Yoshio Sakai

The GaAs inversion-type MIS transistors

Abstract The alloying technique for source and drain n + regions and the chemical-vapor-deposited double layer films of Al 2 O 3 and SiO 2 were found to be useful for the realization of the inversion channel GaAs MIS transistors. This is because the alloying was carried out at much lower temperature than donor diffusion and the stability was remarkably improved by using the double layer above mentioned. The transistor had an effective mobility of 2240 cm 2 /V.sec, and the threshold voltage was controlled by changing the thickness ratio of the two films. The characteristics of the transistor were compared with the theoretical curves which were calculated by considering several limiting factors; bulk charges, a saturation velocity of carriers and series resistances. The fairly good agreement between the two was found. Some discrepancies, recognized in some cases, seemed to be attributable to some unknown parameters in the theory and to influences of interface states.

High efficiency n-CdS/p-InP solar cells prepared by the close-spaced technique

Abstract Heterojunction solar cells have been made by epitaxial growth of CdS on p-type InP using the close-spaced technique. Good rectification and photovoltaic properties have been observed in the cells grown on the (110) face of InP. The characteristics of the most efficient cell are Voc = 807 mV, the fill factor = 0.74 and the power conversion efficiency = 14.4% under the solar input of 77 mW/cm2. The photovoltaic properties of the cells obtained in this experiment are better than those reported elsewhere, and this is attributed to the superiority of the growth system to those of others in points that the junction is formed at relatively high temperature in a short time.

Electrical and Optical Properties of Sputtered CdO Films

CdO films were prepared by a D–C reactive sputtering method with various sputtering voltages. The characters of the prepared films are compared with the reflection electron diffraction and X-ray diffraction patterns. Especially, the effects of the sputtering voltage and partial pressure of oxygen were investigated concerning the electron densities and the Hall mobilities. The observations on lattice parameters lead to the conclusion that CdO films with high carrier concentrations contain some amount of interstitial excess Cd atoms. The absorption edge variation of annealed films prepared by high voltage sputtering agrees with the theoretical curve which is accounted from the Fermi level shift caused by the change in carrier concentrations.

Growth and properties of CdS epitaxial layers by the close‐spaced technique

CdS layers were epitaxially grown on GaAs in an atmosphere of hydrogen gas by the close‐spaced technique. Then the thermodynamics of the reaction, the morphology, and electrical properties of the CdS epitaxial films were studied. Examinations of the temperature dependence of the evaporation rate of source CdS powder, of film growth rates, and of surface morphology demonstrated that the growth kinetics are between the mass‐transfer control case and the surface‐reaction control case, but closer to the former. The electrical properties of the films were greatly influenced by growth conditions, especially by substrate temperature. Film resistivity increased from 10−3 to 1 Ω cm as a function of substrate temperature, and the carrier concentration in the film increased exponentially as the temperature of the substrate was raised: Carrier concentration = 1.31×1029 exp (−1.98/kTsub) cm−3. The dominant donor species in CdS films was shown to originate from the autodoping of Ga by the GaAs substrate. Electron mobil...

Optical and electrical properties of selenium-cadmium sulfide photovoltaic cells

Abstract Se-CdS photovoltaic cells prepared by vacuum evaporation of CdS on Se layer are studied. In particular, measurements are carried out on the transmission of evaporated CdS films, on the photo-current and potential as functions of illumination, external resistance, and temperature; and the spectral sensitivity is compared with the human eye sensitivity. It was shown that the photovoltaic effect under low illumination is superior to that of ordinary Se-CdO cells, that the spectral sensitivity is very close to the visual sensitivity, and that the temperature coefficient has positive values so far as the load resistance is high. Possible causes for these behaviours are discussed. The method of fabrication and experimental results are compared with those of ordinary Se-CdO cells.

Electrical properties of InSb‐based mixed crystal films

High‐carrier‐mobility InSb‐based mixed crystal films, InAsxSb1−x (0<x <0.37) and In1−xGaxSb (0<x <1), were prepared by a vacuum evaporation technique for application to galvanomagnetic devices. Temperature dependence of the Hall coefficients and Hall mobilities were measured at temperatures between 90 and 570 °K. The absolute‐zero energy gap estimated from the Hall measurement of the InAsxSb1−x films exhibits a minimum of 0.16 eV at about 35 ∼ 37 mole% InAs. The transport properties of the mixed crystal films are both dominated by an unknown scattering process which decrases the electron mobility of InSb films at low temperatures.

Optical properties of SiAs single crystals

Single crystals of silicon arsenide have been grown by the Bridgman technique. SiAs was found to have an optical energy gap of 2.18±0.05 eV at room temperature and seemed to exhibit a direct optical transition. The temperature coefficient of the energy gap was about −(2.8±0.5)×10−4 eV/K. From the multiple interference fringes of some SiAs samples, the refractive index was calculated. Over a wavelength equal to infinity, it had a value of 3.1±0.1, thus leading to a value of 9.6±0.6 for the high‐frequency dielectric constant. The extinction coefficient near the absorption edge has also been deduced.

Preparation of replicated germanium films and their applications to sensors

Germanium thin films were formed on flexible organic substrates by using a replica method, in order to obtain a sensitive transducer for stress and thermal energy. The average values of measured gauge factor were in the range from 45 to 65. The Seebeck coefficient was up to 560 μV/deg for p‐type films. With regard to flexibility of the films, stiffness is more than three orders of magnitude smaller than that of a glass substrate. According to dynamic tests, the element attached to a beam could respond to mechanical vibrations up to a frequency of 20 kHz. From the study of the thermal properties using infrared and laser beams, a response time of about 100 msec or less and a responsiveness of about 40μV/μW were obtained.