Abstract
Molecular Doping (MD) involves the deposition of molecules, containing the dopant atoms and dissolved in liquid solutions, over the surface of a semiconductor before the drive-in step. The control on the characteristics of the final doped samples resides on the in-depth study of the molecule behaviour once deposited. It is already known that the molecules form a self-assembled monolayer over the surface of the sample, but little is known about the role and behaviour of possible multiple layers that could be deposited on it after extended deposition times. In this work, we investigate the molecular surface coverage over time of diethyl-propyl phosphonate on silicon, by employing high-resolution morphological and electrical characterization, and examine the effects of the post-deposition surface treatments on it. We present these data together with density functional theory simulations of the molecules–substrate system and electrical measurements of the doped samples. The results allow us to recognise a difference in the bonding types involved in the formation of the molecular layers and how these influence the final doping profile of the samples. This will improve the control on the electrical properties of MD-based devices, allowing for a finer tuning of their performance.
Highlights
Doping of semiconductors, i.e., the introduction of dopant impurities into the intrinsic material to modulate its electrical properties, is one of the main steps in device fabrication.Conventional doping methods present issues related to cost, safety, crystal lattice damage, and difficulties in obtaining conformal doping profiles, essential in nano-device fabrication, especially when non planar architectures are used
We study the surface coverage of Diethyl-Propyl Phosphonate (DPP) at 10% dilution and the morphology of the aggregates over the Si substrate by Scanning Electron Microscopy (SEM)
We corroborate these results with Density Functional Theory (DFT) simulations of the grafted molecule over Si, which has been observed in a previous work [37]. We present these data together with electrical measurements of carrier concentration depth profiles produced with the Molecular Doping (MD) process at different synthesis conditions by Spreading Resistance Profiling (SRP)
Summary
I.e., the introduction of dopant impurities into the intrinsic material to modulate its electrical properties, is one of the main steps in device fabrication.Conventional doping methods (ion implantation and diffusion based methods) present issues related to cost, safety, crystal lattice damage, and difficulties in obtaining conformal doping profiles, essential in nano-device fabrication, especially when non planar architectures are used. I.e., the introduction of dopant impurities into the intrinsic material to modulate its electrical properties, is one of the main steps in device fabrication. Monolayer Doping, known in the literature as Molecular Doping (MD), has been demonstrated as a low-cost alternative to conventional doping techniques [1,2]. From another literature process, where guest molecules—working as charge transfer layer—are put in contact with the host material [3,4,5,6,7], the method involves the deposition of dopant-containing molecules from the liquid phase, called precursors, and the subsequent drive-in of the dopant atoms by thermal annealing. In the work of Javey and their group [1], during the MD process, the Si substrate is immersed in a solution containing the molecular precursor, kept
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