JPS62123783A - Photodiode - Google Patents

Abstract

PURPOSE:To apply an incident light which is not absorbed in semiconductor layers forming a P-N junction to the P-N junction again and reduce the loss and improve conversion efficiency by providing a reflective layer which reflects the light at the bottom of the semiconductor layers. CONSTITUTION:A reflective layer 20 made of electrical conductor such as metal is formed on a polycrystalline silicon substrate 11 with a silicon oxide film 14 between and a photodiode 17, composed of the 1st conductivity type semiconductor layer 12 and the 2nd conductivity type semiconductor layer 13 is formed. A P-N junction is formed between the 1st semiconductor layer 12 and the 2nd semiconductor layer 13 and a high concentration layer 12a into which donors are introduced with a high concentration is formed at the boundary between the 1st semiconductor layer 12 and the reflective layer 20 and a metal wiring 15 is connected to the surface of the layer 12a through a metal layer 21. In the same way, a metal wiring 16 is connected to the surface of the 2nd semiconductor layer 13.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a photodiode, more specifically, to a photodiode, in which incident light transmitted through a semiconductor layer forming a PN junction is reflected by a reflective layer formed at the bottom of the semiconductor layer to create a PN junction. This invention relates to a photodiode in which the junction is irradiated again to improve its conversion efficiency.

<Prior Art> As a conventional photodiode, for example, one shown in FIG. 2 is known. FIG. 2 is a cross-sectional view of a conventional photodiode. In the figure, αυ is a substrate made of polysilicon, and on the substrate UD, a first semiconductor layer a of two types and a second semiconductor layer OJ forming a photodiode αη are made of a dielectric material such as silicon oxide. They are electrically insulated via an insulating layer α. A large number of photodiodes αη are arranged on the substrate 0υ and connected in series by wiring as described later.

The first conductor layer α2 is formed from a semiconductor of one conductivity type (hereinafter referred to as n-type for convenience of explanation) on the insulating layer (14), and the second semiconductor layer a3 is formed from a semiconductor of one conductivity type (hereinafter referred to as n-type for convenience of explanation), and the second semiconductor layer a3 is formed from a semiconductor of one conductivity type (hereinafter referred to as n-type for convenience of explanation). The first semiconductor O2 is formed on the first semiconductor (12) and is made of a semiconductor of an opposite conductivity type (hereinafter referred to as P type for convenience of explanation).
A PN junction is formed between the two.

The first semiconductor layer Qz includes a high concentration layer (12a) of an n-type semiconductor into which donors are introduced at a high concentration at the boundary with insulation No.
) is formed this high! The metal wiring 05) made of aluminum or the like is established on the surface of the first layer (12a), and similarly, the metal wiring σ is formed on the surface of the second semiconductor layer α2.
6) is connected. The first semiconductor layer (a) and the second semiconductor layer (alpha)3) directly connect the photodiodes (alpha) arranged on the substrate (alpha) 71J.

Although not shown, the surfaces of the first semiconductor layer α and the second semiconductor /m(13) have a light-reflecting layer made of silicon oxide (for example, SiO, 5i(J□, 'I' 102)). A preventive film is formed.

Such a photodiode (1η) is a photodiode in which electrons e and holes e, which are carriers, are generated in the first semiconductor layer (1z) and the second semiconductor layer (13) by the incident light 4, and are polarized by an internal electric field. The hole () diffuses into the second semiconductor layer U of P-type semiconductor, and the electron e diffuses into the first semiconductor layer α4 of N-type semiconductor, causing a diffusion current to flow.Then, the photodiode C17) connected in series As a result, an electromotive force, which is the sum of the diffusion current, is generated.

Problems that this invention attempts to solve〉However,
In such a conventional photodiode, 20% to 30% of the incident light is not absorbed within each semiconductor layer and passes through to the substrate 01). Therefore, there was a problem in that it was difficult to improve the conversion efficiency due to the loss.

