Adhesive bonding and miscellaneous chemical manufacture – Delaminating processes adapted for specified product – Delaminating in preparation for post processing recycling step
Patent
1982-09-27
1985-11-05
Bernstein, Hiram H.
Adhesive bonding and miscellaneous chemical manufacture
Delaminating processes adapted for specified product
Delaminating in preparation for post processing recycling step
C30B 2102
Patent
active
045511969
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of growing crystalline cadmium mercury telluride, the method comprising the steps of preparing a melt of cadmium mercury telluride in a sealed ampoule, and growing the crystalline cadmium mercury telluride from the melt by a vertical Bridgman process. Throughout this specification a vertical Bridgman process is understood to be a process in which a crystal is grown by slowly lowering a sealed ampoule containing a melt through a temperature gradient extending in a vertical direction so that crystallization begins at the bottom of the ampoule. The invention also relates to crystalline cadmium mercury telluride grown by this method.
When manufacturing semiconductor devices from a ternary semiconductor compound, a significant problem is to obtain adequate quantities of the crystalline ternary compound within a given range of compositions so as to provide material having desired properties, for example in the case of cadmium mercury telluride used in the detection of infra-red radiation, desired electro-optic properties. The usefulness of this crystalline material also depends on imperfections in the material.
The Accelerated Crucible Rotation Technique (A.C.R.T.) was proposed by H. J. Scheel and E. O. Schulz-Dubois in an article "Flux Growth of Large Crystals by Accelerated Crucible-Rotation Technique" in Journal of Crystal Growth 8 (1971) pp. 304-306. A.C.R.T. has been used in various crystal growth processes, for example in Czochralski growth and in solution and flux growth processes conducted in sealed containers. Problems of high vapour pressure of solvents used for the growth of crystals from high temperature solutions necessitated the use of sealed containers, and this prevented the use of normal stirring techniques. The main improvement in using A.C.R.T. in such cases has usually been to increase the size of the crystals grown by reducing nucleation, when compared with growth without stirring. Faster stable growth rates can be used because of the reduction of the thickness of the diffusion boundary layer induced by the stirring effects. A.C.R.T. has been used in Czochralski growth, for example to control the oxygen content gradient in silicon crystals, described in U.S. Pat. No. 4,040,895.
F. V. Wald and R. O. Bell describe (in Journal of Crystal Growth 30 (1974) pages 29-36) a travelling heater method of solution growth of CdTe from a solution in tellurium which was subjected during growth to A.C.R.T. The results obtained by this method showed that A.C.R.T. was only of modest effect (it could only increase the growth rate for which inclusion-free crystals could be obtained by a factor of two), because the natural convection currents generated under the particular experimental conditions were already very strong indeed. Furthermore, it was found that the undesirable tendency of CdTe crystals grown by this method to twin, form stacking faults or low angle grain boundaries, was still present when using A.C.R.T.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings,
FIG. 1 is a graph on which the molar fraction x of CdTe in Cd.sub.x Hg.sub.1-x Te ingots grown from melts having an initial composition Cd.sub.0.19 Hg.sub.0.81 Te is plotted against L, the distance from the tip of the ingot, and
FIG. 2 is a graph in which the radial composition variation of cadmium mercury telluride ingots produced from melts having an initial composition of Cd.sub.0.19 Hg.sub.0.81 Te is plotted against .lambda..sub.e.
FIG. 3 is a schematic longitudinal section of a rocking furnace,
FIG. 4 is a schematic side-sectional elevation of a furnace used for growing crystalline cadmium mercury telluride by a method according to the invention,
FIG. 5 is a longitudinal temperature profile of the furnace shown in FIG. 4, and
FIG. 6 is a graph in which the radial composition variation of cadmium mercury telluride ingots produced from melts having an initial composition of Cd.sub.0.12 Hg.sub.p.88 Te is plotted against .sub.e.
An ingot of cadmium mercury telluride grown at a rate of 0.5 mm per ho
REFERENCES:
Bartlett et al., Jl. of Crystal. Growth 46, (1979), pp. 23-29.
Scheel et al., Jl. of Crystal. Growth 8, (1971), pp. 304-306.
Capper Peter
Gosney John J.
Bernstein Hiram H.
Spain Norman N.
U.S. Philips Corporation
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