Process for the construction of semiconductor lasers and lasers

Details Process for the construction of semiconductor lasers and lasers Process for the construction of semiconductor lasers and lasers

1990-07-24

1991-10-08

Chaudhuri, Olik

Fishing, trapping, and vermin destroying

148DIG95, 357 20, 372 46, 437133, 437152, 437905, 437987, H01L 2120, H01L 21225

Patent

active

050554220

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to processes for the construction of semiconductor lasers and lasers constructed in this manner.
A semiconductor laser is essentially composed of a crystalline-type active medium based, for example, on gallium arsenide, to which medium an electrical energy referred to as the "pumping electrical energy" is applied by means of two electrodes situated respectively on either side of the crystalline material.
Moreover, in order to obtain the stimulation of the optical radiation energy, the active medium is placed, as for all lasers, in a resonant optical cavity formed from two reflecting mirrors, at least one of which is partially transparent in order to permit the light energy stimulated inside the optical cavity to emerge from this cavity.
In the field of semiconductor lasers, the mirrors of the optical cavity are formed, for example, of multidielectric layers placed directly on the crystalline active material. This process for the construction of the elements of a resonant optical cavity is, moreover, conventional and well-known. However, there are other processes in existence, for example the stacking of semiconductor layers integrated into the actual structure of the crystal or of the substrate which supports the crystal.
The current techniques permit fairly well the respecting of all these features but there are still a certain number of problems, especially to arrange on the active medium the electrodes for supplying the pumping electrical energy. This problem arises more particularly in the case where a plurality of active media are implanted on a single base substrate, alongside one another essentially for the purpose of obtaining a plurality of light beams having substantially parallel directions of emission, all the more so as, in order to obtain a composite beam equivalent to a relatively dense and homogeneous single beam, it is essential that the active media should be disposed side by side, as close as possible and in such a manner that the axes of the resonant cavities are all oriented substantially perpendicularly to the surface through which the beam must be emitted.
The problem posed is then the construction of the electrodes for the supply of the electrical energy, being aware that these electrodes can be disposed only on the face with which at least one of the two mirrors of the optical cavity is flush.
A construction of semiconductor lasers is already known, in which the supply of the electrical energy is undertaken substantially in the plane of one of the mirrors of the optical cavity of the laser. This construction is obtained in the following manner. A start is made by depositing, on a support substrate, a first set of layers constituting a first mirror of the optical cavity. On this first set of layers there is deposited by epitaxy a second set of crystalline layers, for example of gallium arsenide, over a thickness equal to that which is necessary to obtain the desired laser active medium, and then a third set of layers, for example multidielectric, constituting the second mirror of the optical cavity, the lateral dimensions, length and width, of these three sets of layers being greater than those of the semiconductor laser to be obtained finally.
When this multilayer stack has been completed, a circular channel known by persons skilled in the art under the name of "mesa" is hollowed out, by removing a part of the two or three sets of layers to form, to some extent, a column.
In the channel there are then disposed, by any means, two types of differing materials, by laterally surrounding the column and in contact at least with the second set of layers; this forms the two electrodes. These two materials are, for example, semiconductor materials of P type and of N type respectively, such as gallium and aluminium arsenide doped respectively with zinc and silicon. The two materials fill the channel flush with the upper level of the third set of layers and, on their face flush with this level, there are respectively fixed two conductors of the electrical energy

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