Effect of dislocations on charge carrier mobility–lifetime product in synthetic single crystal diamond

Abstract

The authors report correlations between variations in charge transport of electrons and holes in synthetic single crystal diamond and the presence of nitrogen impurities and dislocations. The spatial distribution of these defects was imaged using their characteristic luminescence emission and compared with maps of carrier drift length measured by ion beam induced charge imaging. The images indicate a reduction of electron and hole mobility-lifetime product due to nitrogen impurities and dislocations. Very good charge transport is achieved in selected regions where the dislocation density is minimal. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2711754͔ Diamond has been studied for many decades as a solid state ionization chamber for radiation detection. 1,2 It combines a number of extreme properties, such as large charge carrier saturation velocities, radiation hardness, tissue equivalence, chemical inertness, and high thermal conductivity. Its large band gap of 5.48 eV results in solar blindness and low leakage currents during room temperature operation, 3 for example, in high energy physics experiments, 4 medical dosimetry, 2 beam monitoring, 4 and neutron detection. 5 The detector performance and stability are determined by structural imperfections and impurities in the material, which influence the induced current signal. In polycrystalline diamond detectors it is known that grain boundaries act as charge trapping centers, severely limiting the spectroscopic performance. Ion beam induced charge ͑IBIC͒ imaging has been used routinely to study diamond radiation detectors, their priming behavior, and interactions due to optical illumination. 6 Recently, single crystal chemical vapor deposited ͑CVD͒ diamond has been synthesized successfully in a number of laboratories. [7][8][9] This material allows us to study the effect of defects on charge transport in the absence of grain boundaries.In this work, we present a combination of luminescence and IBIC imaging in a synthetic single crystal diamond provided by Element Six Ltd. ͑UK͒. The spatial defect distribution of the material has been investigated using a photograph of the luminescence excited by Ͻ227 nm wavelength ultraviolet ͑UV͒ irradiation of a xenon lamp. Cathodoluminescence ͑CL͒ spectral imaging at room temperature has been carried out at the University of Strathclyde 10 with an electron energy of 10 keV and typical beam currents of 4 -10 nA. IBIC images were acquired at room temperature at the nuclear microbeam facility of the Surrey Ion Beam Centre. 11 The IBIC spatial resolution is limited to 10 m by the number of pixels in the scan area.Each proton interaction produces electron hole pairs, corresponding to a charge Q 0 in the device, and the charge carriers drift through the material according to the electric field. The induced current pulse is integrated by an Ortec 142 A charge sensitive preamplifier followed by an Ortec 570 shaping amplifier. The amplitude Q of each interaction is proportional to the carrier drift length; it is calibrated...

A review of ion beam induced charge microscopy

“…These semi-insulating materials are 'super-depleted' at low bias voltages and so operate with an effective space charge region extending throughout the device thickness. [93]. This material was grown by microwave enhanced chemical vapour deposition (CVD) and is a truly monocrystalline epitaxial diamond layer, typically grown in pieces of 5 · 5 mm 2 and up to 1 mm thick.…”

Mapping of polarization and detrapping effects in synthetic single crystal chemical vapor deposited diamond by ion beam induced charge imaging

“…The horizontal luminescent lines are the introduced nitrogen rich layers. A cathodoluminescence experiment 34 has shown that these nitrogen rich layers emit a signal with a zero phonon line at 2.15 eV, originating from a neutral nitrogen vacancy complex. 35 Additionally, vertical line structures with enhanced blue band A luminescence are also distinguishable.…”

Formation of secondary electron cascades in single-crystalline plasma-deposited diamond upon exposure to femtosecond x-ray pulses

“…In addition, single-crystalline chemical vapor deposition ͑SC-CVD͒ diamond exhibits a high saturation drift velocity, high carrier mobilities, 2,3 and high charge collection efficiency with good spatial homogeneity. 4 The maximum resolution, e.g., in imaging biological materials, that can be achieved in x-ray diffraction is today limited by damage. Ultrashort high-intensity x-ray pulses from sources like x-ray free electron lasers, which currently are under development, are expected to extend this limit significantly.…”