308
V. Melnik et al.
Fig. 3 XRD pattern of a
65.8-nm thick ZnO film
Of further significance is the fact that the ZnO films with thicknesses less than
50 nm are textured. At greater thicknesses, a polycrystalline structure of hexagonal
modification is formed (Fig. 3). This may originate from the large difference in the
lattice parameters of Si and ZnO, which leads to an inhomogeneous growth of the
ZnO film at small thicknesses.
From XRR studies, thickness, density, and root mean squared (rms) roughness of
deposited films are determined. This procedure yields the values given in Table 1. It is
found that the roughness of the Si/ZnO interface does not significantly change upon
increasing the film thickness, for the thicknesses less than ≈70 nm, as evidenced by
the data shown in Fig. 4. In turn, the surface roughness exhibits a noticeable increase
within the thickness range.
Further insight into the processes associated with the growth of ZnO:Al (AZO)
films can be obtained by analyzing the SEM images shown in Fig. 5. It is seen that
the surface relief has an irregular grainy structure character, whereas the inner region
of the film forms a consolidated layer, which can be due to Al inclusions in ZnO.
Mass spectrometric studies given in Fig. 6 shows an ultra-thin SiO 2 oxide film
layer having the thickness of about 2 nm that is formed on the boundary of the phase
separation, implying that AZO/SiO 2 /Si interface is formed in the samples. This is a
prerequisite for considering tunneling through the oxide film (tunnel current) as the
Table 1 Parameters of ZnO-on-Si films discussed in this work
Sample No.
Film thickness
(nm)
Film density
(g/cm 3 )
ZnO/Si interface rms
roughness measured
by XRR (nm)
ZnO surface rms
roughness measured
by XRR (nm)
1
10.2
5.9
0.4
0.54
2
20.8
5.62
0.34
0.52
3
41.6
5.59
0.02
0.51
4
65.8
5.60
0.05
0.6
V. Melnik et al.
Fig. 3 XRD pattern of a
65.8-nm thick ZnO film
Of further significance is the fact that the ZnO films with thicknesses less than
50 nm are textured. At greater thicknesses, a polycrystalline structure of hexagonal
modification is formed (Fig. 3). This may originate from the large difference in the
lattice parameters of Si and ZnO, which leads to an inhomogeneous growth of the
ZnO film at small thicknesses.
From XRR studies, thickness, density, and root mean squared (rms) roughness of
deposited films are determined. This procedure yields the values given in Table 1. It is
found that the roughness of the Si/ZnO interface does not significantly change upon
increasing the film thickness, for the thicknesses less than ≈70 nm, as evidenced by
the data shown in Fig. 4. In turn, the surface roughness exhibits a noticeable increase
within the thickness range.
Further insight into the processes associated with the growth of ZnO:Al (AZO)
films can be obtained by analyzing the SEM images shown in Fig. 5. It is seen that
the surface relief has an irregular grainy structure character, whereas the inner region
of the film forms a consolidated layer, which can be due to Al inclusions in ZnO.
Mass spectrometric studies given in Fig. 6 shows an ultra-thin SiO 2 oxide film
layer having the thickness of about 2 nm that is formed on the boundary of the phase
separation, implying that AZO/SiO 2 /Si interface is formed in the samples. This is a
prerequisite for considering tunneling through the oxide film (tunnel current) as the
Table 1 Parameters of ZnO-on-Si films discussed in this work
Sample No.
Film thickness
(nm)
Film density
(g/cm 3 )
ZnO/Si interface rms
roughness measured
by XRR (nm)
ZnO surface rms
roughness measured
by XRR (nm)
1
10.2
5.9
0.4
0.54
2
20.8
5.62
0.34
0.52
3
41.6
5.59
0.02
0.51
4
65.8
5.60
0.05
0.6