Passivation of silicon surfaces by heat treatment in liquid water at 110 °C

Abstract

We report the effective passivation of silicon surfaces by heating single-crystalline silicon substrates in liquid water at 110 °C for 1 h. High photoinduced effective minority carrier lifetimes τ eff were obtained ranging from 8.3 ' 10 %4 to 3.1 ' 10 %3 s and from 1.2 ' 10 %4 to 6.0 ' 10 %4 s for the n-and p-type samples, respectively, under 635 nm light illumination, while the τ eff values of the initial bare samples were lower than 1.2 ' 10 %5 s. 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 the n-and p-type samples, respectively. The photo-conductivity of the n-type sample was increased from 3.8 ' 10 %3 (initial) to 1.4 ' 10 %1 S/cm by the present heat treatment under air-mass (AM) 1.5 light illumination at 100 mW/cm 2 . The thickness of the passivation layer was estimated to be only approximately 0.7 nm. Metal-insulator-semiconductor-type solar cells were demonstrated with Al and Au metal formation on the passivated surface. Rectified current voltage and solar cell characteristics were observed. The open circuit voltages were obtained to be 0.52 and 0.49 V under AM 1.5 light illumination at 100 mW/cm 2 for the n-and p-type samples, respectively.

Photoinduced carrier annihilation in silicon pn junction

“…In advance of the present experiment, the G value was determined using two control samples with high τ eff values of 1 × 10 −3 -2 × 10 −3 s with surfaces coated with 100-nm-thick thermally grown SiO 2 layers and with 1-nm-thick SiO 2 layers formed by liquid water heat treatment, whose optical reflectivity spectrum was almost the same as that of bare silicon. 28) The multiply periodic pulsed illumination method directly gave τ eff values of the two control samples under the detection limit of the measurement of τ eff of 2 × 10 −5 s. 19) Using the τ eff values of the control samples, the G values were determined for samples with surfaces coated with SiO 2 and bare surfaces in the present CW light illumination measurement system. The best coincident between experimental T d =T p and calculated T d =T p results in the most probable τ eff for each illumination mode.…”

Passivation of cut edges of crystalline silicon by heat treatment in liquid water

“…We recently developed a heat treatment method in liquid water at temperatures ranging from 90 °C to 110 °C for low-temperature surface passivation. [30][31][32] The formation of a 0.7 nm thick passivation oxide layer on the silicon surfaces was achieved, with an effective minority carrier lifetime τ eff longer than 1 ms. The high τ eff values were maintained for at least 2 months when the samples were kept in air atmosphere at RT.…”

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

“…Many famous passivation techniques have been developed for surface passivation, for example, formation of thermally grown SiO 2 layers [20], hydrogenation treatment [21,22], fieldeffect passivation caused by fixed charges in SiN or aluminum oxide [23,24], and high-pressure H 2 O vapor heat treatment [25][26][27][28][29]. We have recently proposed simple heat treatment in liquid water at 110°C for low-temperature surface passivation techniques for silicon substrates [30,31]. That simple heat treatment achieved the minority carrier effective lifetime s eff longer than 1 ms in the case of 17-Xcm single-crystalline silicon.…”