Mode reduction, Q loss, gain saturation, and bandfilling modification of the light versus current characteristics of thin (∼0.9 μm) quantum well heterostructure lasers

Data are presented demonstrating the effect that cavity length, and thus Q, has upon quantum well heterostructure edge‐emitting laser diodes that are reduced to microcavity thickness. The lasers, with reduced mode density and enhanced spontaneous emission, are defined vertically by a Ag top‐contact mirror and a closely spaced (∼0.9 μm) high‐contrast AlAs native oxide‐GaAs distributed Bragg reflecting bottom mirror. For shorter and shorter diode lengths (700→70 μm, and still lesser mode density) the light versus current (L–I) characteristic below threshold is at first steeper and steeper (amplified stimulated emission), until, at a diode length of ∼100 μm, the loss in Q and insufficient gain are manifest as a downward bend in the L–I curve and a shift to higher threshold current where bandfilling to a higher state (shorter wavelength) contributes more gain.