Electrochemical pore formation on n-InP has been firstly been evidenced in HCl by P. Kohl in 1983 [1]. Since then, numerous studies have been carried out and have revealed a strong influence of the electrolyte in the porosification process [2]. Liquid ammonia, due to its low viscosity, low dielectric constant and its strong basic feature, appears to be relevant to investigate the porosification of semiconductors under true water-free conditions [3]. In this work, anodic pore formation of n-InP was performed in acidic liquid ammonia (NH₃+NH₄Br) by galvanostatic treatments (U-t). Morphologies were characterized by scanning electron microscopy (SEM) and the evolution of optical properties was analysed by ex-situ photoluminescence (PL) with four different wavelengths (442 nm; 488 nm; 514 nm and 633 nm). According to the current density (J) range, two different morphologies have been observed. For low J (<1 mA/cm²) the morphology is comparable to a "sponge", whereas for high J (>1 mA/cm²) to a "coral". The "sponge" morphology is anisotropic; there are only few aperiodic irregularities on the U-t. The pores of the "coral" structure grow tortuously and perpendicularly to the surface in hemispherical depressions. For high J, the periodic lift off of the porous layer is correlated to voltage oscillations and can form multilayered structures [3]. PL experiments combined with SEM characterisation demonstrate that the porosified surfaces exhibit a dead layer behaviour [4]. From these results, the porosification process in this solvent will be explained and compared with those observed in aqueous media.

[1] P.A. Kohl, et al., J. Electrochem. Soc., 130, 2288 (1983)

[2] P. Schmuki, et al., Phys. Status Solidi A, 182, 51 (2000); C. O'Dwyer, et al., J. Electrochem. Soc., 153, G1039 (2006)

[3] A.M. Gonçalves, et al., Electrochem. Solid State Lett., 10, D35 (2007)

[4] D.B. Wittry, et al., J. Appl. Phys., 38, 375 (1967)

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