H. G. Brion

Yield point and dislocation mobility in silicon and germanium

Measurements of the lower yield point in silicon and germanium, covering wide ranges of temperature and strain rate, are presented. The results indicate that Haasen’s model for the beginning of the plastic deformation of semiconductors has to be modified for germanium, while it is confirmed for silicon.

Dynamical recovery and self-diffusion in InP

Abstract Single crystals of InP with ⟨123⟩ orientation have been deformed at constant strain rates at temperatures between 540 and 780°C. The resulting stress–strain curves are rather similar to those obtained for other semiconductors such as Ge, Si and InSb, and two stages of dynamical recovery can be clearly identified. From the strain-rate and temperature dependences of the stress τiii at the beginning of the first recovery stage, an activation energy of 2.3 eV is deduced. This may be regarded as a lower bound for the activation energy of self-diffusion of the slowest-moving species; for the pre-exponential factor D0 of the diffusion coefficient a value between 10−3 and 10−2 cm2 s−1 is estimated.

A REGIME OF THE YIELD POINT OF SILICON AT HIGH TEMPERATURES

We present measurements of the lower yield point of undoped floating-zone silicon at temperatures between 800 and 1300 °C. The knowledge of the defect structure in this temperature range is of considerable importance for the numerical simulation of dislocation generation in various solar silicon materials. Above about 1050 °C, we find marked deviations from the well-known low-temperature behavior, thus establishing a further deformation regime. It is characterized by an activation energy of 4.1 eV. Comparison to preliminary work indicates that this effect depends on the as-grown dislocation density, but not on the ambient during deformation. We tentatively assume that it may reflect the change in the mechanism of self-diffusion typical for silicon at high temperatures.

The deformation regimes of the yield point of silicon

Abstract The upper yield point of undoped floating-zone silicon has been investigated. The measurements were performed on dislocation-free single crystals deformed at temperatures between 800 and 1300°C and a strain-rate range extending over three orders of magnitude. The upper yield point emerges up to 1250°C. In principle, the data reflect the behaviour of the lower yield point, thus confirming the existence of a novel deformation regime of silicon at high temperatures and small strain rates. There are, however, features which resemble the behaviour of highly doped material to some extent. This surprising similarity raises questions concerning the interpretation of the different deformation regimes observed in undoped and doped silicon.

The yield point of In‐doped GaAs between 500 and 900 °C

In‐doped (5×1019/cm3) GaAs single crystals with 〈123〉 orientation are compressed at different strain rates and temperatures between 500 and 900 °C. Two different regimes are observed. At high strain rates and temperatures below 700 °C, the strain‐rate dependence of the lower yield stress is characterized by a power law with a stress exponent of 3.7, while its temperature dependence obeys an Arrhenius law with an activation energy of 0.93 eV. The latter value is smaller than that found for undoped GaAs, but the stress exponent is practically unchanged. This regime is interpreted in terms of a kink mechanism; the rate‐controlling process is assumed to be governed by a strong interaction of In atoms with α dislocations. The regime occurring at low strain rates and temperatures above 700 °C is characterized by strong hardening and a weak temperature and strain‐rate dependence of the lower yield stress. This behavior is ascribed to a direct alloying effect. Different types of interaction between dislocations a...

Yield point of as-grown and predeformed GaAs:Zn

Single crystals of highly Zn-doped GaAs are compressed along 〈123〉 in a constant strain-rate test at temperatures between 330 and 700 °C. The yield point is studied for both the as-grown and the predeformed state, the latter achieved by strain-rate and temperature-change tests. For as-grown material two deformation regimes are established. At low temperatures the deformation is governed by a kink mechanism typical for tetrahedrally coordinated semiconductors. The activation energy and the stress exponent are deduced as U=1.44 eV and n=3.0, respectively. These values are similar to those obtained for undoped GaAs, thus indicating that Zn additions do not appreciably influence the activation energies of kink formation and migration. Nevertheless, a strong efficiency of Zn for locking dislocations in GaAs is observed. At higher temperatures a different regime emerges, which has been also observed in other highly doped semiconductors, the basic mechanism of which, however, has not yet been elucidated. Materia...

The effect of solutes on the dynamical recovery of silicon and germanium

Abstract The present investigation reports on the influence of high doping on the stress-strain curves of Si and Ge with 〈123〉 orientation. As it is known for undoped semiconductors, two stages of dynamical recovery are observed. In contrast to these materials, however, the first recovery stage can no longer be interpreted by a diffusion-controlled mechanism. Rather a behavior similar to that found for the stationary deformation of metal alloys at high stresses may be realized. Although this effect is still under discussion in the literature, it is assumed that it has to do with the influence of the solute on the dislocation sub-structure evolving in the steady-state regime of the deforming crystals. The second stage of dynamical recovery shows the same behavior as observed in the undoped semiconductors; it is interpreted by a cross-slip mechanism.

The interaction of boron and phosphorus with dislocations in silicon

We present measurements of the lower yield point of highly boron doped silicon. Comparison to similar investigations on phosphorus doped material reveals a principally different temperature dependence of the lower yield stress, although the doping concentration of the crystals and the strain-rate and temperature ranges of the experiments were the same. In boron doped silicon, a temperature independent domain emerges, while for phosphorus doping there remains a well-defined temperature dependence. Apparently the interaction of boron with dislocations in silicon is different from that of phosphorus. Suitable models are available to describe the different influence of both dopants on the yield point.

High temperature creep and transmission electron microscopy of GaAs

Abstract GaAs single crystals are compressed in the 〈111〉 direction in creep experiments. The dynamical recovery is investigated in the regime of steady state creep. It is controlled by cross-slip at higher temperatures ( T > 820 K) and by climb at lowe temperatures ( T E q 0 = 5.1 eV for cross slip and Q = 3.7 eV for self-diffusion (climb). The energy E q 0 leads to a stacking fault energy γ = 52 mJ m −2 . The microstructure is investigated by transmission electron microscopy. A microscopic deformation model is proposed on the basis of the observed dislocation reactions in the analysed dislocation networks.

The yield point of GaAs:Zn pre-deformed in the Peierls regime

In previous work by the present authors, the influence of pre-deformation at 600°C on the strain-rate and temperature dependence of the yield point of GaAs:Zn was investigated. Marked deviations in comparison with the behaviour of as-grown material were found in subsequent deformation at lower temperatures. In the present study the specimens were pre-deformed at 420°C, and the second tests were performed at temperatures between 270 and 390°C. This is the range in which the dislocation motion governing plasticity is dominated by a Peierls mechanism. Again, marked deviations from the properties of as-grown material were observed. They are mainly characterized by a distinctly smaller strain-rate dependence of the yield stress. Only close to the ductile-brittle transition in a rather limited temperature and strain-rate range does the behaviour of pre-deformed crystals approximate that of as-grown material.