Dislocation-related deep states induced by irradiation in HVPE n-GaN
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L11.32.1
Dislocation-related deep states induced by irradiation in HVPE n-GaN
A. Castaldini, A. Cavallini and L. Polenta INFM and Dipartimento di Fisica Viale Berti Pichat 6/2, I-40127 Bologna, Italy ABSTRACT This paper deals with defects induced by proton irradiation in n-GaN. The samples were HVPE grown, irradiated with 24 GeV protons. DLTS was performed on both as-grown and irradiated samples with planar and normal collector configurations to evidence the dislocation effect. Two electron traps were identified in the as-grown material by both diode structures: trap EC1 (EC – 0.19eV) and trap EC2 (EC – 0.25eV), EC2 being the dominant one. Irradiation consistently affects the pre-existing levels in such a way so as their appearance strongly depends on the diode structure, hence on the region probed by DLTS. This contribution focuses on the actual existence of two deep traps EC1 and EC2 emitting in GaN at low temperature and on the different nature of the deep levels associated to EC1 and EC2. Their filling kinetics was studied since we supposed that EC2 would be associated to extended defects, as already reported in literature. Indeed, the site density of EC2 logarithmically depends on the filling pulse width, demonstrating that this trap is definitely associated to extended defects. The trap EC1, on the contrary, exhibits the filling kinetics peculiar of point defects.
INTRODUCTION Recently, a strong effort has been devoted to the study of defects induced by irradiation in gallium nitride (GaN) and a wide debate [1,2] is currently running on the nature of the electron traps emitting at low temperature. Indeed, III-nitride semiconductors are in use for space-based applications and it is therefore of major importance to know how irradiation, mainly by electrons and protons, affects the GaN-based device properties. Furthermore, as proved from ages for what concerns silicon, irradiation is a powerful tool to investigate the defect properties since it introduces in a controlled way elemental defects. Concerning deep level transient spectroscopy (DLTS) investigations, for long time it was suggested that low temperature spectra were due to the convolution of three traps, the levels of which would range from 60 to about 200 meV. However, DLTS conclusions are hard to be drawn because of the closeness of the trap energy values involved, hence of the overlapping of their DLTS peaks. Thus, not a definitive confirmation of how many traps contribute to the low temperature emission nor their association to specific defects has been up to now reached. This contribution deals with such low temperature emitting traps, comparing their features before and after irradiation with high energy protons. In addition, measurements were carried out in both planar and cross-sectional diode configuration, which produces a depth-dependent variation in the DLTS spectra. As a matter of fact, the two geometries probe regions with different distribution and densities of dislocations so as to evidence possible dislocation-related effects.
L11.32
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