Formation and annealing of dislocation loops induced by nitrogen implantation of ZnO

Abstract

Although zinc oxide is a promising material for the fabrication of short wavelength optoelectronic devices, p-type doping is a step that remains challenging for the realization of diodes. Out of equilibrium methods such as ion implantation are expected to dope ZnO successfully provided that the non-radiative defects introduced by implantation can be annealed out. In this study, ZnO substrates are implanted with nitrogen ions, and the extended defects induced by implantation are studied by transmission electron microscopy and X-ray diffraction (XRD), before and after annealing at 900 • C. Before annealing, these defects are identified to be dislocation loops lying either in basal planes in high N concentration regions, or in prismatic planes in low N concentration regions, together with linear dislocations. An uniaxial deformation of 0.4% along the c axis, caused by the predominant basal loops, is measured by XRD in the implanted layer. After annealing, prismatic loops disappear while the density of basal loops decreases and their diameter increases. Moreover, dislocation loops disappear completely from the sub-surface region. XRD measurements show a residual deformation of only 0.05% in the implanted and annealed layer. The fact that basal loops are favoured against prismatic ones at high N concentration or high temperature is attributed to a lower stacking fault energy in these conditions. The coalescence of loops and their disappearance in the sub-surface region are ascribed to point defect diffusion. Finally, the electrical and optical properties of nitrogen-implanted ZnO are correlated with the observed structural features.

Influences of defects evolvement on the properties of sputtering deposited ZnO:Al films upon hydrogen annealing

“…This can be attributed to the migration and agglomeration of PD and SF. 31 At this annealing temperature, O i has been effectively removed (refer to Fig. 3(b)), thus new PD and SF can hardly be generated, and the grain size will no longer be reduced, as seen in Fig.…”

“…This is because at high annealing temperatures, PD and SF will diffuse to the grain surface and disappear there. 31 Thus the grain size increases again (see Fig. 3(c)).…”

“…The migration barrier of Zn i (0.57 eV) in ZnO is much lower than O i (at least 0.9 eV) and it is highly mobile even at room temperature. 31,32 Zn i tends to diffuse to O i sites and form bonds with O i . Both Zn i and O i then become lattice atoms causing local lattice distortion, forming partial dislocations and finally leading to the formation of stacking faults.…”

Defect formation and thermal stability of H in high dose H implanted ZnO

“…2(a), the elongation of the lattice constant normal to the surface, as created by H implantation in the ZnO samples can also be found in N implanted ZnO, 44 and in other implanted Wurtzite semiconductors, such as Eu implanted AlN 45 and He implanted 4H-SiC, 46 as well as in implanted cubic semiconductors. 47 In Fig.…”

“…This result is similar to what has been reported in N implanted ZnO, which is annealed for a shorter time (15 min) but at a higher temperature (900 C). 44 Thus, annealing at a temperature higher than 800 C to 900 C or a longer annealing duration may be needed to completely recover the lattice distortions caused by H implantation. This is especially important for doping of ZnO based devices and structures using ion implantation as the damage could be detrimental for the optical and electrical device properties.…”