JPH01140679A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To make it possible to photoelectrically convert selectively only a wavelength concerned in 4f orbital level of erbium, by specifying forbidden band widths of semiconductors constituting various regions and doping a low- concentration region with erbium (Er). CONSTITUTION:Semiconductor layers 2-4 are formed to have a band gap larger than 0.8eV so that, at least in these semiconductor layers 2-4, there is no inter-band absorption with respect to light of wavelength of 1.55mum. Further, position of a p-n junction 9 and dopant concentration and thickness of the semiconductor layer 3 doped with erbium (Er) at low concentration are designed such that a depletion layer formed in the P-N junction 9 reaches the semiconductor layer 2 at least when reverse bias is applied between electrodes 7 and 8. In this manner, it is possible to photoelectrically convert only light of the wavelength concerned in 4f orbital level of erbium, namely of 1.55mum selectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor light-receiving device, and particularly to a semiconductor light-receiving device that selectively absorbs light with a wavelength of 1.55 μm.

[Conventional technology]

As shown in FIG. 3, the operating principle of a conventional semiconductor light receiving element utilizes interband light absorption in a depletion layer formed at a pn junction, which is a contact point between a p region and an n region. That is, light is absorbed in the depletion layer to generate carriers. The generated carriers reach the edge of the depletion layer, become a photocurrent, and undergo photoelectric conversion.

[Problem that the invention seeks to solve]

As mentioned above, the operating principle of the conventional semiconductor photodetector is p
It utilizes interband optical absorption in the depletion layer formed at the n-junction. Therefore, all light with energy above the forbidden band width is absorbed, resulting in poor wavelength selectivity, and even though it is possible to photoelectrically convert a complete substance in a certain wavelength range, only a specific wavelength can be converted. cannot be selectively photoelectrically converted. For this reason, for example, in FIG. 4, when a semiconductor light-receiving element having a light-receiving sensitivity region 24 receives light having the optical spectrum distribution shown in FIG. It will be photoelectrically converted. In particular, when it is desired to separate spectrum 21 and spectrum 22 and receive only spectrum 22, a semiconductor light receiving element having a light receiving sensitivity region 25 including the wavelength number of spectrum 22 is configured in combination with a demultiplexer. There is. Even in this case, there is a drawback that in addition to the spectrum 22 of the signal component, a stray light component 23 included in the light-receiving sensitivity region 22 is received. Such a drawback may become a particularly important problem if, for example, wavelength division multiplexing communication systems become increasingly used in the field of optical communications.

[Means for solving problems]

The semiconductor photodetector of the present invention has a pin structure made of a semiconductor with a forbidden band width larger than 0.8 eV, and has a low carrier concentration region, i.e., an erbium (E)
r) is doped.

In other words, while the conventional semiconductor photodetector operates on the principle of operation using the valence band and the interband light absorption of a conductor, the semiconductor photodetector of the present invention uses atoms related to the 4f orbital value of erbium (Er). It is distinctive in that it uses internal levels.

[Example-1] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a longitudinal sectional view of a first embodiment of the invention. In the figure, 1 is a semiconductor substrate made of an n''-InP layer, and 2 is an InP layer.
3 is an n''--InP layer doped with low carrier concentration and 4 is an n-InP semiconductor layer with selective Zn diffusion. A semiconductor region 5 made of p-I n P is formed by forming a semiconductor region 5 made of p-I n P.A surface protective film 6 is formed on top of the semiconductor layers 4 and 5, and a surface electrode is formed so as to be in contact with the n-type semiconductor region 5. 7 is formed, and a back electrode 8 is formed on the back surface of the semiconductor substrate 1. What is important here is that first of all, at least the semiconductor layer 2.3.4 for light with a wavelength of 1.55 μm. The band gear peak of the semiconductor layers 2 and 3.4 is larger than 0.8 eV so that there is no interband light absorption.Secondly, a reverse bias is applied at least between the electrodes 7° and 8. (put it in working condition)
Therefore, it is important to design the concentration and thickness of the semiconductor layer 3 and the position of the pn junction 9 so that the depletion layer formed in the pn junction 9 reaches the semiconductor layer 2c. In this case, the pn junction 9 may be located inside the semiconductor N3.

Here, before explaining the operating principle, the characteristics of erbium (Er) and the lanthanide series to which erbium belongs will be briefly explained. Lanthanide series elements have a 4f orbital, and this 4f orbital is located near the atomic nucleus. For this reason, chemical bonds with other elements involve only the 5d electron orbital, which has an electron orbit that is much more spatially expanded than the 4f orbital, and ν
).

Therefore, the 4f orbital electrons have very little interaction with other orbital electrons due to chemical bonds, etc.). Therefore, 4f
Emission absorption spectrum between orbital electrons (it has a characteristic that the spectrum width is extremely narrow and the spectrum does not change due to changes in the chemical bond state. Among the elements of the lanthanide series, erbium (Er) has a wavelength of 1. 55μm
It has an absorption spectrum of

