Growth on a-plane sapphire

To eliminate the orientational domains often observed in ZnO thin films grown on (0001) sapphire, (11 20) sapphire substrates have been used for ZnO epitaxy. The lattice parameter a = 0.3250 nm of ZnO and parameter c = 1.299 nm of sapphire are related almost exactly by a factor of 4, with a mismatch less than 0.08% at room temperature. On the basis of this fact and coining the term uniaxial locked epitaxy,  

The orientation of the sapphire substrate was determined in a separate measurement using the sapphire (11 26) poles [filled circles in (b)]. (Ref [101].) 

130cm V s and electron concentration of 1.4 x 10 cm were grown with good reproducibility by using the H pretreatment. A Ga preexposure after H and O pretreatment of the sapphire (0001) surface was adopted by Du et al. just before the ZnO growth to eliminate the rotational domain structures [104]. The ZnO (000 2) 

The ZnO film was of O polarity. The observed surface morphology was explained as follows for growth conducted on the O-polar surface, the surface diffusion length of 

Zn adatoms was smaller under the Zn-rich conditions than under the stoichiometric or 0-rich conditions. ZnO layers grown under stoichiometric flux conditions had high crystalline quality, the lowest dislocation density, and the highest electron mobility ( 130cm s ) when compared to ZnO Aims grown under nonstoi- 

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The shift of the A line in the epilayers has been connected with the variation of the lattice parameters of GaN [1,11,12], The shift of this line was also measured in samples subjected to hydrostatic pressure (see Datareview A3.1). Combination of all these data permits one to obtain the whole series of excitonic deformation potentials [6,16], Two sets of data are available which are consistent with each other and are given in TABLE 1. The discrepancies between them are linked to the differences in the values of the stiflhess coefficients of GaN used by the authors. Gil and Alemu [6] in their work subsequent to the work of Shan et al [16] used data not available when Shan et al calculated their values. The notations are the same and are linked to the relationship with the quasi cubic model of Pikus and Bir [17], Deformation potentials as and a6 have been obtained by Alemu et al [8] who studied the anisotropy of the optical response in the growth plane of GaN epilayers orthorhombically distorted by growth on A-plane sapphire. For a detailed presentation of the theoretical values of deformation potentials of GaN we refer the reader to Suzuki and Uenoyama [20] who took the old values of the stiflhess coefficients of GaN [21]. 

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