JPH0543309B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a semiconductor laser.

(Prior art) Conventionally, in order to oscillate a semiconductor laser with high efficiency and achieve high-speed modulation of several Gb/s or more,
Instead of a current constriction structure using an np reverse bias layer, semi-insulating semiconductor layers 24 formed on both sides of the active region 21 are used to block leakage current and reduce parasitic capacitance as shown in FIG. A structure has been proposed and implemented, and is detailed in Applied Physics Letters, Vol. 47, 1985, pp. 1127-1129. In FIG. 2, 20 is a p-type cladding layer, 21 is an active region, and 22 is an n-type cladding layer, forming a double heterostructure on an n-type InP substrate 23. The semi-insulating InP layer 24 and the SiO ₂ layer 15 formed on both sides of the active region 21 narrow the current, and the absence of the np reverse bias layer reduces parasitic capacitance.

(Problems to be Solved by the Invention) However, the conventional semiconductor laser using a semi-insulating buried layer has the following drawbacks.

First, residual capacitance removal is not sufficient.
Modulation above 10GHz was difficult. In this semiconductor laser, the p _- type electrode 17 and the high concentration p
This is because the type semiconductors are oriented toward each other, which generates residual capacitance.

Second, the controllability of the active layer width was poor, making it difficult to obtain uniform oscillation characteristics. This is because in order to make a semiconductor laser oscillate in a single transverse mode, an active layer with a width of 1 to 2 microns is required, but the controllability of photolithography and wet etching is not sufficient to form this layer. .

(Objective of the Invention) An object of the present invention is to provide a semiconductor laser that enables high-speed modulation by reducing parasitic capacitance and can be expected to have a high manufacturing yield due to its structure with excellent controllability.

(Means for Solving the Problems) According to the present invention, in a semiconductor laser using a semi-insulating semiconductor substrate, the first cladding portion of the first and second cladding portions arranged on the left and right sides of the active layer is , a conductive semiconductor having a forbidden band width larger than the forbidden band width of the active region, and two semi-insulating semiconductors sandwiching the conductive semiconductor layer above and below and having a forbidden band width larger than the forbidden band width of the conductive semiconductor layer. and the second cladding portion is composed of a semiconductor layer having a conductivity type opposite to that of the conductivity type semiconductor layer and having a forbidden band width larger than a forbidden band width of the active region. It has a characteristic configuration.

(Function) In the semiconductor laser according to the present invention, of the two types of carriers injected into the active region, the carriers passing through the first cladding portion are formed by the two semi-insulating semiconductor layers constituting the first cladding portion. It is sandwiched between the conductive type semiconductors.

Therefore, the injection current flows only to the active region in the active layer, and the leakage current can be significantly reduced compared to the conventional method, making it possible to oscillate with high efficiency. In addition, the conventional location where parasitic capacitance occurs is
Because there is no structure in which SiO ₂ is sandwiched between an electrode and a highly doped semiconductor, residual capacitance can be significantly reduced compared to conventional methods. Furthermore, since both the thickness and width of the active region are determined by the precision of epitaxial growth, they can be controlled with high precision by using an epitaxial growth method with high controllability such as vapor phase growth.

(Example) Embodiments of the present invention will be described using the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention.

The semiconductor laser of this example was manufactured using the following procedure. First, a semi-insulating buffer layer 11 having an InP composition,
An n ⁺ conductive layer 12 of InGaAsP composition and a semi-insulating cap layer 13 of InP composition are formed. The buffer layer 11, the conductive layer 12, and the cap layer 13 form a first cladding portion. Next, after forming the SiO ₂ layer on the entire surface, a window is made in the SiO ₂ layer by ordinary photolithography and chemical etching, and using this as a mask, a groove (300 μm width) with a vertical surface is created by chemical etching. Form. Next, InGaAsP layer (active layer) 1 was grown using vapor phase growth.
9 and a p-type conductive layer 18 constituting the second cladding part.
grow sequentially. Finally, electrodes 14 and 17 are formed. In the above manufacturing process, hydride vapor phase epitaxy was used to form the active layer on the vertical side surfaces with good control, but it is also possible to use MOCVD.

