Interface states in polyfluorene-based metal–insulator–semiconductor devices

• Published in: Organic electronics Vol. 8; no. 5; pp. 591 - 600
• Main Authors: Yun, M., Gangopadhyay, S., Bai, M., Taub, H., Arif, M., Guha, S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-10-2007; Elsevier
• Subjects: Applied sciences; Capacitance–voltage characteristics; Compound structure devices; Diodes; Electronics; Exact sciences and technology; Interfaces; MIS diode; Polyfluorene; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; 84.37.+q; 73.61.Ph; Polyfluorene; Capacitance–voltage characteristics; 61.41.+e; MIS diode; 72.80.Le; Aluminium oxide; Interface state; Atomic force microscopy; Density of states; Frequency dependence; Semiconductor insulator contact; Oxide layer; Dielectric materials; Thermal cycle; Doped materials; MIS structure; Polymer; Liquid phase; 61.41.+e; 72.80.Le; 73.61.Ph; 84.37.+q; Liquid crystals; Nematic crystals; MIS diode; Polyfluorene; Capacitance-voltage characteristics; Flat band voltage; p type semiconductor; Silicon; Time constant; MIS devices; Voltage capacity curve
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2007.04.007

Hybrid metal–insulator–semiconductor structures based on ethyl-hexyl substituted polyfluorene (PF2/6) as the active polymer semiconductor were fabricated on a highly doped p-Si substrate with Al
2O
3 as the insulating oxide layer. We present detailed frequency-dependent capacitance–voltage (
C–
V) and conductance–voltage characteristics of the semiconductor/insulator interface. PF2/6 undergoes a transition to an ordered crystalline phase upon thermal cycling from its nematic-liquid crystalline phase, confirmed by our atomic force microscope images. Thermal cycling of the PF2/6 films significantly improves the quality of the (PF2/6)/Al
2O
3 interface, which is identified as a reduced hysteresis in the
C–
V curve and a decreased interface state density (
D
it) from ∼3.9
×
10
12
eV
−1
cm
−2 to ∼3.3
×
10
11
eV
−1
cm
−2 at the flat-band voltage. Interface states give rise to energy levels that are confined to the polymer/insulator interface. A conductance loss peak, observed due to the capture and emission of carriers by the interface states, fits very well with a single time constant model from which the
D
it values are inferred.