Optical factors in the photoemission of thin films.
Expressions are derived for the dependence of the photoemission from thin films deposited on transparent substrates on the direction of illumination, as determined by optical factors alone. For normal incidence, the photoemission of very thin-film transparent photocathodes may be expected to be about 1.4 times as great for illumination from the glass side as for illumination from the vacuum side. Furthermore, if the index of refraction of the film is large compared with that of the substrate, the ratio, for natural light, is also almost independent of the angle of incidence for a wide angular range. For thicker films, both the optical constants of the film and the mean depth of origin of the photoelectrons play an important role. However, for strongly absorbing as well as nearly transparent photoemissive films, substantially higher photocurrent should be obtainable from a photoemissive film of optimum thickness illuminated through the substrate than for a thick film with similar optical constants illuminated from the vacuum side. An assumed simple proportionality between optical stimulus, here given by the square of the field intensity within the photosensitive film, and photoexcitation implies that the photoeffect studied is a volume effect and not dependent on the direction of the electric vector within the film.
Vectorial selective surface effects in the optical absorption and photoelectric emission of thin metal films
The “surface effect” is expected to become observable in the photoelectric emission, and even more early in the optical absorption of very thin metal films. It corresponds to a modified Drude absorption where the electron mean free path is of the order of magnitude of the film thickness. But there is a strong “vector effect” in films with perfectly plane surfaces. The quantum mechanical calculation yields the same result as the modified classical Drude theory, with the additional prediction of a film-thickness dependent absorption-threshold. Other related surface effects are briefly discussed, and it is suggested that the excitation of surface plasmons may also lead to a “vectorial, selective photoelectric emission”. 
 
 
 
„L'effet de surface” pourrait devenir observable dans l'emission photoelectrique. et surtout dans l'absorption optique des couches metalliques tres minces. Il correspond, en effet, a une absorption de Drude modifiee, ou le libre parcours moyen de l'electron est de l'ordre de grandeur de l'epaisseur de la couche. Mais il y a un „effet vectoriel” important pour des couches a surfaces parfaitement planes. Le calcul quantique fournit lea mȩmes resultats que la theorie classique de Drude modifiee, avec en plus, la prevision d'un seuil d'absorption dependant de l'epaisseur de la couche. D'autres effets de surface apparentes sont brievement discutes, et l'on propose la possibilite d'un „effet photoelectrique vectoriel, selectif” par l'intermediaire de l'excitation d'un plasmon de surface.
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