First-Principles Calculation of Charge Transfer at the Silicon–Organic Interface

5 years ago

First-Principles Calculation of Charge Transfer at the Silicon–Organic Interface

Mona Zebarjadi, Xiaoming Wang, Keivan Esfarjani

Organic dopants are frequently used to surface dope inorganic semiconductors to increase their functionality. In this paper, we introduce a methodology to screen out materials for optimal surface doping and predict accurately band offsets and charge transfer using the GW method. To illustrate the approach, we study charge transfer at hybrid silicon–molecule interfaces. The goal is to find the best molecular acceptors to surface dope silicon with hole densities as high as 10¹³ cm^–2. We use the chemical hardness method for quick screening, followed by first-principles density functional theory (DFT) and more accurate GW calculations for a handful of the most optimistic candidates. The chemical hardness method is derived from the thermodynamic analysis of the energy levels of the two subsystems in contact. This method is simple, fast, and relatively accurate. Therefore, as our first step, we use it to narrow our search for molecular dopants. Then, for the most optimistic candidates, we perform first-principles DFT calculations and discuss the necessity of GW corrections. Consistent with experimental observations, we find 3,5-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane to be good p-dopants with charge transfer densities larger than 10¹³ cm^–2 when placed in the nitrogen-terminated orientation on the silicon substrate. This screening approach is quite general and applicable to other hybrid interfaces.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b03275

DOI: 10.1021/acs.jpcc.7b03275