Raman measurements were performed on molecular beam epitaxially grown GaN before and after implantation with Ar+, Mg+, P+, C+, and Ca+ ions. With increasing ion dose, new Raman peaks arise at 300, 360, 420, and 670 cm−1, independent of the ion species. After rapid thermal annealing at temperatures between 900 and 1150 °C for 15 s, the intensities of the Raman modes decrease with increasing temperature with the exception of the 360 cm−1 mode which shows a maximum in intensity after annealing at 900 °C. The mode at 300 cm−1 is attributed to disorder-activated Raman scattering, whereas the other three modes are assigned to local vibrations of vacancy-related defects.
This paper deals with the results of a systematic investigation of damage generation and accumulation until amorphization induced by 180 keV Ca ϩ and Ar ϩ implantation in GaN films at liquid-nitrogen temperature. The structure of GaN films before and after implantation was characterized by Rutherford backscattering/ channeling, cross-sectional transmission electron microscopy, and high-resolution x-ray diffraction. The asimplanted GaN films exhibits an expanded lattice. Its texture was determined by pole figure measurement. An amorphous component has been found after Ca ϩ implantation at doses not less than 3ϫ10 14 cm Ϫ2. This suggests that Ca ϩ implantation for p-type doping be carried out below this dose, in order to avoid unrecoverable structural damage and to achieve better transport properties. On the other hand, implantation with higher doses is generally needed to compensate for the native electron background of GaN and to realize p-type reversal. This conflict uncovers the essential difficulty for p-type doping of GaN by ion implantation. The maximum damage concentration exists in a depth of 100 nm below the surface, which corresponds to the mean projected range, and broadens gradually towards surface and greater depth with increasing ion fluence. The thresholds for the amorphization of GaN films are revealed to be 6ϫ10 15 cm Ϫ2 for both Ca ϩ and Ar ϩ implantation. The amorphization mechanism is discussed and the accumulation of amorphous clusters seems to be the reason for the collapse of GaN crystalline. ͓S0163-1829͑98͒02904-X͔
The time-dependent evolution of the potential, the electrical field, and the particle movement surrounding two-dimensional trenches during a high voltage pulse in the context of plasma immersion ion implantation is studied by a particle-in-cell simulation. The numerical procedure is based on the solution of Poisson‘s equation on a grid and the determination of the movement of the particles on the grid. This simulation is combined with simulation codes for the calculation of depth profiles and sputtering yields. The retained ion dose and the depth resolved concentration distribution were determined in dependence on the rise time of the pulse between 0.1 and 2 μs, pulse durations between 1 and 10 μs and the ion mass (m=20–131, i.e., Ne,…,Xe) for trenches with two different aspect ratios (η=3:1 and 3:2). The results are discussed on the basis of the temporal evolution of the energy of the ions and the impact angle of the ions during the pulse.
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