhrchen als Reaktionsraum dient. Der Transporteffekt entspricht bei hinreichend hoher Temperatur dér Erwartung, wenn man als Modell die Diffusion zwischen Räumen zugrunde legt, in denen Gleichgewicht zwischen TiN und der Gasphase herrscht. Unterhalb 1200°C bleibt der Transport aus kinetischen Gründen – wegen der Stabilität der N2‐Molekel – unmeßbar klein.

The Transport of Gallium Arsenide in the Vapor Phase by Chemical Reaction

“…The data of Tables I and II show that for reactions [1] and [2] the equilibria are well over to the left so that the partial pressures of free halogen will be small (less than 10 -12 atm). Considering the 1 reaction 2AsC13(g) ~ 3C12(g) ~ ~-As4(g), for which from the data of Table I, AF%000 ~ +122.8 kcal, it may be seen that AsC18(g) will be negligible.…”

“…The species GaI2(g) and AsIs(g) are unstable in this temperature range. Ga (1) and As2(g) are only important at very low total (free and combined) iodine pressures. Calculations show that they may be neglected in determining the transport equilibria in the temperature range here considered.…”

“…The following reactions, in which X denotes C1 or I, are sufficient to describe the equilibria between the species involved in the transport of gallium arsenide by iodine or chlorine in the presence of hydrogen, between 800 ~ and 1300~ GaX~(g) ~ GaX(g) + X2(g) [1] 1 2GaX(g) +~-As4(g)e~--2GaAs(s) -~ X2(g) [2] X2(g) ~ 2X(g) [3] H2(g) § X2(g) ~ 2HX(g) [4] If no hydrogen is present, reaction [4] is not involved, and because the pressure of free halogen is small, reaction [3] may be omitted and reactions [1] and [2] replaced by the single reaction…”

“…The standard free energy changes as a function of temperature for reactions [1][2][3][4] are obtained directly from the values of Table I and are listed in Table II. They are compared with the available experimental data in Table III.…”

“…Deposition from chemically reacting species from the vapor phase offers particular advantages in the preparation of crystalline stoichiometric semiconducting compounds which cannot readily be obtained by freezing a melt because of peritectic decomposition, incongruent melting, or the need to work at excessively high temperatures or pressures. Since the extensive work on chemical transport reactions by Sch~fer (1) and the observation by Antell and Effer (2) of the transport of gallium arsenide contained in a sealed tube, down a temperature gradient by reaction with iodine, the adoption of such methods has been widespread both for the preparation of gallium arsenide in quantity and for its deposition in the form of thin films. The aims of this paper are to analyze the physical chemistry of the reactions in the gallium-arsenic-halogen-hydrogen systems for the transport of this compound by iodine or chlorine and to determine the rate of transport in specific processes.…”