Papers by Keyword: Recombination

Abstract: Changes in the concentration of interstitial iron in multicrystalline silicon wafers after high temperature annealing (900°C) have been monitored by carrier lifetime measurements. Two cooling rates were investigated. The first was considered ‘fast’, meaning the interstitial Fe had no time to diffuse to precipitation sites, and should therefore be frozen-in, despite being far above the solubility limit at lower temperatures. A second ‘slow’ cool down to 650°C allowed ample time for the Fe to reach the surfaces or other internal precipitation sites. Surprisingly, in both cases the Fe remained in a supersaturated state. This indicates the precipitation process is not diffusion-limited, and that another energetic barrier to precipitate formation must be present. Since the slow cooling used here is similar to the cooling rate experienced by multicrystalline ingots after crystallisation, this precipitate-impeding mechanism is probably responsible for the surprisingly high interstitial Fe concentrations often found in as-grown multicrystalline silicon wafers.

Abstract: The effect of gamma-ray and neutron irradiation on recombination current, injection electroluminescense and the value of the lifetime of nonequilibrium carriers for 4H-SiC pn structures was investigated. The irradiation was carried out with gamma-ray (dose 5x106 rad) and 1 MeV neutrons in the doses range from 1.2x1014 cm-2 to 6.24x1014 cm-2. Neutron irradiation with a dose 1.2x1014 cm-2 increased the recombination current, decreased the lifetime for deep-level recombination in the space charge region and decreased the intensity of the edge injection electroluminescense (hnmax » 3.16 eV) by 1.5-2 orders of magnitude; the neutron irradiation with high dose (6.24x1014 cm-2) resulted in increase of the recombination current up to 2 orders of magnitude and decrease of lifetime at least up to 2 orders of magnitude. Gamma-ray irradiation and annealing at temperatures in the range 350-650 K left the recombination current and lifetime practically unchanged.

Abstract: Recombination-induced passivation (RIP) experiments were conducted on p-type SiC after plasma treatment in deuterium. Higher sensitivity of SIMS to deuterium allowed us to confirm that recombination-induced athermal migration of hydrogen is indeed a driving mechanism for the RIP phenomenon. Hydrogen (or deuterium) athermally migrates from the plasma-induced hydrogen- or deuterium-reach near-surface layer down to more than a micron in depth, which under certain conditions creates a sufficiently thick layer of the n-type conductivity in the originally ptype epilayer. Thermal admittance spectroscopy was applied to investigate the defect levels in the top portion of the bandgap of the RIP-induced n-type layer. A few different levels located close to the conduction band of the originally p-type material were investigated.

Abstract: We applied picosecond four-wave mixing technique to investigate carrier diffusion and recombination in n-type 4H-SiC epilayers. The dependence of bipolar diffusion coefficient D on photocarrier density was measured in range from ~ 1017 to ~ 1020 cm-3. We determined a decrease of D value from 3.4 to 2.2 cm2/s with increase of the photoexcitation level in range from ~ 1017 to ~ 1019 cm-3, and found its increase up to 3.8 cm2/s at carrier density above 1020 cm-3. Auger recombination governed decrease of carrier lifetime from 11 ns at ~ 1017 cm-3 to 1.8 ns at ~ 1020 cm- 3 has also been observed.