A part of the InGaAsP layer active layer 19 with a forbidden band width of 0.95 eV serves as the active region 16, and the wavelength is 1.3 μm.
It emits light. The first cladding part consists of a semi-insulating buffer layer 11 of InP composition and a forbidden band width of 1.2 eV.
It consists of an n ⁺ -type conductive layer 12 made of an InGaAsP layer, and a semi-insulating cap layer 13 of InP composition, and the second cladding part consists of a p-type conductive layer 18 of InP composition. The active region 16 is sandwiched between the first cladding portion and the second cladding portion from the left and right, and
Forms a double heterojunction.

Of the carriers injected into the active region 16, electrons are n
However, due to the high resistance of the semi- ^insulating cap layer 13 and the semi-insulating buffer layer 11, electrons leak to the InGaAsP layer 19 other than the active region 16. Can be ignored.
On the other hand, holes are injected from the p-type electrode 17 through the p-type conductive layer 18 into the InGaAsP layer 19, but recombination with electrons mainly occurs in the active region 16. Therefore, the injection current flows only to the active region 16, allowing highly efficient oscillation. In addition, the electrode 14
and 17 are separated by the SiO ₂ layer 15, leakage current between the electrodes can also be ignored.

Parasitic capacitance occurs between the n-type electrode 14 and the p-type electrode 17, which are separated by the SiO ₂ layer 15. In addition, it also occurs between the heat sink and the n-type electrode 14 or the p-type electrode 17, which are placed opposite to each other with the semi-insulating semiconductor substrate 10 in between. Here, the electrode spacing, resonator length, and substrate thickness are each 5 μm.
When 300μm and 100μm, the total parasitic capacitance is
The value was extremely low at 0.05pF.

As a result, even if a relatively large residual inductance of about 3 nH is generated due to mounting such as wire bonding, the cutoff frequency will be 1 GHz or more.
This enabled high-speed modulation of 10 Gb/s.

Furthermore, the width of the active region 16 is equal to the width of the n ⁺ type conductive layer 12.
Since it is determined only by the thickness of the layer, it does not depend on the accuracy of photolithography and chemical etching. Therefore, by using highly controllable vapor phase growth,
The size of the active region 16 could be controlled with high precision. Further, by setting the composition of the n ⁺ type conductive layer 12 to be an InGaAsP layer having a higher refractive index than InP, it was possible to realize refractive index waveguiding desirable for a semiconductor laser for optical communication.

In the above embodiment, the forbidden band width of the active region 16 is
Although a laser oscillating at 1.3 μm was obtained due to the 0.95 eV, this mixed crystal composition can also be set to oscillate at any wavelength from 1.1 μm to 1.65 μm.

Although InGaAsP/InP-based crystals were used in the above embodiments, other crystals such as AlGaAs/GaAs-based and AlInGaP/GaAs-based crystals may also be used.

(Effects of the Invention) The semiconductor laser according to the present invention oscillates with extremely high efficiency, is capable of high-speed modulation exceeding 10 Gb/s, and can reproducibly obtain the size of the active region that provides a single transverse mode. Therefore, it was possible to obtain oscillation characteristics with very high uniformity.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor laser illustrating an embodiment of the present invention, and FIG. 2 is a sectional view of a semiconductor laser illustrating a conventional example. In the figure, 10... semi-insulating semiconductor substrate, 11...
Semi-insulating buffer layer, 12...n ⁺ type conductive layer, 1
3... Semi-insulating cap layer, 14... N-type electrode,
15...SiO ₂ layer, 16...active region, 17...
p-type electrode, 18... p-type conductive layer, 19...
InGaAsP layer, 20... p-type cladding layer, 21...
...active layer, 22...n-type cladding layer, 23...n
InP type substrate, 24 . . . indicates a semi-insulating InP layer, respectively.

Claims (1)

[Claims] 1. A structure in which first and second cladding parts are arranged on the left and right sides of an active layer is provided on a semi-insulating semiconductor substrate, and the first cladding part has a forbidden band width larger than the forbidden band width of the active layer. It has a laminated structure in which a semiconductor layer is sandwiched between two semi-insulating semiconductor layers having a bandgap larger than the bandgap of the semiconductor layer, and the second cladding part has a conductivity opposite to that of the semiconductor layer. The semiconductor layer is made of a semiconductor layer exhibiting a type and has a forbidden band width larger than the forbidden band width of the active layer, and further includes electrodes in the semiconductor layer of the first cladding part and the second cladding part, respectively. Features of semiconductor laser.