Narrow-beam five-layer (GaAl)As/GaAs heterostructure lasers with low threshold and high peak power

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Abstract
A variety of (GaAl)As/GaAs heterostructure injection lasers have been fabricated with two pairs of heterojunctions, the inner pair for carrier confinement and the outer pair for optical confinement. Asymmetrical versions of this design have given, at one extreme, threshold current density Jt at 300 K as low as 500 A/cm2 and at the other extreme far‐field angular beam widths to the half‐power point of 15° with Jt2, for 500‐μm‐long sawn cavity lasers with reflectors on one face. The incremental quantum efficiency from one end of 300‐μm‐long lasers with reflectors was over 40%. The peak optical power from lasers of 100 μm width was up to 3 W for 200‐ns pulses. The temperature variation of threshold over the range 290–355 K was Jt355/Jt290∼1.5. Double‐heterostructure lasers with narrow active layers and 20% AlAs confinement steps gave almost comparable performance in Jt and beam width (650 A/cm2 for 33° and 1200 A/cm2 for 15°), but the linearity of light versus current was poorer, the temperature sensitivity of threshold was Jt355/Jt290⩾2, and efficiency also dropped with temperature. The optical distribution has been calculated for various multilayer heterostructure waveguides and related both to the far‐field beam width and to the threshold current. A universal gain/current density relation for the active layer has been deduced from the measurements and agrees reasonably with published theory.