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Group III Nitride Based Compound Semiconductor Laser Description OF Preferred Embodiments

A plurality of such devices were formed on a single wafer of sapphire substrate and cut apart with a diamond cutter in directions parallel to the optical path of each cavity and by means of cleavage in directions perpendicular to the optical path (i.e., normal to the paper).

The sapphire crystal is a hexagonal prism,in which the relationship between the c axis and the face a is also shown. Obviously, the c axis lies in the plane of face a of the sapphire substrate 1. Hence, the sapphire substrate 1 and the overlying layers 2 - 8 are cleaved along two lines, producing a laser cavity whose end faces A and B are specular.

Sapphire substrates 250 - 300 µm that had GaN grown on the face a could be readily cleaved in directions parallel to the c axis of the substrate but could be cleaved only with much difficulty in directions not parallel to the c axis. When GaN was grown on face c of sapphire substrates, it was difficult to create a laser cavity with an enhanced degree of parallelism between both end faces since the substrates readily broke in all directions. It should be noted that the crystal direction of GaN aligned with the c axis irrespective of whether it was grown on face a or c of the sapphire substrate.

Therefore, one can understand from these experimental data that planes of the highest surface precision are achieved if GaN grown on face a of a sapphire substrate is cleaved in directions parallel to the c axis of the substrate.


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