JPS63301573A - Light emitting diode - Google Patents

Abstract

PURPOSE:To obtain a high light emission output by providing an active layer composed of a p-n junction on one surface of a low impurity concentration semiconductor substrate. CONSTITUTION:An active layer 12 composed of a p-n junction is provided on one surface of a low impurity concentration semiconductor substrate 10. For instance, on the circumference side part where an insulating layer 15 is not formed, a p-type electrode 16 is provided so as to be brought into contact with a p-type InP layer 11 exposed at the bottom of a recessed part 21 and, on the center part where the insulating layer 15 is not formed, an n-type electrode 17 which is brought into contact with an n-type InGaAsP layer 14 is provided. Moreover, the opposite side of the nondoped InP substrate 10 is shaped into a convex lens form. As light is absorbed only a little by the low impurity concentration semiconductor substrate, the light emitted by the active layer is hardly absorbed and emitted with a high output power.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a light emitting diode suitable for optical communication, which has high output and can efficiently input light into an optical fiber.

[Conventional technology]

A light emitting diode with a monolithic lens as shown in FIG. 3 has been known. This light emitting diode is used to extend the distance of optical communication systems and improve transmission margins.
Along with high output, n-1nP formed in a convex lens shape
The structure is such that light can be focused by the substrate 30 and efficiently input into the optical fiber. That is, this light emitting diode has an n-InP substrate 30.
On the back surface of the nlnP layer (buffer layer) 31, p-InG
aAsP layer (active layer) 32, p-1nP layer (buffer layer) 33, n-InGaAsP layer (current limiting layer) 34
It has a structure in which these are sequentially epitaxially grown. A region 42 in which Zn is diffused from the back surface side to the active layer 32 is provided at the center of the back surface. This Zn diffusion region 42 is used for current limitation and impurity as described later. i! This is to increase the I concentration and obtain ohmic contact with the p-electrode 37. Further, by etching from the back side, a donut-shaped recess 41 is formed that penetrates the active layer 32 and reaches the buffer layer 31. 5 on the center side of the inner surface of this donut-shaped recess 41 and on the periphery of the top surface of the central protrusion.
An i02 layer (insulating layer) 35 is provided. In other words, the central part and the peripheral part are the parts where the 5i02 layer 35 is not formed. On the peripheral side where the 5i02 layer 35 is not present, an n-
An electrode 36 is provided, and a p-electrode 37 is provided in the central portion where the 5i02 layer 35 is not present. These electrodes 37
．． 36, a current flows from the p-electrode 37 through the current limiting layer 34, buffer layer 33, active layer 32, and buffer layer 31 to the n-electrode 36, and the active layer 3
2, light emission occurs in the Zn diffusion region 4 where the current injected from the p-electrode 37 becomes p-type due to the diffusion of Zn.
2, the current is limited. Since the light emitted from the active layer 32 is focused by the n-1nP substrate 30 formed in the shape of a convex lens, the light can be efficiently input into the optical fiber having a small entrance aperture.

[Problems to be solved by the invention]

However, conventionally, as mentioned above, n-I
An nP substrate is used, and since this n-1nP substrate has a large absorption of light, there is a problem that light is absorbed by this substrate and the optical output inevitably decreases. An object of the present invention is to provide a light emitting diode that can provide high light emission output.

[Means to solve the problem]

The light emitting diode according to the present invention is characterized in that an active layer formed by a pn junction is provided on one surface of a semiconductor substrate with a low impurity concentration.

[For production]

A semiconductor substrate with a low impurity concentration absorbs little light. Therefore, the light emitted in the active layer is not absorbed and is emitted with high output.

