JPH02181987A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To lower the electrostatic capacity of the electrode section of a semiconductor laser without sacrificing the workability and bonding strength of wire bonding so as to raise the cut-off frequency by forming at least part of the electrode on a dielectric insulating film to a comb-like or grating-like shape in which the electrode is divided into numerous electrode branches. CONSTITUTION:The electrode 5a of a contact section which is parallel with stripes for supplying an electric current has a width of 70mum and the electrode 5b of a wire bonding section connected with the electrode end of the contact section is composed of a plurality of electrode branches, each of which has e width of 10mum and length of 50mum, arranged in parallel with each other as teeth of a comb, with the comb being composed of nine teeth arranged at regular intervals of 10mum. Since the entire area of the wire bonding section is 8500mu, a plurality of wire bonding can be performed simultaneously without lowering the bonding strength even when gold wires of 30mum in diameter are used as lead wires.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to semiconductor lasers.

[Conventional technology]

High-speed operation of semiconductor lasers has been pursued as a key device for optical fiber communications, which is capable of high-speed direct modulation. For this reason, efforts have been made to improve the relaxation oscillation frequency fR and the cutoff frequency fC.

In order to improve the relaxation oscillation frequency fa, for example, in a distributed feedback semiconductor laser equipped with a diffraction grating in the region through which light propagates, the differential gain coefficient must be increased so that the gain peak is on the long wavelength side of the oscillation wavelength. etc. are being attempted. on the other hand,
To improve the cutoff frequency fc, it is effective to reduce the capacitance of the semiconductor laser by forming a dielectric insulating film on the semiconductor layer. High-speed direct modulation of 1QGIIz or higher has been achieved by removing metal other than the wire bonding part and lowering the capacitance. In order to further improve the cutoff frequency, measures such as increasing the thickness of the dielectric insulating film to reduce capacitance and using multiple wires to reduce the effect of inductance of the lead wire bonded to the electrode are available. It is taken.

[Problem to be solved by the invention]

In this case, we will particularly discuss the problems associated with improving the cutoff frequency. In order to achieve a cut-off frequency of 10 GHz or more with a margin, the above-mentioned measures have been taken, but these have had the following problems. First, in the method of reducing capacitance by increasing the thickness of the dielectric insulating film,
As the dielectric insulating film becomes thicker, distortion occurs in the semiconductor due to the difference in coefficient of thermal expansion between the dielectric and the semiconductor. This distortion has a large effect on a semiconductor laser having a waveguide structure, such as a distributed feedback semiconductor laser, and has an adverse effect on reliability. Furthermore, the following problems occur when multiple lead wires are used to reduce the influence of lead wire inductance. In order to use a plurality of lead wires, it means that the electrode area of the wire bonding portion increases accordingly. The area of the wire bonding part can be made as small as possible electrically, but in order to ensure mechanically sufficient wire bonding strength and considering the workability of the wire bonding work, the area of the wire bonding part must be made as small as possible. This requires a limited effective area, which is the reason why the capacitance of the electrode portion cannot be lowered beyond a certain level. An object of the present invention is to provide a semiconductor laser capable of highly reliable and high-speed operation according to the above-mentioned aspects.

[Means to solve the problem]

The present invention provides a semiconductor laser in which a dielectric insulating film is formed on a multilayer structure including an active layer that participates in light emission as an injection current narrowing structure, in which at least a large number of electrode portions are formed on the dielectric insulating film. The structure is characterized by having a shape divided into electrode columns or a grid-like shape.

[Effect]

The capacitance generated by the semiconductor junction inside the semiconductor laser is usually smaller than the capacitance generated between the metal-dielectric insulating film and the semiconductor in the electrode section, so the capacitance of the semiconductor laser can be approximated by the capacitance of the electrode section. can. The capacitance in this case is expressed by the following formula, where ε is the permittivity of the dielectric insulating film,
S is the area where the electrode metal is in contact with the dielectric insulating film, and d is the thickness of the dielectric insulating film. Also, the cutoff frequency f. is expressed by the following equation.

Here, R is the differential resistance of the element. Therefore, by reducing S and C, fC can be increased.

〔Example〕

Next, the present invention will be explained in more detail using the drawings. FIG. 1 is a perspective view of a first embodiment of the invention. 1 is an lnP substrate, on which a multilayer structure including an active layer made of InGaAsP with a composition of Ij μm is formed. Reference numeral 2 denotes a light emitting section, which extends to the active layer and its vicinity. The size of the semiconductor laser is a cavity length of 300 μm, width of 300 czm, and thickness of 100 μm, and the light emitting part is located about 5 μm below the center of the device. The width of the mesa top of the striped mesa with the light emitting part is 20 μm, and the grooves on both sides of the mesa are 20 μm wide and 1 deep.
It is 0 μm. 3 is the thickness of 450 mm provided on the surface of the multilayer structure
It is a dielectric insulating film made of silicon oxide. The upper part of the mesa is a contact part 4 that comes into contact with the electrode, and a striped window with a width of 10 μm is provided in the dielectric insulating film in this part. 5a and 5b are electrodes made of, for example, chromium, gold, titanium-platinum-gold. The width of the electrode 5a of the contact part parallel to the current injection stripe is 70 μm, and the electrode 5b of the wire bonding part connected to the electrode end of the contact part has a width of 10 μm and a length of 5 μm.
It has a comb tooth shape in which a plurality of electrode columns of 0 μm are arranged in parallel, the spacing between the teeth is 10 μm, and the number of teeth is 9. The entire area of wire bonding part is 8500μm
2, even if a gold wire with a diameter of 30 μm is used as the lead wire, multiple wire bonding is possible and the bonding strength is not impaired. A close-up view shows the state in which three gold wires 7 of 30 μmφ are bonded.

Shangj-eup

Claims (1)

[Claims] In a semiconductor laser, a dielectric insulating film having a window is formed on the surface of a multilayer structure including an active layer that participates in light emission, and an electrode is provided on the dielectric insulating film and connected to a semiconductor layer through the window. . A semiconductor laser, wherein a portion of the electrode formed on the dielectric insulating film has a shape in which the electrode portion is at least partially divided into a large number of electrode branches, or a lattice shape.