Surface Photo-Voltage Spectroscopy: A Versatile Technique …
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Ru−SrTiO 3 :Rh/ BiVO 4 particle tandem, which can be used as water splitting photocatalyst [124]. The SPV spectroscopy has also been employed to understand the role
of the selective contacts and the Tauc gap in organic perovskites for photovoltaic
applications (CH 3 NH 3 PbI 3 and MAPbI 3−x Cl x ) [125, 126]. Such an extensive use
of SPS in characterizations of nano- and low-dimensional structures result from
its ability measure directly effective band gaps, sub-band gap states, and built-in
potentials.
Cavalcoli et al. [4] have reported the doping induced phase changes in Silicon
nano wires by observing electronic transitions in Si nanowires. They have also
discussed in detail the application of SPS to investigate the thermal treatment induced
phase transitions in nanoporous Ge, enhanced light trapping owing to gold nanoparticles embedded in the np-Ge matrix and finally the quantum confinement effects in
nanoporous Ge films.
Cavalcoli et al. [127] also earlier used the SPS in combination with the spectral photocurrent measurements to probe the GaN nanowires. They observed below
bandgap absorption and an exponential tail below the energy gap using the SPS.
Zhao et al. [122] have used the SPS measurements to study the photochemistry of
mercaptoethanol-ligated CdSe quantum dot (2.0 − 4.2 nm diameter) films on indium
doped tin oxide (ITO) in the absence of an external bias or electrolyte. Using the
SPS measurements, they proposed that the photovoltages in CdSe quantum dot (QD)
films on ITO are produced by one of the two distinct mechanisms: [128], photochemical electron injection from the QDs into the ITO substrate, [129] polarization
of QD-based polaron pairs by an electrical field at the CdSe−ITO interface. Both
processes are controlled by the built-in voltage at the CdSe−ITO interface, degree
of quantum confinement in the dots, and thickness of the films.
The SPS can also be employed for rapid evaluation of photo-catalytic activates of
nano-structured semiconductors [78]. The ability of SPS to directly measure builtin voltages, space charge layer thickness, sub-band gap states, and effective band
gaps make it one of the versatile characterization tools to probe nano-structured and
low-dimensional semiconducting materials.
5.7 Wafers and Device Testing
The SPS has also been used in quality testing of semiconductor wafers and devices
at industrial scales in addition to its usual applications in materials characterizations.
Its applications, as far as the device testing is concerned, include the prediction of
ultimate performance of solar cells and identification of defective batches [36], the
determination of lasing wavelength and energy levels in heterostructure lasers [38,
130] and estimation of narrowing of the bandgap as well as gain of heterojunction
bipolar transistors [37, 131].
Votoˇ cek et al. [132] have discussed the applications of SPS for diagnostics
of Si wafers and monocrystalline Si solar PV devices. They have also presented
some deformed experimental photovoltage spectra measured on Si wafers, which
631
Ru−SrTiO 3 :Rh/ BiVO 4 particle tandem, which can be used as water splitting photocatalyst [124]. The SPV spectroscopy has also been employed to understand the role
of the selective contacts and the Tauc gap in organic perovskites for photovoltaic
applications (CH 3 NH 3 PbI 3 and MAPbI 3−x Cl x ) [125, 126]. Such an extensive use
of SPS in characterizations of nano- and low-dimensional structures result from
its ability measure directly effective band gaps, sub-band gap states, and built-in
potentials.
Cavalcoli et al. [4] have reported the doping induced phase changes in Silicon
nano wires by observing electronic transitions in Si nanowires. They have also
discussed in detail the application of SPS to investigate the thermal treatment induced
phase transitions in nanoporous Ge, enhanced light trapping owing to gold nanoparticles embedded in the np-Ge matrix and finally the quantum confinement effects in
nanoporous Ge films.
Cavalcoli et al. [127] also earlier used the SPS in combination with the spectral photocurrent measurements to probe the GaN nanowires. They observed below
bandgap absorption and an exponential tail below the energy gap using the SPS.
Zhao et al. [122] have used the SPS measurements to study the photochemistry of
mercaptoethanol-ligated CdSe quantum dot (2.0 − 4.2 nm diameter) films on indium
doped tin oxide (ITO) in the absence of an external bias or electrolyte. Using the
SPS measurements, they proposed that the photovoltages in CdSe quantum dot (QD)
films on ITO are produced by one of the two distinct mechanisms: [128], photochemical electron injection from the QDs into the ITO substrate, [129] polarization
of QD-based polaron pairs by an electrical field at the CdSe−ITO interface. Both
processes are controlled by the built-in voltage at the CdSe−ITO interface, degree
of quantum confinement in the dots, and thickness of the films.
The SPS can also be employed for rapid evaluation of photo-catalytic activates of
nano-structured semiconductors [78]. The ability of SPS to directly measure builtin voltages, space charge layer thickness, sub-band gap states, and effective band
gaps make it one of the versatile characterization tools to probe nano-structured and
low-dimensional semiconducting materials.
5.7 Wafers and Device Testing
The SPS has also been used in quality testing of semiconductor wafers and devices
at industrial scales in addition to its usual applications in materials characterizations.
Its applications, as far as the device testing is concerned, include the prediction of
ultimate performance of solar cells and identification of defective batches [36], the
determination of lasing wavelength and energy levels in heterostructure lasers [38,
130] and estimation of narrowing of the bandgap as well as gain of heterojunction
bipolar transistors [37, 131].
Votoˇ cek et al. [132] have discussed the applications of SPS for diagnostics
of Si wafers and monocrystalline Si solar PV devices. They have also presented
some deformed experimental photovoltage spectra measured on Si wafers, which