Next, the operating principle of the semiconductor light receiving element of the present invention will be explained using FIG. 2. FIG. 2 shows the band structure of the semiconductor light-receiving device of the present invention in an operating state when a suitable reverse bias voltage is applied. Here, 11 is an n-type semiconductor region, 12 is erbium (
13 is an n-type semiconductor region doped with low carrier concentration; 14 is an erbium (E) doped i-type semiconductor region with a low carrier concentration;
r) shows the intraatomic level of erbium due to 4f orbital electrons. Here, light hvl having energy larger than the semiconductor forbidden band width 18 formed from the n-type semiconductor region 11 side in the figure, and light h2 with a wavelength of 1.55 μm. Forbidden band width 18
Assume that light hv3 having an energy smaller than that and having a wavelength other than 1655 μm is incident. The light hv1 is absorbed at the interband transition shown at 15 in the figure. Here, the distance from the semiconductor surface to the depletion layer region, that is, the thickness of the n-type semiconductor region in the example shown in the figure, is set to be sufficiently thicker than the carrier diffusion length and several times or more than the light absorption length of hν1. When set to
Carriers generated by photoexcitation in the n-type semiconductor region 11 are recombined, and no photocurrent is generated, and light with energy hvl cannot reach the i-type semiconductor region 12 where a depletion layer is formed. Furthermore, since the forbidden band width 18 is 0.8 eV or more, light with a wavelength of 1.55 μm reaches the i-type semiconductor region 12 in which the depletion layer is formed. In this i-type semiconductor region 12, light with a wavelength of 1.55 μm is emitted from erbium (
It is absorbed by the transition 16 using the intraatomic level of Er), and electronic excitation to the conduction band occurs using a tunneling process or a thermal excitation process. However, light hv317 having an energy smaller than the forbidden band width 18 and a wavelength other than 1.55 μm is not absorbed (17 in the figure). It can be seen that by doping only the region 12 where the depletion layer is formed with erbium (Er), only a wavelength of 1.55 μm is photoelectrically converted.

Now, in the semiconductor photodetector of the present invention as explained above,
Consider the case where light having the optical spectrum distribution shown in FIG. 4 is received. Here, the light-receiving sensitivity region of the semiconductor light-receiving element of the present invention is limited to light with a wavelength of 1.55 μm, which is determined by the absorption spectrum of 4f orbital electrons of erbium (Er), and this is expressed by 26 in FIG. In particular, if the signal component light that we want to detect is spectrum 22 in the figure, and if this signal component light is also an emission spectrum using the 4 orbital level of erbium (Er), then this 4f orbital orbit value is Since it does not change depending on the temperature or the chemical state of erbium, the wavelength of the spectrum 22 and the light receiving sensitivity region 26 of the present invention completely match, and light of other wavelengths is not received.

Therefore, in this case, a receiving system with extremely high receiving sensitivity is possible.

[Example 2] A second example of the semiconductor light receiving element of the present invention is shown in FIG. This second embodiment is an example in which the present invention is applied to a back-illuminated light receiving element, and in the figure, 31 is a semiconductor substrate made of n+-InP, 32 is an n-type semiconductor layer made of InP, and 33 is n-- A low carrier concentration i-type semiconductor layer made of InP and doped with erbium (E r ,'), 34
is a semiconductor layer made of n-InP, and a semiconductor region 35 made of p-InP is formed by selectively diffusing Zn. A surface protective film 36 is formed on the semiconductor layers 34 and 35, and an electrode 37 is formed in contact with the p-type semiconductor region 35. On the other hand, a back electrode 38 and an optical An anti-reflection coating film 39 is formed at the entrance window.

In this second embodiment, according to the same principle as explained in the first embodiment, only the wavelength of 1.55 μm, which is involved in the orbital level in erbium (Er) 4, is selectively photoelectrically converted. is possible.

〔Effect of the invention〕

As explained above, the semiconductor photodetector of the present invention has p i
In a semiconductor light receiving element having a Ni structure, p, i, n
The forbidden band width of the semiconductor constituting each region is larger than 0.8 eV, and i has a low carrier concentration where a depletion layer is formed.
Doping the region with erbium (Er) has the effect of selectively photoelectrically converting only the wavelength of 1°55 μm involved in the 4f@-level of erbium.

[Brief explanation of the drawing]

1 and 5 are longitudinal sectional views of the first and second embodiments of the semiconductor light receiving device of the present invention, respectively, and FIG. 2 is an energy band structure diagram showing the operating principle of the semiconductor light receiving device of the present invention, and FIG. 3
The figure is an energy band structure diagram showing the operating principle of a conventional semiconductor light-receiving element, and FIG. 4 is a diagram explaining the light-receiving sensitivity regions of the conventional semiconductor light-receiving element and the semiconductor light-receiving element of the present invention. 1.31...Semiconductor substrate, 2.32...N-type semiconductor layer, 3.33...Erbium (Er)-doped semiconductor layer with low carrier concentration, 4,34...N-type semiconductor layer , 5.35...p-type semiconductor region, 6,36...surface protective film, 7,37...electrode, 8,38...back electrode, 9...pn junction surface, three...・・Non-reflective coating film, 1
DESCRIPTION OF SYMBOLS 1...p-type semiconductor region, 12...low carrier concentration semiconductor region doped with erbium, 13...n
type semiconductor region, 14...4f orbital value of erbium,
15...Light absorption between bread 1~, 16...Light absorption between erbium's 4f orbital values, 17...Light not absorbed, 1
8...Forbidden band width, 21.22...Spectrum, 23
... Backlight component, 24... Photosensitivity area of conventional semiconductor photodetector, 25... Photosensitivity area of conventional semiconductor photodetector when combined with a demultiplexer, 26... Semiconductor of the present invention Light-receiving sensitivity area of the light-receiving element.

Claims (1)

[Claims] In a semiconductor light-receiving element having a structure including at least a low concentration semiconductor region between a p-type semiconductor region and an n-type semiconductor region, the forbidden band width of each semiconductor constituting each region is 0.
1. A semiconductor light-receiving element characterized in that the concentration is higher than 8 eV and a low concentration semiconductor region is doped with erbium (Er).