【Example】

In FIG. 1, p-I nP layer (buffer layer) 11, InGaAsP layer (active layer) 12, n-1nP layer (buffer layer) 13, n
-rnGaAsP layers 14 are epitaxially grown in sequence. Next, etching is performed from the back side to form a pattern with a width of, for example, 20 μm around the light emitting region of about 30 μm in diameter.
A donut-shaped recess 21 is formed. This recess 21 penetrates the active layer 12 and its bottom surface is p-I.
It is formed so deep that it reaches the nP layer 11. After that, a 5i02 layer (insulating layer) 15 is formed on the entire back surface, and other parts are removed so that this insulating layer 15 remains only on the center side of the inner surface of the donut-shaped recess 21 and around the top surface of the central convex part. , the central part and the peripheral part are the parts where the 5i02 layer 15 is not formed. A p-electrode 16 is provided in the peripheral portion where the insulating layer 15 is not present, so as to contact the p-In P layer 11 exposed at the bottom of the recess 21, and a p-electrode 16 is provided in the central portion where the insulating layer 15 is not present. An n-electrode 17 is provided in contact with the n-InGaAsP layer 14. Further, the opposite side of the non-doped InP substrate 10 is formed into a convex lens shape. When the relationship between carrier concentration and light transmittance in the InP substrate is measured, data as shown in FIG. 2 is obtained. From this FIG. 2, the above non-doped InP substrate 1
It can be seen that in the case of 0, almost no light is absorbed at a wavelength of 1.3 μm. Therefore, there is no light absorption by the substrate 10, and a large light output can be obtained. In addition, the active layer 12 is scraped away by the donut-shaped recess 21, and current flows only through the remaining active layer 12, which functions as a light emitting region. Therefore, the light emitting region is limited to a small area, and the emitted light is can prevent the spread of. Therefore, the coupling efficiency with optical fiber increases,
The power of the incident light on the optical fiber I\ can be increased, making it suitable as a light source for optical communications. Furthermore, an n-electrode 17 is provided on the top of the central convex portion that remains unetched by the donut-shaped four portions 21, and the impurity concentration on the semiconductor surface of the n-electrode 17 is lower than that of the p-electrode. Good ohmic contact can be obtained even at a relatively low concentration, so there is no need to diffuse impurities such as Zn (in the conventional case shown in Figure 3, the impurity concentration is increased to
- Due to the need to obtain ohmic contact with the electrode 37, Z
n diffusion process is essential, which is a factor in increasing costs). In addition, the p-electrode 16 is in contact with the p-InP layer 11 through a ring-shaped portion with a relatively large radius, and since the contact area is large, good ohmic contact can be achieved without a Zn diffusion process. It will be done. In this way, Zn
Eliminating the need for a diffusion step simplifies the process and contributes to lower prices. Note that from FIG. 2, instead of the non-doped InP substrate 10, an n
It can be seen that similar effects can be obtained by using -InP substrates, 5I-1nP substrates, p-1nP substrates, etc., so these can also be used.

【Effect of the invention】

In the light emitting diode according to the present invention, the light generated in the active layer is emitted from the substrate to the outside without being absorbed, so that high light output can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, and FIG. 2 is an InP
A graph showing the relationship between substrate light transmittance and carrier concentration,
FIG. 3 is a sectional view of a conventional example. 10... Non-doped InP substrate, 11.33-p-I
n P layer, 12.32--active layer, 13.31--
n-1nP layer, 14.34-n-1nGaAsP layer, 1
5.35...5i02 layer, 16.37-p-electrode, 1
7.36...n-electrode, 21.41...doughnut-shaped recess, 30...n-1nP substrate, 42...Zn diffusion region.

Claims (3)

[Claims] (1) A light emitting diode characterized in that an active layer formed by a pn junction is provided on one surface of a semiconductor substrate with a low impurity concentration. (2) The light emitting diode according to claim 1, wherein the other surface of the semiconductor substrate is formed into a convex lens shape. (3) A donut-shaped recess that penetrates the active layer is formed on one surface of the semiconductor substrate, and an electrode that contacts the top of the remaining portion surrounded by the donut-shaped recess contacts the bottom of the recess. 2. The light emitting diode according to claim 1, further comprising an electrode.