InGaAsP/InP QW Impurity Free Intermixing for Variable ZrO2 Cap Thickness

Impurity free quantum well intermixing (IFQWI) by cap layer thickness variation for InGaAsP/InP multiquantum wells (MQWs) is reported for the first time. The blue-shift is observed to be enhanced or inhibited depending on the thickness of the ZrO₂ cap layer used (100-600 nm) for anneal conditions of 600 °C-750 °C for 40 s. The group-V intermixing in InGaAsP/InP dominates the IFQWI resulting in a blue-shift of the MQW bandgap and the blue-shift increases with increasing ZrO₂ thickness to 400 nm. A 600-nm ZrO2 cap is found to inhibit the blue-shift. For higher anneal temperatures similar inhibition nature is observed, with larger blue-shifts. An interdiffusion model shows that the diffusion length ratio for group-V to group-III initially increases from 1.25 to 1.6 for 100-400 nm ZrO₂ thickness, but decreases to 1.1 for 600-nm ZrO₂. This technique is promising for the fabrication of tapered waveguides for photonic integration of InGaAsP/InP by IFQWI.