JPH07105522B2 - Semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor photodetection device for detecting light irradiation.

[Conventional technology]

FIG. 4 is a sectional view showing a conventional semiconductor photodetector disclosed in, for example, Japanese Patent Laid-Open No. 61-141175. A P ⁺ region 12 is formed on an N-type silicon substrate (N layer) 11, and a polycrystalline semiconductor isolation region 14 is formed in each region to isolate a PN junction 13 from the N-type silicon substrate 11. , The upper surface is covered with the silicon dioxide film 15. Reference numerals 16 and 17 denote a back surface electrode and a front surface electrode, respectively.

The semiconductor photodetection device in which a plurality of photodiodes are arranged in an array on the same substrate as described above is used for position detection and spectroscopic measurement. In such a photodiode array type semiconductor photodetector, various problems occur when the integration degree of the photodiodes is increased in order to improve the resolution of the incident position of the incident light.

First, the first problem is optical crosstalk in which light incident between adjacent photodiodes causes mutual interference between elements. This optical crosstalk will be described with reference to FIG.

FIG. 5 is a sectional view of an apparatus for explaining optical crosstalk in a photodiode array type semiconductor photodetecting apparatus. In the optical crosstalk, light having a small absorption coefficient reaches a deep portion away from the PN junction 13 of the semiconductor photodetector, internally generates an electron-hole pair, and these carriers are diffused in the same array. It occurs by reaching the adjacent photodiode of the. For example the carrier generated in the deep portion of the N layer 11 under the P ⁺ region 12, next to the P ⁺
That is the case when reaching region 12 '.

Secondly, there is physical crosstalk called blooming. This physical crosstalk will be described with reference to FIG.

The physical crosstalk is caused by saturation of the charge accumulated in the depletion layer indicated by the broken line in the figure due to intense light irradiation, and diffusion within the device to reach the adjacent photodiode. Or when the carrier generated in the N layer depletion layer 11 formed below the P ⁺ region 12 reaches the P ⁺ region 12 'is it. These cross-talks blur the position boundaries to the position sensor and obscure the peaks of two adjacent signals in the analytical sensor.

Conventionally, a structure as shown in FIG. 4 has been taken against such crosstalk. The carriers generated in the photodiode on the left side of the drawing are collected in the PN junction 13 and detected as an optical signal. At this time, since the two photodiodes are completely separated by the isolation region 14, for example, carriers generated in the left photodiode are PN junctions on the right side.
Optical and physical crosstalk can be significantly reduced without mixing with 13.

[Problems to be solved by the invention]

In the conventional semiconductor photodetector, in order to receive light of a wavelength having a small absorption coefficient, the N layer 11 must first be thickened, and therefore the isolation region 14 also becomes deep. Furthermore, when the number of pixels is large and the resistivity of the N layer 11 is large, it is necessary to provide an electrode on the N layer 11 side for each pixel, and it is difficult to form the electrodes except the back surface in the conventional structure. Further, if the N layer 11 is an epitaxial crystal, it becomes very difficult to form an electrode.

The present invention has been made to solve the above problems, eliminates crosstalk, can receive light of a wavelength having a small absorption coefficient, and can easily form electrodes, and causes inconvenience. The purpose is to obtain no semiconductor device.

Another object of the present invention is, in addition to the above objects, an object of the invention is to obtain a semiconductor device capable of reducing a leak current at a surface exposed portion of a PN junction portion.

[Means for solving problems]

In a semiconductor device according to the present invention, a semiconductor layer of a first conductivity type is formed on a semi-insulating semiconductor substrate having a plurality of mesas and recesses, and a semiconductor layer of the first conductivity type in each recess of the semiconductor substrate is formed. A second conductivity type semiconductor layer is formed in the layer, and a high-concentration first conductivity type semiconductor reaching the mesa portion of the semiconductor substrate is formed in the first conductivity type semiconductor layer on each mesa portion of the semiconductor substrate. A layer is formed.

A semiconductor device according to another invention is a semiconductor layer of the first conductivity type in which a forbidden band width of a surface layer portion is larger than a bulk portion on a semi-insulating semiconductor substrate in which a plurality of mesa portions and recesses are formed. To form a second conductivity type semiconductor layer in the first conductivity type semiconductor layer of each recess of the semiconductor substrate, and in the first conductivity type semiconductor layer on each mesa portion of the semiconductor substrate. A high-concentration first conductivity type semiconductor layer reaching the mesa portion is formed.

[Action]

According to the present invention, the PN junction portion serving as the light receiving portion and the first conductive type semiconductor layer thereunder are completely formed by the mesa portion and the high-concentration first conductive type semiconductor layer formed on the mesa portion. Since they are separated, crosstalk does not occur. Further, the electrode on the side of the first conductivity type semiconductor layer can be taken from the high-concentration first conductivity type semiconductor layer on the mesa portion, so that the degree of freedom of the element shape is widened.

