Impurity induced layer disordering of Si implanted Al_xGa _1-xAs-GaAs quantum-well heterostructures: Layer disordering via diffusion from extrinsic dislocation loops

Extensive data are presented on impurity-induced layer disordering (IILD) of Al_xGa_1-xAs-GaAs quantum-well heterostructures and superlattices that are Si implanted and annealed (Si⁺-IILD) at three different implant doses. We show that impurity activation is not critical to the layer disordering process and that Si diffusion from the implanted profile initiates Si⁺-IILD. When the implant dose is as high as φ≥5×10¹³/cm² (n_Si ≥2×10¹⁸/cm³), Si interstitial loops (Si-ILs) form by diffusion and agglomeration of the implanted Si atoms during the initial stages of annealing. If a source of Ga vacancies is provided (e.g., via an As overpressure or SiO₂ encapsulation), the Si-ILs dissociate and supply Si atoms for diffusion and hence Si⁺-IILD during the latter stages of annealing. If a Si₃N₄ encapsulant is employed, however, fewer Si-ILs form and Si diffusion is inhibited. For an implantation dose as low as φ=1×10¹²/cm ² (n_Si =3×10¹⁶/cm ³), extensive Si⁺-IILD is realized via capless annealing and Si-ILs are not observed. It is significant for device applications that the layer-disordered material operates as a cw 77 K photopumped laser, which indicates that the layer averaging (IILD) does not damage the crystal.