Tuning the Performance of Organic Spintronic Devices Using X-Ray Generated Traps

Rybicki, James; Lin, Ran; Wang, F; Wohlgenannt, M.; He, Chao; Sanders, T. D.; Suzuki, Yuri

doi:10.1103/physrevlett.109.076603

Cited by 68 publications

(74 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1a, where the band does not have a local minimum to keep extra charges inside the organic once a bias is removed. While impurities or deep traps have been shown to influence the MR in the OSVs 23 , the present model suggests that the impurity band due to high-density impurities is responsible for charge/spin transport in the OSVs.…”

Section: Forward Biasmentioning

confidence: 63%

Impurity-band transport in organic spin valves

2014

Nat Commun

View full text Add to dashboard Cite

The central phenomenon in the field of organic spintronics is the large magnetoresistance in thick organic spin valves. A prerequisite for understanding the magnetoresistance is a reliable description of the device resistance, or the I-V characteristics. Here I show that the observed I-V characteristics in the organic spin valves is incompatible with charge injection into the organic's lowest unoccupied molecular orbital or highest occupied molecular orbital but can be explained by electrons tunnelling into a broad impurity band located in the gap between these molecular orbitals. Voltage drop takes place mainly across depletion layers at the two electrode/organic interfaces, giving rise to electrode-limited charge transport. Spin-dependent electron tunnelling into the impurity band from the ferromagnetic electrodes results in spin accumulations inside the organic, which rapidly diffuses through the organic primarily via the exchange between impurity-band electrons. This picture explains the major magnetoresistance features and predicts enhanced capacitance in these devices.

show abstract

Section: Forward Biasmentioning

confidence: 63%

Impurity-band transport in organic spin valves

2014

Nat Commun

View full text Add to dashboard Cite

show abstract

“…Interestingly, a first step on this road was recently taken in Alq 3 devices by exposing them to x rays, leading to an enhancement of the MC. 47 Whether this same process could be applied to other devices is debatable as the exact nature of traps is still under investigation. Recently, an elaborate study suggested that hydrated oxygen complexes can explain the electron traps in most semiconducting polymers.…”

Section: Discussionmentioning

confidence: 99%

Traps and trions as origin of magnetoresistance in organic semiconductors

et al. 2013

View full text Add to dashboard Cite

The large effect of a small magnetic field on the current, magnetoconductance (MC), in organic semiconductors-so-called organic magnetoresistance-has puzzled the field of organic spintronics during the last decade. Although the microscopic mechanisms regarding spin mixing are well understood by now, it is still unknown which pairs of spin carrying particles are influencing the current in such a drastic manner. Here, a model for the MC is presented based on the spin selective formation of metastable trions from triplet exciton-polaron pairs. Additionally, the magnetic-field and voltage dependence of the MC are experimentally investigated in materials showing large effects. Using a combination of analytical and numerical calculations, it is shown that the MC is perfectly described by a process in which trions are created at polaron trap sites.

show abstract

“…At the same time the shadow mask protects the OSC in the active area inside the AlOx window from any damage by the electron beam evaporation by high energy electrons or X-ray Bremsstrahlung. 19 Finally the sample is bonded for measurements in the cryostat.…”

Section: Nanosized Vertical Organic Spin-valvesmentioning

confidence: 99%

Nanosized perpendicular organic spin-valves

Göckeritz

Homonnay

Müller

et al. 2015

Applied Physics Letters

View full text Add to dashboard Cite

A fabrication process for vertical organic spin-valve devices has been developed which offers the possibility to achieve active device areas of less than 500x500 nm² and is flexible in terms of material choice for the active layers. Characterization of the resulting devices shows a large magnetoresistance of sometimes more than 100 %, however with equally large variation from device to device. Comparison with large-area spin-valves indicates that the magnetoresistance of both, large and small devices most likely originates from tunneling through pinholes and tunneling magnetoresistance.Organic spin-valve devices are promising candidates for low cost non-volatile electronics, for example for RF-ID tags.1 Nevertheless, a deeper understanding of the underlying device physics is still necessary, especially of the charge transport mechanisms through the organic material and the origin of the magnetoresistance. In vertical organic spin-valves (OSV) an organic semiconductor (OSC) thin film is sandwiched between two ferromagnetic electrodes and the device is operated by a current flow perpendicular through the layers.2 Similar to giant magnetoresistance (GMR) 2-5 and tunneling magnetoresistance (TMR) 6-9 the device resistance depends on the relative magnetization of the two electrodes. However, in contrast to GMR in all-metal structures or TMR in metal/oxide structures it is still an open question whether the origin of the magnetoresistance (MR) effects in OSVs published so far is dominated by spin polarized charge transport through the organic spacer layer or by tunneling processes. 10,11 There is, however, a possible approach to gain deeper insight into this problem which takes into account the scaling of the MR effect with device size. In the case of spin injection and charge transport (GMR) the complete device area is expected to contribute to the current path through the OSC. Reducing the size of the device in this case should keep the resistance area product and the relative magnetoresistance constant. Tunneling processes, however, most likely occur in just a small part of the active area.12 Most probable candidates for tunneling sites would be pinholes at which the thickness of the OSC is reduced to such an extent that tunneling and thus TMR becomes possible. [8][9][10][11][12][13] Pinholes, however, follow certain statistics resulting in a different resistance change upon downscaling. They vary in size and also exhibit a varying thickness of the remaining OSC layer. Each pinhole thus contributes to the total device characteristics by a different resistance and MR contribution. In order to appreciate the necessary density of pinholes we can use results published by Barraud and coworkers.14 They create artificial pinholes in an OSC layer using conducting tip atomic force microscopy (AFM) and study the magnetoresistance after the pinhole is filled up with a ferromagnetic metal. The resistance of the pinholes is typically in the range of 100 MΩ while the magnetoresistance can be as high as 300%. In addition, they ob...

show abstract

Tuning the Performance of Organic Spintronic Devices Using X-Ray Generated Traps

Cited by 68 publications

References 36 publications

Impurity-band transport in organic spin valves

Impurity-band transport in organic spin valves

Traps and trions as origin of magnetoresistance in organic semiconductors

Nanosized perpendicular organic spin-valves

Contact Info

Product

Resources

About