JPH0512872B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to a lens for an optical semiconductor device, a method for manufacturing a lens for an optical semiconductor device, and an optical semiconductor device.

Conventional technology and its problems Surface-emitting light-emitting diodes (also called ballast-type LEDs, hereinafter referred to as ballast-type LEDs) are widely used as light sources for analog optical communications due to their good output linearity and high element reliability. There is.

In general, light sources for optical communication require directivity in the emitted light in order to enhance coupling with optical fibers that are optical transmission bodies. However, ballast LEDs have drawbacks because the directivity of the emitted light is blunt due to their structural characteristics and it is difficult to couple them with optical fibers.

In order to compensate for this drawback, various methods have been proposed to improve coupling with optical fibers by providing an external lens or an internal lens.

The external lens method is a method in which a so-called microlens, such as a spherical lens, is attached to a ballast LED, and by appropriately selecting the optical constants such as the focal length, it is possible to improve the coupling with the optical fiber. However, this method uses microlens and ballast LED.
It is necessary to precisely adjust the optical axis with the optical axis, which has the disadvantage that adjustment and assembly are not easy. In particular, consideration must be given to how to handle the microlens and how to securely hold it.

In addition, the internal lens method is a method that improves the coupling with the optical fiber by processing the light extraction surface of the ballast LED, and is a method that is easy to adjust and assemble because it can be coupled without using an external lens.

However, this method requires precise spherical processing, and the processing technology is difficult and it is difficult to mass produce.

OBJECT OF THE INVENTION The object of the invention is to
The purpose of the present invention is to improve the radiation directivity of LEDs and provide a highly productive light emitting diode.

Summary of the Invention A feature of the present invention is that a semiconductor substrate that is transparent to the emission wavelength is used, and a lens portion with a locally high refractive index is provided in the substrate, thereby increasing the radiation directivity of the semiconductor light emitting device. .

Effects of the Invention According to the present invention, the radiation directivity of a ballast LED can be improved and coupling with an optical fiber can be facilitated. Furthermore, the ballast LED according to the present invention has high productivity and is suitable for mass production.

Embodiment of the invention Here, as a balanced LED for optical communication
This article describes InGaAsP/InP-based crystal materials.

FIG. 1 shows the process of providing a lens portion on an n-type InP substrate 1 by a diffusion method.

First, in this step, an oxide film such as SiO ₂ (or nitride film such as Si ₃ N ₄ ) is placed on both sides of the InP substrate 1 as a diffusion mask.
2 and a pinhole on one side to form a diffusion window [Figure a]. However, if the surface on which the pinhole is not provided is to be polished later, the diffusion mask 2 only needs to be provided on the surface on which the lens portion is provided.

Thereafter, Zn is diffused in the InP substrate 1 in a high temperature atmosphere containing Zn and P [Figure b]. Then, the diffusion mask 2 is removed [Figure c].

As a result, the region 3 in which Zn is diffused has a refractive index about 0.001 higher than other regions,
Furthermore, because of the diffusion from the pinhole, the refractive index increases in a hemispherical manner because it is diffused in the same direction from the pinhole. As a result, a lens portion is formed in the InP substrate by locally increasing the refractive index.

An example using the InP substrate thus prepared is shown in FIGS. 2a and 2b. 2' in the figure is the same film as 2 in FIG. 1, but here it is used as a current limiting insulating film. First, Figure a shows an example in which crystal growth is performed on the surface where the lens portion is provided. Also, figure b is a
This is an example in which crystal growth was performed on the opposite side to the one shown in the figure. It can be seen that in both cases, the lens portion formed by diffusion acts to impart directionality to the light emitted from the ballast LED. As described above, according to the present invention, a ballast having an internal lens can be manufactured by a simple manufacturing process.
LEDs can be made. Compared to the conventional internal lens method, this method does not require special equipment to process hemispheres, and it is possible to manufacture a large number of lenses at once, making it suitable for mass production. Next, FIG. 3 shows an embodiment of the present invention in which the manufacturing process is changed. In this embodiment, instead of first providing the lens portion in the InP substrate as shown in FIG. 2, the lens portion is provided after crystal growth is performed on the InP substrate. The feature of this example is that since the crystal growth is performed first, it is possible to check and screen the characteristics such as luminous efficiency of the grown wafer. This reduces the chance of damage to the wafer due to defects caused by crystal growth. Figure a in the figure is
Similar to FIG. 1b, this figure shows the state of manufacturing the lens part.

FIG. 4 shows an example in which lens portions are provided on opposite sides of the InP substrate in the manufacturing method shown in FIG.
This has the feature that the design range of optical constants can be widened by making the lens portion on one side smaller by polishing.

FIG. 5 shows an example using the embodiment of FIG.
This is an example in which the InP layer is selectively removed.

Selective etching of n-type InP includes techniques such as photo etching and electric field etching. for example,
When light irradiation is performed in FeCl ₃ aqueous solution, n-type
It is generally known that only the parts of InP that are irradiated with light are selectively etched, and the parts that are not irradiated with light are hardly etched. Furthermore, at this time, p-type InP is hardly etched regardless of whether or not it is irradiated with light.

By using this method, the embodiment shown in FIG. 5 can be manufactured. This embodiment is also one of the methods in which the design range of optical constants is widened, similar to the embodiment shown in FIG.

Other Embodiments of the Invention Although the present invention has been described with respect to InGaAsP/InP-based materials, the present invention can also be applied to materials such as GaAs/GaAlAs-based materials. In addition, although the embodiments of the present invention describe lens fabrication using the Zn diffusion method, other methods such as ion implantation and selective crystal growth are also possible.
It goes without saying that there are other viable substances besides Zn.

In other words, the present invention can be applied in various ways without departing from its scope and essence.

[Brief explanation of drawings]

1 to 5 are cross-sectional views of embodiments of the present invention. 1...n-type InP substrate, 2... _SiO2 , _{Al2O3 ,}
Diffusion mask such as Si ₃ N ₄ , 2'...SiO ₂ , Al ₂ O ₃ ,
Insulating film such as Si ₃ N ₄ , 3... Zn diffused p-type region (lens part), 4... n-type InP buffer layer, 5...
InGaAsP light emitting layer (active layer), 6... p-type InP cladding layer, 7... p-type InGaAsP ohmic contact layer, 8... p-side electrode metal, 9... n-side electrode metal.

Claims (1)

[Claims] 1. A semiconductor substrate that is transparent to the wavelength used;
A lens for an optical semiconductor element, comprising a lens mechanism formed on the surface of the semiconductor substrate and having a high refractive index due to impurity distribution. 2. Forming a mask film having pinholes on the surface of a semiconductor substrate that is transparent to the wavelength to be used, and then diffusing impurities from above the mask film to form a lens mechanism portion with a high refractive index on the surface of the semiconductor substrate. 1. A method for manufacturing a lens for an optical semiconductor element, comprising the steps of: 3. A semiconductor substrate that is transparent to the wavelength used,
A lens mechanism section formed on the surface of the semiconductor substrate and having a high refractive index due to impurity distribution, and a light emitting section formed adjacent to the semiconductor substrate and irradiating the lens mechanism section with emitted light. Features of optical semiconductor devices.