Deep-level luminescence at 1.0 eV in 6H SiC

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Deep-level luminescence at 1.0 eV in 6H SiC B. Magnusson1 , A. Ellison2 , N.T. Son1 , and E. Janzen1 1 Department of Physics and Measurement Technology, Linkoping University, SE-581 83 Linkoping, Sweden 2 Okmetic AB, Hans Meijers vag 2, SE-581 83 Linkoping, Sweden ABSTRACT

Results from photoluminescence (PL) and Zeeman e ect measurements of a PL center, labeled UD-1, in 6H SiC are presented. The spectrum consists of three no phonon-lines (NPLs) at 0.9952, 1.0015 and 1.0020 eV. The luminescence starts decreasing in intensity above 40 K and is completely quenched at 80 K. The observed Zeeman splitting reveals a spin one half of the ground state of the two highest energy lines. No splitting of the 0.9952 eV line is detected. The gk -value for the 1.0015 eV and 1.0020 eV lines are gk = 1:4 and gk = 1:7, respectively. For both lines, g? = 0. The C3v symmetry indicates that the UD-1 center is either a substitutional defect or a complex with its constituents lying along the c-axis of the lattice. INTRODUCTION

We have studied the infrared luminescence around 1.0 eV from an unidenti ed defect center, labeled UD-1, found in as-grown high-temperature CVD (HTCVD) [1] 6H SiC samples. The samples are transparent and usually have high resistivities, even when they are not intentionally doped with vanadium. Some other sharp luminescence lines (UD-2 at 1.1 eV , UD-3 at 1.35 eV) [2] are usually also observed in the infrared region together with the luminescence from vanadium [3] and chromium [4]. The intensities of the above mentioned luminescence centers vary in relative intensity between di erent samples. However, the PL of the vanadium or UD-1 centers usually dominant. The UD-1 luminescence is also detected in commercial substrates, especially in p-type material. Since the UD-1 NPLs in the commercial substrates usually are so broad and overlapping with each other, it is therefore diÆcult to obtain good results from optical investigations. In this study we have performed PL and Zeeman measurements. The luminescence is also measured at di erent temperatures and polarizations. EXPERIMENT

The material used in this study was HTCVD 6H SiC bulk samples. The residual doping concentrations of boron and nitrogen are in the 1015 1016 cm 3 range. For aluminum and the common transition metals (Ti, V and Cr) the concentration are below the detection limit of secondary ion mass spectrometry (less then approximately 5  1014 cm 3 ). The Fourier transformed PL (FTPL) measurements were performed either in a continuous

ow cryostat at 10 K or in a bath cryostat, which allows temperature regulation in the range

H7.11.1

from 1.6 K to room temperature. The samples were excited using the ultraviolet lines (351.1-363.8 nm) from an Ar ion laser. To detect the luminescence, a Bomem DA8 Fourier Transform spectrometer equipped with a quartz beamsplitter and a North Coast Ge detector is used. In the polarization experiments the sample was excited through the front side of the sample (parallel to the c-axis) and the luminescence is collected from th