Abstract: A heat treatment chamber (30) is provided comprising a treatment region containing a charge (5) of compound material comprising a plurality of n atomic species, each atomic species being associated with at least one gas species. The chamber (30) is placed in a furnace (7). The chamber has a gas permeable barrier, constituted by a plug (4) and wadding (6), which partially encloses the treatment region. The barrier serves as an effusive hole to inhibit, but not prevent, gas vapour release, thereby to elevate the gas vapour pressure in the treatment region. Application of inert gas through a valve (8) is also used to increase background pressure in the treatment region during heat treatment. The elevated gas pressures present in the treatment region during treatment are measurable in an absorption cell (3) adjacent to the treatment region. It is thus possible to monitor the gas pressures during heat treatment and thereby stop the heat treatment once a desired charge stoichiometry is achieved.

Abstract: A heat treatment chamber (30) is provided comprising a treatment region containing a charge (5) of compound material comprising a plurality of n atomic species, each atomic species being associated with at least one gas species. The chamber (30) is placed in a furnace (7). The chamber has a gas permeable barrier, constituted by a plug (4) and wadding (6), which partially encloses the treatment region. The barrier serves as an effusive hole to inhibit, but not prevent, gas vapour release, thereby to elevate the gas vapour pressure in the treatment region. Application of inert gas through a valve (8) is also used to increase background pressure in the treatment region during heat treatment. The elevated gas pressures present in the treatment region during treatment are measurable in an absorption cell (3) adjacent to the treatment region. It is thus possible to monitor the gas pressures during heat treatment and thereby stop the heat treatment once a desired charge stoichiometry is achieved.

Abstract: An interface circuit to the output of a programmable voltage ramp generator for decreasing the minimum voltage step of such a generator having two voltage channels and a minimum voltage step greater than 1 millivolt. The interface circuit receives an input from each of the two voltage channels (V.sub.2, V.sub.3), along with an inserted voltage (V.sub.1). The circuit includes a summing amplifier for (i) compressing the minimum voltage step from one voltage channel (V.sub.2) by a factor equal to or greater than such minimum voltage step, (ii) adding the voltage from the other channel (V.sub.3) to the compressed voltage, and (iii) subtracting the inserted voltage (V.sub.1) (or adding an inserted voltage which is negative). The inserted voltage (V.sub.1) is equal in magnitude to the maximum output value from the voltage channel that has the voltage compressed (V.sub.2). The output of the summing amplifier (V.sub.out) may be represented by:V.sub.out =(V.sub.3 /X)+(V.sub.2 /Y)+(V.sub.

Abstract: Undoped GaAs single crystals with low dislocation density, low impurity content, 0.20-1 Kg in weight and constant diameter of 1"-2" (inches), said single crystals being obtained with LEC technology at low or high pressure with synthesis of the polycrystal in situ and subsequent growth of the single crystal.