Evaluation of Intrinsic Charge Carrier Transport at Insulator-Semiconductor Interfaces Probed by a Non-Contact Microwave-Based Technique

Abstract

We have successfully designed the geometry of the microwave cavity and the thin metal electrode, achieving resonance of the microwave cavity with the metal-insulator-semiconductor (MIS) device structure. This very simple MIS device operates in the cavity, where charge carriers are injected quantitatively by an applied bias at the insulator-semiconductor interface. The local motion of the charge carriers was clearly probed through the applied external microwave field, also giving the quantitative responses to the injected charge carrier density and charge/discharge characteristics. By means of the present measurement system named field-induced time-resolved microwave conductivity (FI-TRMC), the pentacene thin film in the MIS device allowed the evaluation of the hole and electron mobility at the insulator-semiconductor interface of 6.3 and 0.34 cm2 V−1 s−1, respectively. This is the first report on the direct, intrinsic, non-contact measurement of charge carrier mobility at interfaces that has been fully experimentally verified.

Unraveling Unprecedented Charge Carrier Mobility through Structure Property Relationship of Four Isomers of Didodecyl[1]benzothieno[3,2‐b][1]benzothiophene

“…[ 10,17 ] The observation of a drastic difference of mobility at short length-and time-scales on several OSCs and the infl uence of the charge carrier density for molecular semiconductors exhibiting mobilities higher than 100 cm 2 V −1 s −1 tend to support the difference of charge transport mechanism taking place in these materials. It is worth noting here that a decrease of mobility has already been observed consistently at room temperature on monolayer graphene and MoS 2 devices upon increase of the charge carrier density, as a result of scattering effects.…”

“…Holding great promises for the rapid screening of a large number of semiconductor/dielectric pairs, this technique has also recently proved its effi ciency for quantitative probing of interfacial trap sites. [ 10,[15][16][17] It must be emphasized that FI-TRMC is complementary to OFET and Hall-effect methods because it probes charge transport over shorter lengthand time-scales, allowing thus to investigate the elementary steps of charge transport. FI-TRMC will certainly contribute to elucidate the charge transport mechanism exhibited by weakly van der Waals bonded systems.…”

“…FP-TRMC is a completely non-contact device-less method where the average lateral motion of charge carriers (parallel to the quartz substrate), photogenerated in the bulk of thin fi lm samples, is monitored through GHzorder microwave spectroscopy (the interested reader can fi nd additional information relative to the FP-and FI-TRMC measurement techniques in the Experimental Section, Figure S6 (Supporting Information) and recent articles and review articles). [ 10,15,32 ] As shown in Figure 3 a, all drop casted fi lms of 1 -4 gave conductivity transients ( ϕ Σ µ ) with a prompt rise and slow decay upon injection of photogenerated charge carriers ( ϕ and Σ µ represent the quantum yield of generation and sum of the mobilities of positive ( µ + ) and negative ( µ − ) charge carriers, respectively). Interestingly, 2 provided the highest photoconductivity with a maximum value of ( ϕ Σ µ ) max = 1.4 × 10 −3 cm 2 V −1 s −1 .…”

Non-contact, non-destructive, quantitative probing of interfacial trap sites for charge carrier transport at semiconductor-insulator boundary

“…Using this technique, it was determined that a Au/ pentacene/PMMA/SiO 2 /Au MIS device had hole and electron mobilities of 6.3 and 0.3 cm 2 V À1 s À1 , respectively. 10 Non-contact, fully experimental evaluation of intra-domain carrier mobility at interfaces is quite unprecedented, and is a characteristic feature of this system. In this Letter, we further report that the FI-TRMC technique can distinguish between mobile charge carriers at the interface and immobile charges trapped at defects, thus enabling quantification of both the charge carrier mobility and the density of trap sites at insulator-semiconductor interfaces.…”

Angular-Dependent EDMR Linewidth for Spin-Dependent Space-Charge-Limited Conduction in a Polycrystalline Pentacene

“…Because of these latter properties, thermally evaporated thin films of pentacene have been considered for use as active layers in organic field-effect transistors (OFETs), and in this context, the relationship between the morphology of these films and carrier mobility has been the subject of a number of studies (Yang et al, 2005;Gershenson et al, 2006;Honsho et al, 2013;Kim et al, 2014). Thin films produced by thermal evaporation contain both crystalline grains and disordered regions at the grain boundaries, with the degree of crystallinity being controllable by altering the evaporation conditions.…”