Coating processes – Electrical product produced – Welding electrode
Patent
1984-11-02
1987-05-12
Page, Thurman K.
Coating processes
Electrical product produced
Welding electrode
427 85, 427 86, 118641, 219121L, B05D 512
Patent
active
046649409
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the formation of a flux of atoms of an element, which is more particularly usable in a process and an apparatus for the deposition by epitaxy or deposition under ultravacuum of layers based on III-V semiconductors or their ternary and quaternary derivatives.
For some years now, the development of components for optoelectronics and microelectronics has required the formation of thin layers based on III-V semiconductors or their ternary and quaternary derivatives. Generally, such layers are produced by epitaxy on a binary substrate and the presently used epitaxy procedures are liquid phase epitaxy, vapour phase chemical epitaxy and molecular beam epitaxy. The latter has intrinsically higher performance levels, particularly for obtaining very thin layers having e.g. a thickness of a few .ANG., which are also very flat, have a widely varying stoichiometry and have very abrupt interfaces. However, the development of this procedure of deposition by epitaxy remains difficult and causes certain problems, because it is difficult to avoid contamination of the layer and to accurately check the incorporation of the doping elements and the elements of group V of the periodic classification of elements.
In this epitaxy procedure, the molecular beams of element V, e.g. P or As, are formed either by using a Knudsen cell containing the solid element or one of its compounds, or by using gases decomposed in situ and as described in the documents: S. L. Wright and H. Kroemer, J. Vac. Sci. Technol 20(2), 143 (1982) M. B. Panish, J. Electrochem. Soc. 127(12), 2729 (1981) and A. L. Cawa Appl. Phys. Lett. 38(9) 701 (1981). In such methods, the element of group III is brought onto the substrate in the form of an atomic beam or a molecular beam obtained by heating a crucible containing the said element in the pure state. Therefore, these methods have certain disadvantages due either to the complexity of the growth equipment, or to the presence of hot furnaces in the deposition enclosure, which produces a difficultly controllable contamination. However, in view of the fact that certain chemical species are brought onto the substrate in the form of molecules, whereas other species are brought in the form of atoms, the superficial reaction of the beam with the substrate is complex and is often the origin of unintentional doping or the creation of deep centres.
For the deposition of layers of compound III-V, such as GaAs, the use of pulsed lasers has also been considered for producing GaAs films from a GaAs target, as described in the article: Crystal Research and Technology Vol. 16, No. 8, 1981, pp. 887-891.
However, under the conditions described in this article, it is not possible to obtain a beam of atoms of element V and this does not make it possible to eliminate the complex reactions referred to hereinbefore with respect to the substrate.
The present invention relates to a process for the formation of a flux of atoms of an element, which can more particularly be used for the deposition of layers by epitaxy or by deposition under an ultravacuum, in order to obviate the disadvantages referred to hereinbefore.
The inventive process for forming a flux of atoms of an element is characterized in that it consists of irradiating a target constituted by a compound of said elements by means of a pulsed laser, whose energy density by pulse is at least equal to the emission threshold of atoms of said element and is below the ablation threshold of said element or said compound.
Thus, by appropriately choosing the energy and pulse duration of the laser used,it is possible to extract a target constituted by a compound of an element, a flux essentially constituted by atoms of said element. It was known that by irradiating a solid target with a high power laser beam, a vaporization on the target surface was obtained, together with a desorption of the atoms constituting the same in the form of different atom groups. When the target is irradiated by means of a continuous laser, the target surface is h
REFERENCES:
patent: 4463028 (1984-07-01), Laude
patent: 4511595 (1985-04-01), Inoue
patent: 4529617 (1985-07-01), Chenevas-Paule et al.
Bensoussan Marcel
Moison Jean-Marie M.
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