Organic field-effect transistors (OFETs) in which the active semiconductor is made of polycrystalline octithiophene (8T) were fabricated and characterized. Several methods have been used to extract the parameters of the polycrystalline (8T) transistors as function of gate voltage at room and at low temperatures. These parameters such as the mobility, the threshold voltage, contact resistance and density of traps are extracted from the current-voltage characteristics of OFETs. The first method consists of deriving the drain current as function of gate voltage (transconductance), leading to the so-colled field effect mobility. It appears that the data must be corrected for the substantial source and drain contact resistance. In the second method, the carrier mobility has been corrected for the contact resistance. It is found to increase quasi linearly with gate voltage. Therefore, the contact resistances have been directly extracted from the experimental channel conductance. In the third method, data are interpreted according the multiple thermal trapping and release model using a power law dependence of the mobility with gate voltage together with a constant resistance. Finally, using a model where charge transport is limited by trapping and thermal release at localized states located at grain boundaries, the barrier height at grain boundaries in polycrystalline octhithiophene FETs has been estimated. It is shown that is gate bias dependent.

In this work, we demonstrate P3HT (poly 3-hexylthiophene) organic rectifier diode both in rigid and flexible substrate with a rectification ratio up to 10⁶. This performance has been achieved through tuning the work function of gold with a self-assembled monolayer of 2,3,4,5,6-pentafluorobenzenethiol (PFBT). The diode fabricated on flexible paper substrate shows a very good electrical stability under bending tests and the frequency response is estimated at more than 20 MHz which is sufficient for radio frequency identification (RFID) applications. It is also shown that the low operating voltage of this diode can be a real advantage for use in a rectenna for energy harvesting systems. Simulations of the diode structure show that it can be used at GSM and Wi-Fi frequencies if the diode capacitance is reduced to a few pF and its series resistance to a few hundred ohms. Under these conditions, the DC voltages generated by the rectenna can reach a value up to 1 V.

An efficient technique for determining the small-signal equivalent-circuit model of a Metal collector-up Heterojunction Bipolar Transistor (C-up MHBT) is presented. The technique employs analytically derived expressions for direct calculation of HBT T-Model equivalent circuit element values in terms of the measured S-parameters. This approach avoids errors due to uncertainty in fitting to large, over determined equivalent circuits and does not require the use of test structures and extra measurement steps to evaluate parasitics. Physically realistic results are demonstrated under various biasing conditions for the n-p-n InP/InGaAs HBT with metallic collector up structure. The agreement between the measured and model-produced data is excellent over the large frequency range and for several polarizations conditions for devices.