JPS62226674A - Light-emitting diode - Google Patents

Abstract

PURPOSE:To form the intensity distribution of a light emitting section to an approximately rectangular shape, and to improve coupling efficiency to an optical fiber by forming a projection with a circular surface at the central section of a substrate surface and prcviously surrounding the periphery of the projector by a high resistance semi conductor layer when an active layer, a clad layer and a contact layer are liquid- grown on a semiconductor substrate in an epitaxial manner. CONSTITUTION:A circular projection having tbe area of a top of anproximately 30mum<2> is shaped to the surface of an n-type InP substrate l through etching, and the peripheral section of tbe projection is surrounded by a high-resistance InP layer 2 through a liquid phase epitaxial method. An InGaAsP active layer 3, a p-type InP clad layer 4 and a p-typo InGaAsP contact layer 5 are liquid-grown on tbe whole surface including the projection in an epitaxial manner in succession, and a p side electrode 8 is applied onto the layer 5 and an n side elcctrode 9 onto the back of tbe substrate l respectively. A window for cxtracting beams having a diameter of approximately 120mum is bored to the electrode 9, and the window is coated with an antireflection film 10. Accordingly, since a current blocking layer is formed to the peripheral section of the projection, a current injection section is limited, thus equalizing the density of current injection to the active layer.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to light emitting diodes for optical fiber communications.

[Conventional technology]

A conventional light emitting diode, as shown in FIG. 3, was fabricated by sequentially epitaxially growing an active layer, a cladding layer, and a contact layer on a flat semiconductor substrate. In FIG. 3, 1 is a semiconductor substrate (for example, InP), 2 is a high-resistance layer (InP), 3 is an active layer (1nGaAsP), 4 is a cladding layer (p-type InP), and 5 is a contact layer (p-type InG).
aAsP ), 8 is a p-side electrode, 9 is an n-side electrode, and 10 is an antireflection film.

[Problem that the invention seeks to solve]

In the conventional light emitting diode described above, the epitaxial growth layer is uniform in the plane direction, but in order to increase the coupling efficiency to the optical fiber, the light emitting part must be limited to the diameter of the optical fiber's core. By forming an electrical insulating film on the surface of the epitaxial growth layer except for a part,
The current is injected only into one part, limiting the light emitting part. However, in the conventional method, since the part that limits current injection is separated from the active layer, the current spreads in both directions in the active layer, making the current density within the light emitting part not constant. For this reason, the light emission intensity gradually decreases around the light emitting part, and the coupling efficiency with the optical fiber deteriorates.The light emission wavelength and response speed change depending on the location, so the light emission wavelength and response speed vary depending on the way of coupling with the optical fiber. There was some variation in speed.

In particular, when light from the periphery of the light emitting part is received by an optical fiber, the response speed becomes slow. In addition, with conventional light emitting diodes,
Since the pn junction extends over the entire surface of the chip, the pn junction capacitance is large and the response speed is slow.

In order to eliminate the above-mentioned drawbacks, at least the active layer is epitaxially grown, and the epitaxially grown layer is removed by etching the area around the light emitting part, leaving the light emitting part.
Furthermore, a structure in which a current blocking layer is epitaxially grown around the light emitting part (for example, Japanese Patent Laid-Open No. 59-125679)
, a current injection part is formed by first epitaxially growing a current blocking layer, then making a hole that partially reaches the semiconductor substrate, and epitaxially growing a layer including an active layer thereon (for example, Japanese Patent Laid-Open No. 121885/1985). A method has been considered in which the current is limited within the epitaxial growth layer to prevent the current structure from becoming distorted, but both methods require epitaxial growth to be performed twice.

The purpose of the present invention is to limit the current injection part in the epitaxial growth layer in one epitaxial growth, to make the injection current density to the active layer uniform, to improve the coupling efficiency to the optical 7 eyeper, and to improve the emission wavelength and Small variation in response speed,
Another object of the present invention is to provide a light emitting diode that can reduce pn junction capacitance and improve response speed.

