Slow and fast states of clean and oxidized germanium surfaces are studied. Density of fast state increases and that of slow state decreases remarkably, if the surface was treated to become clean. A proposition for surface bond is made basing upon the s-p hybridization.
The surface electronic properties of n-type molybdenite are investigated by the measurements of surface potential, surface conduction, surface photovoltaic effect and field effect, in a gas ambient which is cycled between NH3 and HNO3. The surface potential which is measured by Kelvin method is rather complicated showing an unusual behavior. The surface photovoltage and surface conduction give a regular result similar to the case of n-type germanium. The surface barrier rises in the ambient of HNO3 and the reverse is the case with NH3. The field induced conduction increases in the ambient of NH3 and decreases in HNO3 but the reversal of the sign is not observed. All the above effects except surface potential can be explained by a model of surface potential barrier qualitatively, but the quantitative discussion of the surface state is not given in this paper.
The variations of the surface conductance, surface recombination velocity and field effect in terms of surface potential are measured on thin single crystal silicon wafers. Surface potential is varied in several gaseous ambients by so-called Brattain-Bardeen ambient cycle. From surface conductance measurement, values of surface potential are deduced and from the photoconductance measurement, surface recombination velocity is obtained. By combining these measurements, the surface recombination velocity is plotted as a function of the surface potential. It is found that the surface recombination velocity for p-type silicon sample of 112 ohm cm varies over about a factor of ten in a 0.6 V range of the surface potential. As the sample was exposed repeatedly to the ambient cycle, the surface potential shifted gradually to positive direction and the variation of surface conductance with ambient was smaller than that on the freshly etched sample. The fast decay time of the field effect was several milliseconds and sensitive to illumination.
The effects of various surface treatments on the annealing process of thermally converted germanium single crystals are studied. Surface treatments are as follows: (a) CP4 etching. (b) roughening the surface by emery paper and dipping in conc. HNO3. (c) depositing So layer by vacuum evaporation. With surface treatment (b) and heat treatment at 600°C, sucking of the thermal acceptors out of thermally converted Ge crystals is most efficiently achieved. By roughening the surface, a large number of lattice deffects can be introduced at the surface of germanium samples where thermal acceptors -or Cu atoms precipitate during cooling. It is believed that this is one of the most efficient methods of sucking the thermal acceptors out of germanium crystals.
An attempt is made to purify InSb by the method' of zone refining. InSb crystal, which was prepared by the reaction of 0.95% In and 99.99% Sb, is charged in a fused silica tube and evacuated. After sealing off, the silica tube is made to pass the zone 1520 times to purify the charged InSb crystal. After such processes, it is found that the major impurities; Pb, So, Bi and Fe etc; are gathered at the tail end, and minor impurities; As and Zn; gathered at the top of the ingot. It is also found that the zone melting method is not effective to segregate the impurities such as Mg, Si and Al from InSb. Finally, analysing the data of the impurity distribution in zone refined InSb, the values of 0.52 and 1.4 are obtained for the tentative values of the distribution constants of Pb and Zn in InSb.
A Simple differentiation method is discussed by which relatively long time constant of monomolecular and bimolecular type photoconductivity, luminescence or allied phenomena can be easily determined with usual amplifier and oscilloscope for audio-frequency, and without any special equipment for extra low frequency or DC. An example of practical design and construction of the experimental set is also described which is applicable to photoconductive cells of CdS single crystals.
Electroluminescent characteristics of ZnS : Cu, Pb, phosphors excited by rectangular pulse fields which have a fast rise time, are investigated. The widths of these electric pulse fields are 200μ sec to 2 m sec with the frequencies of below 100 cps. Especially the experiments in relation with the wave forms, decay times, voltage and temperature-dependencies regarding the light out-puts are performed. Wave forms of the light out-puts with these fields have two peaks at the leading and trailing edges of pulse voltages, and the luminescence decays following these two peaks are simillar in shape, the decay times of which are about 100 μ sec at room temperature and about 300 μ sec at 100°C. Wave forms of green and blue luminescence seem to be of essential difference, and the ratio of secondary to primary peaks of the green luminescence increases with temperature. The experiments on thermoluminescence in this phosphor indicate the existence of two types electron traps, one of which has the depth of about E=0.33 eV and the other about E =0.47 eV. The values of these trap depths seem to correspond to the experimental values of luminescence decay times, namely the traps of E=0.33 eV correspond to the experimental decay time at room temperature and E=0.47 eV to the decay time at 100°C. Some speculations relating to these electroluminescent phenomena are made. It is likely that the primary electrons might be thermally generated from the surface traps and excite the luminescence centers, and the electroluminescent decay times might correspond .to the rate of generation of the primary electrons at the grain surfaces of phosphors. Other detailed characteristics of the electroluminescent wave forms are discussed based on this consideration.
Referring to metal- and SiC-SiC contact characteristics, potential energy of an electron in SiC surface is discussed and volt-ampere characteristics of SiC-SiC contact are derived for which the existence of both space charge and oxide layer is considered. In order to avoid the tunnelling mechanism of the current flow, assumptions are made that the potential of the latter is nearly equal to that of the former, φ0, and the motion of the electron through these barriers is described by diffusion theory. Then, for Va<4φ0μ/μ'δ/L0. i=σ(μ'/μ)e-eφ0/kTVa/δ and for Va>4φ0μ/μ'δ/L0. _??_ are obtained, where L=Q/eN, φ=πeNL2/2κ, Q is the total space charge, μ and μ' the carrier mobility in SiC and oxide respectively, δ the thickness of the oxide film and subscript 0 referred to those values when Va=0. The total space charge should vary with the applied voltage, which is determined experimentally in the case of no existence of oxide film as: Q=Q0/2(l+β√1+Va/φ0) β_??_0.9. V-i characteristic of SiC-SiC contact and its variation with the thickness of the oxide film are satisfactorily explained.
By cascading cooling junctions in thermoelectric refrigeration, the temperature decrease of 30 deg. is obtained by two stage cascade, whereas the maximum cooling attainable with aa single junction is 23 deg.