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[ODCAD] Schottky Effect: Junction with Organic Semiconductor (OLED)

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ODCAD

Jan 1, 1970
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Electric current vs voltage of an organic device such as OLED is
important factor to decide the device performance. When field is at
medium strength and the device is at junction control, one factor in
device model is Schottky effect.

This effect reduces energy barrier for charge carrier injection from
the electrode. This is due to the image force while charge carrier
leaving electrode. The equation can be expressed as

[qE/(4 Pi e0)]^1/2 where e0 is dielectric constant of the
semiconductor.

In the following discussion, we assume organic device has structure of
Electrode/Organic semiconductor/electrode. Also, we assume one
junction is ohmic.

In terms of equation, there is nothing new for organic semiconductor
(compared with Si technology). A few points we have to pay attention
when you use the model to describe your device behavior.

1. The derivation of the equation assumes that the field in the
semiconductor is uniform. This may not be true if the organic material
has high impurity such as ions that can redistribute under field
effect. In such case, the field E may need to be carefully related
with external electric voltage.

2. This is effect for junction control. Do not apply it when the
device is at bulk control. It is easy to be confused with Poole
Frenkel Model.

3. It is applicable when the field is relatively strong say E>10^3
V/cm, but not too strong say E~10^6V/cm. At very strong field, see if
it is tunneling in control.

4. Compared with Si material, Schottky effect is much stronger for
organic semiconductor. This is because the organic material has much
smaller dielectric constant (ususally it is ~3,much less than ~11 of
Si).

The article was originally posted on OrganicDevice group
http://groups.yahoo.com/group/OrganicDevice/.

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