nan Vandana

Influence of deposition temperature of thermal ALD deposited Al2O3 films on silicon surface passivation

The effect of deposition temperature (Tdep) and subsequent annealing time (tanl) of atomic layer deposited aluminum oxide (Al2O3) films on silicon surface passivation (in terms of surface recombination velocity, SRV) is investigated. The pristine samples (as-deposited) show presence of positive fixed charges, QF. The interface defect density (Dit) decreases with increase in Tdep which further decreases with tanl up to 100s. An effective surface passivation (SRV<8 cm/s) is realized for Tdep ≥ 200 °C. The present investigation suggests that low thermal budget processing provides the same quality of passivation as realized by high thermal budget process (tanl between 10 to 30 min).

Spectral and Injection Level Dependence of Recombination Lifetimes in Silicon Measured by Impedance Spectroscopy

The effect of photo-generated carrier concentration on recombination lifetime is studied on silicon wafers using the impedance spectroscopy technique. The induced p+-p-n structures are created by depositing semitransparent layers of high (Pd) and low (Al) work function (w.r.t silicon) metal layers on crystalline silicon (c-Si) wafers. The measurements are carried out by illuminating the device from the p+-p side. The impedance data are analyzed by assuming a network consisting of a number of RC circuits, which, in turn, give recombination times (τ) controlled by defects in bulk and at the interfaces of the device. The maximum value of the effective recombination lifetime (τ) is found to be 12.3 ± 0.4 μs at an intensity of ~100 mW/cm2, which matches closely with the maximum value 11.4 ± 1.0 μs obtained under forward bias (+ 0.4 V) conditions in the same sample in the dark. These values match well with the effective minority carrier lifetime obtained using the microwave photoconductive decay technique on the same silicon wafer prior to device fabrication.

Crystalline silicon surface passivation by thermal ALD deposited Al doped ZnO thin films

The evidence of good quality silicon surface passivation using thermal ALD deposited Al doped zinc oxide (AZO) thin films is demonstrated. AZO films are prepared by introducing aluminium precursor in between zinc and oxygen precursors during the deposition. The formation of AZO is confirmed by ellipsometry, XRD and Hall measurements. Effective minority carrier lifetime (τeff) greater than 1.5ms at intermediate bulk injection levels is realized for symmetrically passivated p-type silicon surfaces under optimised annealing conditions of temperature and time in hydrogen ambient. The best results are realised at 450°C annealing for >15min. Such a layer may lead to implied open circuit voltage gain of 80mV.

Estimation of Photovoltaic Cells Model Parameters using Particle Swarm Optimization

Swarm intelligence based technique has been used in this work for the estimation of parameters of photovoltaic cells using the two-diode model of the photovoltaic cell. Particle Swarm Optimization algorithm was used to fit the calculated current–voltage characteristics of the photovoltaic cells to the experimental one. The estimated parameters were the generated photocurrent, saturation currents, series resistance, shunt resistance and ideality factors. The proposed approach was validated using industrial photovoltaic cells.

X-ray photoelectron spectroscopic study of silicon surface passivation in alcoholic iodine and bromine solutions

We report an X-ray photoelectron spectroscopic (XPS) study of silicon surfaces passivation using alcoholic solutions of iodine and bromine where different behavior with two systems is observed. The minority carrier lifetime determined by microwave photoconductive decay method showed better surface passivation for iodine-alcoholic system with HF preconditioning step. The iodine–ethanol (I–E) passivated samples show strong Si–I bonding (two times) in Si core level spectra for the samples without oxide (25.5%) compared with oxide (10.2%) counterpart. However, bromine–ethanol (B–E) passivated samples show higher Si–Br bonding strength in the samples with oxide (24.7%) compared to without oxide specimens (12.0%). This may be the reason of difference in passivation behavior of I–E and B–E systems. Higher O–Br bonding in O core level spectra of B–E passivated samples with oxide (35.8%), compared to without oxide (20.7%), results in comparable lifetime values in both with and without preconditioning. To understand the effect of solvent on the passivation, experiments are performed using iodine–methanol (I–M) and bromine–methanol (B–M) solutions and XPS analysis shows similar Si–I, Si–Br, and O–Br bonding trends.

Silicon Surface Passivation by Al2O3 film using Atomic Layer Deposition

Silicon surface passivation is studied using Al2O3 thin film deposited by thermal process using atomic layer deposition (ALD) method. Minority carrier lifetime measurements showed that the film passivate the silicon surface effectively. Capacitance–voltage measurement confirms the activation of negative fixed charges after sintering at 400 °C.