Electrical Transport in ZnO Single Crystals

First reliable conductivity data were given by Fritsch already in 1935, shown in Fig. 2.2. Significant progress was achieved when the semiconductor era started [11], Hahn [15] and Harrison [16] were the first who reported 

The maxima of the mobilities around 50-100 K are caused by the onset of ionized impurity scattering. The highest measured mobility at about 80 K is 

This scattering process is due to the interaction of electrons with the electric field induced by the lattice vibration polarization (polar longitudinal-optical phonons) occurring in polar semiconductors with partially ionic bonding. According to Devlin [55], the optical Hall mobility can be calculated by 

Acoustic phonons lead to lattice deformation scattering because of a local energetic shift of the band edges. According to Bardeen and Shockley [56] the acoustical lattice mode Hall mobility is  

This scattering mode occurs only in piezoelectric materials, i.e., in crystals without inversion symmetry, and is caused by the electric field associated with acoustical phonons. Zinc oxide exhibits very high electro-mechanical coupling coefficients P (see later), exceeding that of quartz [42,59], which is one of the mostly used piezoelectric materials. Zook [60] has calculated the piezoelectrically limited mobility on the basis of the elastic and piezoelectric constants as (see also Rode [54])  

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