Change in Thermal Conductivity upon Low-Temperature Electron Irradiation: GaAs

Abstract

Measurements of the change in thermal conductivity of high-purity single-crystal GaAs were made upon 2-MeV electron irradiation and annealing. Two GaAs samples were irradiated at maximum temperatures of 100 and 80 °K. A linear increase in the additive thermal resistivity near 50 °K is observed upon bombardment. The results yield 1/K-1/K Q = (3.15±0.2) X 10~1 9 cm-deg/Wper 2-MeV electron/cm 2 . The experimental ratio of the point-defect thermal resistivity to the induced lattice strain at 50°K is (1/K-l/Ko)/ (3AL/L) = (1.0 ±0.2) X10 4 cm-deg/W. Using estimates for the introduced defect concentration (based upon the change in strain rate as a function of electron energy) together with the observed increase in thermal resistivity, one obtains 1/K-1/K 0 = (94±10)X10 2 C cm-deg/W, where C is the fractional point-defect concentration. This value is intermediate between those predicted by the point-defect scattering theories of Klemens and Ziman. Isochronal anneals carried out above 50°K with all measurements made at 50 °K demonstrate low-temperature annealing in GaAs. Annealing is observed to begin near 55°K and accelerate near 190°K. About 70% of the additive thermal resistivity stable at 50°K anneals below 325°K. Definite minima are observed in the temperature dependence of the thermal conductivity, suggesting localized-impurity-mode scattering. The annealing, however, takes place over too large a temperature range to be due to a single thermally activated process. The change in shape of the temperature dependence of the thermal conductivity upon annealing indicates that below 325°K the defects anneal as point defects. For anneal temperatures between 325 and 575°K the point defects no longer remain isolated, and clustering or precipitation is suggested.

Unstable displacement defects and hydrogen trapping in GaAs

“…Annealing stages in GaAs centered near 235 ad 280 K were observed in electrical measurements by Stein 10 and by Thommen 11 after electron irradiation of n-type GaAs at 80 K. An annealing stage at 235 K was also reported to occur after 60 Co ␥-ray irradiation of n-type GaAs at 77 K. 26 Vook 9 reported lattice parameter and thermal conductivity measurements that showed defect annealing in GaAs below room temperature following electron irradiation. The thermal conductivity data showed two overlapping annealing stages centered near 225 and 300 K. 9 Recovery of thermal conductivity upon annealing is consistent with a removal of high lattice strain detected in measurements of the lattice parameter.…”

“…9,12 The defects that anneal below room temperature also exhibit a higher threshold energy for displacement than the defects that remain at room temperature. 11,12 Multiple displacements in a localized region have been suggested to explain the higher threshold energy and large lattice strain.…”

“…1, [6][7][8] It is widely accepted that these bonds form at As vacancy (V As ) or Frenkel pair (V As -As i ) displacement defects on the As sublattice. 1,6-8 It is known from irradiation damage studies on GaAs, however, that significant defect annealing can occur below room temperature [9][10][11][12] so that the Ga-H centers may not be the initial bonding site for hydrogen. Relatively little use has been made of hydrogen interactions for decoration and characterization of defects that are unstable below room temperature in compound semiconductors.…”

Thermal Conductivity of Electron-Irradiated Silicon

“…1 fore very few exist. 5 -6 However, low-temperature thermal conductivity has been shown to be highly sensitive to lattice defects introduced into high-purity GaAs, 7 InSb, 8 and Ge, 9 by electron irradiation. It has also been shown that measurements of the temperature dependence of the low-temperature thermal conductivity on annealing are related to changes in the structural properties of the defects and are therefore useful in distinguishing between the annealing behavior of radiation-induced defects in different semiconductors.…”

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

“…This method has since been applied to investigate the radiation damage in a number of materials and particularly in dielectricI 2 -14 and ionic crystals l 5-18 irradiated by neutrons, x or 'Y rays. For semiconducting materials, Vook has recently investigated changes in thermal conductivity on low-temperature electron irradiation on GaAs, 19 InSb,20 Ge,21 and Si.22 In the present paper, thermal Curves [(2)-(5)]: Irradiated silicon at the respective doses, 1.1 X 10 17 , 2.5 X 10 17 , 1.7XI0 18 , and 3.4XI0 18 n/cm 2 , Curve (T): Theoretical curve computed for boundary and isotope scatterings and B=3.8XlO-24 sec·deg-3 • conductivity data on fast-neutron-irradiated silicon and germanium are presented and analyzed on the basis of the phenomenological model developed by Callaway,23 They are compared to Vook's data on irradiated semiconductors and to some other results were impurity-induced scattering is associated with electron-phonon interaction,…”