Low threshold microcavity light emitter

DETAILED DESCRIPTION It is a purpose of the present invention to provide a vertical cavity surface emitter wherein the spacer layer separating two cavity reflectors contains both internal optical and electrical confinement to achieve strong light confinement to a small area, low loss optical mode.
While previous teachings suggest that the strong optical confinement need be achieved along the full length of the laser cavity (Jewell et al.
, 1991; Numai et al.
, 1993), a discovery of the present invention is that index confinement is optimally placed within the laser cavity spacer layer of the otherwise planar cavity to greatly reduce lateral diffraction loss but without the increase of optical scattering loss due to sidewall roughness or multiple apertures, and achieve a small area, low loss optical mode.
In addition, by retaining a planar cavity a low electrical conductivity contact is made to the cavity, and both high electrical current injection efficiency and high optical mode confinement is readily achieved.
Furthermore, for the vertical cavity surface emitting laser the index confinement is optimally placed within a lateral dimension characteristic of the vertical cavity design for laser operation, and more optimally within a lateral dimension characteristic of the coherence of the spontaneous emission from the electrical semiconductor charge carriers of electrons and holes.
For present day AlAs/GaAs/InGaAs semiconductor light emitters, these lateral dimensions are less than 10 .
mu.
m and easily reach 2 .
mu.
m in diameter.
Using such designs the present inventors have substantially reduced the required threshold drive level of a vertical cavity surface emitting laser over that of prior art in which threshold drive currents were typically greater than 0.
5 mA, and more often greater than 2 mA, to less than 0.
1 mA with room temperature operation.
The low refraction index layer allows the lateral size reduction of the optical mode below that characteristic of the otherwise planar vertical cavity design, while maintaining low diffraction loss