SEMICONDUCTORS AND SEMIMETALS pot

[...]... wide-band-gap doped layers that are degenerate or highly conductive In such a case, the Fermi levels would lie very close to the band edges, and the built-in polential would approach the band gap There are two mechanismsthat limit the built-In potential in a-Si :H solar cells One is the existence of band-tail states as mentioned earlier, and the other is the low doping efficiency of a-Si :H Spear and. .. electroreflectance and electroabsorption, Raman scattering, luminescence, photoconductivity, photoemission, relaxation processes, and metastable effects Volume 2 1, Part C, is concerned with electronic and transport properties, including investigative techniques employing field effect, capacitance and deep level transient spectroscopy, nuclear and optically detected magnetic resonance, and electron spin... dependent on temperature, and independent of illumination The diode remains indefinitely in the ON or OFF state until the appropriate threshold is exceeded REFERENCES Nakayama, Y., Wakita, K., Nakano, M., and Kawamura, T (1983) J Non-Cryst Solids 59/60, 1231 Nishikawa, S., Hakinuma, H., Watanabe, T., and Kaminishi, K (1983) J Non-Crysf Solids 59/60, 1235 SEMICONDUCTORS AND SEMIMETALS, VOL 21, PART... commercial for some time In Volume 21, Part A, the preparation of a-Si:H by rf and dc glow discharges, sputtering, ion-cluster beam, CVD, and homo-CVD techniques is discussed along with the characteristics of the silane plasma and the resultant atomic and electronic structure and characteristics The optical properties of this new family of semiconductors are the subject of Volume 2 1, Part B Phenomena discussed... conduccally tion band in phosphorus-doped a-Si :H (Spear, 1977) and is 0.5 eV above the valance band in boron-doped a-Si :H (Jan et al., 1980) Since the optical gap of undoped a-Si :H is typically about 1.7 eV, the built-in potential of a-Si: H p- i-n solar cells is about 1.0 eV (Williams et al., 1979) Improving the conductivity of the doped layers should lead to larger built-in potentials and consequently... wider band gap of a-Si :H (- 1.6- 1.8 eV) as compared to crystalline silicon (1.12 eV) Other defect levels may arise from interactions between nearby dangling bonds that may form weak or stretched bonds, from dangling bonds on impurity atoms, and from weak bonds between silicon atoms and impurity atoms The net result is that there is a distribution of defect levels throughout the band gap of a-Si :H, and. .. band, whereas topological disorder affects the edge of the conduction band Variiitions in bond lengths and bond angles contribute also to tail states, but these contributions are relatively small Both the optical gap and the extent #of tail states appear to be the influenced by the hydrogen content Under illumination tail states can become recombination centers as quasi-Fermi levels approach the band... where their characteristics may be adequate In Chapter 6, LeComber and Spear review the design, fabrication, and performance of a-Si : H FETs They point out the need for good ohmic connec- 1 INTRODUCTION 3 tions to source and drain and the problem of achieving a good dielectric under the gate Sheet conductance of several lo-* m h o n and switching times on the order of a microsecond have been obtained... emitting diodes, fast modulators and detectors, hybrid structures, and memory switching R K WILLARDSON ALBERT BEER C Preface Hydrogenated amorphous silicon, a new form of a common element, is a semiconductor that has come of age Its scientific attractions include a continuously adjustable band gap, a usable camer lifetime and diffusion length, efficient optical transitions, and the capability of employing... 1983), and the dc proximity mode (Catalano et al., 1982) Comparable performance has also been reported for devices that were apparently made from glow discharges in silicon tetrafluoride (SiF,) and hydrogen (Hack and Shur, 1982) Glow discharges in disilane 2 9 SOLAR CELLS TABLE I SOLAR-CELL EFFICIENCIES VARIOUS GROWTH FOR TECHNIQUES Deposition technique Glow discharge in SiH, Sputtering in Ar and H2 .