Doping Effects on Rake-Line Formation in LPE Growth of AlxGa1--xAs DH Lasers

The absence or near absence of the active layer in the region of the stripe of a DH laser (rake lines) is one of the more easily assigned causes poor device yield and performance in semiconductor lasers. A description is given of a scanning photocurrent technique to detect the presence of rake lines and other nonuniformities in DH laser structures with a GaAs top-contacting layer that precludes the use of conventional photoluminescence evaluation. This technique is simple, nondestructive and of comparable resolution to photoluminescent techniques. The presence of rake lines in DH laser structures is shown to be due to inhibited nucleation of the active-layer growth on the n-type ternary layer. The volatile dopant commonly used to dope n-type ternary layers, enhances the formation of rake lines while the effect is significantly reduced when nonvolatile Sn is used as a dopant.19 refs.--AA