Non-Arrhenius Reorientation Kinetics for the B-H Complex in Si: Evidence for Thermally Assisted Tunneling

Abstract

The B-H complex in Si can be aligned by stress and reorients with an activation energy of roughly 0.2 eV. We combine new measurements of the reorientation kinetics of the B-H complex made by the stress-induced dichroism technique with previous internal friction results to show that the reorientation kinetics are non-Arrhenius.These results support Stoneham's suggestion [Phys. Rev. Lett. 63, 1027] that reorientation occurs by thermally assisted tunneling.We have also discovered the remarkable fact that the reorientation rate for B-D is greater than that of B-H for T & 57 K. PACS numbers: 61.72.Ji, 78.30.Hv, 78.50.6e The thermally activated reorientation of acceptorhydrogen complexes in semiconductors is well known [1 -8]. The activation energies for reorientation are typically a few tenths of an eV. The best studied example is the B-H complex in Si for which the reorientation kinetics have been studied by stress-induced dichroism[1] at low temperature (=65 K) and internal friction [7,8] at high temperature (=130 K). Adiabatic total energy surfaces have been calculated theoretically for the B-H complex [9],and the agreement of the measured activation energy for reorientation with the calculated barrier height is excellent.In spite of what appears to be good agreement between experiment and theory, Stoneham [10,11] has suggested that the reorientation of the acceptor-H complexes is by a thermally assisted tunneling mechanism and that a model in which the hydrogen jumps over a barrier is inappropriate. This is well known to be the case for hydrogen diffusion in metals [12] and has been studied for many years. One of the classic signatures of quantum diffusive motion of light interstitials in metals is non-Arrhenius hopping kinetics. Here, by combining new stress-induced dichroism data with previous results obtained by internal friction [7,8], we show for the first time that the reorientation kinetics of the B-H complex are non-Arrhenius and thereby provide experimental support for a tunneling mechanism for reorientation. Further, the reorientation kinetics of the B-H and B-D complexes have been measured together in the same samples to convincingly show that the activation energies for reorientation are different and that the reorientation rate of the B-D complex is faster than that of B-H above 57 K.The samples for most of our experiments were prepared from floating zone silicon that had been ion implanted with B at energies of 30, 100, and 180 keV, each to a dose of 7 X 10' cm . The implants were activated by a rapid thermal anneal at 1200 C for 60 s. Oriented bar-shaped samples with dimensions 2 x 2 x 9 mrn were prepared for stress studies. Both hydrogen and deuterium were introduced into each sample at 120 C in a Technics Planar Etch II plasma reactor. In order to check that our results were independent of the sample fabrication procedure and doping level, stress samples were also prepared with a lower implantation dose, i.e. , 2 X 10' cm at 30, 100, and 180 keV, and from bulkdoped material with [B] = 2 X 1...

Hydrogen motion in the Cu-H complex in ZnO

“…36 We want to compare this value with the reorientation barrier of H in the acceptor-hydrogen complexes in Si. Two defects, B-H and Al-H, were investigated and it was found that E a Ϸ 0.2 eV for the B-H complex, 26 whereas E a = 0.37 eV for hydrogen bound to Al. 27 Obviously, of these two complexes, it is Al-H that has to be compared with isolated hydrogen since Al and Si are next neighbors in the Periodic Table. Indeed, in this case, the activation barrier for hydrogen reorientation in the Al-H complex is only 20% off from E a of isolated hydrogen.…”

“…An enhancement of the reorientation temperature with replacement of hydrogen by deuterium is observed for acceptor-hydrogen complexes in Si and is normally attributed to zero-point energy effects. 26 It follows from Fig. 3 that hydrogen motion in the Cu-H complex is thermally activated and tunneling is not a dominating mechanism resulting in the defect alignment under stress.…”

“…Such frequencies are typical for hydrogen-related defects in other semiconductors and characterize hydrogen vibrations. [24][25][26][27][28][29] The reorientation temperature, on the other hand, is very sensitive to the value of E a . From the data shown in the figure, we find that E a = 0.52± 0.04 eV.…”

“…31,32 Even so, from the studies of the acceptor-hydrogen complexes in Si, it is known that corrections to the Arrhenius-type behavior are small. 26 Equation ͑6͒ was employed to fit the experimental data presented in Fig. 3.…”

Al-H and Al-D complexes in Si: A uniaxial-stress study of the hydrogen vibrational modes

“…33 Recent work suggests that the B-H complex in Si reorients by a thermallyassisted tunneling mechanism. 34,35 We show in Sec. V that the Al-H complex can also be aligned by stress, but with a small stress coupling, and that it too exhibits thermally activated reorientation.…”