Tuning Charge Transport at the Interface between Indium Phosphide and a Polypyrrole−Phosphomolybdate Hybrid through Manipulation of Electrochemical Potential

• Published in: The journal of physical chemistry. B 2002-02, Vol.106 (7), p.1622-1636
• Main Authors: Daniels-Hafer, Carrie, Jang, Meehae, Boettcher, Shannon W, Danner, Robert G, Lonergan, Mark C
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp013022w

The temperature-dependent current−voltage and capacitance−voltage characteristics of interfaces between InP and a polypyrrole−phosphomolybdate hybrid material (PMH) are reported as a function of the redox potential, E PMH, of the PMH (as controlled by its extent of oxidation or p-type doping level). The current−voltage characteristics of the interfaces are sensitive to E PMH and can be controlled over a much wider range than possible with analogous InP|metal interfaces. For the n-InP|PMH interfaces, the ability to tune the current−voltage characteristics by controlling E PMH stems from control over the interfacial potential barrier φb characteristically present at semiconductor interfaces. The spatially averaged φb from capacitance−voltage measurements shifts from 0.59 to 1.05 V with a shift in E PMH from −0.05 to +0.99 V vs SCE, leading to an index of interface behavior of S = dφb/dE PMH = 0.39. For the n-InP|PMH interfaces, heterogeneous electron transfer is slower than at the semiconductor|metal interfaces:  the transmission coefficient κ, describing the probability that a carrier with sufficient thermal energy to surmount φb will actually cross the interface, is observed to be 0.003, independent of E PMH and less than the semiconductor|metal limit of κ = 1. For the p-InP|PMH interfaces, the extent to which the current−voltage characteristics can be controlled through manipulation of E PMH depends on both φb and κ. The S value for the p-InP interfaces is nearly identical with that for the n-InP|PMH interfaces:  the spatially averaged capacitance−voltage φb shifts from 0.83 to 0.49 V with a shift of E PMH from −0.07 to +0.65 V vs SCE, leading to S = 0.37. Over the same range of E PMH, the value of κ decreases from the range of 1−0.1 to the range 0.05−0.0001 as E PMH increases, suggesting that the majority carrier transfer rate depends on the details of the electronic structure of the PMH. The S values and empirical ideality factors observed for both the n-InP and p-InP interfaces are inconsistent with classic interface state models describing Fermi-level pinning. Nearly all of the interfaces demonstrate characteristic signatures of a heterogeneous barrier potential, such as, (1) ideality factors greater than unity and a decreasing function of temperature and (2) disagreement between the φb extracted from capacitance−voltage and temperature-dependent current−voltage measurements (Richardson plots). The quantitative application of Tung's barrier inhomogene