<Means to Solve the Problems> The photodiode according to the present invention has been made in view of the above problems, and includes a reflective layer that reflects the source at the bottom of the semiconductor layer forming the PN junction, and the semiconductor layer The incident light that was not absorbed within the f P N junction is irradiated again to reduce loss and improve conversion efficiency.

<Example> Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing an embodiment of a photodiode according to the present invention. Hereinafter, the same parts as in FIG. 2 described above will be denoted by the same reference numerals, and the explanation will be omitted.

As shown in the figure, the high concentration layer (12
A reflective layer (20) made of a good electrical conductor such as metal (M, W, etc.) is provided between the first semiconductor layer O2 and the insulating layer circle.
It is formed to reflect the light (b) that passes through the groove.

The reflective layer (2σ) is ohmically connected to the first semiconductor layer 0z by the high concentration layer (12a), and the exposed end portion is connected to the metal wiring (2σ) via the metal layer (21) formed on the surface.
151. The reflective layer (1) and the metal layer (21) are bonded together by thermal diffusion.

Note that the reflective layer (a) and the metal layer (21) are preferably made of a metal with a high melting point as described above for convenience of the process, but low-temperature processing is required in the subsequent steps such as generation and diffusion of the insulating layer. It can also be constructed from aluminum if it is introduced.

Even in such a photodiode, as in the conventional photodiode described above, each semiconductor layer (1
2) Electrons e and holes ■ are generated in (+3), but the light i that has passed through α3 of the semiconductor layer α without being absorbed by the semiconductor layer α203 is also reflected by the reflective layer 120;
2 generates electrons and holes. Therefore, the loss of light incident on the semiconductor layer a is reduced, and its conversion efficiency is improved.

After that, as mentioned above, holes diffuse into the second semiconductor layer of the n-type semiconductor according to the internal electric field, and electrons diffuse into the first semiconductor layer of the n-type semiconductor, resulting in A diffusion current flows. At this time, the electrons diffused into the first semiconductor layer Oz pass through the high concentration layer (12a), and from the high concentration layer (12a) through the reflective layer (20) to the metal wiring (16).
1, the number of electrons that decrease due to recombination and the like decreases, and furthermore, the diffusion resistance thereof also decreases. As a result, the efficiency of the photodiode as a whole is further improved.

In the above embodiment, the first semi-quadruple layer α is made of an n-type semiconductor, but the first semiconductor dove α2 is made of P.
It goes without saying that the present invention can be similarly achieved even if the device is constructed from a type semiconductor.

<Effects of the Invention> As explained above, according to the photodiode according to the present invention, since a reflective layer that reflects light is formed at the bottom of the semiconductor layer on the substrate side, loss can be reduced and efficiency can be improved. You can get the effect that you can.

Furthermore, in the embodiments described above, the reflective layer is made of a metal that is a good conductor and is connected to the wiring, so that the diffusion resistance is reduced and the efficiency can be further improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of a photodiode according to the present invention, and FIG. 2 is a sectional view of a conventional photodiode. ■...Substrate, housing 2...first semiconductor layer,
(12a)... High concentration layer, 03... Second semiconductor layer, I... Insulating layer, (15) (161
...metal wiring, α-coupling...photodiode, wire...reflection layer, ■)...metal layer. Agent Patent Attorney Uchihara -′′ ゝSheep I V /f - Board/2,73-Semi-Rumors/2shi-Chronology■ /d --? Irobeshi surprise /, 5° noro ≦ S Mimitan 5 times, Useong / 7 - Phytotyauto - 20 - Manpokei layer 21 - Enthusiastic layer R - Human agent's R' - Anti 1〒尤

Claims (2)

[Claims] (1) A photodiode in which two types of semiconductor layers made of semiconductors of opposite conductivity types forming a PN junction are electrically insulated via an insulating layer on a substrate, and power is extracted by connecting wiring to these semiconductor layers. 2. A photodiode according to claim 1, further comprising a light reflecting layer formed on the semiconductor layer side of the insulating layer to reflect light transmitted through the semiconductor layer. (2) The photodiode according to claim 1, wherein the reflective layer is made of a metal good conductor, and is ohmically connected to the anticonductor layer and connected to the wiring.