Lateral diffusion limitations of InGaAs/GaAs for nanostructure fabrication

We have investigated the technique of implantation enhanced interdiffusion (IEI) for optical nanostructure fabrication in strained In _xGa _1-xAs/GaAs quantum wells. Implantation masks with widths from 40 nm to 40 μm were fabricated on the surface of In _xGa _1-xAs/GaAs (x=0.1, 0.2) 3.5 nm quantum well material which was implanted with 100 kV As ⁺ with doses ranging from 5 × 10 ¹² to 8.5 × 10 ¹³ ions/cm ². After mask removal and a high temperature anneal, cathodoluminescence (CL) spectroscopy was used to investigate the optical properties of the resulting structures. We have measured electron-heavy hole recombination energy shifts due to quantum well interdiffusion of up to 60 meV for the highest doses used here with broad area implants. However, while quantum well emission under large (40 μm) masks is preserved, smaller masks show an emission blue shift not due to ions penetrating through the mask. A simple model of the width dependence of this shift yields an enhanced lateral diffusion length of approximately 1 μm which is many times larger than the lateral straggle of the implanted As ⁺. We conclude that lateral diffusion effects may impose a limit on nanostructure fabrication in the In _xGa _1-xAs/GaAs system with this technique.