Evidence of different conduction channels in bulk ZnO using f-MEMSA Analysis of transport properties
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1035-L04-06
Evidence of different conduction channels in bulk ZnO using f-MEMSA Analysis of transport properties C. Tavares Chevalier, J. Rothman, and G. Feuillet CEA – LETI, Minatec, 17 rue des Martyrs, Grenoble, 38054, France
ABSTRACT The characterization of transport properties in Zn0 is known to be challenging, particularly due to surface (in the case of bulk) or interface (in the case of heteroepitaxial layers) conduction channels, which puts severe limitations on the interpretation of Hall Effect measurements. In this communication, we report on the study of transport properties of n-type ZnO bulk material using Hall mobility spectrum analysis estimated through the algorithm known as full Maximum Entropy Mobility Spectrum Analysis : f-MEMSA. The electrical properties of bulk Zn0 are measured using a Hall setup for applied magnetic fields µ0H in the range 0T-9T and for temperatures between 50K and 400K. The f-MEMSA analysis highlights the existence of two types of conduction channels in the considered ZnO substrate. We also show that surface conductive channel can be suppressed using appropriate annealing conditions.
INTRODUCTION Most of the devices based on ZnO material are hampered by the lack of reliable p-type doping mainly because of the natural intrinsic n-type conductivity of bulk ZnO. However, in order to obtain either ZnO epilayers with controlled electrical properties or p-doped layers in an unambiguous way, it is essential to well characterize these electrical properties. In fact, the surface conductivity of ZnO crystals is documented by the community and has been reported several times in the literature. Schmidt et al. noticed
that the electrical behavior of epitaxially grown p-type films was hidden by the surface conductivity1 . Markevich et al.2 suggested the formation of a surface layer due to adsorbed oxygen. Look at al. reported effects of surface conduction on Hall measurements and showed how the conductance is dominated by electrons in the bulk above 50K and by the surface conductivity below. The same group also reported the positive effect of oxygen plasma or of electron irradiation for reducing surface conduction3. In this present paper, we characterize the transport properties of bulk ZnO using magnetic field dependent Hall measurements through an original Mobility Spectrum Analysis (MSA). Moreover, the presence of a surface conductive channel, which also has a considerable impact on the measured electrical properties, is demonstrated. After introducing the experimental details of the experimental setup and the particularity of our MSA, we shall discuss the Hall measurements results and the corresponding mobility spectrum for one hydrothermal ZnO substrate before and after annealing under different conditions.
EXPERIMENTAL DETAILS All the considered ZnO substrates originally come from the same supplier. They are hydrothermally grown 10 x10 x 0.5 mm3 bulk ZnO and the Rocking curve obtained on the ZnO diffraction has a FWHM of 20 arsec. The magneto-transport measurements were performed
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