Method of making a compound semiconductor laser

DETAILED DESCRIPTION An object of the invention is the devising of a way of regulating epitaxial growth so that it will proceed to the vicinity of a given line and there be temporarily arrested without recourse to the use of a mask physically to effect this arrest.
The present invention is concerned with using the property of different nucleation characteristics for growth on different crystal planes to regulate epitaxial growth.
Planes providing easy nucleation will be covered rapidly during epitaxial growth while those on which nucleation is difficult will initially remain uncovered.
Thus selective epitaxy can be achieved.
According to the present invention there is provided a method of making a compound semiconductor buried rib heterostructure laser including the steps of epitaxially growing upon a semiconductor substrate three layers comprising an active layer sandwiched between upper and lower passive layers of higher band gap and lower refractive index material than that of the active layer, of selectively etching through said active and passive layers to leave a protruding rib whose sides are profiled having regard to the crystal orientation such that in a subsequent step of epitaxial regrowth the nucleation on the sides of the rib at and above the active layer is discriminated against by said profile in favour of nucleation beneath said active layer whereby in said regrowth the regrowth up the sides of the rib is temporarily arrested in the vicinity of the junction between the active layer and the lower passive layer.
The invention is applicable to lasers fabricated in compound semiconductor materials generally, but will be exemplified in the context of compound semiconductors of the zinc blende type.
The selective growth properties are not usually noticeable in the GaAs/(Ga,Al)As system under growth conditions normally used for growth of these materials, but are more pronounced in the growth conditions typically used for liquid phase epitaxy in the InP/(In,Ga)(As,P) system.
The reason for this selectivity is believed to originate in the structure of zinc blende type crystals and its manner of growth by liquid phase epitaxy