Gallium nitride (GaN) is a relatively new semiconductor material that has the potential of replacing gallium arsenide (GaAs) in some of the more recent technological applications, for example chemical sensor applications. In this paper, we introduce a triangular quantum well model for an undoped AlGaN/GaN high electron mobility transistor (HEMT) structure used as a chemical and biological sensor for pH and dipole moment measurements of polar liquids. We have performed theoretical calculations related to the HEMT characteristics and we have compared them with experimental measurements carried out in many previous papers. These calculations include the current–voltage (I–V) characteristics of the device, the surface potential, the change in the drain current with the dipole moment and the drain current as a function of pH. The results exhibit good agreement with experimental measurements for different polar liquids and electrolyte solutions. It is also found that the drain current of the device exhibits a large linear variation with the dipole moment, and that the surface potential and the drain current depend strongly on the pH. Therefore, it can distinguish molecules with slightly different dipole moments and solutions with small variations in pH. The ability of the device to sense biomolecules (such as proteins) with very large dipole moments is investigated.
In this work, the structural and optical properties of the InSe/ CdSe heterojunction are investigated by means of X-ray diffraction and ultraviolet-visible light spectrophotometry techniques. The hexagonal CdSe films that were deposited onto amorphous InSe and onto glass substrates at a vacuum pressure of 10 À5 mbar, exhibited interesting optical characteristics. Namely, the absorption, transmission, and reflection spectra that were recorded in the incident light wavelength range of 300-1100 nm, for the InSe, CdSe, and InSe/CdSe interface revealed direct allowed transition energy bandgaps of 1.44, 1.85, and 1.52 eV, respectively. The valence-band offset for the interface is found to be 0.36 eV. On the other hand, the dielectric constant spectral analysis displayed a large increase in the real part of the dielectric constant associated with decreasing frequency below 500 THz. In addition, the optical conductivity spectra that were analyzed and modeled in accordance with the Drude theory displayed a free-carrier average scattering time of 0.4 fs and a drift mobility of 6.65 cm 2 V À1 s À1 for the InSe/CdSe interface. The features of this interface nominate it as a promising member for the production of optoelectronic Schottky channels and as thinfilm transistors. 1 Introduction Owing to the remarkable optical properties they exhibit [1][2][3][4][5][6][7], the cadmium selenide and InSe thin films are attractive materials in optoelectronic technology. The quantum dot-sensitized solar cells (QDSCs) of CdSe displayed high power conversion efficiency of 3.26 AE 0.10% under one sun illumination [2]. In addition, the ZnTe/CdSe QD-based QDSCs showed a champion power conversion efficiency of 7.17% and an efficiency of 6.82% under one full sun illumination [3]. Moreover, the CdTe/ CdSe nanocrystal (NC) solar cells with the inverted structure (ITO/ZnO/CdSe/CdTe/Au) that had been fabricated by the simple solution process coupled with the layer-by-layer sintering technique displayed an annealing strategydependent device performance [4]. The efficiency of these NC devices reached 5.81% at an annealing temperature of 340 8C. Furthermore, very small size (3-5 nm) particles of zinc-blende cadmium selenide nanocrystals modified with oleic acid showed an NC solar cell efficiency of $1.08% [5]. The most beneficial property of the last two types is the ability of preparation from solutions.On the other hand, the n-InSe/p-Si heterojunction is reported to exhibit a photovoltaic characteristic with a
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