Photosensitive Area Research Articles

Planar InP avalanche photodiode with Zn-diffused guard ring

A guard ring structure with a p+-n−-n junction formed by Zn diffusion at 450°C gave a high gain planar InP avalanche photodiode. A maximum multiplication factor of more than 50 was obtained uniformly within the photosensitive area without edge breakdown.

Photoinduced anomalous oscillations in reach-through avalanche photodiodes

Some reach-through avalanche photodiodes are found to exhibit anomalous oscillations when illuminated by high-level optical power. Experimental study of the phenomena shows that the anomalous oscillation occurs below a voltage at which the depletion layer begins to extend into the layer. Some relations of oscillation frequency with biasing voltage, optical power density incident on the photosensitive area, and diode parameters are also described. These results should prove useful in the design of a reach-through avalanche photodiode free from anomalous oscillations.

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Spectral characteristics of bulk extrinsic photo-conductive detectors have been measured under conditions that only partially illuminated the photo-sensitive areas. The data presented were obtained at background photon flux levels of 10" to 10" photons/sec-cm'. The geometry of the detectors was such that the applied electric field was perpendicular to the incident radiation. Substantial changes in spectral responsivity have have been measured. These changes are dependent upon which portion of the detector's sensitive area is illuminated.

High reliability photodiodes for space applications

This paper presents the techniques used to manufacture a high performance silicon photodetector having several precisely defined photosensitive areas. The principle of the device design is based on a PIN structure. Metallic layers are used to mask parisitic photosensitive areas. The metal layers are used in such a way that they do not degrade the electrical characteristics of the junction. Special care has been taken during manufacturing to assure the reliability of the product, which is to be used in a meteorological satellite. Problems were encountered in defining significant tests characterizing the reliability of the device under various environmental conditions. The reliability characterization is difficult due to the semiconductor and optical aspects of the structure. Tests were therefore imposed to specifically monitor the reliability of either the electrical or optical parameters. The device was then required to withstand both sets of reliability tests.

Self-aligning comparison beam methods for one-, two- and three-dimensional optical velocity measurements

The automatic beam superposition properties of the Wollaston prism are used to develop comparison beam systems for the simultaneous optical measurement of one, two and three components of the velocity vector in fluids. The systems do not require beam alignment for heterodyning, thus removing a traditional disadvantage of comparison beam systems compared with cross-beam systems and permitting full use of the fact that comparison beam systems are inherently better suited for multidimensional velocity measurement than cross-beam systems. The systems discussed use photodiodes (having one or more photosensitive areas) without preamplification. No electronic or optical high, low or narrow pass filters are used.

Coupling a scintillator to a small photosensitive area

A model is developed to describe a scintillation counter coupled to a photosensitive area which is small in comparison with the dimensions of the scintillator. It is shown that the reciprocal of the pulse height is a linear function of the reciprocal of the photosensitive area, and that the constants in this relation are determined by the albedo of the material surrounding the scintillator and by the refractive index of the medium coupling the window to the photosensitive device. This relation has been verified experimentally.

Limiting resolution of low-light-level imaging sensors.

Through the aid of electronic light amplifiers, observers can view terrain on moonless nights with near-daylight acuity. This improvement in vision is obtained by using imaging sensors with larger lenses, greater quantum efficiencies, wider spectral responses, and larger photosensitive areas than those of the unaided eye. The observer’s improved resolving power using these sensors can be calculated in terms of a limiting resolution vs light level and an elemental signal-to-noise ratio at any operating point. The analysis facilitates the comparison of sensors on an equal basis and provides the system designer with more detailed sensor operating data. As examples, the limiting performance is calculated for the image orthicon and the secondary-electron conduction camera tube with and without cascaded image intensifiers. The calculated results are compared to those measured and are found to be in good agreement.

The podial pit--a new structure in the echinoid Diadema antillarum Philippi.

A glandular pit with an orally directed opening has been revealed at the base of the aboral podia, in the precise region known to be the most photosensitive area of the skin. The pit is associated with a thickening of the superficial nerve felt to form the podial organ. The fine structure is unremarkable aside from the large number of fine nerves housed in spaces between the cells of the lining epithelium. The underlying nerve felt is composed of densely packed varicose axons with little evidence of synapses and no indication of sub-cellular photosensory specialization. It is tentatively suggested that the remarkably superficial location of the fine nerve fibres may be correlated with the relatively high photosensitivity of this region.

A Simple Optically Recording Flowmeter for Drop or Integrated Flow Measurements

Page 137 : The CdS-3 photocell specified has been discontinued. The following may be substituted without circuit modification: Clairex CL-3, available from radio supply dealers, or Hupp CdS-10, available from Hupp Electronics, Forrest Park, Ill. The photosensitive area should be masked to a circle of 1–2 mm diameter for best results.

THE PHOTIC SENSITIVITY OF CIONA INTESTINALIS

1. Ciona possesses two means of responding to an increase in the intensity of illumination. One is by means of a local reaction; the other is by a retraction reflex of the body as a whole. 2. The "ocelli" are not photoreceptors. The photosensitive area is in the intersiphonal region containing the neural mass. This area contains no pigment. 3. The reaction time to light is composed of a sensitization period during which Ciona must be exposed to the light, and of a latent period during which it need not be illuminated in order to react to the stimulus received during the sensitization period. 4. The duration of the reaction time varies inversely as the intensity. Analysis shows the latent period to be constant. The relation between the sensitization period and the intensity follows the Bunsen-Roscoe rule. 5. During dark adaptation the reaction time is at first large, then it decreases until a constant minimum is reached. 6. A photochemical system consisting of a reversible reaction is suggested in order to account for the phenomena observed. This system includes a photosensitive substance and its precursor, the dynamics of the reaction following closely the peculiarities of the photosensitivity of Ciona. 7. It is shown that in order to produce a reaction, a constant ratio must be reached between the amount of sensitive substance broken down by the stimulus and the amount previously broken down. 8. From the chemical system suggested certain experimental predictions were made. The actual experiments verified these predictions exactly. 9. The results obtained with regularly repeated stimulation not only fail to show any basis for a learning process or for the presence of a "higher behavior," but follow the requirements of the photochemical system suggested before.

A Device for Projecting a Small Spot of Light Suitable for Exploring Photosensitive Areas

A Device for Projecting a Small Spot of Light Suitable for Exploring Photosensitive Areas