The modulation of electrical carrier transport in metal-MPCVD diamond due to the microcrystalline inhomogeneous barriers J.C. Madaleno * , L. Pereira Departamento de Fı ´sica, Universidade de Aveiro, Campus Universita ´rio de Santiago, 3810-193 Aveiro, Portugal Available online 8 January 2005 Abstract In the present work, we successfully related the macroscopic electrical transport to the microscopic inhomogeneities of the diamond film. A set of MPCVD diamond Schottky devices shows two distinct Schottky Barrier Heights (SBH), one near 1.1 V (dispersionc0.15 V) and other near 0.2 V (dispersionc0.02 V). Two activation energies were found: one near 150 meV (high temperature ionization region) and a very low activation energy near 2 meV (low temperature region, due to hopping effects). The study of the bulk conduction shows some evidence of space charge limited conduction influenced by shallow trap levels, as shown by the differential conductivity analysis. A discussion about a Poole-Frenkel model is included. The calculated macroscopic electrical current is obtained and the correlation with the physical structure is made. D 2005 Elsevier B.V. All rights reserved. Keywords: MPCVD diamond; Electrical properties; Schottky diodes; Grain boundary; SCLC 1. Introduction Diamond has been intensely studied during the last years regarding electronic applications [12] and devices with promising characteristics have already been developed [3– 5]. Nevertheless, homoepitaxial diamond wide application is impaired by the low-area films available. Heteroepitaxial polycrystalline diamond has the same characteristics that make diamond interesting for electronic applications. Some electronic devices have already been proposed [6,7]. In spite of these exceptional preliminary results, there are still some difficulties to be overcome: the carrier transport phenomena and the influence of structural defects and impurities in the electrical behavior are not yet understood. Some results show the influence of the structural defects on the electrical behavior [8] and our previous work [9] shows clearly that the belectrical channelQ lies in grain boundaries and not in diamond microcrystals. An electrical transport model taking into account different contributions from a heterogeneous semiconductor can establish the macroscopic behavior as the result of the electrical bmodulationQ of the microscopic structures. The main goal is a model that can predict the macroscopic electrical behavior as a result of the microscopic constrains imposed by the different structures present in the polycrystalline diamond film. In the present work, a simulation of a current–voltage (I – V) curve for a diamond-metal Schottky diode in the presence of barrier inhomogeneities is made and used to explain the experimental results. At higher applied voltages, the space charge limited conduction (SCLC) seems to control the macroscopic current. 2. Experimental The diamond films were grown on n-type silicon substrates in an AsTex PDS-16 MPCVD (microwave plasma assisted CVD) system. The growth parameters were 3900 W, 100 Torr, 450 sccm H 2 , 18 sccm CH 4 and 0.7 sccm O 2 . The deposition took 3 h. After deposition, the Si substrate was removed in a HF solution, and the free- 0925-9635/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2004.12.003 * Corresponding author. Tel.: +351 234370356; fax: +351 234424965. E-mail address: joana@fis.ua.pt (J.C. Madaleno). Diamond & Related Materials 14 (2005) 584 – 588 www.elsevier.com/locate/diamond