Impact of germanium on vacancy clustering in germanium-doped silicon

Abstract

The formation energy and thermal equilibrium concentration of vacancies in Ge doped Czochralski-grown Si are studied by quenching of samples annealed at temperatures between 1200 and 1350°C for 1 h under hydrogen atmosphere. After quenching, the majority of the formed vacancy and hydrogen containing point defect clusters are transformed into VH 4 defects by a 1 h anneal at 450°C. Measuring the amplitude of the vibrational band of VH 4 at 2223 cm −1 as function of the quenching temperature allows estimating the vacancy formation energy. An apparent formation energy of about 2 eV is obtained for Ge doping between 7 ϫ 10 17 and 6.5ϫ 10 20 cm −3 which is significantly lower than the 4 eV obtained for high purity Si. In the whole quenching temperature window, the vacancy thermal equilibrium concentration is significantly higher than in Si without Ge doping. It is shown that this lower apparent formation energy can be explained by the presence of vacancy traps. © 2010 American Institute of Physics. ͓doi:10.1063/1.3449080͔Intrinsic point defects in semiconductors play an important role in a wide range of processes ranging from Czochralski ͑Cz͒ crystal growth to device processing. In order to control and to optimize these processes, it is crucial to have a quantitative knowledge of the intrinsic point defect properties.In the early days already quenching from high temperatures has been explored to study the intrinsic point defects in Si. It was indeed observed that by quenching from high temperatures, donors are formed which change the resistivity of the Si material and can easily be detected using resistivity and Hall measurements. Unfortunately, it soon turned out that in most cases these donors were due to iron contamination either grown-in during crystal growth and activated by the quenching treatment or diffusing in from the surface of the samples during the high temperature treatment. 1 Often the concentration of iron was so high that it was the main cause of the observed resistivity changes. Only in few careful studies also donors were observed that could not be related to metallic impurities 2,3 but even in these cases the relation with the intrinsic point defects was not clear.For those reasons, beginning of the 1990s a new quenching technique was developed at Tohoku University which is based on performing the high temperature anneal and the quenching step itself with the sample kept under hydrogen ambient. [4][5][6][7] The originality of this approach is to detect vacancies as vacancy-hydrogen complexes. Isolated vacancies can indeed not exists after quenching because of the very small vacancy migration energy. Further more, ab initio calculations reveal that the binding energy of the various vacancy-hydrogen complexes that can be formed is larger than that of vacancy-only clusters with a similar number of vacancies. 8 Due to this, vacancies will preferentially cluster with hydrogen atoms/molecules during the quench and during subsequent low temperature anneals. After the quench from high temperature, an annea...

Fluorine codoping in germanium to suppress donor diffusion and deactivation

“…27 Mass action analysis has been previously applied to address cluster formation in semiconductors. 5,8,[28][29][30] Using Eq. ͑2͒, two sets of simultaneous equations for F n V m clusters were considered.…”

Germanium doping for improved silicon substrates and devices

“…The described effects of germanium doping can have important consequences not only for radiation induced defect formation and population dynamics but also for defect formation during crystal pulling. Vacancy trapping by germanium atoms was also claimed by Chen et al [14] based on density functional theory calculations although recent theoretical work of Chroneos et al [15] suggests that the impact of germanium is negligible compared to vacancy clusters themselves acting as trap/sink for vacancies. Also recent quenching experiments [16] and a study with scanning infrared microscopy of voids in as-grown Czochralski silicon crystals with and without germanium doping [17], both revealed only a limited impact of germanium doping on the thermal equilibrium vacancy concentration at high temperatures.…”

Vacancy-oxygen defects in p-type Si1−xGex

“…Importantly, vacancies in Si 1-x Ge x preferentially reside near at least one Ge atom as was determined by the positron annihilation spectroscopy (PAS) study of Sihto et al 13 This has also been supported by recent density functional theory (DFT) studies. 11,14 The defect processes of oxygen-related defects in Si 1-x Ge x alloys are not understood or studied to the level they are in Si. [15][16][17] The A-center is composed of a V and an O interstitial (O i ) atom therefore the energetics of its formation will be the balance of these two constituent point defects.…”