Photoelectron holography studies of Bi on Si(111)
Photoelectron holography is applied to Bi atoms adsorbed on Si(111) for a determination of the three-dimensional atomic structure. Instead of measuring the absolute intensity as a function of photon energy as is traditionally done, a differential measurement is carried out to yield the logarithmic derivative of the intensity. This leads to intensity self-normalization, and significantly improves the accuracy. The resulting images show a well-resolved trimer structure for the adsorption geometry.
Low-energy electron diffraction studies of Si(111)-(√3 × √3)R30°-Bi system: Observation and structural determination of two phases
Abstract The initial epitaxial growth of Bi on a Si(111)-7 × 7 surface has been studied as a function of overlayer coverage and deposition conditions using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Experiments show for the first time that two equilibrium phases are formed in the growth process, each displaying a (√3 × √3)R30° LEED symmetry: an α-phase occurring at 1 3 ML Bi coverage and substrate temperature of 360° C, and a β-phase at 1 ML and 300°C. Quantitative structural information for each phase was determined by multiple scattering analysis of I - V curves. The analysis is facilitated by comparing LEED intensity data measured for each phase with calculated values using appropriate structural models. The T 4 geometry for the α-phase and a trimer geometry for the β-phase are revealed to be the “best” models; detailed atomic coordinates have been determined for each phase.
Real time composition monitoring methods in physical vapor deposition of Cu(In,Ga)Se{sub 2} thin films
Three real-time composition monitoring methods in physical vapor deposition process of CIGS thin films were proposed. One is the detection of near infrared (NIR) transmittance through the CIGS films from the IR source such as a heater back side of the substrate. One is the detection of NIR reflectance of the incident light from the films. The other is the measurement of the substrate temperature during the preparation of the CIGS films. These methods utilize the difference of the carrier density between Cu-rich ({approximately}10{sup 20}/cm{sup 3}) and (In+Ga)-rich (<10{sup 16}/cm{sup 3}) films. The NIR transmittance through and reflectance from the Cu-rich film decrease due to high free carrier absorption. The temperature of the Cu-rich films was lower than that of the (In+Ga)-rich ones under the constant heating power because the Cu-rich films have larger radiation in proportion to absorption. Therefore, the change of Cu/(In+Ga) ratios at stoichiometry an be monitored by the variation of the NIR transmittance, NIR reflectance or the film temperature in real time. These composition monitoring methods are very useful and easily applied to the physical vapor deposition process of the CIGS films for photovoltaic application. The solar cell with active area of about 0.5 cm{sup 2},more » fabricated by obtaining the CIGS film using the latter monitoring method, showed an efficiency of 17.0%.« less