Effective Minority Carrier Lifetime Τeff Research Articles

Field-effect passivation of Si by ALD-Al2O3: Second harmonic generation monitoring and simulation

This paper investigates the ability of second harmonic generation (SHG) to probe the passivation quality of atomic layer deposited Al2O3 on Si by estimating the induced interface electric field due to fixed charges in the oxide. Samples with various oxide charges (Qox) and interface state densities (Dit) were fabricated, using different deposition parameters. The samples were characterized by capacitance-voltage (C-V) and microwave photoconductance decay measurements in order to evaluate Qox and Dit, as well as the effective minority carrier lifetime τeff. The SHG results were consistent with Qox, Dit, and τeff values, proving the ability of the technique to monitor the interfacial quality in a contactless and non-destructive way. Optical simulations which use the electric field values obtained from the C-V measurements could reproduce the measured SHG signal. This demonstrates that SHG coupled with optical simulation can give access to the electric field magnitude and thus characterize the electrical properties of oxide/Si interfaces.

Optoelectronic effect of porous silicon surface treatment with samarium ions for different deposition times and characterizations

The goal of the present investigation is to reduce the stress, strain, and defects of porous silicon through a passivation process. We have investigated different layers of porous silicon (PSL) which were intentionally doped with samarium (Sm) by the electrochemical deposition. The used precursors were samarium oxides (Sm2O3) 0.05 M mixed with sulfuric acid (H2SO4) 0.05 M. The influence of samarium on the distribution of oxygen was studied by Fourier transform infrared spectroscopy (FTIR). Indeed, the glancing incidence X-ray diffraction proves the degree of structural order in PS and the presence of these complex metals (Sm) on its surface. The dispersion of the Sm metals on the PS surface (Sm/PSLs) exhibited better performances for the treated wafers in regard to the untreated ones. That means, we obtained a noteworthy increase in the effective minority carrier lifetime τ eff and an apparent enhancement in photoluminescence (PL) intensity. Particularly, the chief goal of the current study is to clarify that the large enhancement of the electronic quality of the wafers is related to the presence of Sm.

Degradation behavior of electrical properties of inverted metamorphic tri-junction solar cells under 1 MeV electron irradiation

In this study, the degradation effects of inverted metamorphic tri-junction (IMM3J) solar cells were investigated after 1MeV electron irradiation using spectral response and photoluminescence (PL) signal amplitude analysis, as well as electrical property measurements. The results show that, similar to traditional tri-junction (TJ) GaInP/GaAs/Ge solar cells, the electrical properties (such as Isc, Voc, and Pmax) degrade as a function of logφ, where φ represents the electron fluence. In particular, the degradation of Voc is more serious than that of Isc because of the sum rule for Voc and the limit rule for Isc in IMM3J cells. Analysis of the spectral response curves indicates that, unlike traditional TJ cells, the bottom In0.3Ga0.7As (1.0eV) sub-cell exhibits the most severe damage in the irradiated IMM3J cells. Meanwhile, the PL amplitude measurements qualitatively confirm that the degradation in the effective minority carrier lifetime τeff of single junction (SJ) In0.3Ga0.7As cells is more drastic than that of SJ GaAs cells after irradiation. Thus, the output current of the In0.3Ga0.7As sub-cell should be the rate-limiting cell in the irradiated IMM3J cells.

Heat treatment in 110 °C liquid water used for passivating silicon surfaces

The simple passivation method of heat treatment in liquid water is discussed. Photo-induced effective minority carrier lifetime τ eff increased to 3.3 × 10−3 s above 110 °C for 1 h for 17-Ωcm n-type crystalline silicon. Increase in τ eff was observed ranging from 3.5 × 10−4 to 3.7 × 10−3 s for n-type silicon with resistivity ranging from 2 to 17 Ωcm. τ eff maintained high values ranging from 1.5 × 10−4 to 1.4 × 10−3 s for 1270 h. The metal-insulator-semiconductor-type diodes were formed on the top surfaces of the n-type and p-type substrates by forming Al and Au metals on the 0.7-nm-thin passivated layers. Rectified and Fowler–Nordheim current characteristics were observed in the dark field because of the difference of the work function between Al and Au. High photo-induced current density of 31.1 mA/cm2 and photovoltaic effect were observed in case of light illumination of AM 1.5 at 100 mW/cm2 to the rear surface. The recombination velocity in the regions under the metal electrode in the MIS structure was determined by lateral diffusion of photo-induced carriers. They were 1000 and 11,000 cm/s under Al and Au, respectively, in the n-type Si substrate.

