Extremely low reflectance was obtained from InP porous nanostructures in UV, visible, and near-infrared ranges. Porous samples were electrochemically prepared on which 130-nm-diameter nanopores were formed in a straight, vertical direction and were laterally separated by 50-nm-thick InP nanowalls. The reflectance strongly depended on the surface morphology. The lowest reflectance of 0.1% in the visible light range was obtained after the irregular top layer had been completely removed. Superior photoelectrochemical properties were obtained on the InP porous structures due to two unique features: the large surface area inside pores, and the large photon absorption enhanced on the low reflectance surface.Keywords: Indium Phosphide, porous structure, surface reflectance, photoelectrochemical solar cellauthor. E-mail: taketomo@rciqe.hokudai.ac.jp (Taketomo Sato). IntroductionIndium phosphide and related materials have attracted attention over the years as effective materials for high-speed electronics and optoelectronic devices. Photosensitive devices such as photodetectors in long-wavelength optical fiber communication systems [1,2] and high-efficiency solar cells with multi-junction structures [3] are excellent examples of technologies that utilize the superb optical properties of InP-based systems. With the aforementioned devices, however, surface reflection is a serious problem that degrades the device performance because is reduces the efficiency of photon energy conversion [4]. Surface texturing of V-grooves [5][6][7], formation of insulator films [8], wide bandgap semiconductor films [9], and transparent conducting oxide films [10] have been investigated as anti-reflective layers on top of InP. However, most of these techniques exhibit minimum reflectance values as low as 2-10% and satisfactory anti-reflective performance only in a limited wavelength range.In this letter, we report that extremely low reflectance below 0.4% was observed from the InP porous nanostructures in UV, visible, and near-infrared ranges. Our porous structures are electrochemically formed using a very simple setup at extremely low cost. The surface reflectance spectroscopy was systematically carried out on various porous samples, leading to finding that the reflectance strongly depended on the surface morphology and the pore depth. Photoelectrochemical measurements on the porous structures revealed that the photocurrents increased in the samples that had low reflectance surfaces with deeper pores.
The electrocatalytic activity of n-type InP porous nanostructures was investigated in terms of their application to amperometric biochemical sensors. The current sensitivities for H 2 O 2 detection were strongly dependent on the structural properties of these porous We demonstrated the direct detection of H 2 O 2 amperometrically by using porous nanostructures formed on highly-doped n-type InP substrates. We recently succeeded in electrochemically forming arrays of straight nanopores on n-InP (001) substrates. [11][12][13][14] The nanopores were laterally separated by InP nanowalls several tens of nanometers thick, and formed along a straight vertical direction more than several tens of micrometers. In addition to this, n-type InP has attracted attention as a sensor material due to the well-known surface sensitive nature of InP.
In this paper, we demonstrated that the InP-based open-gate FET worked well as a liquid-phase chemical sensor in acid electrolytes. The open-gate FET clearly exhibited current saturation and pinch-off behavior in the electrolyte, resulted in a rapid response to the gate bias applied via the electrolyte. A series of sensing measurements showed that the surface potential of the InP linearly changed with the pH values of the electrolytes, and their sensitivity was strongly dependent on ion species contained in the electrolyte.
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