Low-Temperature Thermal Conductivity of Fast-Neutron-Irradiated Silicon and Germanium

Abstract

The thermal conductivity K of initially n-type silicon and germanium irradiated at about 30°C at four fast-neutron doses (1.1×1017, 2.5×1017, 1.7×1018, and 3.4×1018 n/cm2) was measured between 5°K and 300°K. The thermal-conductivity behaviors of the two irradiated materials differ by significant features: Pronounced shifts of the maximum of K to higher temperatures are observed in germanium after irradiations, leading to a depression of K which is more pronounced below than above the maximum. No noticeable shift, however, appears in silicon after bombardment, the depressions of K on both sides of the peak remaining comparable. The additive thermal resistivity (K−1−K0−1) at 20°K is found to increase with the integrated flux φ, approximately as 7.9×10−13 φ0.65 cm·deg/W, and 3.8×10−12 φ0.65 cm·deg/W, for irradiated silicon and germanium, respectively. Similar flux dependences were observed by Vook for 2-MeV electron-irradiated silicon and germanium. Using the Callaway model, it is shown that the experimental data for irradiated silicon can be accounted for by considering only an increase in the τ−1=A′ω4 scattering, the factor A′ increasing linearly with the flux. The additional scattering mechanism is most likely to be associated with strain fields arising from bombardment-induced defects instead of an electron-phonon interaction, unless one assumes for the latter a Rayleigh-type scattering law. In agreement with Vook's results on electron-irradiated germanium, the dominant additional scattering in the present irradiated germanium, at least for the lower doses, appears to be due to electron-phonon interaction. On the basis of the Keyes model, the difference between bombardment-induced scatterings in silicon and germanium is attributed to the predominant effects of irradiation in these materials, silicon approaching an intrinsic behavior and germanium becoming highly p type.

Contribution of the electron–phonon interaction to Lindhard energy partition at low energy in Ge and Si detectors for astroparticle physics applications

“…For germanium there is a similar situation. The value of T max is situated between 12.5 [66] and 70 K [67], and the corresponding K Lmax values are 18 and 0.6 W/(cmK) respectively.…”

Effects of Electron Irradiation on the Thermal Conductivity ofn- andp-Type Germanium

“…In a previous paper, 10 we have pointed out that the thermal conductivity K of antimony-doped germanium below the peak was lower than the thermal conductivity limited by boundary effect and isotope scattering. This observation was compared to the phenomenon already noticed by Goff and Pearlman 11 and related, on the basis of the Keyes model, 8 to the scattering of phonons by electrons bound to donors.…”

Positron probing of disordered regions in neutron‐irradiated silicon

“…The vacancy‐rich disordered regions (DR) created in Si by self‐implantation repress the long wavelength phonon modes that contribute strongly to the thermal transport in bulk Si . An approach to create DRs that reduce Si's thermal conductivity in a similar way has been previously shown using neutron irradiation . In order to gain insight into the electron and structural properties of the DRs, we have undertaken the positron probing of these defects created in silicon by irradiation with fast reactor neutrons.…”