Optical energy gap of amorphous selenium: effect of annealing

Bhatnagar, Anil K.; Reddy, K. Venugopal; Srivastava, Vipin

doi:10.1088/0022-3727/18/9/001

Cited by 58 publications

(29 citation statements)

References 14 publications

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“…From the plots, band gap energy is found to be 2·24, 2·26, 2·72 and 2·41 eV for as prepared, 3 h, 1 day and 4 days aging times, respectively. It is observed that the band gap energy of synthesized Se nanostructures is higher than that of bulk α-Se (2·0 eV) and commercial Se powder (1·8 eV) (Bhatnagar et al 1985) due to quantum size effect. Similar to the early report (Liao et al 2010), the band gap of t-Se was found to be blue shifted as the crystallite size is reduced from bulk to 41·02, 39·70, and 42·18 nm.…”

Section: Resultsmentioning

confidence: 90%

Synthesis of selenium nanorods with assistance of biomolecule

et al. 2014

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Nanorods of one-dimensional (1D) trigonal selenium (t-Se) are synthesized using biomolecule substances for five different aging times (1 h, 2 h, 3 h, 1 day and 4 days) by precipitation method. XRD analysis indicates a shift of the (1 0 1) plane towards higher diffraction angle for 1 day aging time. It is observed that the crystallite size decreases with increase in aging time except for an aging period of 4 days. FTIR analysis confirmed that the presence of stretching and bending vibrations of Se-O in both synthesized and commercial selenium samples at 465, 668 and 1118 cm −1 . The FESEM micrographs are evident for the changes of rod size as a function of aging time. It is observed that the optical band gap energy is increased with aging time up to 1 day, whereas it decreases in 4 days aging time.

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Section: Resultsmentioning

confidence: 90%

Synthesis of selenium nanorods with assistance of biomolecule

et al. 2014

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“…and the experimental p-type branch-point energy obtained here for crystalline selenium then give valence-band offsets of 0.29 and 2.22 eV for Se/Si and Se/GaN heterostructures., respectively. Considering the band-gap width of crystalline Se, 1.85 eV [28], the conduction-band offsets result as 1.02 eV for c-Se/Si and 0.68 eV for c-Se/GaN heterostructures.…”

Section: Discussionmentioning

confidence: 99%

On selenium p–n heterojunctions and Schottky contacts

Mönch

2014

J Mater Sci: Mater Electron

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Experimental capacitance-voltage data of selenium p-n heterojunctions on n-type Ge, Si, and GaN and flat-band barrier heights of selenium Schottky contacts are reanalyzed. The resulting built-in potentials of the p-n heterojunctions as well as the flat-band barrier heights of the Schottky contacts are explained by the well established concept of interface-induced gap states (IFIGS) where the interfacial electric dipoles are estimated by using the differences of the respective electronegativities. The analysis of the built-in potentials of the heterojunctions between crystalline p-Se films and n-Si and n-GaN substrates give an energy distance of 0.06 eV between the bulk Fermi level and the branch point of the IFIGS. The evaluation of the Schottky barrier heights reveals the IFIGS branch point of crystalline selenium to lie 0.03 ± 0.15 eV above the valence-band maximum. In summary, the valence-band offsets of c-Se/Si and c-Se/ GaN heterostructures are estimated as 0.29 and 2.22 eV, respectively.

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“…The fitted values of r tv decrease at lower temperatures (r tv = 1.75 × 10 −5 , 0.75 × 10 −5 , and 0.6 × 10 −5 for T = 217, 183, and 166 K, respectively). The mobility gap E g of a-Se is sensitive to temperature; it decreases with increasing temperature [29]. Therefore, longer tails and an exponential increase of g v (i.e, lower r tv ) with the energy length of the tail states are expected at very low temperatures.…”

Section: Hole Mobility and Impact Ionizationmentioning

confidence: 98%

“…2 except a = 1.1 nm, and b = ␤/4. The E g of a-Se has been reported to be 2.0-2.3 eV, and the precise value depends on the particular sample and type of measurement approach [29,32]. While E i ϳ1.5E g in crystalline semiconductors [30], the average E i in amorphous semiconductors can be close to E g considering carrier generation from the localized states within the mobility gap.…”

Section: Hole Mobility and Impact Ionizationmentioning

confidence: 99%

Mechanisms of temperature- and field-dependent effective drift mobilities and impact ionization coefficients in amorphous selenium

Hijazi

Kabir

2015

Can. J. Phys.

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The mechanisms of electric-field-and temperature-dependent effective drift mobility and impact ionization coefficient of both holes and electrons in amorphous selenium (a-Se) are investigated in this paper. An analytical model for the microscopic mobility, momentum relaxation mean free path, and hence the effective drift mobility and impact ionization coefficient of carriers, is proposed in this paper by considering the density of states distribution, field enhancement release rate from the shallow traps, and carrier heating. The results of the model are fitted with the published experimental results on effective mobility and impact ionization coefficient with wide variations of the applied electric field and temperature. A better fitting considering thermally activated tunneling for the field-enhancement release rate indicates that the effective drift mobility at extremely high fields is mainly controlled by the neutral defect states near the band edges. The density of state function near the band edges, consisting of an exponential tail and a Gaussian peak, can successfully describe the electric-fieldand temperature-dependent effective drift mobility characteristics in a-Se. The momentum relaxation mean free path decreases with increasing field and decreasing temperature, which is required to describe the electric-field-and temperature-dependent behaviors of impact ionization coefficient in a-Se. PACS Nos.: 72.20.Jv, 72.20.Ht, 71.23.An.Résumé : Nous étudions ici les mécanismes de dépendance en champs électriques et en température de la mobilité de dérive efficace et du coefficient d'ionisation par impact des trous et des électrons dans le sélénium amorphe (a-Se). Nous tenons compte de la distribution de densité d'états, de la libération du renforcement du champ des pièges peu profonds et du réchauffement des porteurs, afin de proposer un modèle analytique pour la mobilité microscopique, le libre parcours moyen de relaxation d'impulsion et ainsi la mobilité de dérive efficace et le coefficient d'ionisation par impact. Les résultats du modèle sont ajustés avec les résultats expérimentaux publiés sur la mobilité efficace et le coefficient d'ionisation par impact avec de grandes variations du champ électrique et de la température. Un meilleur ajustement qui tient compte d'un effet tunnel dans la libération de renforcement du champ indique que la mobilité de dérive aux valeurs élevées de champ est surtout contrôlée par les états défauts près des bords de bande. La fonction de densité d'états près du bord de bande qui consiste en un pic gaussien et une queue exponentielle peut décrire avec succès les caractéristiques de la dépendance sur le champ électrique et la température de la mobilité de dérive dans le a-Se. Le libre parcours moyen de relaxation de l'impulsion diminue lorsque le champ croît et que la température baisse, ce qui est nécessaire pour décrire correctement la dépendance en température du coefficient d'ionisation par impact dans a-Se. [Traduit par la Rédaction]

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Optical energy gap of amorphous selenium: effect of annealing

Abstract: The optical energy gap of amorphous Se powder has been determined by a photoacoustic method and has been found to be 1.99 ? 0.02 eV. On annealing, the gap decreases linearly as a function of annealing temperature towards that of the crystalline selenium.

Cited by 58 publications

References 14 publications

Synthesis of selenium nanorods with assistance of biomolecule

Synthesis of selenium nanorods with assistance of biomolecule

On selenium p–n heterojunctions and Schottky contacts

Mechanisms of temperature- and field-dependent effective drift mobilities and impact ionization coefficients in amorphous selenium

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