Nm Nick Terlinden

Influence of the Oxidant on the Chemical and Field-Effect Passivation of Si by ALD Al2O3

Differences in Si surface passivation by aluminum oxide (Al2O3) films synthesized using H2O and O-3-based thermal atomic layer deposition (ALD) and plasma ALD have been revealed. A low interface defect density of D-it = similar to 1011 eV(-1) cm(-2) was obtained after annealing, independent of the oxidant. This low D-it was found to be vital for the passivation performance. Field-effect passivation was less prominent for H2O-based ALD Al2O3 before and after annealing, whereas for as-deposited ALD films with an O-2 plasma or O-3 as the oxidants, the field-effect passivation was impaired by a very high Dit

Role of field-effect on c-Si surface passivation by ultrathin (2–20 nm) atomic layer deposited Al2O3

Al2O3 synthesized by plasma-assisted atomic layer deposition yields excellent surface passivation of crystalline silicon (c-Si) for films down to ∼5 nm in thickness. Optical second-harmonic generation was employed to distinguish between the influence of field-effect passivation and chemical passivation through the measurement of the electric field in the c-Si space-charge region. It is demonstrated that this electric field—and hence the negative fixed charge density—is virtually unaffected by the Al2O3 thickness between 2 and 20 nm indicating that a decrease in chemical passivation causes the reduced passivation performance for <5 nm thick Al2O3 films.

Controlling the fixed charge and passivation properties of Si(100)Al2O3 interfaces using ultrathin SiO2 interlayers synthesized by atomic layer deposition

Al2O3 synthesized by atomic layer deposition (ALD) on H-terminated Si(100) exhibits a very thin (∼1 nm) interfacial SiOx layer. At this interface, a high fixed negative charge density, Qf, is present after annealing which contributes to ultralow surface recombination velocities  ∼5 nm), the polarity of the effective charge density changed from negative to positive. The observed changes in Qf and the associated field-effect passivation had a significant influence on the injection-level-dependent minority carrier lifetime of Si.

Influence of the SiO2 interlayer thickness on the density and polarity of charges in Si/SiO2/Al2O3 stacks as studied by optical second-harmonic generation

By accurately tuning the SiO2 interlayer thickness the density and polarity of charges in Si/SiO2/Al2O3 stacks can be controlled. We report on the number density, polarity, and physical location of charges present in the stacks as studied by optical second-harmonic generation (SHG). Depending on the SiO2 interlayer thickness (1–150 nm) the effective charge density in the Si/SiO2/Al2O3 stacks ranges from 1013 to 1011 cm−2 for both n- and p-type silicon. The polarity of the charges switches from negative to positive around a SiO2 interlayer thickness of 5–10 nm at which point the effective charge density in the stacks is negligible. This switch in polarity is apparent from spectroscopic, time-dependent, and azimuthal SHG measurements. The observed trends in charge density and polarity can be explained by tunneling of electrons into defect states at the SiO2/Al2O3 interface as well as the presence of fixed and bulk charges at the Si/SiO2 interface and in the SiO2, respectively. This charge mechanism appears ...

Electric field induced surface passivation of Si by atomic layer deposited Al 2 O 3 studied by optical second-harmonic generation

Recently, we have demonstrated that ultrathin (≪30 nm) films of Al<inf>2</inf>O<inf>3</inf> synthesized by (plasma-assisted) atomic layer deposition (ALD) provide an excellent level of surface passivation of c-Si which may find important applications in (high-efficiency) solar cells. In this contribution, the Al<inf>2</inf>O<inf>3</inf> passivation mechanism has been further elucidated by the contactless characterization of the c-Si/Al<inf>2</inf>O<inf>3</inf> interface by optical second-harmonic generation (SHG). SHG has revealed effective field-effect passivation of the c-Si surface caused by a negative fixed charge density of 5×10¹² cm⁻² in an annealed, 11 nm thick Al<inf>2</inf>O<inf>3</inf> film while it is on the order of 10¹¹ cm^™2 in the as-deposited film which shows negligible passivation. A comparison with SHG measurements on a 84 nm thick a-SiN<inf>x</inf>:H film treated in a conventional firing furnace has revealed the presence of a positive fixed charge density of 2×10¹² cm⁻² which further corroborates the SHG analysis and results.

Second-harmonic intensity and phase spectroscopy as a sensitive method to probe the space-charge field in Si(100) covered with charged dielectrics

A space-charge region (SCR) can develop in silicon due to the presence of built-in charges in dielectric thin films that are used in silicon-based device architectures. To study both the strength and polarity of the electric field in such a SCR, the authors performed second-harmonic (SH) generation spectroscopy in the vicinity of the E1 critical point (2.7–3.5 eV) of silicon. As multiple contributions add coherently to SH intensity spectra, the electric-field-induced contribution cannot always be distinguished unambiguously from the intensity data in the absence of complementary phase information. Combined SH intensity and phase measurements were therefore performed to resolve this ambiguity. Using a coherent superposition of critical-point-like resonances with excitonic line shapes, the intensity and phase spectra of several SiO2- and Al2O3-based samples were simultaneously modeled. This analysis reveals that not only the polarity of the space-charge field can be determined unambiguously but also that th...

Corona charging and optical second-harmonic generation studies of the field-effect passivation of c-SI by Al 2 O 3 films

Aluminum oxide films (Al<inf>2</inf>O<inf>3</inf>) synthesized by atomic layer deposition (ALD) provide an excellent level of surface passivation of n⁻, p⁻, and heavily doped p-type crystalline silicon (c-Si). It has been shown that a negative fixed charge density in the order of 10¹²–10¹³ cm⁻² can be present at the interface of Al<inf>2</inf>O<inf>3</inf> with c-Si, inducing a high level of field-effect passivation. In this contribution we report on results obtained by two complementary, contactless techniques to investigate the field-effect passivation for the Al<inf>2</inf>O<inf>3</inf>/c-Si case: optical second-harmonic generation (SHG) and corona charging. From an extensive data set on Al2O3 thin films, we demonstrate that the combination of SHG and corona charging offers the advantage of probing the presence of fixed charges at the interface non-intrusively (SHG) and of extracting the fixed charge density quantitatively (corona). These two techniques are therefore powerful tools for investigating the mechanisms responsible for the passivation properties of thin films.