Applied Surface Science 257 (2011) 6197–6201 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Effect of different electrolytes on porous GaN using photo-electrochemical etching K. Al-Heuseen a,∗ , M.R. Hashim a , N.K. Ali b a Nano-Optoelectronics Research Laboratory, School of Physics, Universiti Sains Malaysia, 11800 Penang, Malaysia b Material Innovations and Nanoelectronics Research Group, Faculty of Electrical Engineering, Department of Electronic Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia article info Article history: Received 28 July 2010 Received in revised form 13 January 2011 Accepted 1 February 2011 Available online 12 February 2011 Keywords: Electrolyte Gan Photo-electrochemical etching Porosity abstract This article reports the properties and the behavior of GaN during the photoelectrochemical etching process using four different electrolytes. The measurements show that the porosity strongly depends on the electrolyte and highly affects the surface morphology of etched samples, which has been revealed by scanning electron microscopy (SEM) images. Peak intensity of the photoluminescence (PL) spectra of the porous GaN samples was observed to be enhanced and strongly depend on the electrolytes. Among the samples, there is a little difference in the peak position indicating that the change of porosity has little influence on the PL peak shift, while it highly affecting the peak intensity. Raman spectra of porous GaN under four different solution exhibit phonon mode E 2 (high), A 1 (LO), A 1 (TO) and E 2 (low). There was a red shift in E 2 (high) in all samples, indicating a relaxation of stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Raman and PL intensities were high for samples etched in H 2 SO 4 :H 2 O 2 and KOH followed by the samples etched in HF:HNO 3 and in HF:C 2 H 5 OH. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Over the last decades, nanocrystalline semiconductors have been widely studied, due to their physical properties relative to those of bulk crystals. The high surface area, band gap shift, and efficient luminescence have made the use of porous semiconduc- tor over a promising material for a wide range of applications; from optoelectronics to chemical and biochemical sensors [1,2]. Recently, many works [3–9] have been directed towards depositing semiconductor layers on porous substrates, because of the demand for more powerful and sophisticated device applications. One of the reasons for using a porous semiconductor as a substrate for depositing semiconductor layers is that the nano-patterned porous structures can reduce the extended defect density [6]. The interest in porous semiconductor arises from the fact that they can act as a sink for threading dislocations and accommodate the strain. Hence, they are widely used as a buffer or intermediate layer in epitaxial growth to obtain a subsequent layer with less strain and dislocation densities [10,11]. Mynbaeva et al. [12] proposed that the growth of GaN on porous GaN could lead to high-quality strain-released epilayers. One of the most common techniques to fabricate porous semi- conductors is the photo-assisted electrochemical etching [13]. ∗ Corresponding author. Fax: +60 4 6579150. E-mail address: kalhussen@yahoo.com (K. Al-Heuseen). Formation of pores during anodization process has been widely reported for various types of crystalline silicon [14]. In the last several years, besides porous silicon research, attention has been focused on other porous semiconductors, such as InP [15], GaP [16], GaAs [17] and GaN [2,18–20]. One of the main factors that affect the electrochemical etching is the electrolyte. Many electrolytes were reported for etching semi- conductors. HF-based solutions are the most utilized solutions for GaAs, SiC, and GaN porosification [21]. The electrolytes based on H 2 SO 4 or H 3 PO 4 acids are more preferable for GaP porosification, because they allow the attainment of porous structures without vis- ible covering of pore surface by oxides or other reaction products [16]. For InP, better results were obtained in KOH and HCl-based solutions [15]. Due to their different chemical nature, wide ranges of aqueous electrolytes have been used for GaN etching. Many works in photoelectrochemical etching of GaN were done in alka- line aqueous solutions containing inorganic KOH [20,22], and in inorganic acids such as H 2 SO 4 [23], and H 3 PO 4 [24] or into halo- gen acids such as HF and HCl [25]. In addition, the morphology is strongly dependent on the chemical nature of the solvent, the concentration of the conduction salt, the pH, the counter ion and the temperature [26]. Thus, it is very important to investigate the suitable electrolyte for GaN [27]. In this work, we report the properties and behavior of GaN during etching process using different electrolytes in photoelec- trochemical etching, and we aim to find out the suitable effective electrolytes for etching GaN. In the present work, we use lower 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.02.031