[Means for solving problems]

In the light emitting diode according to the present invention, a projection having a circular top is formed on the surface of a semiconductor substrate, and a high-resistance semiconductor layer or a semiconductor layer having a conductivity type opposite to that of the semiconductor substrate is grown on a region other than the top of the projection by liquid phase epitaxial growth. The semiconductor substrate has a structure in which current is injected only into the protruding portions of the semiconductor substrate by forming a current blocking layer and epitaxially growing layers including an active layer, a cladding layer, and a contact layer on the current blocking layer. There is.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a first embodiment of the invention. 1st
As shown in the figure, a circular protrusion with a top having a diameter of 30 μm is formed on the surface of an n-type InP substrate 10 by etching. Next, a high-resistance InP layer 2 is grown on the substrate by liquid phase epitaxial growth around the protrusion, and an InGaAsP active layer 3, a p-type InP cladding layer 4, and a p-type InP cladding layer 4 are then grown on the entire surface.
An InGaAsP type contact layer 5 is successively grown. Next, a p-side electrode 8 is formed on the contact layer, and the InP substrate is mirror-polished to a thickness of 140 μm.
A 1tQ electrode 9 is formed. The n-side electrode has a diameter of 120 μm.
A light extraction window is opened and an antireflection film 1o is formed there.

In the above embodiment, the part that limits current injection is the layer immediately below the active layer, so the current spread in the active layer is reduced and the emission intensity distribution is nearly rectangular, which reduces the input to the optical fiber. Power increases. Second, the response speed characteristics are also improved because the injected current density becomes uniform and the pn junction capacitance is reduced by the high resistance layer.

FIG. 2 is a sectional view of a second embodiment of the invention.

As shown in FIG. 2, a circular protrusion with a top having a diameter of 30 μm is formed on the surface of an n-type 1nP substrate 1 by etching. On top of that, p-type I is formed by liquid phase epitaxial growth.
nP layer5. Two n-type InP layers 7 are sequentially grown around the protrusion. Thereafter, by the same process as in the example of cylinder 1, InG
aAsP active layer 3. p-type InP cladding layer 4+p-type In
GaAsP:M/cladding layer is formed, and then p-side electrode 8. An antireflection film 10 is formed on the n-side electrode 9° to complete the light emitting diode of the second embodiment. In the second embodiment, since a semiconductor layer having a conductivity type opposite to that of the semiconductor substrate is formed, this layer can function as a current blocking layer as in the first embodiment.

〔Effect of the invention〕

As explained above, in the present invention, a protrusion is formed on the surface of a semiconductor substrate, a current blocking layer is epitaxially grown around the protrusion, and then an active layer and a cladding layer are formed.

By epitaxially growing a layer serving as a contact layer, it is possible to obtain a light-emitting diode in which a current injection portion is limited within the epitaxially grown layer and the density of current injected into the active layer is uniform by one epitaxial growth. In the light emitting diode according to the present invention, the intensity distribution of the light emitting part becomes close to a rectangular shape, and the coupling efficiency to the optical fiber is improved, and the variation in the light emission wavelength and response speed within the light emitting part is small, depending on the method of coupling to the optical fiber. Variations in wavelength and response speed can be suppressed. Furthermore, by using a high-resistance semiconductor layer for the current blocking layer, the pn junction capacitance can be reduced and the response speed can be improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a first embodiment of the invention, FIG. 2 is a sectional view of a second embodiment of the invention, and FIG. 3 is a sectional view of an example of a conventional light emitting diode. 1... Semiconductor substrate (n-type 1nP), 2...
... High resistance layer (1nP), 3... Active layer (In
4... Cladding layer (p-type In
P), 5-----Contact layer (p-type InGaA
sP ), 6... p-type InP layer, 7...
・N-type InP layer, 8...p-side electrode, 9...
...N-side electrode, 10...Anti-reflection film, 11...
...5i02i insulation film. Agent Patent Attorney Hara Uchi 1 'day 1 Kunimine Z times Y''51 ¥I

Claims (2)

[Claims] (1) In a light emitting diode comprising an active layer, a cladding layer, and a contact layer that are sequentially formed on a semiconductor substrate by liquid phase epitaxial growth, a protrusion with a circular top is formed on the surface of the semiconductor substrate, and a protrusion with a circular top is formed on the surface of the semiconductor substrate. A high-resistance semiconductor layer is formed on the surface other than the top of the formed protrusion by liquid phase epitaxial growth, and at least an active layer, a cladding layer, and a contact layer are sequentially formed on the entire surface including the high-resistance semiconductor layer. A light emitting diode featuring (2) In a light emitting diode comprising an active layer, a cladding layer, and a contact layer sequentially formed on a semiconductor substrate by a liquid phase epitaxial growth method, a projection having a circular top on the surface of the semiconductor substrate having a first conductivity type is provided. formed,
A semiconductor layer having a second conductivity type is formed on the surface other than the top of the protrusion formed on the substrate by a liquid phase epitaxial growth method, and further thereon, a semiconductor layer having a first conductivity type and an active layer are sequentially formed. A light emitting diode comprising: a cladding layer having a second conductivity type; and a contact layer having a second conductivity type.