Heteroepitaxie von Gruppe III-Nitriden auf Diamantsubstraten für optoelektronische und elektronische Anwendungen
Zusammenfassung der Projektergebnisse
This project has been part of an integrated project to analyze and optimize Ill-nitride heterojunctions on diamond. The task of the group in Ulm had been to grow diamond layer stacks with low defect density and low surface roughness as starting point for the following heteroepitaxy at the WSI in Munich and TU Ilmenau. Thus, a diamond MPCVD growth process has been developed, resulting in a surface roughness well below 1.0 run after substrate plasma polish, buffer layer growth, growth of the backside contact layer and growth of the active layer. In a further task heterojunction diodes, grown by the internal partners and an external partner (NTT) have been analyzed electrically in the temperature and frequency domain. In all cases an interface pinned by defects has been seen in conjunction with a lossy dielectric interfacial layer, most likely representing the disordered nucleation layer of the following A1N growth process. The A1N layers had been Si-doped and grown by MBE and MOCVD. Differences could be observed in the resulting IV-characteristics, presumably because of differences in the A1N nucleation process. However, none of the characteristics allowed to infer an un-pinned interface potential. To gain more insight into the electronic interface characteristics, two further heterostructure configurations have been realized and analyzed. Theses were an (n-type) UNCD / (p-type) diamond heterojunction and a diamond merged diode, where a nitrogen/boron pn-junction was merged with small area Schottky contacts. In both cases the heterogeneous nature of the interface could be clearly identified and in the case of the merged diode also analyzed in respect to the physical parameters involved. In conclusion, despite optimization of the diamond epitaxial layer stack, all AIN heterostructure s have been dominated by their interfacial nucleation layer. The analysis of alternative heterostructures has clearly shown that the density of these interfacial defects dominates the current transport across the junction. The analysis of the interface needs therefore to be based on a heterogeneous model. The most favorable combination would be an AIN heterojunction on 111-oriented diamond substrate. However, 111-oriented diamond substrates are expensive and not commercially available in large quantities with defined surface misorientation and low defect density. The optimization for this case had to be confined to a small number of samples only and it may not have been possible to identify the technological window needed for an optimum performance.
Projektbezogene Publikationen (Auswahl)
- "Ultra-nano-crystalline/single crystal diamond heterostructure diode". Diamond Related Mater. 14 (2005) 416
T. Zimmermann, M. Kubovic, A. Denisenko, K. Janischowsky, O.A. Williams, D.M. Gruen, E. Kohn
- "A new diamond based heterostructure diode". Semicond. Sci. Technol 21 (2006) L32
E. Kohn, A. Denisenko, M. Kubovic, T. Zimmermann, O.A Williams, D.M. Gruen
- Wide Bandgap Diamond Diode. Heterostructure Technology Workshop HETECH 2006 October 2006, Manchester, UK. Book of Abstracts
M. Kubovic, E. Kohn
- "Diamond merged diode". Diamond and Related Mater. 16(2007) 1033
M. Kubovic, H. El-Hajj, E. Kohn
- "Characteristics of Boron δ-Doped Diamond for Electronic Applications". Diamond and Related Mater. 17(2008)409
H. El-Hajj, A. Denisenko, A. Bergmaier, G. Dollinger, M. Kubovic and E. Kohn
