Transition of Carrier Transport Behaviors with Temperature in Phosphorus-Doped Si Nanocrystals/SiO2 Multilayers

Abstract

High-conductive phosphorus-doped Si nanocrystals/SiO2(nc-Si/SiO2) multilayers are obtained, and the formation of Si nanocrystals with the average crystal size of 6 nm is confirmed by high-resolution transmission electron microscopy and Raman spectra. The temperature-dependent carrier transport behaviors of the nc-Si/SiO2 films are systematically studied by which we find the shift of Fermi level on account of the changing P doping concentration. By controlling the P doping concentration in the films, the room temperature conductivity can be enhanced by seven orders of magnitude than the un-doped sample, reaching values up to 110 S/cm for heavily doped sample. The changes from Mott variable-range hopping process to thermally activation conduction process with the temperature are identified and discussed.

Structures, Electronic Properties and Carrier Transport Mechanisms of Si Nano-Crystalline Embedded in the Amorphous SiC Films with Various Si/C Ratios

“…Hence, the localized electrons can hop between the deep localized states originated from the defect states via the multiple phonon hopping process. Identical behaviors were also found in our previous works of the P-doped Si NCs/SiO 2 multilayers, where the grain size of Si NCs was less than 7 nm and the crystalline volume fraction was below 70% [37]. Combined with the previous works, our findings lead us to conclude that the transport process at relatively low temperature region (50 K~240 K) is mainly dominated by the MPH conduction mechanism in the B-doped Si NCs:a-SiC film with R = 1, where the grain size is relatively smaller (about 5 nm) and the crystallinity is relatively lower (X c < 60%).…”

“…It is reasonable since the charge carriers hopping between the neighboring Si NCs are impeded due to the freeze out of acoustic phonons as the temperature goes down to 50 K. At the lower temperature, the charge transport is proposed as the tunneling process of charge carriers between localized states according to Mott's model [35]. The Mott-VRH conduction had been usually reported in un-doped and P-doped Si and Ge NCs films at low temperature as well [27,[36][37][38]. However, once the temperature is above 50 K, the temperature dependence behaviors of conductivity change again and are no longer described by the Mott-VRH process.…”

Doped and codoped silicon nanocrystals: The role of surfaces and interfaces

“…In order to prove that impurities located in Si-NCs effectively act as dopant, it is necessary to assess their electrical activity. This can be done using, for instance, conductivity and resistivity data [40,133,134,207], current density versus electric field measurements [40,200,208,212,224], Hall mobility experiments [225] and field effect transistor analysis [136].…”

“…B-doped Si-NCs were formed by magnetron co-sputtering of Si, SiO 2 and B 2 O 3 targets, while for P-doped Si-NCs, Si, SiO 2 and P 2 O 5 targets were used. Doped Si-NCs were fabricated by PECVD using the superlattice approach, that permits to well control the size and the distribution of the Si-NCs [153,154,156,201,202,203,204,205,206,207,208,209,210,211,212]. The dopants location and the doping effects were studied through SIMS [196,197,201] and time-of-flight-SIMS (ToF-SIMS) [153,209,211], XPS [153,154,193,207,210], FTIR [66,193,195], TEM and HRTEM [40,153,193,195,198,205,207,209,210,212], ESR [199,205], glancing incidence x-ray diffraction (GIXRD) [40,193,200], absorption and PL spectra [40,…”

“…In order to prove that impurities located in Si-NCs effectively act as dopant, it is necessary to assess their electrical activity. This can be done using, for instance, conductivity and resistivity data [40,133,134,207], current density versus electric field measurements [40,200,208,212,224], Hall mobility experiments [225] and field effect transistor analysis [136]. Due to the difficulties in the interpretation of the results obtained in transport measurements, that often depend on a large number of concomitant effects (like for instance transport due to defects, the presence of hyperdoping effects and transport in percolated nano-Si networks), today little is known about the effective electronic activation.…”