Further, according to another invention of the present invention, it is possible to reduce the leak current at the exposed surface portion of the PN junction portion and prevent recombination of carriers on the surface.

Example of Invention

FIG. 1 is a cross-sectional view of a semiconductor device showing an embodiment of the present invention. 5 is a semi-insulating semiconductor substrate having a plurality of mesa portions 6 formed therein, and a plurality of recesses 7 are formed by the mesa portions 6. ing. The first conductivity type semiconductor layer 1 is grown on the semiconductor substrate 5. Since the surface shape acts depending on the growth method, the layer thickness of the top of the mesa 6 is expected to be smaller than the layer thickness of the recess 7. 2 is a semiconductor layer 1 of the first conductivity type in the recess 7 of the semiconductor substrate 5.
The second conductivity type semiconductor layer is formed on the surface of the PN junction, thereby forming the PN junction 3. Further, 4 is a high-concentration first conductivity type semiconductor formed so as to reach the mesa part 6 in the first conductivity type semiconductor layer 1 formed on the top of the mesa part 6 of the semiconductor substrate 5. It is a layer.

Next, a case where the semiconductor device configured as described above is used for an infrared detector will be described.

First, infrared rays incident from the front surface or the back surface are absorbed in the first conductive type semiconductor layer 1 and the second conductive type semiconductor layer 2 to generate carriers. Of those carriers,
Carriers generated in the depletion layer spreading near the PN junction 3 and carriers generated outside the depletion layer and diffused to reach the inside of the depletion layer appear as electromotive force on each side of the PN. This electromotive force is detected to know the infrared light intensity. For example, consider a case where infrared light having a wavelength of about 10 μm is detected using a Hg _1-x Cd _x Te crystal.

The forbidden band width of Hg _1-x Cd _x Te is about 0.1 eV, and the composition at that time x
Is about 0.2. It can be seen that when the crystal thickness is 10 μm, about 63% of infrared optics can be absorbed, and a thicker crystal thickness is better for efficient absorption. When a P-type Hg _1-x Cd _x Te crystal is used for the first conductive type semiconductor layer 1, the minority carriers in the layer are electrons and the diffusion length is about 50 μm.
Considering these points, let us consider the manufacturing process of an infrared detector with a light receiving part of about 25 μm.

The manufacturing process will be described below with reference to FIG. First, as shown in FIG. 2A, a CdTe substrate is used as the semiconductor substrate 5, and the mesa portion 6 and the recess 7 having a step of about 10 μm are formed by wet etching or ion beam milling. Next, as shown in FIG. 2B, P-Hg is formed as a first conductive type semiconductor layer 1 on the semiconductor substrate 5.
Grow a _1-x Cd _x Te (x = 0.2) layer. At this time, the semiconductor substrate 5 is CdTe and the first conductivity type semiconductor layer 1 is
Interdiffusion occurs between Hg _1-x Cd _x Te (x = 0.2) layers,
Since x becomes large from the Hg _1-x Cd _x Te layer to the CdTe substrate, it acts as a barrier against minority carriers in the Hg _1-x Cd _x Te crystal, which is advantageous. Further, if the liquid phase growth method is used, the surface shape acts so as to be flattened. Hg _1-x C in the process of Fig. 2 (c)
Etch d _x Te crystal. Through this step, the surface shape is further flattened. Then, as shown in FIG. 2D, diffusion of impurities from the surface of the Hg _1-x Cd _x Te crystal of the first conductivity type semiconductor layer 1 corresponding to the top of the mesa portion 6 of the semiconductor substrate 5. Then, a P ⁺ —Hg _1-x Cd _x Te crystal layer is formed as the high-concentration first conductivity type semiconductor layer 4. Since the diffusion depth at this time is sufficient to reach the mesa portion 6 of the semiconductor substrate 5, the diffusion depth does not become so deep and the lateral diffusion is also a little. Further, as shown in FIG. 2E, a semiconductor of the second conductivity type is obtained by doping impurities from the surface of the Hg _1-x Cd _x Te crystal corresponding to the recess 7 of the semiconductor substrate 5 by ion implantation or diffusion. An n-Hg _1-x Cd _x Te layer is formed as the layer 2, and a PN junction 3 is formed.

