This work proves that blistering is the partial de-lamination of a thick enough Al2O3 layer caused by gaseous desorption in the Al2O3 layer upon thermal treatments above a critical temperature: the Al2O3 layer acts as a gas barrier and bubble formation occurs. First, using an atmospheric pressure rapid thermal processor with an atmospheric pressure ionization mass spectrometry, desorbing species upon heating of Si / Al2O3 samples are identified: evident desorption peaks are observed around 400 °C for all spectra. The spectrum for m/e = 18, an indication of H2O, illustrates that gaseous desorption from Al2O3 and from the Si substrate itself continues up to 600 °C and 700 °C, respectively. Also, it is shown that in the case of a 30 nm Al2O3 layer, blistering starts at same annealing temperatures as gaseous desorption begins. In the case of a thin enough (≤ 10 nm) Al2O3 film, blistering does not show. To complete the proof, elastic recoil detection measurements clearly show that after annealing a thick Al2O3 film above 400 °C the H content is higher near the c-Si interface as compared to the near surface.Fortunately, effective lifetime and capacitance voltage measurements show that 5 to 10 nm Al2O3 layers can still be adequate passivation layers after being annealed in N2 environment at temperatures up to 500-700 °C: (i) interface trap densities (Dit) can remain below 1x10 11 cm -2 and (ii) fixed charge densities (Qf) stay negative and in the order of -3x10 12 cm -2 .Random local Al back surface field (BSF) solar cells, fabricated using a blistered film as rear surface passivation and no additional contact opening step, clearly show that random local BSFs are created upon firing of a blistered rear passivation layer covered by metal. Therefore, it is clear that blistering should be avoided, since it will reduce the overall rear surface passivation.

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Epitaxial PbSe layers on Si(111) relax nearly completely owing to the easy dislocation glide in the main ͕100͖ ͗110͘ glide system. Threading dislocations introduced by the thermal mismatch strains are able to move distances of several cm and to escape at the edges of the samples. Etch-pit densities as low as 10 6 cm 22 were obtained in layers with a thickness of d 4 mm. The etch-pit density scales with 1͞d 2 , which may be understood as a consequence of the annealing step and of the high mobility of dislocations. By applying several anneal cycles, threading dislocation densities of essentially zero should result. [S0031-9007(97)

Atomic layer deposition (ALD) of thin Al 2 O 3 (≤10 nm) films is used to improve the rear surface passivation of large-area screen-printed p-type Si passivated emitter and rear cells (PERC). A blister-free stack of Al 2 O 3 /SiO x /SiN x is developed, leading to an improved back reflection and a rear recombination current (J 0,rear ) of 92 AE 6 fA/cm 2 . The Al 2 O 3 /SiO x /SiN x stack is blister-free if a 700 C anneal in N 2 is performed after the Al 2 O 3 deposition and prior to the SiO x /SiN x capping. A clear relationship between blistering density and lower open-circuit voltage (V OC ) due to increased rear contacting area is shown. In case of the blister-free Al 2 O 3 /SiO x /SiN x rear surface passivation stack, an average cell efficiency of 19.0% is reached and independently confirmed by FhG-ISE CalLab. Compared with SiO x /SiN x -passivated PERC, there is an obvious gain in V OC and short-circuit current (J SC ) of 5 mV and 0.2 mA/cm 2 , respectively, thanks to improved rear surface passivation and rear internal reflection.

A next generation material for surface passivation of crystalline Si is Al 2 O 3 . It has been shown that both thermal and plasma-assisted (PA) atomic layer deposition (ALD) Al 2 O 3 provide an adequate level of surface passivation for both p-and n-type Si substrates. However, conventional time-resolved ALD is limited by its low deposition rate. Therefore, an experimental high-deposition-rate prototype ALD reactor based on the spatially separated ALD principle has been developed and Al 2 O 3 deposition rates up to 1.2 nm/s have been demonstrated. In this work, the passivation quality and uniformity of the experimental spatially separated ALD Al 2 O 3 films are evaluated and compared to conventional temporal ALD Al 2 O 3 , by use of quasi-steady-state photo-conductance (QSSPC) and carrier density imaging (CDI). It is shown that spatially separated Al 2 O 3 films of increasing thickness provide an increasing surface passivation level. Moreover, on p-type CZ Si, 10 and 30 nm spatial ALD Al 2 O 3 layers can achieve the same level of surface passivation as equivalent temporal ALD Al 2 O 3 layers. In contrast, on n-type FZ Si, spatially separated ALD Al 2 O 3 samples generally do not reach the same optimal passivation quality as equivalent conventional temporal ALD Al 2 O 3 samples. Nevertheless, after ''firing'', 30 nm of spatially separated ALD Al 2 O 3 on 250 mm thick n-type (2.4 V cm) FZ Si wafers can lead to effective surface recombination velocities as low as 2.9 cm/s, compared to 1.9 cm/s in the case of 30 nm of temporal ALD Al 2 O 3 .