Reduction of the dark current in stabilized a-Se based X-ray detectors

Belev, George; Kasap, S. O.

doi:10.1016/j.jnoncrysol.2005.11.086

Cited by 31 publications

(27 citation statements)

References 17 publications

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“…The two sets of samples are labelled S and X respectively. The measurements were on vacuum deposited films and in all cases, during evaporation, the substrates (usually oxidized Al plates) were heated to around 55-60°C, which is above the glass transition temperature, which is known to result in good hole transport [45]. The preparation of a-Se based films has been well described in the literature [32,[46][47][48], including in this journal [8,49].…”

Section: Introduction and Perspectivesmentioning

confidence: 99%

Charge transport in pure and stabilized amorphous selenium: re-examination of the density of states distribution in the mobility gap and the role of defects

Kasap

Koughia

Berashevich

et al. 2015

J Mater Sci: Mater Electron

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We re-examine electron and hole transport in pure and stabilized amorphous selenium (a-Se) and attempt to construct a DOS distribution in the mobility gap below E c and above E v based on time-of-flight (TOF) transient photoconductivity measurements. First, we review the current status of a-Se, its recent use in commercial X-ray detectors, and the scientific information that is available in terms of its density of states (DOS). We review and describe a convenient multiple trapping transport mechanism to calculate the TOF transient photocurrents in a system with a distributed DOS in the mobility gap and invoke a number of assumptions that allow the photocurrent to be calculated as an inverse Laplace transform. The assumptions behind the model are critically examined. Then, by comparing the calculated TOF photocurrent shapes directly with experimental waveforms, the DOS distribution has been extracted in a-Se in the vicinity of conduction and valence bands (below E c and above E v ). Below the conduction band, the DOS distribution seems to demonstrate three peaks at around E c -0.30 eV, E c -0.45 eV and below E c -0.55 eV. First principles atomistic modeling provided insight into the origins of these peaks and the peaks have been assigned to certain valence-alteration pairs (VAPs) appearing in different configurations. In contrast to the conduction band vicinity, the DOS distribution above the valence band seems to be almost totally featureless. Within the range of experimental uncertainties, a featureless DOS below E v down to 0.55 eV seems to be able to explain a vast range of data, that is, it can explain hole transport not only as a function of the electric field and temperature down to 123 K, but also the thickness dependence of the mobility over two orders of magnitude. At room temperature, the hole transport is nondispersive but at temperatures below *200 K, it becomes dispersive exactly along the lines argued by Pfister and Scher (Adv Phys 27:747, 1978), and the mobility evinces a clear thickness dependence. The first principles calculations yield two defect levels related to VAP type defects in this region of the mobility gap but the valence band tail is so broad that it masks these peaks. This seeming asymmetry between the conduction and valence bands may be related to their physical origins: the conduction band arises from antibonding states and valence band is due to interacting lone pairs.

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Section: Introduction and Perspectivesmentioning

confidence: 99%

Charge transport in pure and stabilized amorphous selenium: re-examination of the density of states distribution in the mobility gap and the role of defects

Kasap

Koughia

Berashevich

et al. 2015

J Mater Sci: Mater Electron

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“…Therefore, CTR by ion implantation in chalcogenide glasses could open up a new branch of electronics based on these materials. Amorphous Se can be doped n-type with alkaline elements, which has allowed high-performance X-ray detectors to be fabricated 5 ; however, amorphous Se is limited in its PCM, nonlinear and IR applications. GaLaSO glass is a high-performance PCM material that, compared with standard GeSbTe PCM materials, offers significantly higher thermal stability, and therefore potentially improved endurance, along with more than order of magnitude lower set and reset currents 6,7 .…”

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confidence: 99%

n-type chalcogenides by ion implantation

et al. 2014

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Carrier-type reversal to enable the formation of semiconductor p-n junctions is a prerequisite for many electronic applications. Chalcogenide glasses are p-type semiconductors and their applications have been limited by the extraordinary difficulty in obtaining n-type conductivity. The ability to form chalcogenide glass p-n junctions could improve the performance of phase-change memory and thermoelectric devices and allow the direct electronic control of nonlinear optical devices. Previously, carrier-type reversal has been restricted to the GeCh (Ch ¼ S, Se, Te) family of glasses, with very high Bi or Pb 'doping' concentrations (B5-11 at.%), incorporated during high-temperature glass melting. Here we report the first n-type doping of chalcogenide glasses by ion implantation of Bi into GeTe and GaLaSO amorphous films, demonstrating rectification and photocurrent in a Bi-implanted GaLaSO device. The electrical doping effect of Bi is observed at a 100 times lower concentration than for Bi melt-doped GeCh glasses.

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“…As we have shown recently [7], the hole range l h s h depends on the substrate temperature during fabrication, and an a-Se layer deposited at a low substrate temperature can be n-like, i.e. l h s h << l e s e , and can therefore act as a hole trapping layer.…”

Section: Introductionmentioning

confidence: 89%

“…The vacuum deposition of a-Se layers has been described previously [7]. The a-Se materials were alloyed with 0.2-0.5 wt.% As and doped with 0-5 ppm Cl.…”

Section: Methodsmentioning

confidence: 99%