JPS593870B2 - light detection element - Google Patents

Description

[Detailed description of the invention] The present invention relates to a semiconductor photodetector.

Pn junction diodes and Schottky barrier diodes are generally used as high-speed semiconductor photodetectors.
These diodes are used in a reverse bias state to detect the current generated when carriers excited by light travel in a space charge region. Carriers excited in the space charge region are immediately accelerated by the electric field and reach a saturation velocity of approximately 10<7>. Therefore,
For example, when the space charge region is 10 microns, the travel time is 10-10 seconds, which enables sufficiently high-speed detection.
Photoexcited carriers outside the space charge region diffuse and
Those that reach the edge of the space charge region similarly travel in the electric field and contribute to the signal. This diffusion current is a cause of slowing down the response speed of the photodiode because the lifetime of carriers is much longer than the transit time. In fact, when a Si diode receives long-wavelength light such as GaAs laser light or Nd-doped solid-state laser, the distance at which the light is absorbed and attenuated to l/8.5 is 40 to 400 microns, and the distance is within the space charge region. much larger compared to

For this reason, the contribution of the diffusion current increases, making it difficult to faithfully demodulate ultrafast pulsed light6.In contrast, by lowering the impurity concentration and expanding the space charge region, the diffusion current component is reduced. Although it is possible to consider the method of
The voltage used becomes high, making it impractical. 15 An object of the present invention is to eliminate such drawbacks of conventional photodiodes and provide a photodetecting element that responds at high speed.

The photodetecting element according to the present invention is a pn junction or Schottky barrier type photodiode in which an impurity layer having at least a conductivity type opposite to that of the space charge region is provided behind the light absorption region and beyond the space charge region. The response speed is increased by preventing the diffusion of photoexcited carriers that occur in the process.

25 Next, one embodiment of the present invention will be explained using the drawings.
A p-type impurity layer 2 is formed on a type silicon substrate 1 by an epitaxial growth method, a p-type impurity layer 3 is formed in an annular shape on the surface of the layer 2, and an n''-type impurity layer 4 is formed inside the p-type impurity layer 2. A photodetecting element having the pn junction 5 of Q2 and the pn junction 6 of the third Q2 is obtained.

The layer 2 is a space charge region in the operating state, the width of which is determined depending on the impurity concentration of the layer 2 so that the space charge region does not reach the boundary 5 of the layer 2 under reverse bias. For example, when the impurity concentration of layer 2 is 3x35lo15cm-3, the width is about 10 microns. An n-type impurity was diffused to a depth of about 1 micron at a surface concentration of 1013 cm-3 or higher to form an n1 layer 4, thereby obtaining a photodiode capable of applying a reverse bias of up to 100V. A reverse bias is applied only to the second Pn junction 6 by connecting a load resistor 7 and a power supply 8 between a layer 3 in which a 1P type impurity is diffused at a high concentration in a part of the layer 2 and an n+ layer 4. By applying approximately 100V, layer 2 becomes almost a space charge region, and carriers excited by light incident from the surface of layer 4 travel through layer 2 at a saturation speed, and the pulsed light of the semiconductor laser for less than 0.2 nanoseconds is generated. was able to be faithfully reconstructed. 9 is a bypass capacitor for passing high frequency signals.

Layer 2 and layer 1 are electrically short-circuited by external electrode 10. For this reason, carriers excited in layer 1 drift in the opposite direction to layer 2 due to the diffusion potential generated in Pn junction 5, and are recombined with holes by external electrode 10 to be quenched. The inflowing diffusion current disappears. Therefore, a photodiode with a fast fall rate without generating a slow diffusion current signal as in the conventional case was obtained. Diffusion current from the remaining portion of the p-layer 2 that does not enter the space charge region poses a problem. However, by controlling the applied voltage and making this portion sufficiently thin, it was possible to easily reduce the total photocurrent to less than l (I) and avoid affecting the response speed.

As described above, the photodetecting element according to the present invention is effective in demodulating ultrahigh-speed pulsed light by blocking slow diffusion current by using a reverse conductivity type impurity layer as the substrate of the photodiode.

It goes without saying that the present invention is the same even if the conductivity type of each part is reversed in addition to the embodiments, and can also be applied to other semiconductor materials.

[Brief explanation of drawings]

The drawings are for explaining one embodiment of the present invention together with its operational circuit. In the figure, 1 to 4 are semiconductors, and 1 and 4 and 2 and 3 are of opposite conductivity type. Therefore, 5 and 6 form a Pn48 bond. 7 is a load resistor, 8 is a power supply, 9 is a bypass capacitor, and 10 is a short-circuit electrode.

Claims (1)

[Claims] 1 In a PN junction or Schottky barrier type photodiode, a space charge region is created by applying a reverse bias, and a semiconductor layer used for light absorption and a semiconductor layer in contact with the semiconductor layer exhibit a conductivity type opposite to that of the semiconductor layer. 1. A photodetecting element characterized in that a substrate layer containing impurities is present, and the semiconductor layer and the substrate layer are operated by electrically shorting the semiconductor layer and the substrate layer.