Ali Nawaz

Modification of the charge transport properties of the copper phthalocyanine/poly(vinyl alcohol) interface using cationic or anionic surfactant for field-effect transistor performance enhancement

We report on the performance enhancement of organic field-effect transistors prepared using cross-linked poly(vinyl alcohol) as gate dielectric and copper phthalocyanine as channel semiconductor through gate dielectric surface treatment. The gate dielectric surface was treated using either a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB), or an anionic surfactant, sodium dodecyl sulfate (SDS). We determined the charge-carrier field-effect mobility ( μ FET) in these transistors as a function of the effective channel thickness in the channel bottleneck, near to the transistor source. When compared to the untreated devices, in the devices treated with CTAB or SDS, the channel formation occurs at lower gate voltage and the carrier mobility in the thinnest channel region, corresponding to the immediate vicinity of the insulator/semiconductor interface, is significantly higher. The surfactant treatment leads to a tenfold increase in μ FET and significant enhancement in capacitance, on/off current ratio and transconductance of the transistor.

Gate dielectric surface treatments for performance improvement of poly(3-hexylthiophene-2,5-diyl) based organic field-effect transistors

We report on enhanced performance in poly(3-hexylthiophene-2,5-diyl) (P3HT) based organic field effect transistors (OFETs) achieved by improvement in hole transport along the channel near the insulator/semiconductor (I/S) interface. The improvement in hole transport is demonstrated to occur very close to the I/S interface, after treatment of the insulator layer with sodium dodecyl sulfate (SDS). SDS is an anionic surfactant, with negatively charged heads, known for formation of micelles above critical micelle concentration (CMC), which contribute to the passivation of positively charged traps. Investigation of field-effect mobility (μFET) as a function of channel bottleneck thickness in OFETs reveals the favorable gate voltage regime where mobility is the highest. In addition, it shows that the gate dielectric surface treatment not only leads to an increase in mobility in that regime, but also displaces charge transport closer to the interface, hence pointing toward passivation of the charge traps at I/S interface. OFETs with SDS treatment were compared with untreated and vitamin C or hexadecyltrimethylammonium bromide (CTAB) treated OFETs. All the treatments resulted in significant improvements in specific dielectric capacitance, μFET, on/off current ratio and transconductance.

Poly(Vinyl Alcohol) Gate Dielectric Treated With Anionic Surfactant in C60 Fullerene-Based n-Channel Organic Field Effect Transistors

We report on the preparation and performance enhancement of n-type low-voltage organic field effect transistors (FETs) based on cross-linked poly(vinyl alcohol) (cr-PVA) as gate dielectric and C60 fullerene as channel semiconductor. Transistors were prepared using bottom-gate top-contact geometry and exhibited field-effect mobility (µFET) of 0.18 cm2V-1s-1. Treatment of the gate dielectric surface with an anionic surfactant, sodium dodecyl sulfate (SDS), passivates the positively charged defects present on the surface of cr-PVA, hence resulting in overall transistor performance improvement with an increase in µFET to 1.05 cm2V-1s-1 and additional significant improvements in dielectric capacitance, transistor on/off current ratio and transconductance.