Insulator-to-metal transition in vanadium supersaturated silicon: variable-range hopping and Kondo effect signatures

Abstract

We report the observation of the insulator-to-metal transition in crystalline silicon samples supersaturated with vanadium. Ion implantation followed by pulsed laser melting and rapid resolidification produce high quality single-crystalline silicon samples with vanadium concentrations that exceed equilibrium values in more than 5 orders of magnitude. Temperature-dependent analysis of the conductivity and Hall mobility values for temperatures from 10 K to 300 K indicate that a transition from an insulating to a metallic phase is obtained at a vanadium concentration between 1.1 × 10 20 and 1.3 × 10 21 cm −3 . Samples in the insulating phase present a variable-range hopping transport mechanism with a Coulomb gap at the Fermi energy level. Electron wavefunction localization length increases from 61 to 82 nm as the vanadium concentration increases in the films, supporting the theory of impurity band merging from delocalization of levels states. On the metallic phase, electronic transport present a dispersion mechanism related with the Kondo effect, suggesting the presence of local magnetic moments in the vanadium supersaturated silicon material.

Vanadium supersaturated silicon system: a theoretical and experimental approach

“…All these results are in agreement with time of flight secondary ion mass spectrometry (ToF-SIMS) measurements and high-resolution transmission electron microscopy (HR-TEM) images of similar samples reported previously [25]. In this sense, ToF-SIMS showed that both samples present a vanadium concentration higher than the theoretical limit to obtain an IB material.…”

“…As we have recently shown [25], these V-supersaturated Si samples have electrical transport properties that confirmed the insulator-to-metal transition and the formation of an IB in a high quality material. Since spectral photoconductance is directly related to the absorption coefficient [44], we suggest that the intense sub-bandgap photoresponse of the V supersaturated Si samples, together with the presence of abrupt photoresponse edges is consistent with optical transitions from the VB to the IB and from the IB to the CB.…”

“…Therefore, we decided to use the PLM process for the fabrication of V hyperdoped Si samples. More details on the fabrication process-as well as transmission electron microscopy (TEM) and vanadium concentration depth profiles-of these samples can be obtained from our previous work [25]. Structural information was obtained through RBS.…”

On the insulator-to-metal transition in titanium-implanted silicon

“…3(c) , the reduced activation energy W is nearly zero for the sample PLA-1.2 × 10 16 cm −2 . This means that it exhibits a relatively finite conductivity as temperature tends to zero 34 . The decrease of W at low temperatures for the sample PLA-1.2 × 10 16 cm −2 indicates that this sample lies in the metallic regime.…”

On the Optoelectronic Mechanisms Ruling Ti‐hyperdoped Si Photodiodes

“…Single-crystalline silicon layers with transition metals (Ti, V, Au, and Ag) or chalcogens (S, Se, and Te) at concentrations above 10 19 cm -3 have been obtained by means of ion implantation and subsecond annealing techniques (in a process denominated as supersaturation or hyperdoping). We have shown that silicon hyperdoped with Ti [9,10] or V [11] presents outstanding properties such as a sub-bandgap optical absorption coefficient in the 10 4 cm -1 range [12] or a photoconductive response extended down to 0.2 eV (6.2 µm) at cryogenic temperatures. [13] Gold hyperdoped [14,15] or silver hyperdoped [16] This work deepens the understanding of the optoelectronic mechanisms ruling hyperdoped-based photodevices and shows the potential of Ti hyperdoped-Si as a fully complementary metal-oxide semiconductor compatible material for room-temperature infrared photodetection technologies.…”