Passivation of Surface States

Note that the a-Si H protected diode has more than one order-of-magnitude lower leakage current than the diode protected by Si02. After heating the device at 500°C for hour (a typical metallization treatment), the leakage current is still much lower than the standard oxide-passivated diode. 

---

Myung, N., Bae, Y. and Bard, A. J. (2003) Enhancement of the photoluminescence of CdSe nanocrystals dispersed in CHCI3 by oxygen passivation of surface states. Nano Lett., 3, 747—749. 

First, I shall describe the hydrogenation method I used and then consider the passivation of surface states and that of bulk dangling bonds, including grain boundaries, dislocations and point defects. 

HCl to NH40H). Polyhydrides are found to be more stable than monohydride. Hydrogen termination also serves to passivate grain boundaries. Terrace monohydride has different stability from step monohydride. As a result of hydrogen passivation, HF-treated silicon surface exhibits a very low density of surface states in various acids over a wide concentration range. ... 

The introduction of QDs into aqueous media is usually accompanied by drastic decreases in the luminescence yields of the QDs. This effect presumably originates from the reaction of surface states with water, a process that yields surface traps for the conduction-band electrons [63]. As biorecognition events or biocat-alytic transformations require aqueous environments for their reaction medium, it is imperative to preserve the luminescence properties of QDs in aqueous systems. Methods to stabilize the fluorescence properties of semiconductor QDs in aqueous media (Figure 6.2) have included surface passivation with protective layers, such as proteins [64, 65], as well as the coating of QDs with protective silicon oxide films [66, 67] or polymer films [43, 68, 69). Alternatively, they can be coated with amphiphilic polymers, which have both a hydrophobic side chain that interacts with the organic capping layer of the QDs and a hydrophilic component, such as a poly(ethylene glycol) (PEG) backbone, for water solubility [70, 71). Such water-soluble QDs may retain up to 55% of their quantum yields upon transfer to an aqueous medium. 

It should be mentioned that as well as for metals the passivation of semiconductors (particularly on Si, GaAs, InP) is also a subject of intense investigation. However, the goal is mostly not the suppression of corrosion but either the fonnation of a dielectric layer that can be exploited for devices (MIS stmctures) or the minimization of interface states (dangling bonds) on the semiconductor surface [63, 64]. 

The excellence of a properly formed Si02—Si interface and the difficulty of passivating other semiconductor surfaces has been one of the most important factors in the development of the worldwide market for siUcon-based semiconductors. MOSFETs are typically produced on (100) siUcon surfaces. Fewer surface states appear at this Si—Si02 interface, which has the fewest broken bonds. A widely used model for the thermal oxidation of sihcon has been developed (31). Nevertheless, despite many years of extensive research, the Si—Si02 interface is not yet fully understood. 

---