JPH02220479A - Photoelectric transducer and manufacture thereof - Google Patents

Abstract

PURPOSE:To sufficiently absorb incident light even when the thickness of the title transducer is reduced by a method wherein the transducer is constituted in such a way that the angle of a V-groove in the surface on the light-incident side is different from the angle of a V-groove in the rear. CONSTITUTION:V-grooves are formed in the surface 31 and the rear 41 of a photoelectric transducer 11; angles of the V-grooves formed in the surface 31 and the rear 41 are made different. Accordingly, the surface 31 and the rear 41 are tilted at a certain angle theta to each other; incident light 21 which has passed through the transducer is reflected by the rear 41 and is reflected toward inside by the surface 31 of the transducer. Especially when this angle thetais set to 3 deg. or larger, the light which has reached the rear 41 in the first operation is subjected to total reflection. When an angle theta1 is made different from an angle theta2, the light which has once been incident is confined to the inside of the substrate 11 and is absorbed efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in the light absorption efficiency of a photoelectric conversion element, particularly a thinned photoelectric conversion element.

[Conventional technology]

Conventional photoelectric conversion elements include 5olar Ce1ls,
17 (1986) p., 75-83, it was formed on the front or back surface of a photoelectric conversion element.

The device has a flat plate-like cross-sectional shape, except for surface irregularities such as a V-shaped groove structure whose irregularities are relatively small compared to the thickness of the element, and structures such as electrodes formed on the front or back surface.

[Problem to be solved by the invention]

In the above conventional technology, if the thickness of the substrate that performs photoelectric conversion is not more than several hundred μm, it becomes mechanically fragile, and the device
It is difficult to increase the size to several tens of elf.

Therefore, we considered reducing the substantial thickness of the substrate that performs photoelectric conversion to about several tens of micrometers by processing the substrate into a corrugated plate shape. However, as the thickness of the substrate becomes smaller, it becomes unable to absorb incident light sufficiently.

An object of the present invention is to provide a structure that can sufficiently absorb incident light even if the thickness of the photoelectric conversion element is reduced.

[Means to solve the problem]

The above object is achieved by providing V-grooves on the front and back surfaces of the photoelectric conversion element and changing the angles of the V-grooves on the front and back surfaces.

[Effect]

The above means will be explained using the drawings.

Figure 2 shows the structure of a photoelectric conversion element that has a structure in which V grooves are formed on the front and back surfaces to reduce the actual thickness of the element. In this structure, the V groove angle (θ1) on the front side is It is the same as the groove angle (θ,). As a result, the actual thickness b of the photoelectric conversion element 1 is
can be made smaller. Expanding a part of it, the third
As shown in the figure, incident light 2 enters the front surface 3 of the photoelectric conversion element 1 at a specific angle (θ, = 54.7°), is reflected by the back surface 4, and is emitted from the first surface 3 to the outside again.

In this case, the actual thickness of the element is several tens of μm or less, so if the light absorption coefficient of the substrate of the photoelectric conversion element is small, part of the incident light 2 will be transmitted to the outside. Conventionally, back reflection causes a decrease in the output current of #! 5 was formed, and by specularly reflecting the transmitted light from the substrate, the optical path length was lengthened and light absorption was increased, and the optical confinement rate was about 90%.

In contrast, in the present invention, as shown in the first @, the V-groove angle (θ□) on the front surface 31 on the light incidence side of the photoelectric conversion element 11 and the V-groove angle (θ2) on the back surface 41 are configured to be different. . More details will be explained using FIGS. 4 and 5. FIG. 4 is a partially enlarged view of a semiconductor substrate constituting a V-groove, and FIG. 5 is a sectional view partially showing a photoelectric conversion element in consideration of a plurality of semiconductor pieces.

The incident light 21 is directed to the surface 31 of the photoelectric conversion element 11 at
It is incident at an angle of 4.7°. In this case, the first surface 31 and the back surface 41 are inclined by a certain angle (θ). As a result, the light that has passed through the element is reflected on the back surface 41 and internally reflected on the front surface 31 inside the element. In particular, change this angle (θ) to 3°
With the above settings, the light that reaches the back surface 41 the first time is totally reflected. If there is a mirror on the back surface 41, then θ is 1
．． If it is set to 5@ or more, it will be totally reflected at the surface 31 inside the element. By changing θ and 02 in this manner, and in particular setting θ and >θ2, the light that has once entered is confined within the substrate 11 and efficiently absorbed. FIG. 5 shows this state.

