Wet Chemical Surface Passivation of Germanium Wafers by Quinhydrone–Methanol Treatment for Minority Carrier Lifetime Measurements

Abstract

We have applied quinhydrone/methanol (Q/M) treatment to germanium (Ge) surfaces and shown that this treatment is also effective for passivating Ge surfaces for minority carrier lifetime measurements. Surface recombination velocity (S) of less than 20 cm/s has been obtained, which enables us to accurately evaluate the bulk lifetime of minority carriers, b , in Ge wafers. To the best of our knowledge, this is the first report on wet chemical treatment successfully applied to Ge surfaces achieving low values of S. The effects of quinhydrone concentration and passivation time on the results of lifetime measurements are described and discussed.

Ambient stability of wet chemically passivated germanium wafer for crystalline solar cells

“…3-in p-type Ge wafers with resisitivities of 13-14 O cm were used for this study since these wafers had a long bulk lifetime of t b ( $ 1 ms) and thus were suitable for the study on passivation properties [7]. The thickness of the Ge wafer was 365-370 mm and both sides of the wafers were mirror-polished.…”

“…Measurements of t were performed by a m-PCD method using a WT-85 lifetime scanner (SEMILAB) [7,11,12]. A pulsed laser diode with a wavelength of 904 nm and a pulse width of 200 ns was used.…”

“…They can thus be suitable for the passivation of Ge surfaces. Yablonovitch et al [6] reported that H-terminated Ge surfaces exhibit a very low value (2 cm/s) of S. Swain et al [7] pointed out that quinhydrone-methanol (Q-M) treatment is effective to reduce the value of S at Ge surfaces to less than 20 cm/s. During the measurements of t, Ge wafers are immersed in solutions and the surfaces can be stable for a long time.…”

Adequate Method for Decoupling Bulk Lifetime and Surface Recombination Velocity in Silicon Wafers

“…Therefore, chemical passivation route seems to be fast, simple, not expensive and more adequate to inspect the bulk quality and then to predict the final solar cell efficiency. Chhabra et al [4] and Swain et al [5] have, respectively, used quinhydrone-and iodine-methanol to passivate silicon and germanium, and have obtained high passivation qualities. Another study carried out by Stephens and Green [3] demonstrated that good surface passivation can be achieved using 0.08 M iodine-ethanol solution.…”

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

“…The advantage of chemical passivation is that it can easily be adopted at any stage of device fabrication to determine the minority carrier lifetime during process development, i.e., to act as a check of process induced effect on the material's lifetime. The passivation of silicon surfaces is carried out by using alcoholic solution of iodine, bromine and quinhydrone, etc., [9][10][11][12] besides concentrated HF. However, the mechanism responsible for surface passivation is still not clear and a matter of debate.…”