Ga-doped ZnO

The most detailed NMR study of impurity band formation in a semiconductor in the intermediate regime involved 31P and 29 Si 7). line width and shift measurements at 8 T from 100-500 K for Si samples doped with P at levels between 4 x 1018 cm 3 and 8 x 1019 cm 3 [189], and an alternate simplified interpretation of these results in terms of an extended Korringa relation [185]. While the results and interpretation are too involved to discuss here, the important conclusion was that the conventional picture of P-doped Si at 300 K consisting of fully-ionized donors and carriers confined to extended conduction band states is inadequate. Instead, a complex of impurity bands survives in some form to doping levels as high as 1019 cm 3. A related example of an impurity NMR study of impurity bands is discussed in Sect. 3.8 for Ga-doped ZnO. 

Fig. 2.8. (a) Hall mobility as a function of the temperature for an undoped epitaxial ZnO layer and (b) Hall mobility of Ga-doped ZnO layers as a function of the carrier concentration. The ZnO films were grown epitaxially on lattice-matched ScAlMg04 (SCAM) by Makino et al. [64], In (a) the calculated mobilities for acoustical, polar-optical, piezoelectric, and ionized impurity scattering are shown, together with the total theoretical mobility. In (b) the solid curve is the fit curve (2.24) from Fig. 2.6, while the dashed line is the theoretical curve, calculated by Makino et al. [64]. The dotted line was calculated for transport across depletion regions at grain barriers (see Sect. 2.2.3), also present in epitaxial films [106]... 

Fig. 3.16. Experimental (dotted lines) and best-model calculated (solid lines) IRSE spectra of PLD-grown Ga-doped ZnO thin films on sapphire with different free-charge-carrier concentration and thickness parameters as indicated next to the respective graphs [43]. Spectra are shifted for clarity...

The experimental IRSE data were analyzed assuming an isotropically-averaged effective electron mass parameter of m = 0.28me [135].6 Thereupon, the free-charge-carrier concentration N and the optical mobility parameters p,°pt (i =, L) were obtained [43]. The results of the IRSE-analysis of two sets of Ga-doped ZnO thin films are summarized in Fig. 3.18. 

Fig. 3.18. Free-charge-carrier concentration (a,b) and mobility parameters (c,d) of Ga-doped ZnO thin films on sapphire vs. oxygen pressure during PLD-growth [43]. Triangles and circles correspond to the results determined by IRSE and Hail-effect measurements, respectively. Panels (a,c) and (b,d) contain the results of the films grown with 0.1 and 0.5 mass percent Ga2C>3 powder within the PLD target, respectively. Up- and down-triangles in panels (c) and (d) represent the anisotropic optical mobility parameter /inpt and respectively...

Figure 13.19 The conversion of insulating oxides into semiconductors, (a) (i) Nickel oxide (NiO) doped with hthium oxide (Li20), making it a p-t)fpe semiconductor, and (ii) the energy-band structure of Li+-doped NiO. (b) (i) Zinc oxide (ZnO) doped with gallium oxide (Ga203), making it an n-type semiconductor, and (ii) the energy-band struemre of Ga -doped ZnO...

Miyake, A., Yamada, T., Makino, H., Yamamoto, N., and Yamamoto, T. (2008) Effect of substrate temperature on structural, electrical and optical properties of Ga-doped ZnO films on cycro olefin polymer substrate by ion plating deposition. Thin Solid Films,... 

Research and development was mainly focnsed on the Ga-doped powders and thin ZnO film systems (Bourret-Courchesne et al. 2009, Choi et al. 2008, Derenzo et al. 2002, Ehrentraut et al. 2006, Makino et al. 2005, Neal et al. 2006, Yen et al. 2010) due to the aforementioned Ga-induced scintillation efficiency increase in the UV region and diminished reabsorption problem. An important improvement in the scintillation efficiency of the Ga-doped ZnO was reported recently (Bourret-Courchesne et al. 2007, 2009). Namely, when the annealing in an Ar-H2 atmosphere at a temperature of about 800°C is applied as the last step of the postpreparation treatment of the Zn-vacancy containing ZnO powder, the intensity of UV emission increases dramatically (Figure 4.5). The effect is interpreted as the UV radiative transition caused by the recombination of the Ga + donor-band electrons and the holes trapped at shallow acceptors. The latter are ascribed to H+ ions localized in Zn vacancies. 

An example of its application is given by Ref ( ) by comparing the number of adsorbed oxygen particles and the variations of the number of electrons in the solid, it has been possible to show that on Ga -doped ZnO, oxygen is chemisorbed as O" between 100 and 180 C, and as 0" above 230 C ... 

CLAUDEL There have indeed been cases where such a segregation occurs thus making very unreliable the obtained results and their relations to any charge transfer theory. For the specific case of Ga doped ZnO, see L. Ponsolle and J.E. Germain, C.R. Acad. Sc. Paris, 2 6 3 C 465 (1966]. 

Fig. 7, Scanning electron micrographs (zoom-in series) of a sample with MBE-grown ZnO (material A) and Ga-doped ZnO (material B), processed using positive photoresist and wet-chemical etching. The wavy structures extending over the sample surface are remnants of the sputter coated ZnO layer that had been deposited on the resist sidewalls and hence were not removed in the lift-off step.

Figure 4.1 Room-temperature carrier concentration (circles) and mobility (diamonds) of Ga-doped ZnO films grown on GaN as a function of Ga concentration. Solid line represents a Ga activation ratio of unity. (After Ref [50].)...

Kato, H., Sano, M., Miyamoto, K. and Yao, T. (2002) Growth and characterization of Ga-doped ZnO layers on o-plane sapphire substrates grown by molecular beam epitaxy. Journal of Crystal Growth, 237-239, 538. 

Park, S.-M., Ikegami, T. and Ebihara, K. (2006) Effects of substrate temperature on the properties of Ga-doped ZnO by pulsed laser deposition. Thin Solid Films, 513, 90. 

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