Pore growth on n-type GaAs (100) can be initiated in 1 M HCl solution by electrochemical polarization of the material anodic to a critical potential value—the pore formation potential (PFP). At surface defects, however, the PFP is significantly lower (shifted cathodically). Focused ion beam, implantation of Si++ was used to create defined patterns in the substrate. At these implant sites, the growth of porous GaAs was selectively achieved by polarization below the overall PFP. From the porous GaAs patterns visible photoluminescence at green-yellow wavelengths can be observed. This technique, thus, allows the production of light emitting porous GaAs micropatterns of arbitrary shape by a direct writing process.
Pore formation on n-type GaAs(100) under anodic polarization in 1 M HCl has been studied. Focused ion beam implantation of Si 2ϩ into GaAs was used to write defined surface damage/implant patterns into the substrate. These implant sites represent initiation sites for pore growth and show pore formation at potentials significantly cathodic to the intact surface. Hence, pore growth within the patterns can be achieved selectively if anodic polarization is kept below the pore formation potential of the unimplanted surface. The results show that both the polarization potential and the implantation dose strongly influence the morphology and the photoluminescence behavior of the porous structures. Monte Carlo simulations of the implantation process revealed that the morphology of the etch process and its kinetics are both strongly connected to the implant/damage profile. Furthermore, it is demonstrated that "green"-light-emitting porous GaAs lift-off layers can be produced.
GaAs(100) was implanted with Si++ doses ranging from 3×1013 to 3×1016 cm−2 using a focused ion beam. The surface topology and roughness of implanted lines and squares was studied by atomic force microscopy. Above a threshold dose, protrusions of the ion beam treated areas in the range of 1–15 nm in heights and an increase in surface roughness were found. The height of the protrusions and surface roughness increase with increasing implantation dose up to a saturation level. Both the onset of substrate bulging and saturation of the effect are both dependent on the linewidth of the implant. Different causes for the protrusions are discussed. From Monte Carlo simulations, it is deduced that the volume expansion is most likely due to the creation of vacancies during implantation.
The present work investigates selective metal electrodeposition reactions triggered by intentionally created surface defects on p-type Si͑100͒ surfaces. Defined defects were written into the Si surface by focused ion beam ͑FIB͒ Si 2ϩ implantation. Subsequently, Au was electrochemically deposited on the samples from a 1 M KCNϩ0.01 M KAu͑CN͒ 2 solution. The work demonstrates that selective Au deposition can be achieved; i.e., that electrochemical conditions can be established where Au deposition occurs exclusively on the FIB-treated regions. The key principle is that breakdown of the current blocking situation ͑established at the p-type semiconductor/electrolyte junction under cathodic bias͒ is facilitated at surface defects. Thus this local current flow can be exploited to achieve localized Au deposition. The lateral resolution of the process is in the 100 nm range. The main parameters influencing the nucleation and growth of Au deposits and their morphology, as well as the selectivity and resolution of the process, are the implant dose and the electrochemical conditions during Au deposition. The work shows that the implant dose directly affects the density of nucleation sites for the electrodeposition process. Coverage of an implanted area is obtained, if sufficient nucleation sites are activated in the deposition process either using high implant doses or high deposition potentials. Since the concept presented in this work potentially can be applied for many electrodeposition reactions, it may open new perspectives for patterning of semiconductor surfaces with a large palette of materials in the submicrometer scale.
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