〔Example〕

The present invention will be explained in detail using FIG.

A 250 μm thick Si single crystal (100) is used for the substrate 66, and first a V-groove structure (angle 74°) is formed on the surface of the photoelectric conversion element.
was manufactured by machining. In this machining, a dicing saw with the required blade angle was used. ■The pitch of the grooves is 240 μm. In a form consistent with this surface V-groove structure,
Using a thermal oxide film as a mask, anisotropic chemical etching was performed from the back side of the photoelectric conversion element using a KOH solution to form a V-groove structure.

Its V-groove angle is 70.5@.

On the rear convex part, P"He'y is formed by alloying with Ag. After removing the strained layer, the N4" layer 65 is formed on the surface.
is formed by phosphorus diffusion, its surface is covered with a passivation oxide film 64, and an anti-reflection film 63 is further formed thereon.A surface electrode 61 is formed on a part of the convex part of the surface, and a contact hole is formed in the oxide film. Ag was vacuum deposited on the # back surface which was in ohmic contact with the 01 layer through 62 to form a reflecting mirror 68 which also served as a back electrode. As a result, the light incident from the front surface is reflected by the back surface, and even when it reaches the front surface again, most of the light is totally reflected, and approximately 98% of the incident light is confined within the substrate 66.

In the above explanation, an example was shown in which the V-groove structure on the front surface was created by machining, but it is also possible to create the V-groove structure on the back surface by machining and process the V-groove structure on the first surface by anisotropic chemical etching. good. In this case, the angle of the V-groove on the back surface is preferably about 68'' or less.

〔Effect of the invention〕

As is clear from the above explanation, (1) In a photoelectric conversion element made of a substrate having a groove structure, when the thickness of the substrate is thin and most of the incident light cannot be sufficiently absorbed in one light transmission, the surface V By setting the groove angle to be larger than the V-groove angle on the back surface, total reflection occurs on one surface and the back surface, thereby allowing most of the incident light to be absorbed within the substrate. When the photoelectric conversion element with such a structure was irradiated with light having the same spectrum as sunlight, almost 100% of the incident light was irradiated.
was able to be absorbed within the substrate.

Further, although the present invention has been explained using a Si crystal as an example, it is also applicable to other crystalline semiconductors such as III-V compound semiconductors such as GaAs and InP, and II-VI compounds such as CdS and CdTe.

[Brief explanation of the drawing]

FIG. 1 is an external view showing an embodiment of the present invention, FIG. 2 is an external view of a conventional photoelectric conversion element, and FIG. 3 is a cross-sectional view of a local part showing the path of incident light in the conventional structure. FIG. 4 is a cross-sectional view of a local portion showing the path of incident light in the structure of the present invention. Fifth
The figure is a cross-sectional view showing the path of incident light in the structure of the present invention. FIG. 6 is an external view showing one embodiment of the present invention.

Claims (1)

[Claims] 1. In a photoelectric conversion element made of at least one type of semiconductor and having a structure in which a plurality of V grooves are formed on the front and back surfaces to reduce the substantial thickness of the element, A photoelectric conversion element characterized in that the V-groove angle on the front surface and the V-groove angle on the back surface are configured to be different. 2. A photoelectric conversion element according to claim 1, characterized in that the V-groove angle on the front surface on the light incident side is larger than the V-groove angle on the back surface. 3. In the photoelectric conversion element according to claim 1, the surface V-groove angle on the light incident side is 1 greater than the V-groove angle on the back surface.
．． A photoelectric conversion element characterized in that it is configured to be larger by 5° or more. 4. The photoelectric conversion element according to claim 1, wherein the V-groove structure is not partially formed in a direction transverse to the V-groove structure. 5. The photoelectric conversion element according to any one of claims 1 to 4, wherein the V-groove structure is formed by at least one of anisotropic chemical etching and machining. manufacturing method.