AVS 46th International Symposium
    Organic Electronic Materials Topical Conference Tuesday Sessions
       Session OE+EM+AS-TuM

Invited Paper OE+EM+AS-TuM7
Schottky Energy Barriers and Charge Injection at Metal/Organic Interfaces

Tuesday, October 26, 1999, 10:20 am, Room 616/617

Session: Interfaces and Characterization of Organic Thin Films
Presenter: I.H. Campbell, Los Alamos National Laboratory
Authors: I.H. Campbell, Los Alamos National Laboratory
B.K. Crone, Lucent Technologies
R.L. Martin, Los Alamos National Laboratory
D.L. Smith, Los Alamos National Laboratory
C.J. Neef, University of Texas, Dallas
J.P. Ferraris, University of Texas, Dallas
Correspondent: Click to Email
We present independent measurements of metal/organic Schottky energy barriers and their charge injection characteristics in metal/organic/metal structures. The Schottky energy barriers were measured using internal photoemission and built-in potential techniques. The Schottky energy barriers to a poly (p-phenylene vinylene) based polymer (MEH-PPV) and to Alq were measured for a variety of metals with work functions ranging from 2.7 eV (Sm) to 5.6 eV (Pt). For MEH-PPV we find good agreement with the ideal Schottky model. In contrast, for Alq we find that the ideal Schottky picture is not applicable and that electron injecting contacts are pinned about 0.6 eV below the electron conducting states. The charge injection characteristics of these contacts were investigated by measuring the current-voltage characteristics of single carrier structures. The dependence of the current-voltage characteristics on the Schottky energy barrier is quantitatively described by a device model which includes charge injection, transport and space charge effects in the structure. For Schottky barriers less than about 0.3 eV the current in the structure is space charge limited and the contact is ohmic. Finally, we present results using organic self-assembled monolayers to manipulate the metal/organic Schottky energy barrier and to control charge injection into the organic material. The monolayers are used to insert a thin (1 nm) dipole layer between the metal contact and the organic material. Depending upon the orientation of the dipole layer the Schottky energy barrier may be increased or decreased and the corresponding charge injection properties degraded or enhanced.