Low energy tail spectra of characteristic x-rays detected with a Si(Li) x-ray detector

Characteristic X-ray spectra are inherently accompanied by the tail spectra in the low energy side when X-rays are detected with a semiconductor X-ray detector. The tail spectra of Mg,Al,Si,P,S,Cl,K,Ca,Ti,Cr and Mn KX-rays have been observed using two different Si(Li) X-ray detectors. An annular source of 55Fe has been used to excite the Mg (1.25 keV) to Ti (4.5 keV) KX-rays, and 54Mn and 55Fe sources have been used for the detection of Cr (5.4 keV) and Mn (5.9keV) KX-rays, respectively. Observed intensity ratios of the tail area Nsub(t) to the Gaussian X-ray peak area Nsub(p) have exhibited to change remarkably at the Si-K adsorption edge energy 1.84 keV. When X-ray spectra detected with different Si(Li) detectors are compared at some specific characteristic X-ray, different values of Nsub(t)/Nsub(p) intensity ratios as well as different line shapes of tail spectra have been observed. Using a simple model, the thickness of Si layer which generates the tail spectrum has been estimated, i.e., the thicknesses are about 0.05 μm for one detector and 0.09μm for the other detector. The generation of the tail spectrum is known to be partially due to the escape effect of photoelectrons or Auger electrons from the intrinsic region. In this paper, in addition to the above effect, it is proposed that the carrier diffusion effect is also an important origin for the appearance of the tail spectrum. Model calculation has been performed for the carrier diffusion process, and comparison has been done between the calculation and the observed results with respect to the tail spectral line shape as well as Nsub(t)/Nsub(p) intensity ratio. (author)