(GaAl)As lasers with a heterostructure for optical confinement and additional heterojunctions for extreme carrier confinement

This paper shows the design advantages of using four- and five-layer heterostructure lasers in order to separately optimize the optical distribution and carrier confinement for a particular application. Given an arbitrary gain/carrier density relationship the parameters can be optimized for minimum threshold current. Theoretical results for both wide optical cavity and close confined lasers are given. These show the optical distributions for four- and five-layer lasers and how the threshold current varies with the active region width. Experimental results report a reduction from 55° half-power polar diagram width to 32° by the addition of a fourth layer to increase the optical cavity width of a double-heterostructure laser. The threshold current against reciprocal length characteristics for three- and four-layer devices are considered in terms of the theory given and hence a plot of gain against injected carrier density is obtained that extends over an order of magnitude of gain.