Next, the operation will be described. First, Hg, which is the semiconductor layer 1 of the first conductivity type outside the depletion layer that causes crosstalk,
_For minority carriers generated in _1-x Cd _x Te crystals,
The high-concentration first conductivity type semiconductor layer 4 P ⁺ -formed on the top of the mesa portion 6 and the interdiffusion layer between the Hg _1-x Cd _x Te layer and the CdTe substrate which is the semiconductor substrate 5. Since the Hg _1-x Cd _x Te layer serves as a barrier, crosstalk does not occur, and at the same time, the action of the barrier increases the probability of minority carriers reaching the depletion layer. In addition, even if the CdTe substrate is semi-insulating,
The electrode of the P-Hg _1-x Cd _x Te layer can be taken without problems from the surface of the P ⁺ -Hg _yx Cd _x Te layer. Further, even when a reverse bias is applied between the P and N layers in order to widen the depletion layer, it operates well by the action of the barrier.

Although there is a portion where the P-Hg _1-x Cd _x Te crystal formed as the first conductivity type semiconductor layer 1 is exposed on the surface in the above-mentioned embodiment, as shown in FIG. A barrier can also be formed on the exposed portion.

That is, in FIG. 3, the first conductive type semiconductor layer 1
P-Hg _1-y as the first conductivity type semiconductor layer 8 having a larger forbidden band width than the bulk portion on the surface layer portion of the P-Hg _1-x Cd _x Te layer.
A Cd _y Te (y> x) layer is provided. The other structure is the same as that of the embodiment shown in FIG. This P-Hg _1-y Cd _y Te layer with a large forbidden band can eliminate the carrier surface recombination, and the exposed bandgap of the PN junction has a large forbidden band. There is also an effect of reducing the surface leak current.

The same effect can be obtained by using a high concentration P ⁺ -Hg _1-x Cd _x Te substrate as the semiconductor substrate 5.

Further, in the above embodiment, the case of the infrared detector has been described, but other photodetectors and semiconductor devices may be used,
The same effect as that of the above embodiment is obtained.

〔The invention's effect〕

As described above, according to the present invention, a semiconductor layer of the first conductivity type is formed on a semi-insulating semiconductor substrate having a plurality of mesas and recesses, and the first conductivity type of each recess of the semiconductor substrate is formed. A second conductivity type semiconductor layer is formed in the semiconductor layer, and a high concentration first conductivity type reaching the mesa portion of the semiconductor substrate is formed in the first conductivity type semiconductor layer on each mesa portion of the semiconductor substrate. Since the semiconductor layer of 1 is formed, the pn junction portion that becomes each pixel is separated from the semiconductor substrate in which the mesa portion is formed and the high-concentration semiconductor layer, so that crosstalk can be effectively prevented, and fabrication is also possible. It's easy.

Further, according to another invention of the present invention, since the surface layer portion of the semiconductor layer of the first conductivity type is covered with the semiconductor layer of the first conductivity type having a forbidden band width larger than that of the bulk portion, the leakage current of the PN junction is reduced. There is an effect that it can be reduced and the surface recombination of the carrier can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor device showing an embodiment of the invention, FIGS. 2 (a) to 2 (e) are sectional views showing a manufacturing process of an infrared detector according to the invention, and FIG. 3 is a sectional view of the invention. 4 is a sectional view showing another embodiment, FIG. 4 is a sectional view showing a conventional semiconductor photodetector, FIG. 5 is a sectional view for explaining optical crosstalk, and FIG. 6 is for explaining physical crosstalk. It is sectional drawing for doing. In the figure, 1 is a first conductive type semiconductor layer, 2 is a second conductive type semiconductor layer, 3 is a PN junction, 4 is a high concentration first conductive type semiconductor layer, 5 is a semiconductor substrate, Reference numeral 6 is a mesa portion, 7 is a concave portion, and 8 is a semiconductor layer of the first conductivity type having a large forbidden band width. The same reference numerals in each drawing indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A semiconductor layer of a first conductivity type is formed on a semi-insulating semiconductor substrate in which a plurality of mesas and recesses are formed, and the first conductivity of each recess of the semi-insulating semiconductor substrate is formed. A second conductive type semiconductor layer is formed in the first conductive type semiconductor layer, and the second conductive type semiconductor layer is formed in the first conductive type semiconductor layer on each mesa portion of the semi-insulating semiconductor substrate. A semiconductor device having a high-concentration first-conductivity-type semiconductor layer reaching a mesa portion. 2. A semiconductor layer of a first conductivity type having a forbidden band width of a surface layer portion larger than that of a bulk portion is formed on a semi-insulating semiconductor substrate having a plurality of mesa portions and recesses, and the semi-insulating semiconductor substrate is formed. A second conductivity type semiconductor layer is formed in the first conductivity type semiconductor layer of each recess of the semiconductor substrate, and in the first conductivity type semiconductor layer on each mesa portion of the semi-insulating semiconductor substrate. A semiconductor device having a high-concentration first-conductivity-type semiconductor layer reaching the mesa portion.