Improved Silicon Surface Passivation by ALD Al₂O₃/SiO₂ Multilayers with In‐Situ Plasma Treatments

Abstract

total fixed negative charge density Q tot of ≈1 × 10 13 cm −2 in combination with a low interface defect density D it of ≈1 × 10 11 eV −1 cm −2 . [4][5][6][7][8][9] While the low D it represents a rather good chemical surface passivation, the high negative Q tot causes a reduction of the electron density at the surface, which results in an important field effect contribution to the c-Si surface passivation. Thus, this high negative Q tot induces an inversion layer on n-type Si surfaces, while an accumulation layer is formed on p-type surfaces. The inversion layer at n-type Si surfaces makes its application prone to parasitic shunting effects at n-type metal contacts. [10] Therefore, Al 2 O 3 is predominantly applied to p-type c-Si surfaces, such as the rear surface of passivated emitter and rear cell (PERC) passivated emitter and rear cell solar cells -the current mainstream cell design in high-volume production [11,12] -or the front-side boron-doped p + emitter of n-type c-Si tunneling oxide passivating contact (TOPCon) solar cells, which are becoming currently increasingly attractive due to their higher efficiency potential. [11,[13][14][15] Al 2 O 3 is also very interesting for advanced cell designs with efficiencies in the range of 26%, such as the rear emitter (TOPCon) cell [16] or the polycrystalline Si on oxide-interdigitated back contact (POLO-IBC) cell, [17] where a highly effective but transparent passivation of the bare (undiffused) p-type c-Si front surface is required.Recently, a direct comparison of different surface passivation schemes indicated that there is still room for improvement for Al 2 O 3 [3] which becomes increasingly important as device performance improves. In contrast to single layers, multilayers with thicknesses of only a few nanometers of the individual layers open the opportunity to modify material properties on a nanometer scale. One interesting example are the so-called interface dipole layers, which are currently intensively investigated especially for the application in metal-oxide-semiconductor field-effect transistor (MOSFETs) to adjust the desired flat-band voltage. [18][19][20] They are multilayers consisting of two or three different dielectric layers and can provide the possibility of increasing the flat-band voltage simply by varying the number of the bi-or trilayers. The origin of this flat-band voltage shift are dipoles, which are formed only at specific interfaces of this multilayer with only one polarity. For instance, SiO 2 /Al 2 O 3 stacks have been reported, where dipoles are formed only at the SiO 2 /Al 2 O 3 interfaces with one polarity but not at the Al 2 O 3 / SiO 2 interfaces with the opposite polarity. [19] Al 2 O 3 is one of the most effective dielectric surface passivation layers for silicon solar cells, but recent studies indicate that there is still room for improvement. Instead of a single layer, multilayers of only a few nanometers thickness offer the possibility to tailor material properties on a nanometer scale. In this study, the effect of various ...

Development of Schottky barrier field-effect transistors (SB-MOSFET) with ultra-low thermal budget

“…It can be observed that without passivation, (0 min curve) the forward and inverse currents are close in magnitude, resembling an ohmic contact. With an increase in passivation time, the inverse saturation current decreases several orders of magnitude and this is attributed to a reduction in the density of silicon dangling-bonds by the passivation procedure [21][22][23][24]. The resulting chemical oxide layer (IPL formed after passivation) has a much lower defect density than the original silicon surface, which reduces the number of carrier trap states and improves the quality of the silicon-oxide interface [21].…”