High-precision metal masking for multiple-wavelength laser diode fabrication using single-step-ion-implantation-induced quantum well intermixing

In this paper we report the development of a new and versatile ion implantation mask system which takes advantage of the high precision offered by recent deposition methods. A stack of alternate layers of two different materials which can be selectively etched is first deposited on the sample. Selective etching is then performed to remove a given number of layers from the stack in the various region of the sample. Owing to a high etching selectivity between the two materials, the thickness of the mask can be fixed very precisely in each region. During ion implantation, a different amount of ions will pass through the mask to reach the sample, according to mask thickness over each region. This method therefore provides a way to achieve a spatial control over the implantation dose, in a single implantation step. Thermal annealing can then be performed to induce quantum well intermixing in the underlying heterostructure, which brings about a blueshift of the emission wavelength. The results obtained with our method, which makes use of low energy ion implantation, for the fabrication ofsingle step graded blueshifting of InP/InGaAs/InGaAsP integrated laser heterostructures are presented. We also present a study of pairs of materials suitable for the mask fabrication, as well as the results of numerical simulations to determine the appropriate thickness ofthe mask layers.