Abstract

Low dimensional structures such as quantum well wires and quantum dots have attracted much interest in the past few years.¹ Quantum well intermixing is one of the promising techniques for fabricating such structures, as opposed to the conventional techniques of dry-etching² and metal-organic vapour phase epitaxy selective growth.³ For the GaAs/AIGaAs system, Ga and As, being native matrix elements, are the most promising ions for implantation. Low dimensional structures formed using Ga implants have been reported.⁴ In this paper we report the fabrication of GaAs/AIGaAs quantum well wires using implantation of As at 45 keV to induce quantum well intermixing. The intermixing process was first characterised giving optimised annealing parameters of 875°C for 30 s and an implantation dose of 1× 10¹³ cm^-2. Wire widths from 35 nm to 1000 nm were defined using e-beam lithography followed by lift-off, where SrF₂ was used as a mask for implantation and annealing. Photoluminescence spectra from the non-intermixed regions, lateral wells, and the intermixed regions, barriers, were observed from samples with wires as narrow as 50 nm. The energies of the lateral wells were found to remain constant for wire widths between 1000 nm and 150 nm, and start to shift significantly towards high energy for 80 nm wires, showing 1-D confinement effects. The signal from the lateral well eventually merges with that from the lateral barrier for 35 nm wires, as can be seen in Fig. 1, hence an intermixing radius of about 17 nm was estimated for the process. Photoreflectance measurements were also carried out on these wire samples, showing that the wires appear to have a parabolic lateral potential and clear interwire coupling was observed from samples with barriers narrower than 50 nm, as can be seen in Fig. 2.

© 1998 IEEE