TIPS-pentacene based MIS structure using a polymer insulator: role of interface traps studied using HMDS treatment, frequency and light intensity

Abstract

Though it is well known that the characteristics of solution-processed polymer based organic thin film transistors depend crucially on the semiconductor/polymer interface. The mechanisms of charge processes are not understood well. We show that the nature of the interface charge processes is best studied using metal-insulator-semiconductor (MIS) structure. We choose to study the model material system of TIPS-pentacene based MIS capacitor with poly-4-vinylphenol (PVP) as the gate dielectric. We investigate the nature of the interface traps through the effect of frequency, and white light on the capacitance-voltage (C-V) characteristics with and without hexamethyldisilazane (HMDS) treatment of the PVP surface. The lower threshold voltage in bare PVP devices is due to gate field enhancement with electron traps which get suppressed with HMDS treatment. The capacitance-frequency (C-f) measurements show a single slope in case of HMDS treated PVP surface while two distinct slopes are observed for the case of bare PVP surface confirming the presence of two traps in bare PVP organic semiconductor interface. The effect of white light intensities on the threshold of both treated and untreated interfaces confirm the presence of electron traps which on being trapped modify the net gate field. The observed effects are attributed to the large number of ions, such as oxygen (O2 ̶) and hydroxyl ions (OH−) which give rise to electron traps of approximate concentration ∼2.1 × 1011 cm−2, which can be neutralized by HMDS treatment.