Correspondence
Effect of metallic contacts diffusion on Au/GaAs and Au/GaN/GaAs SBDs electrical quality during their fabrication process

https://doi.org/10.1016/j.jallcom.2021.159596Get rights and content

Abstract

Au/GaN/n-GaAs Schottky Barrier Diodes (SBDs) were fabricated by N2 plasma Nitridation of n-GaAs (100) surface yielding to the formation of GaN ultra thin film interfacial layer between AuSchottky contact and n-GaAs substrate.

Samples were divided in two groups according to their fabrication processes. Choice of these groups was in order to study the effect of high temperatures on both Schottky and Ohmic contacts. Each group contains a Au/n-GaAs SBD as reference sample and two GaN different thicknesses Au/GaN/n-GaAs SBDs, controlled by nitridation time of 10 and 120 min. Fabrication steps were followed by XPS measurements in order to determine the samples’ composition surfaces and estimate thicknesses and oxygen rates of the created GaN layers. Fabricated SBDs were electrically tested by Current–Voltage measurements in dark and room temperature.

Results

show a strong dependence of electrical parameters and device performances on the chemical composition of the semiconductor surface and the quality of the Metal/Semiconductor interface. GaN interfacial interlayers lead to an improvement of the electrical quality of the fabricated devices in the case of a so deteriorated Au/GaAs starting interface. Hence, electrical parameters were widely improved as ideality factor n was reduced after nitridation. In another hand, electrical parameters do not varied remarkably with the increase of nitridation time even in the case of a better fabrication process. Ideality factor was around 1.15 and one could say that these GaN layers were electrically transparent and acted as well as passivation of the GaAs surface.

Introduction

Metal-semiconductor (MS) structures elaborated with gallium arsenide (GaAs) usually known as Schottky barrier diodes (SBDs) have been a topic of several studies [1], [2], [3], [4]. Such structures are widely used in various electronic and optoelectronic applications. However, the major obstacle encountered in the elaboration of these SBDs is the oxidation of the GaAs surface which incurs a poor quality of the interfaces between the III-V’s and the metal leading to the degradation of the electronic properties of the device. Thereby the passivation of the GaAs surface appears as a key point to improve the performance of GaAs based devices. Different surface passivation methods have been developed to remove this undesirable effect as anodization process [5], Se treatment [6] and N2 plasma treatment [7]. Ebeoglu and al [8] studied the influence of a GaN interfacial layer achieved by chemical anodic nitridation method. Authors calculated the interface state density with and without taking into account the series resistance and they saw whether this interfacial layer improved the electrical quality of the studied structure. Benamara et al. [9] solved the problem of contactless determination of interface state density in GaN/GaAs (100) structures. Zougagh et al. [10] and Ameur et al. [11] investigated in detailed the electrical transport properties of Hg/GaN/GaAs structures using I–V and C–V measurements. Also, electrical and photoelectrical properties of Au/GaAs and Au/GaN/GaAs SBDs fabricated by nitridizing the GaAs surfaces using a nitrogen glow discharge source (GDS) were investigated in our previous works [12], [13], [14], [15], [16]. These studies clearly showed the importance of the cleaning and nitridation steps of GaAs (100) surface and the effect of the thermal annealing (at T = 620 °C) of the fabricated structures using I-V measurements in both dark and under illumination and C-V measurements at high frequency. Indeed, in this work, GaAs surfaces have been cleaned using Ar+ ions sputtering in ultra-high vacuum condition in order to remove contaminations. However, Ar+ ions cleaning lead to an amorphous GaAs surface. Moreover, electrical results on Au/GaN/GaAs Schottky diodes showed that the formation of Au-Ga compounds at the Au/GaN interface could reduce the Schottky barrier height yielding a large reverse leakage current after the modification of the GaAs (100) surface morphology by the Ar+ ions cleaning process. In another hand, thermal annealing leads to the crystallization of the GaN created layers causing a high mismatch lattice parameter at the GaN/GaAs interface.

Nevertheless, attention was focused in this work, on the improvement of the electrical quality of SBDs based on nitridating n-GaAs (100) using a new fabrication process. The fabricated structures are electrically tested by current-voltage measurements at dark and room temperature conditions. This study allows us to analyze the effect of the nitridation process and the impact of the technological steps of fabrication on the electrical quality of realized SBDs.

Section snippets

Materials and methods

The commercially available GaAs (001) wafers are n-type with concentration ND= 4.9 × 1015 cm−3. One used a cleaning process developed by Tereshchenko et al. [17], [18] and which was validated in the works of Alperovich et al. [19] and H. Mehdi et al. [20]. This process consists in two steps, a chemical cleaning (ex-situ) and a heating of the substrate under UHV condition (in-situ).

Then, the nitridation process has been performed in-situ using an ECR N2 plasma source normal to the surface, at

Results and discussion

In order to monitor the nitridation process, As3d, Ga3d, O1s and N1s photoelectron peaks have been recorded. These peaks were decomposed using Gaussian-Lorentzian curves and a Shirley background. The decomposition parameters were taken from [20], [21]. Fig. 2 shows spectra before and after nitridation for the sample A2.

Before nitridation step, the As3d and the Ga3d peaks are decomposed by only one peak corresponding to the contribution of the GaAs substrate and no oxygen was detected. After

Conclusion

In this study of Au/GaN/GaAs SBDs, one observed a strong and intimate correlation between electrical parameters of such devices and variations of their chemical and structural properties mainly due to the fabrication process. Electrical parameters and device performance were strongly controlled by chemical composition of the semiconductor surface and the quality of the Metal/Semiconductor interface. Then, SBDs based on nitridated GaAs were elaborated using two different fabrication processes.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This work was financially supported by the Algerian Ministry of Higher Education and Scientific Research within the framework of the Exceptional National Program (PNE), Djillali Liabes University of Sidi Bel Abbes (ALGERIA) and Clermont Auvergne University of Clermont-Ferrand (FRANCE).

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