Papers by Keyword: Thermal Donor

Abstract: In order to investigate the performance of silicon single crystal depended on the annealing temperature, the minority carrier lifetime, the resistivity and oxygen concentration after different temperature annealing in Ar ambient were examined. And the effect of oxygen and related defects formed during annealed on the minority carrier lifetime were analyzed by microwave photoconductivity method, Fourier transform infrared spectrometer and four-probe measurement. The results indicate that after 450°C annealing for 30h, the resistivity and minority carrier lifetime of silicon increase significantly, while the concentration of interstitial oxygen decreases. After the annealing at 650°C, oxygen donor can be removed and the resistivity and the minority carrier lifetime decrease. During the high-temperature (above 650°C) annealing, the oxygen precipitation can decrease the minority carrier lifetime silicon.

Abstract: The generation of Thermal Donors in Si is a nucleation process controlled by several mobile On clusters. The rate-limiting transitions are found to be O1  O2 and O4  O5. The individual transition rates G12 and G45, and also G23 and G34 are deduced from the experimental data. From the transient variation of the generation rate G(t), the equilibrium concentration of the dimers is found, and with it the dimeric diffusivity is also defined. In samples pre-treated at high T, the G(t) dependence has a maximum, due to quenched-in fast-diffusing oxygen monomers (FDMs). The concentration and diffusivity of FDMs were determined.

Abstract: In order to identify an appropriate low-temperature surface passivation that could be used for bulk lifetime estimation of high resistivity (HR) (> 1 k
·cm) silicon for radiation detectors, different passivating layers were evaluated on n-type and p-type standard Czochralski (CZ), HR magnetic CZ and HR float zone (FZ) substrates. Minority carrier lifetime measurements were performed by means of a μW-PCD set-up. The results show that SiNx PECVD layers deposited at low temperatures (≤ 250°C) may be used to evaluate the impact of different processing steps and treatments on the substrate characteristics for radiation detectors. First results are obtained about a preliminary thermal treatment experiment to evaluate the thermal stability of the passivating layers, as well as the potential impact of the generation of thermal donors on minority carrier lifetime.

Abstract: The thermal donor formation at 425oC - 450oC in Ge doped Czochralski (GCZ) silicon having about 1016 cm-3 Ge content pretreated by rapid thermal annealing (RTA) and conventional furnace annealing (CFA) has been investigated using low-temperature infrared spectroscopy (LT-IR). The measurements prove that lightly Ge doping can enhance the formation of thermal double donors in the initial stage of the low temperature annealing after RTA process. Ge induced additional grown-in oxygen precipitates during silicon ingot growth and the abundant self-interstitials during RTA may be the reason for the enhancement. However, after extending the annealing time at the low temperatures, the thermal donor concentration in the GCZ silicon is lower than that in the conventional CZ silicon. In final, the mechanism is also discussed.

Abstract: The time dependence of thermal donor (TD) concentration, N(t), during annealing at 450oC was measured in samples cut from a single slab of silicon containing bands of grown-in microdefects of different types. An enormous impact of the microdefect type on the kinetic curve was observed. Samples from the interstitial region showed simple linear rise in N(t). The samples from an inner part of the vacancy region showed a complicated oscillating variation with an abrupt disappearance of the TDs at some moment followed by an immediate restoration of a linear rise. In samples from the marginal H-band of the vacancy region, an initial anneal does not produce TDs. However if this anneal was followed by a quench, subsequent anneals produce a linear rise in N(t). On the other hand, if the sample was slowly cooled, the subsequent production of TDs remained almost negligible. These observed peculiarities are accounted for by enhanced TD growth in the presence of self-interstitials (I) - due to IO species serving as vehicles for oxygen transport.

Abstract: Oxygen precipitation in Si is a complex set of processes which has been studied over many years. Here we review theoretical work relating to the precipitation process. At temperatures around 450°C oxygen atoms become mobile and form a family of thermal double donors. The structure of these defects and the origin of their electrical activity is discussed. At temperature around 650°C these donors disappear and there is a growth of SiO2 precipitates along with rod like defects which are extended defects involving Si interstitials. At higher temperatures these collapse into dislocation loops. The structure and electrical properties of the rod like defect are described and compared with those of dislocations.

Abstract: The effect of high-energy hydrogen and helium implantation and subsequent annealing on generation of radiation defects and shallow donors in the low-doped oxygen-rich FZ n-type silicon was investigated. Samples were implanted with 7 MeV 4He2+ or 1.8 MeV 1H+ to fluences ranging from 1x109 to 3x1011 cm-2 and 1.4x1010 to 5x1012cm-2, resp., and then isochronally annealed for 30 minutes in the temperature range up to 550°C. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when annealing temperature exceeds 375°C, i.e. when the majority of vacancy-related recombination centers anneals out. The excess concentration of TDs is proportional to the helium fluence and peaks at 1.6x1014cm-3 if annealing temperature reaches 475°C. Proton irradiation itself introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Formation and annealing of shallow and deep hydrogen-related levels are strongly influenced by electric field at annealing temperatures below 175°C. If annealing temperature exceeds 350°C, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by radiation enhanced TDs.

Abstract: P-n junctions are created in p-type Czochralski silicon after a low temperature (270°C) hydrogen plasma exposure. This is attributed to the formation of hydrogen-related shallow donors. A deep level (E1) with an activation energy of about EC-0.12 eV is observed by DLTS measurement and assigned to a metastable state of the hydrogen-related shallow donors. At an annealing temperature of 340°C, the E1 centres disappear and oxygen thermal donors appear. The concentrations of the oxygen thermal donors are found typically to be 2-3 decades lower than that required for over-compensating the initial p-type doping and for contributing the excess free carriers.

Abstract: Effects of compressive stress on oxygen agglomeration processes in Czochralski grown silicon heat treated at T= 450OC, used as a reference temperature, and T= 600OC to 800OC are investigated in some detail. Compressive stresses of about P= 1 GPa lead to enhanced formation of Thermal Double Donors in materials annealed over a temperature range of T= 450OC – 600OC. It has been shown that the formation of thermal donors at T= 450OC under normal conditions and compressive stress is accompanied with loss of substitutional boron. In contrast, the concentration of the shallow acceptor states of substitutional boron in silicon annealed under stress at T≥ 600OC remains constant. An enhancement effect of thermal donor formation is gradually weakened at T≥ 700OC. The oxygen diffusivity sensitive to mechanical stress is believed to be responsible for the observed effects in heat-treated silicon.