Recomendaciones sobre reparación integral y transformadora (mecanismos de no repetición).

In order to achieve the best quality devices (InN based), scientists have been devoted during last few decades on experimental investigations on the growth of InN thin films by various growth methods with different substrates. However, free carrier concentrations of those layers are still in the range of 1018_- 1020 _cm-3_{, with an exception for the MBE growth films, it was achieved to the order 10}17 _cm-3_{. As dis-} cussed in Section 1.2, several possible reasons have been suggested for the cause of the high background carrier concentration. However, it is still a mysterious. Recently, more researches have been focused on the development of InN films for plasmonic applications extending to the infrared (IR) and THz regimes due to its lower plasma frequency and its smaller real permittivity than those of the metals [1]. As an ex- ample, Qian et al. has been shown that aptness of InN films as plasma filters for GaSb and GaInAsSb photovoltaic cells in thermophotovoltaic systems with different carrier concentration, mobility, and film thickness [2]. Additionally, due to the high superficial electron concentration, the high sensitivity to charges in the environment, and the high chemical stability, InN has also been recently considered as ma- terial for biosensing. For instance, Naveed Alvi et al. has been suggested a development of an efficient InN QDs (quantum dots) based biosensor for medical diagnosis and shown it for the ability to detect real time changes in the concentration of cholesterol in the human body [3].

Based on these unique properties and its applications, the need of further studies of InN properties cannot be disregarded. Hence, studies of optical response in the IR regime is necessary since phonon modes (lattice vibrations), free carriers, and their coupling, etc. of InN are associated with the IR photon energies. Furthermore, these studies will also expose these physical properties of the commonly used sub- strates such as GaN, AlN, and sapphire used in the growth of InN films. Thus, especially, understanding of the IR optical anisotropy properties of InN play a significant role in devices designing due to the high

anisotropy in the wurtzite structure. Also, studies of the influence of the substrate properties on the InN films properties is crucial for the device fabrication because most physical properties of the materials such as point defect, strain, etc. originate from the substrate.

Y. Ishitani et al. found the dependence of the broadening of InN E1(LO) phonon-plasmon coupled states with the electron concentration (from 8×1017 _{to 1×10}19 _cm-3_{) and the crystal temperature by analyz-} ing the S-polarized IR reflectance spectra [4]. As well as, by analyzing the IR reflectance spectra of InN down to 200 or 250 cm-1 _{including longitudinal phonon and plasmon coupling lower energy branch (LPP-} ) and higher energy branch (LPP+), Y. Ishitani et al. have extracted the electron concentration and mobil- ity of inside region of the bulk nature by resolving the contribution of electron accumulation to the spectra [5]. One of the important properties of InN is the LO-plasmon coupling, and this has been studied using Raman spectra of InN [6] and IR reflectance spectra has been used to compare this features [5]. Moreo- ver, the role of plasmon and LO-phonon damping on the IR spectra of InN films has also been studied [7]. Furthermore, A. Kasic et al. used IR spectroscopic ellipsometry to obtain the electron effective mass. These analysis results indicated the average electron effective mass of 0.14m0 for InN [8]. Later, Y.F. Chen et al. used IR reflectance measurements and obtained a smaller electron effective mass of 0.05m0 for InN films [9]. In addition to these studies, IR ellipsometry and IR reflectance analysis has been used to understand other properties of InN, such as the electron accumulation at nonpolar (112-0)-oriented and semi-polar (101-1)-oriented InN, hole properties of p-type InN films; surface, bulk, and interface elec- tronic properties of nonpolar InN films [10-12]. Z. G. Qian et al. have reported the first detailed investiga- tion of the free carrier concentration, carriers mobility, lattice vibration properties (phonon modes) [2]. A similar study has been conducted by K. Fukui et al. [13]. However, these studies have focused only iso- tropic properties of InN layers. Recently, C. C Katsidis et al. analyzed FTIR reflectance spectra of InN layers, taking into account a three-layer model and found the capability of separating the contribution of free carriers between the bulk, the surface and interface in InN films [14]. In this study, 2×2 matrix alge- bra based on a general transfer matrix method has been considered to interpret the optical response of ar- bitrary multilayers with homogeneous anisotropic layers from IR reflectance spectra.

The work presented in this chapter is a detailed study of free carrier concentrations, mobility of the carriers, high frequency dielectric constant, layer thicknesses and phonon modes of InN layers grown on different substrates, Ga-polar, N-polar, n- and p-type doped GaN, AlN, and sapphire by analyzing FTIR reflectance spectra (at normal and angle incidence un-polarized). Here, isotropic and anisotropic properties of InN layers were analyzed using Multilayer stack model and Model of IR dielectric function described in Chapter 4.

Furthermore, the structural properties of InN layers obtained from Raman spectroscopy analysis are presented. Additionally, surface morphology analysis of these layers by AFM are discussed.