@misc{oai:ir.soken.ac.jp:00000224,
 author = {田中, 仙君 and タナカ, センク and TANAKA, Senku},
 month = {2016-02-17},
 note = {In this thesis, he describe the newly developed core-level photoelectron spectroscopy, which is based on the combination of synchrotron radiation (SR) and Baser light, and the advanced investigation of the surface photovoltage (SPV) effect and its dynamics in a GaAs (TOO) and two kinds of GaAs-GaAsP superlaltices (SLs), which are designed as a spin-polarized electron source.  The thesis is composed of five chapters and an appendix.
  Chapter 1 includes the introduction of the present work.  He has been developing the combinational experiment with SR and laser light.  This new and unique method has advantages in studying the transient non-equilibrium conditions.  He applied this method to study of SPV effects in a GaAs (100) and two kinds of GaAs-GaAsP SLs, which are designed as a spin-polarized electron source.  The SPV effect and its dynamics have particularly been interested in the saturation problem of the spin polarized electron sources.  The purpose of present study is therefore to investigate the SPV and its dynamics using the combination of SR and laser, and to make it clear the relation of the SPV with the saturation problem in the spin-polarized electron sources.
  In Chapter 2, the newly developed experimental systems of the core-level photoelectron spectroscopy with the combination of SR and Baser lighbre explained in details.  The advantages of this method are excellent surface sensitivity due to few tenth of kinetic energy of the core-level photoelectron, which has only few monolayers of the mean free path in solid, and a capability of temporal profile measurements of the photoelectron spectrum using the pulse character of two light sources.  The synchronous of Baser and SR pulses was achieved by the Synchro-lock system.  The pump-probe experiment has been conducted to observe the time-resolved photoelectron spectra in 11 ns, which is repetition time of SR pulses.  To measure the Temporal profile of SPV in microsecond range, the system of time-to-amplitude converter (TAC), multi channel analyzer (MCA), and a Baser with the frequency of 10 kHz has also been developed.
  In Chapter 3, the studies of the SPV effects ink>-type GaAs (100) are presented.  The photoelectron spectrum with laser illumination shifted to higher kinetic-energies about 0.39 eV compared to that without laser illumination at 90 K.  It indicates that the shift of the photoelectron spectrum is due to the flattening of the surface band-bending because of the generation of the SPV.  The photon-flux and temperature dependences of the SPV are well explained in terms of a thermionic emission model.  The temporal change of the SPV has a fast lifetime component of less than 1 ns and a slow lifetime component of more than 11 ns at 125 KJt was found that the temporal profile of the SPV in microsecond range is strongly affected by the sample temperature.  On the base of these results, the SPV process consisting of three steps is discussed.  The first step is a generation of carriers by photo-excitation.  The second step is a transportation of photo-excited carriers.  The third step is a recombinalion of photo excited carriers.  The effects of the first and the second steps are too fast to be observed with the present experimental system.  The third step affects the temporal profiles of the SPV in microsecond range.  As the recombination process, two ways to pass through the potential barrier are considered.  One is the thermionic way and the other is the tunneling one.  The observed temporal profiles of the SPV are interpreted using Schottky's barrier model for the thermionic way and a WKB approximation for the tunneling way.  The present result is therefore the first evidence to indicate that the annihilation of the SPV at 95 K is dominantly due to the thermionic process and that at 90 K icontrolled by the tunneling way.
  Chapter 4 gives the SPV effects in GaAs-GaAsP SL samples, which are designed as a spin-polarized electron source.  Two kinds of the SLs (SL #1 and SL #16 have surface layers with the doping concentration of 5x 10 18 cm-3 and 6 x 10 19 cm-3, respectively) were measured by same experimental procedure as described in Chapter 3, and the results are compared with those in the bulk sample.  At 295 K, there is no obvious difference between the photoelectron spectra with and without laser illumination While, at 110 K, the core-level spectra of the SL #1 and the SL #16 shifted to higher kinetic-energies about 0.12 and 0.03 eV under the laser illumination, respectively.  In the SLs, no appreciable change of the SPV values was observed in the time range of 1.5 - 11 ns.  In the SL #1, the temporal profiles in the microsecond range showed the similar structure as that in the bulk GaAs.  These experimental results are also discussed by using the three-step model of the SPV generation mnnihilation process.  In the SL #1, the transportation of photo-generated carriers would be disturbed in the SL layers and the initial value of SPV was suppressed.  In the SL #16, it is supposed that both the initial value and the lifetime of the SPV are suppressed due to the high doping layer in the SL surface, since it makes the surface space-charge region narrower than that in the bulk GaAs.  The same measurements described above were performed in a negative electron-affinity (NEA) surface on the GaAs and the SLs.  Under the illumination of the laser with the repetition frequency of 10 kHz, the SPV in NEA surfaces was remarkably suppressed in comparison with that in clean surfaces.  The escaping of photo-excited electrons from the NEA surfaces decreases the lifetime of the SPV All experimental results support that the SPV is well suppressed in the SL #16.  It is stressed that the suppression of the SPV is important to develop the useful spin-polarized electron photocathode.         
  In Chapter 5, the concluding remarks are described.  It is stressed that the present newly developed core-level photoelectron spectroscopy based on the combination of SR and laser is one of the most powerful methods to measure the SPV effect and its dynamics insemiconductor surfaces.  The observed temporal change of the SPV in GaAs (100) with nano to microsecond range is interpreted with the recombination process of photo-generated carriers between the surface and bulk regions.  The present results give the clear evidence to indicate that the thermionic process and the tunneling recombination process play important roles in the annihilation dynamics of the SPV.  The relation of the SPV with the suppression of the photocurrent from the spin-polarized electron photocathode has been directly confirmed for the first time., 総研大甲第662号},
 title = {Surface Photovoltage in Semiconductors Studied with Photoelectron Spectroscopy Using Synchrotron Radiation and Laser},
 year = {}
}