Analyte chemisorption and sensing on $n$- and $p$-channel copper phthalocyanine thin-film transistors

Chemical sensing properties of phthalocyanine thin-film transistors have been investigated using nearly identical $n$- and $p$-channel devices. $P$-type copper phthalocyanine (CuPc) has been modified with fluorine groups to convert the charge carriers from holes to electrons. The sensor responses to the tight binding analyte dimethyl methylphosphonate (DMMP) and weak binding analyte methanol (MeOH) were compared in air and $N2$⁠. The results suggest that the sensor response involves counterdoping of pre-adsorbed oxygen $(O2)$⁠. A linear dependence of chemical response to DMMP concentration was observed in both $n$- and $p$- type devices. For DMMP, there is a factor of 2.5 difference in the chemical sensitivity between $n$- and $p$-channel CuPc thin-film transistors, even though it has similar binding strength to $n$- and $p$-type CuPc molecules as indicated by the desorption times. The effect is attributed to the difference in the analyte perturbation of electron and hole trap energies in $n$- and $p$-type materials.