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

Abstract

The change in the low-temperature thermal conductivity K of antimony-doped germanium was investigated in the ^-to-^-type conversion region induced by 4-MeV electron irradiation (1.3X10 17 to 1.6X10 18 electrons/cm 2 ) performed at about 40°C. The thermal conductivity was found to decrease in the neighborhood of the peak and just below it, after the first electron dose (1.3X10 17 electrons/cm 2 ). With higher electron fluxes, K increased over the whole temperature range 5-80 °K, reaching values higher than that of unirradiated germanium. The initial decrease of K is at present not well understood, but is likely to be related to scattering of phonons by bombardment-introduced levels. The further increase of K appears to be characteristic of the depletion of donor electrons by radiation-induced acceptor defects. This explanation is consistent with the Keyes model relative to scattering of phonons by occupied donors. No noticeable change in K was obtained in ^-type germanium for electron doses up to 1.7 X10 18 electrons/cm 2 . This behavior indicates that either the radiation-induced levels involve no particular modification of the initial scattering mechanisms, or most likely the defect introduction rate is much lower than in w-type, the small amount of defects produced being of negligible effect on K. B I. INTRODUCTIONETWEEN the different mechanisms of phonon scatterings which take place in the low-temperature range 1 " 5 (boundary effect; mass-difference, strain-field, and dislocation scatterings; phonon-phonon collisions), it is shown that electron-phonon interaction 6 " 9 can be an important scattering source, allowing to account for certain thermal conductivity results, which are unexplainable on the basis of only the above mentioned scatterings.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. The effects of electron 12 and fast-neutron 10 ' 13 irradiations on the thermal conductivity of initially ^-type germanium were also studied: A pronounced decrease of K on the lowtemperature side of the peak was obtained. In both studies, however, the electron and fast-neutron doses used were such that the crystals measured after irradia-

Contribution des phonons transverses et longitudinaux à la conductibilité thermique de réseau de l'antimoniure de gallium à basse température

“…Ce mécanisme a été mis en évidence par l'étude de l'effet du dopage sur la conductibilité thermique d'un certain nombre de semiconducteurs tels que le germanium [7]- [11], l'antimoniure d'indium [12] et l'antimoniure de gallium [13] [14]. Par ailleurs, l'influence d'irradiations électroniques et neutroniques sur le germanium [15]- [18] et l'antimoniure d'indium [19], et en particulier le comportement de K dans la région de transition de type n en type p du germanium [18], ont souligné l'importance du processus de diffusion électron-phonon. Plusieurs analyses de ce mécanisme de diffusion ont été proposées, suivant que les électrons se trouvent dans une bande dégénérée [20], ou sont liés aux centres d'impuretés [21] [22].…”

Combined Investigation of Nonuniform-Field Electroreflectance and Surface Galvanomagnetic Properties in Germanium

“…If the mobility were known, the surface carrier concentration and thus the surface field could be determined. 8,9 We have overcome this difficulty by 8 taking combined surface Hall effect and conductance measurements, which enable both carrier mobility and concentration to be directly obtained. ER data have been taken at room temperature in a number of ways, by square-wave modulation and by sine-wave modulation (first and second harmonic), for a wide range of values of the surface electric field, but always requiring that the field vary between zero and its peak value in accordance with condition ii.…”