624
A. Jariwala et al.
4.5 Microscopic SPS Measurements
The semiconductor wafers or thin films, particularly with large surface area, may
so lateral inhomogeneity in their chemical composition or structural characteristics.
These may translate to spatially non-uniform opto-electrical properties through the
surface of the wafers or films. Such variations of properties are important to know to
be able to use them reliably in devices. Surface photovoltage spectroscopy may come
handy in such cases. The scanning measurements are possible with both, Kelvin
probes and MIS structures. These measurements may facilitate the recording of
SPV signal by laterally scanning the surface with a small probe [84] or a wellfocused light beam [85], respectively. However, the lateral resolution in both these
technique is of the order of a micrometer. The applications that require even finer
lateral resolution of SPV rely on [86]: scanning tunnelling microscopy (STM) [87],
and atomic force microscopy (AFM) [88]. Saraf et al. have demonstrated microscopic
surface photovoltage spectroscopy method based on a tunable illumination system
combined with a kelvin probe force microscope, and reported spatial resolution of as
high as 100 nm in regions where the minority carrier transport is driven by drift [89].
Sadewasser et al. [90] have also employed similar Kelvin probe force microscopy to
obtain the localized SPV signals with very high lateral resolution and investigated
the optoelectronic effects of Zn doping.
4.6 Other Variants
In addition to the parameters describe above, there are quite a few other conditions
that can be controlled and combined with the SPS measurements to make it more
productive. These include combining external electric field along with the SPS, using
a specific wavelength DC light to pump the excess carriers while doing the SPS,
transient SPV measurements with short laser pulses under different DC illumination,
etc. or changing surface ambience under controlled manner, etc.
4.6.1 Electric-Field-Induced Surface Photovoltage Spectroscopy
(EFISPS)
EFISPS combines application of external electric field with the surface photovoltage
spectra (SPS). Liqiang et al. [78] have shown that the EFISPS facilitates a detailed
examination of the transfer processes of photoinduced charge carriers [91]. In principle, the external electric field on a semiconductor influence separation of photoinduced charge carriers and also affect the emission of trapped charge carriers by
altering the trap states barriers. Thus, the density of charge carriers in the presence of an external electric field deviates significantly from its equilibrium value
and results in an SCR in the vicinity of a semiconductor surface. This can allow a
A. Jariwala et al.
4.5 Microscopic SPS Measurements
The semiconductor wafers or thin films, particularly with large surface area, may
so lateral inhomogeneity in their chemical composition or structural characteristics.
These may translate to spatially non-uniform opto-electrical properties through the
surface of the wafers or films. Such variations of properties are important to know to
be able to use them reliably in devices. Surface photovoltage spectroscopy may come
handy in such cases. The scanning measurements are possible with both, Kelvin
probes and MIS structures. These measurements may facilitate the recording of
SPV signal by laterally scanning the surface with a small probe [84] or a wellfocused light beam [85], respectively. However, the lateral resolution in both these
technique is of the order of a micrometer. The applications that require even finer
lateral resolution of SPV rely on [86]: scanning tunnelling microscopy (STM) [87],
and atomic force microscopy (AFM) [88]. Saraf et al. have demonstrated microscopic
surface photovoltage spectroscopy method based on a tunable illumination system
combined with a kelvin probe force microscope, and reported spatial resolution of as
high as 100 nm in regions where the minority carrier transport is driven by drift [89].
Sadewasser et al. [90] have also employed similar Kelvin probe force microscopy to
obtain the localized SPV signals with very high lateral resolution and investigated
the optoelectronic effects of Zn doping.
4.6 Other Variants
In addition to the parameters describe above, there are quite a few other conditions
that can be controlled and combined with the SPS measurements to make it more
productive. These include combining external electric field along with the SPS, using
a specific wavelength DC light to pump the excess carriers while doing the SPS,
transient SPV measurements with short laser pulses under different DC illumination,
etc. or changing surface ambience under controlled manner, etc.
4.6.1 Electric-Field-Induced Surface Photovoltage Spectroscopy
(EFISPS)
EFISPS combines application of external electric field with the surface photovoltage
spectra (SPS). Liqiang et al. [78] have shown that the EFISPS facilitates a detailed
examination of the transfer processes of photoinduced charge carriers [91]. In principle, the external electric field on a semiconductor influence separation of photoinduced charge carriers and also affect the emission of trapped charge carriers by
altering the trap states barriers. Thus, the density of charge carriers in the presence of an external electric field deviates significantly from its equilibrium value
and results in an SCR in the vicinity of a semiconductor surface. This can allow a