Study of Radiation-Induced Defects in p-Type Si1−xGex Diodes before and after Annealing

Abstract

In this work, electrically active defects of pristine and 5.5 MeV electron irradiated p-type silicon–germanium (Si1−xGex)-based diodes were examined by combining regular capacitance deep-level transient spectroscopy (C-DLTS) and Laplace DLTS (L-DLTS) techniques. The p-type SiGe alloys with slightly different Ge contents were examined. It was deduced from C-DLTS and L-DLTS spectra that the carbon/oxygen-associated complexes prevailed in the pristine Si0.949Ge0.051 alloys. Irradiation with 5.5 MeV electrons led to a considerable change in the DLT spectrum containing up to seven spectral peaks due to the introduction of radiation defects. These defects were identified using activation energy values reported in the literature. The double interstitial and oxygen complexes and the vacancy, di-vacancy and tri-vacancy ascribed traps were revealed in the irradiated samples. The interstitial carbon and the metastable as well as stable forms of carbon–oxygen (CiOi* and CiOi) complexes were also identified for the electron-irradiated SiGe alloys. It was found that the unstable form of the carbon–oxygen complex became a stable complex in the irradiated and the subsequently annealed (at 125 °C) SiGe samples. The activation energy shifts in the radiation-induced deep traps to lower values were defined when increasing Ge content in the SiGe alloy.

5.5 MeV Electron Irradiation-Induced Transformation of Minority Carrier Traps in p-Type Si and Si1−xGex Alloys

“…This result is supported by the BELIV characteristics, where a deeper trap level associated with the same species defect in SiGe alloy relative to that in p-Si can be inferred from Figure 4 c. This shows the contrary result relative to n-type silicon–germanium alloys [ 25 , 26 ] where the enhancement of the majority carrier activation energy with Ge content is inherent. In p -type SiGe ( Figure 5 a), the activation energy of majority carrier traps shifts to the lower energy values with an increase in Ge content [ 7 , 27 , 28 ].…”

“…Routine modes of the minority carrier deep-level transient spectroscopy by using electrical (MC-DLT) [ 7 ] and optical (MCT) [ 12 , 13 , 14 , 15 ] excess carrier injection were applied to highlight the minority carrier traps. A HERA-DLTS 1030 instrument (PhysTech GmbH) was employed to record the MC-DLT and MCT spectra using different correlation functions.…”

“…The tentative identification of traps revealed in DLT spectra of boron-doped and electron-irradiated p-Si was performed by comparing values of activation energy extracted from Arrhenius plots and those reported in the literature, as indicated in Table 2 . The hole trap H1 is assigned to the multi-vacancy (V 2 + V 3 ), while H2 trap with components H2-1 and H2-2 is related to the carbon–oxygen complex, with H2-1 being the metastable state (C i O i *) and H2-2 the stable state of this interstitial complex, respectively [ 7 ]. The minority carrier trap E1 with activation energy of 0.150 ± 0.005 eV can be associated with a vacancy–oxygen complex (VO) [ 5 ].…”

“…Additionally, some of radiation induced defects in Si are thermodynamically metastable [ 6 ], such as interstitial carbon–interstitial oxygen (C i O i *) complexes in p -type Si, as reported in our previous article [ 7 ]. The bi-stable defects can change their state under certain conditions.…”

“…The spectrum of deep traps of majority carriers in p -type Si and SiGe alloys, the meta-stability of the carbon–oxygen complexes and shifts of the activation energy of these defects were investigated in our previous article [ 7 ]. In this work, the minority carrier trap spectra obtained in 5.5 MeV electron-irradiated p -type Si 1−x Ge x (with x = 0–0.05) materials were considered.…”