Vanadium supersaturated silicon system: a theoretical and experimental approach

Abstract

The effect of high dose vanadium ion implantation and pulsed laser annealing on the crystal structure and sub-bandgap optical absorption features of V-supersaturated silicon samples has been studied through the combination of experimental and theoretical approaches. Interest in V-supersaturated Si focusses on its potential as a material having a new band within the Si bandgap. Rutherford backscattering spectrometry measurements and formation energies computed through quantum calculations provide evidence that V atoms are mainly located at interstitial positions. The response of sub-bandgap spectral photoconductance is extended far into the infrared region of the spectrum. Theoretical simulations (based on density functional theory and many-body perturbation in GW approximation) bring to light that, in addition to V atoms at interstitial positions, Si defects should also be taken into account in explaining the experimental profile of the spectral photoconductance. The combination of experimental and theoretical methods provides evidence that the improved spectral photoconductance up to 6.2 /jm (0.2 eV) is due to new sub-bandgap transitions, for which the new band due to V atoms within the Si bandgap plays an essential role. This enables the use of V-supersaturated silicon in the third generation of photovoltaic devices.

Energy Levels of Defects Created in Silicon Supersaturated with Transition Metals

“…On the other hand, the spectral photoconductivity of the samples studied in this work (implanted with V), but implanted with a dose of 10 15 cm 2 , was measured (the Mott limit has been overtaken and the IB has been formed). 20 The photoconductivity started to increase for photons with an energy near 0.4 eV. Perhaps, the energy level observed is not in the position where the intermediate band is formed, due to the constant value for the energy of the traps and because no spectral photoconductivity was detected at this low energy.…”

Transition Metal-Hyperdoped InP Semiconductors as Efficient Solar Absorber Materials

“…Concretely, GW calculations were carried out to correct the PBE eigenvalues without further interactions, i.e., the G 0 W 0 approach [48], wherein the calculation starts from the DFT eigenvalues and eigenfunctions to obtain many-body GW self-energy. It has been successfully proven that this method yields results that are in good agreement with the experimental results for IGB materials [34,35]. The G 0 W 0 approach was carried out with a Γ-centered 4 × 4 × 4 k-point to sample the Brillouin zone and 512 bands.…”

“…The main goal of this paper is the study of the structural and electronic properties of several TM-hyperdoped InP (TM@InP) compounds in order to find new IGB materials with improved absorption features. Concretely, the selected TM were early 3d-block elements, whose ability to form an IGB has been previously demonstrated [17,20,22,23,25,26,[28][29][30][31][33][34][35][36][38][39][40][41][42][43][44]. Hence, in this work we investigate the structural, stability and electronic properties of several TM@InP (TM = Ti, V, Cr, Mn).…”

“…Although PBE+U formalism would be adequate for the native host material, such an approach has not been applied to in-gap band materials. Our previous works have demonstrated that the many-body perturbation theory in GW approximation (concretely G 0 W 0 approach) [48], yields electronic structure information according to experimental data for other transition metal semiconductors with an in-gap band [24,34,35]. As a result, the electronic structure and optical absorption features were calculated using DFT+U, while G 0 W 0 was used as benchmark method.…”

“…In addition, the IGB must meet some additional requirements to improve its photovoltaic efficiency: (i) have its own small dispersion, without it being at a discreet level; (ii) be well isolated from the VB and CB to avoid thermalization between VB and CB; (iii) be partially filled to allow comparable rates between VB-IGB and IGB-CB transitions; (iv) have high concentrations of IGB states to produce high absorption coefficients for those sub-bandgap absorptions and avoid non-radiative recombination obtained through the formation of a highly delocalized energy band [14-16]. Among the major approaches considered in designing IGB materials, our group have extensively studied the formation of an IGB through the substitutional doping of some cations by a transition metal (TM) [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. In this way, the d-orbitals of the TM might be located within the bandgap of the semiconductors, allowing for the formation of an isolated energy band, while the filling of the IGB can be finetuned through the adequate selection of the TM.…”