Carrier lifetime, diffusion length and mobility in (100) CVD diamond samples pre-treated in an O 2 /H 2 -plasma
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Carrier lifetime, diffusion length and mobility in (100) CVD diamond samples pre-treated in an O2/H2-plasma W. Deferme1, K. Haenen1,2, M. Nesládek1,2, T. Malinauskas3, L. Lubys3, K. Jarašinjnas3 1
Hasselt University, Institute for Materials Research (IMO), Diepenbeek, Belgium 2 IMEC vzw, Division IMOMEC, Diepenbeek, Belgium 3 Vilnius University, Institute of Applied Research, Vilnius, Lithuania
ABSTRACT In this article, (100) Ib diamond substrates are pre-treated for different durations in an O2/H2-plasma, influencing the etching of defects like unepitaxial crystals, flat top hillocks, and pyramidal hillocks [1-3]. Such procedure is used to prevent those to incorporate into the ~ 100ȝm thick CVD diamond film, which is subsequently grown on top. While the surface morphology and structure of substrates and films are studied by SEM, the time-resolved LightInduced Transient Grating (LITG) technique provides information on the excess carrier parameters close to the front surface of the grown layers. This technique is particularly useful as it does not requires a separation of the CVD film from its substrate. It will be shown that O2/H2plasma treatments of more than 150 minutes but less than 240 minutes largely reduce the incorporation of defects in the bulk of the grown film. This, in turn, influences the carrier dynamics as measured by LITG, but also the surface roughness and growth rate as shown by SEM. INTRODUCTION The recent advances in the deposition of high quality homoepitaxial CVD diamond make this material increasingly interesting for device applications [4-6]. An important aspect of the growth is the pursuit of quality improvement of the diamond crystal with its thickness, related to the coalescence of individual growth sectors, and the suppression of the propagation of certain dislocations during the initial stages of growth [7]. Hence, there is a large interest in understanding how the defects (intrinsic and extrinsic) related to these initial stages, influence the charge carrier parameters like mobility and lifetime. To ensure the high efficiency of charge collection, the carrier diffusion length should be as high as possible which can be achieved by reducing the density of electrically active point and extended defects. An etching step prior to the growth step has been shown to be efficient [2,4,7] but it is unclear until now how the duration of this pre-treatment is influencing the removal of defects or the eventual formation of new defects. Therefore it is of great interest to differ the etching time and evaluate the influence of this duration on the electronic properties such as carrier lifetime, diffusion coefficient, mobility and carrier diffusion length [8,9]. The time-resolved light-induced transient grating technique, used in this work, has already shown its great potential for other materials such as doped CdTe and GaN [10,11]. As no contacts are needed on the sample under study and no lift-off from the substrate is required this technique is also very promising for thick diamond layers grown on I
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