Control of the n-type doping in AlxGa1 − xSb: DX-center behavior of the Te impurity

Photoionization cross-section of the DX center in Te-doped AlxGa1−xSb

“…The upper curve ͑ᮀ͒ refers to the saturated PPC condition. 5 ͑c͒ R(t) data taken by C -V measurements on a xϭ0.41 sample, whose doping level is similar to the one of the n.196 sample (xϭ0.41) ͓the decreasing rate of R(t) is different in the C -V and Hall measurements owing to different photon fluxes͔. The straight line is a guide for the eyes.…”

“…The interval of time during which this detail is observed corresponds to an increase of the density of the photoexcited electrons approximately up to the critical n c density (n c Ϸ10 17 cm Ϫ3 ), over which a semiconductor-tometal transition has been reported in the same samples. 5 At longer times the trend becomes linear. On the contrary, in the xϭ0.31 sample, where the electron density is always higher than n c , even in the dark condition, 5 the ln͓R(t)͔ curves do not present any evidence of this initial sublinearity.…”

“…The calculation was made under the assumptions of neutral state for the DX center ͑positive-U model͒, a negligible density of acceptors (N a ϭ0), and a thermal ionization energy E d ϭ26 meV. 5 This E d value was obtained in Ref. 5 from the Arrhenius plot of n(T) experimental data under the hypothesis of significant compensation of the material, otherwise twice as much as the actual value should be obtained.…”

“…[2][3][4] It has been ascertained that: ͑i͒ the concentration of the DX center is of the order of the concentration of donors, as revealed by the intensity of the characteristic effect of persistent photoconductivity ͑PPC͒, 5 and not a sensitive function of the alloy composition, as previously asserted; 6 ͑ii͒ the occupancy level of the DX center is deeper in energy as the AlSb molar fraction increases, 5,6 although an accurate estimation of this energy is still lacking. ͑iii͒ Concerning the E n optical ionization energy, only one datum was reported for Tϭ100 K and xϭ0.5.…”

“…͑iv͒ In the temperature range of the PPC effect, where the DX center can no more equilibrate the states of the conduction band ͑CB͒, the electrical properties are controlled by another donor bound state, which is also responsible for a semiconductor-to-metal transition as the density of the photoexcited electrons becomes sufficiently high. 5 In this work we report results on the dependence of the DX center optical cross section on the photon energy in the range 0.3рxр0.5 at two different temperatures. A critical analysis of the advantages and the limitations of the Hall effect technique in obtaining the photoionization transients is also given in this work with particular attention to a nonexponential time variation of the free electron density.…”