Electrical characterization of alpha-particle irradiation-induced defects in germanium

Abstract

Recent advances in semiconductor growth techniques have led to the production of high quality Ge that plays a vital role in the fabrication of electrical devices. Germanium (Ge) is mainly used as a detector material being highly sensitive to X-rays, gamma rays and ionizing radiation, and also shows promise for high speed applications. However, the performance of the devices is strongly influenced by radiation damage. Antimony (Sb), being one of the most common dopants in Ge semiconductor devices, forms the well-known Sb-vacancy complex, also known as the E-center, when the fabricated device is exposed to high energy particle radiation. In this study, the defects induced by high energy alpha-particle irradiation were investigated by means of deep level transient spectroscopy (DLTS). Previous studies found that the DLTS peak traditionally ascribed to the E-center anneals out in two steps, with the first step at room temperature and the second at about 390 K. Possible explanations in the literature for this behavior include interstitials being released by other defects annealing out reacting with the Sb-vacancy. In this study, we have shown that, contrary to previous theories, the DLTS peak that was assigned to the E-center consists of two peaks relating to two defects of similar nature. The peaks were resolved using two techniques: Laplace-DLTS with manual input of regularization parameters and a technique referred to as subtraction of transients. It was found that the peak annealing at high temperatures corresponded to the well-known E-center while the peak annealing at lower temperatures was a new defect which was denoted the E’. Using these techniques, it was shown that, although the two defects had very similar emission characteristics (DLTS signatures: E-center was determined to have an ionization enthalpy of 0.0370±0.005 eV with an apparent capture cross section of 7.9 × 10?15 cm2 while the corresponding values for the E’ were 0.0375±0.005 eV and 6.2 × 10?15 cm2). Other properties of the defects differed significantly, for instance the true capture cross sections at T ? ? were 2.2 × 10?15 cm2 and 1.0 × 10?13 cm2 respectively and the capture barriers were 0.043 eV and 0.092 eV. The annealing activation energy of the E-center was 1.05 eV and that of the E’ was 0.73 eV with frequency factors of 2.5 × 109 s?1 and 2.7 × 108 s?1 respectively. Furthermore, the study showed that the defects had significantly different introduction kinetics, mainly a linear introduction rate for the E-center and the E’ introduced quadratically and being dependent on the introduction and presence of another defect. It is believed that the evidence presented in this study provides conclusive proof for the existence of an up to now unobserved defect in Ge which has up to now been confused with the well-known E-center.