Intensive studies have been made on thin film electroluminescent (EL) devices because of their considerably higher potential in the commercial demands for a flat-type display unit. A doubly insulated ZnS:Mn a-c operated device, showing a good display performance in brightness, efficiency, and life, has approached the practical stage (1-3). The tremendous strides have been followed by the film preparation methods of molecular beam epitaxy (4), atomic layer epitaxy (5), and metal organic chemical vapor deposition (6). In contrast to a yellowish-orange emitter, more informative multicoloring devices have been fabricated by employing the rare earth fluorides as luminescent centers (7, 8). The doubly insulated ZnS:TbFa device, prepared usually by an electron beam evaporation, exhibits 0.1-0.2 lm/W of highest efficiency among rare earths (8, 9). Attention has been paid to the rf sputtering method because of high productivity, impurity controllability, etc. The authors have conducted a series of studies on the electroluminescence from ZnS

Photovoltaic polarity is studied on obliquely deposited CdTe films. The sign of the photopotential that appears on the electrode on the far side of an evaporator is always negative in the case of front illumination. The polarity reverses from positive to negative with an increase of the wavelength of light in the case of illumination through a glass substrate. The critical wavelength of inversion shifts towards longer wavelengths with a decrease of the substrate temperature and an increase of the film thickness.

A dc-operated thin-film electroluminescent cell with the threshold voltage of ∼53 V has been developed in the system of ITO-(ZnSe→ZnS:Mn)-Al. The emissive layer of the cell is made of compound which varies from ZnSe to ZnS:Mn in composition. The brightnesses of up to 241 and 48.3 fL have been measured in the injection level of 50 mA/cm2 and 4.45 mA/cm2, respectively, at power efficiencies in the range 1.12×10−4–2.58×10−4 W/W.

The conductance of the reactance circuit used in the tuning circuit of the CR tuned amplifier is a function of frequency with negative minimum value. If the external parallel resistance to the tuning circuit is reduced so that a high selectivity is obtained, the conductance becomes negative at a frequency other than the resonance frequency and the circuit will oscillate. We have obtained a stable high‐gain tuned amplifier with high selectivity by selecting the values of resistor and capacitor in the voltage phase‐shift circuit so that the conductance of the tuning circuit is minimum at the resonance frequency. The amplifier with the resonance frequency of 10 kHz fabricated according to this design method exhibits the maximum selectivity of about 700 and the voltage gain of about 100 dB. These values agree well with the computed values. The rate of change of the resonance frequency for the temperature has been made rather small with the use of circuit components with small temperature coefficients. However, the rate of change of the gain (and hence selectivity) is extremely large. With the use of an ac resistive circuit with a positive temperature coefficient consisting of PTC thermistors and transistors, the rate has been reduced to the extent tolerable in the practical temperature range.