Hydrogen Migration in Single Crystalline ZnO

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1035-L03-10

Hydrogen Migration in Single Crystalline ZnO Klaus Magnus Håland Johansen1,2, Jens Sherman Christensen2, Edouard V. Monakhov2, Andrej Yu. Kuznetsov2, and Bengt Gunnar Svensson2 1 Centre for Materials Science and Nanotechnology, University of Oslo, PB 1126 Blindern, Oslo, 0318, Norway 2 Department of Physics, University of Oslo, PB 1048 Blindern, Oslo, 0316, Norway ABSTRACT Hydrogen has been proposed as one of the contributors to the native n-type doping in asgrown Zinc Oxide and can also be used as an active (intentional) n-type dopant. In this work we have employed Secondary Ion Mass Spectrometry (SIMS) to study deuterium diffusion profiles in single crystalline ZnO. The samples used are hydrothermally grown, high-resistive (10 kΩ cm) monocrystalline ZnO implanted with deuterium to a dose of 1×1015 cm-2 yielding a peak concentration of approximately 5 × 1018 cm-3 at a depth of 2.2 µm. Diffusion profiles have been studied after 30 minutes isochronal heat treatments from 100 ºC up to 400 ºC in steps of 50 ºC. The observed redistribution can be explained by employing a diffusion model which includes trapping of 2H by Li-impurities and an activation energy of 0.85 eV is extracted for the diffusion of 2H. INTRODUCTION Hydrogen is one of the most common impurities in ZnO[1, 2]. Its diffusion properties were studied already in the 1950's and are now revisited due to the increased interest in ZnO as a semiconductor material for optoeletronic devices. One of the first studies on the diffusion of H in ZnO was performed by Thomas and Lander[3]. They studied hexagonal ZnO needles with diameters of 50 - 150µm grown by the Schwarowsky's technique and heating the samples in H atmosphere led to an increase in the electrical conductivity. This increase was attributed to indiffusion and electrical activation of H as a shallow donor. When the H was subsequently removed by out-diffusion the conductivity returned to the original value. Under the assumptions that all H atoms are activated as donors and that the electron mobility is independent of concentration the diffusivity was extracted for different temperatures. This resulted in an activation energy (Ea) for H diffusion perpendicular to the wurtzite c-axis in ZnO of 0.91 eV with a prefactor D0 = 3 ×10-2 cm2s-1. More recently, Ip et al. [4] and Nickel [5] studied the diffusion of 2H in bulk wurtzite (0001) single crystal ZnO by SIMS in plasma-exposed samples. In Ref. 4, the samples were exposed to 2H-plasma at temperatures of 100 ºC -300 ºC allowing 2H to diffuse into the samples for 30 min. Assuming a semi-infinite source model, Ip et al. deduced a 2H diffusivity with an activation energy of 0.17 ± 0.12 eV and a prefactor D0 = 2.5 × 10-8 cm2s-1. In Ref. 5, two diffusion regions have been reported: (i) a region with slow diffusion ranging from the surface down to 1 µm and (ii) a fast diffusion bulk region from 1 µm to 3 µm deep. Assuming the semiinfinite source model, the data in the fast diffusing region have been fitted by the complementary error function. From this f

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