Passivation of Silicon Surfaces by Treatment in Water at 110°C

ABSTRACTWe report effective passivation of silicon surfaces by heating single crystalline silicon substrates in liquid water at 110°C for 1 h. High values of photo-induced effective minority carrier lifetime τeff in the range from 1.9x10-4 to 1.8x10-3 s were obtained for the n-type samples with resistivity in the range from 1.7 to 18.1 Ωcm. τeff ranged from 8.3x10-4 to 3.1x10-3 s and from 1.2x10-4 to 6.0x10-4 s over the area of 4 inch sized 17.0 Ωcm n- and 15.0 Ωcm p-type samples, respectively. The heat treatment in liquid water at 110°C for 1 h resulted in low surface recombination velocities ranging from 7 to 34 cm/s and from 49 to 250 cm/s for those 4 inch sized n- and p-type samples, respectively. The thickness of the passivation layer was estimated to be approximate only 0.7 nm. Metal-insulator-semiconductor type solar cell was demonstrated with Al and Au metal formation on the passivated surface. Rectified current voltage and solar cell characteristics were observed. Open circuit voltage of 0.47 V was obtained under AM 1.5 light illumination at 100 mW/cm2.

3D determination of the minority carrier lifetime and the p-n junction recombination velocity of a polycrystalline silicon solar cell

This work presents a theoretical and experimental transient tri-dimensional study conducted for the determination of the bulk component of the minority carrier lifetime and the p-n junction recombination velocity of a bifacial polycrystalline silicon solar cell. The theoretical analysis is based on the columnar model of the grains in the polycrystalline silicon solar cell. The boundaries conditions are defined in order to use Green's function to solve the three-dimensional diffusion equation. This leads to a new expression of the transient photovoltage. The value of the constraint coefficients at interfaces of the grain are computed while those of the effective minority carrier lifetime τeff is extracted from the experimental curve of transient voltage. The bulk lifetime and the p-n junction recombination velocity are deduced and have been compared to those obtained from transient state by one-dimensional modelling of carrier's diffusion. This comparative study permitted us to show grain effects on the lifetime and consequently the inadequacy of one-dimensional modelling of carrier's diffusion in the polycrystalline silicon solar cells.

Sol–gel derived hydrogen annealed ZnO:Al films for silicon solar cell application

A study of the effect of hydrogen annealing on antireflection and surface passivation properties of sol–gel derived aluminum rich zinc oxide (AZO) films coated on silicon wafers has been done in 300–600°C temperature range. The minority carrier lifetime in silicon wafers coated with AZO films was measured using microwave photoconductive decay (μ-PCD) technique. After annealing of AZO coated silicon wafer in hydrogen ambient for 30min between 400 and 600°C the effective minority carrier lifetime τeff improved above the initial value of ∼16μs and attained a maximal value of ∼71μs for annealing at 500°C. It may be that above 400°C the molecular hydrogen gets dissociated into atomic hydrogen in presence of Al induced defects at the AZO coated silicon surface and passivates them by formation of Si–H–Al complex. The annealing in air in the same temperature range did not affect the lifetime. AZO films annealed at 500°C in hydrogen or air show high transmittance in 400–1200nm wavelength range and are suitable as AR coatings for silicon solar cells. We have applied a hydrogen annealed AZO antireflection coating on n+ front surface and an equally thick hydrogen annealed AZO coating on the p-back surface of an n+-p multi crystalline silicon solar cell. The observed improvement in Jsc, Voc values of the cell established that while AZO film on front acted as a good AR coating the AZO film on the back surface passivated the back surface effectively.