A cathodoluminescence study of boron doped {111}-homoepitaxial diamond films
Introduction
With the increasing interest for diamond in electronic devices, the high quality of p-type boron doped homoepitaxial diamond films with different orientations becomes an important challenge [1]. Though {111}-homoepitaxial diamond films are very important in p–n junctions and other applications; their crystalline quality is still to be improved [2]. Grown in the same conditions, {100}-homoepitaxial diamond films exhibit higher crystalline quality than {111} films [3]. A higher deposition temperature and the addition of oxygen to the gas mixture during the growth have been reported to improve the crystalline quality of diamond films [4], [5], but their advantage was limited. Therefore, we look for an alternative way to improve the crystalline quality of diamond films grown by MPCVD, in particular {111}-homoepitaxial films.
In this work, we use for the first time an original position of the substrate during the growth. Instead of setting the substrate inside the plasma ball [1], we placed it at 2–3 mm downstream (outside) the edge of the visible plasma ball. Our boron doped {111} samples grown at this position have been investigated by cathodoluminescence spectroscopy at liquid helium temperature.
Section snippets
Experimental
The {111}-oriented homoepitaxial diamond films studied in this work were grown at 800 °C and 50 Torrs, during 4 or 4.5 h on standard 2 × 2 mm2 HPHT Ib substrates from Element six in a NIRIM-type growth reactor by the MPCVD technique. The reaction chamber has been evacuated in the range of 2 to 5 × 10− 6 Torr before introducing the gas mixture. During the growth, the Ib substrates were lying at 2–3 mm below the edge of the visible plasma ball (Fig. 1). In other words, they were set outside the plasma ball
Results and discussion
Fig. 2 displays the details of the excitonic energy range from the cathodoluminescence spectrum of the {111}-homoepitaxial diamond layer D-1, non-intentionally doped (n.i.d). The peak at 5.254 eV is the signature of the free exciton assisted by a transverse optical phonon FETO [7]. The position of this peak is slightly shifted from its usual energy reported by several groups (5.268 eV [9], 5.270 eV [10]). The energies of the other peaks in the excitonic range of the CL spectrum from our
Conclusion
In this work we have used cathodoluminescence to investigate the boron incorporation and its effects on the properties of {111}-homoepitaxial diamond films grown by the microwave plasma-assisted chemical vapor deposition (MPCVD) technique, when the growth is achieved outside the visible plasma ball. The cathodoluminescence measurements have also showed the good crystalline quality of these films; in particular those with lowest doping levels.
The incorporation of silicon from the quartz-made
Acknowledgements
The authors would like to thank the French Ministry of Industry for its support by funding this work in the framework of the project NitraDiam, Dr. Hadwig Sternschulte and Prof. A. Deneuville for the valuable discussions and Eng. Fabrice Donatini from Laboratoire de spectrométrie physique CNRS and university Joseph Fourier for his help with the cathodoluminescence set-up.
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