GaN and related semiconductor compounds are important materials for optoelectronic and electronic applications, especially in high-temperature, high-power and high-efficiency systems. In order to exploit the full potential of these materials more effective methods of surface passivation are highly required. The standard methods of surface passivation of GaN-based devices rely on the use of silicon oxides or nitrides SiO₂, Si₃N₄ and SiON. Several sulphur passivation processes including chemical treatments in (NH₄)₂S, Na₂S and CH₃CSNH₂ aqueous or alcoholic solutions have been proposed without definitive achievements. On the other hand, chemical bath deposited CdS films have been proven useful to passivation of III-V semiconductors surfaces [1].

In this paper we present the results on passivation of GaN surface using Chemical Bath Deposition (CBD) technique, forming CdS thin layers. 0.1M SC(NH₂)₂ as sulphur source, 0.1M CdSO₄ as source of Cd and 2.4M NH₄OH as solution for hydrolysis were used in the experiments. Variable Angle Spectroscopic Ellipsometry (VASE) was chosen to provide information of thickness, refractive index and dielectric function of passivating layers. Surface morphology was examined by optical microscopy with phase contrast and by Atomic Force Microscopy (AFM). To study the influence of CBD - CdS passivation on electronic properties on GaN surface, Ir/p GaN Schottky diodes were prepared on passivated and nonpassivated GaN samples. The results show, that Chemical Both Deposition from 0.1M SC(NH₂)₂ - 0.1M CdSO₄ ammonia solution enables to form thin (d = 20nm) CdS films, with good insulating properties (ε₂ = 0.0003 at E = 1.1eV) and smooth surface (rms = 1.2nm). Increasing of height of Ir/p GaN barrier from 0.56 to 0.81 indicates that CdS layer deposited by Chemical Bath Deposition techniques enhanced performance of Schottky barrier.

Part of the research was supported by the grant from the EC HYPHEN Contract Number: FP6-027455.

[1]. O. Vigil-Galan, J. Vidal Larramendi, I. Riech, G. Pena Rodriguez, A. Iribarren, J. Aguilar-Hernandez, G. Contreras-Puente, Semicond. Sci. Technol. 17, 1193, 2002.

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