Saturday, May 01, 2004

[ODCAD] Schottky Effect: Junction with Organic Semiconductor
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).

This article is from Organic Device group

ODCAD from OD Software Incorporated (ODSI)( expert and tool kit provider of electronic material, device.

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