Field-effect threshold voltage, determination

Photoconductivity and SCLC experiments have been used to obtain information on localized states in the bulk of organic crystals. However, information about the surface states that are relevant to the OFET operation is stiU very limited. Fortunately, the calculation of several basic OFET parameters does not require a detailed knowledge of the trap spectrum. For example, the field-effect threshold voltage is determined by the total density of deep traps... 

Table 8.2 Field effect hole mobilities //, threshold voltages Fj, and channel lengths L of the samples A to F (see Table 1). The values were determined according to method A. denotes the thermal activation energy of the field effect mobility determined from the slopes of the plots in Figure 8.8.

It is of crucial importance that the extracted field-effect mobility and threshold voltage obtained from transistor characteristics are therefore not exclusively channel properties but influenced by the contact formation at the source and drain electrodes. Commonly, the transfer line method (TLM) is used to extract the contact resistance from the OFET current/voltage dependence [69]. The method stems from a conventional technique to estimate contact resistances, and was developed for amorphous silicon TFTs. The prevailing contact resistance is determined by varying the channel length L of the transistor. Since the total resistance is the sum of the channel resistance Vd//d and the total contact resistance R =Ris, +I id), the total resistance 7 tot in the linear region can be written as... 

---