JPH01186691A - Semiconductor laser array - Google Patents

Abstract

PURPOSE:To improve the reliability of insulating properties between respective electrodes even through each array has a fine laser pitch, by insulating by providing an organic layer between respective electrodes. CONSTITUTION:The top parts of ridges that are stripe-like in an element are designated as current injection regions of respective elements and an ohmic electrode 7 is formed at each region. The ohmic electrode 7 in each element is kept separate one from the other by an electrode isolation region 11. That is to say, they are semiconductor laser arrays wherein the part lower than the ohmic electrodes 7 are composed in common by respective elements. Further, each extraction electrode 9 is laminated on each ohmic electrode 7 through an organic insulation layer 10 and electrical contact between electrodes 7 and 9 is just made by a through hole 12 that is prepared at the organic insulation layer 10. Moreover, a gap between each electrode isolation region 11 and each ohmic electrode 7 located on the above region 11 is filled with the organic insulation layer 10. In this way, the reliability of insulating properties between respective electrodes 7 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser array constructed by monolithically arraying a plurality of semiconductor laser elements, each of which can be driven independently.

[Conventional technology]

Conventionally, semiconductor lasers have been widely used as light sources in various information and industrial fields, typified by, for example, optical fiber communications, printers, and various measurement fields.

In addition, in recent years, in order to expand the application of semiconductor lasers, a plurality of semiconductor laser elements have been formed into a flat plate to form an array or a monolithic array) 6, and independent electrodes have been formed for each element, and each element has been It has been attempted to construct a laser array that can be driven independently. Furthermore, attempts have been made to make the interval between lasers (laser pitch) of adjacent elements of the laser array finer.

[Problem to be solved by the invention]

However, in order to make the pitch of the laser array finer, the spacing between each electrode must also be made finer, and if the spacing between the electrodes is made too fine, the space between the electrodes will become narrow and the reliability of the insulation will be reduced. will decrease. Furthermore, in conventional semiconductor laser arrays, for example, plasma CVD
Inorganic insulators such as silicon nitride and 5i02 formed by the D method are usually used as interlayer insulating layers.
It is difficult to form these inorganic insulators in the spaces between the miniaturized electrodes. Therefore, conventionally, it has been difficult to miniaturize the space between each electrode, and this has been one of the factors that hinders miniaturization of the laser pitch.

On the other hand, the oscillation threshold current of a normal semiconductor laser device is very sensitive to temperature, and when a laser device with boat-like characteristics is used at a steady environmental temperature, the oscillation threshold current is 1 mA.
In many cases, the differential efficiency of the laser light output with respect to the drive current in a semiconductor laser device is extremely large, 20 to 40%, so even if a temperature change of about 1°C occurs, the light The output varies by hundreds of μW. Therefore, in order to accurately control laser characteristics such as laser light output and threshold current in a semiconductor laser array, the temperature of each laser element depends on unspecified factors. That is not desirable.

However, in general, the active layer of a semiconductor laser element when driven exhibits a temperature increase of several tens of degrees Celsius compared to when not driven. Therefore, for example, when one of two adjacent elements is driven and the other is not, the mutual thermal influence is large, and the finer the pitch, the greater the mutual thermal fQN. It ends up.

Therefore, if the laser pitch of the laser array is made finer, the temperature of each element will tend to change due to unspecified factors (the influence of heat from adjacent elements), so the laser characteristics of each element will no longer be constant. It becomes difficult to perform the control accurately.

The present invention has been made to solve these problems, and its purpose is to improve the laser characteristics because the insulation between each electrode is highly reliable and the influence of heat between each laser element is small. An object of the present invention is to provide a fine pitch semiconductor laser array that can be controlled with high precision.

[Means to solve the problem]

The present invention provides a semiconductor laser array having a plurality of semiconductor laser elements arranged in a plane and a plurality of electrodes arranged to enable each of the laser elements to be driven independently. The invention includes a semiconductor laser array characterized in that an organic insulating layer is used.

The term "electrode for enabling independent driving of laser elements" as used in the present invention means electrodes provided independently on each semiconductor laser element. The organic insulating layer in the present invention may be provided at the required portion between the electrodes. However, in order to ensure the reliability of the insulation between the respective electrodes whose laser pitch has been reduced, it is desirable to provide an organic insulating layer between all the electrodes. Furthermore, in the so-called lead-out electrodes drawn out from each independent electrode to the wire bonding part, it is desirable to further provide an organic insulating layer in the areas where the lead-out electrodes are densely arranged.

As described above, since the organic insulating layer is provided between the electrodes of the semiconductor laser array of the present invention, conductive dust, etc. cannot enter between each electrode, and there is no short circuit due to external impact. Good insulation between each electrode can be ensured.

The organic insulating layer also acts as a heat insulating layer between each electrode,
Furthermore, since the thermal conductivity of the organic insulating layer is usually lower than that of the substrate, the heat generated in the active layer is mainly transferred to the substrate side, is dissipated by the heat sink, and the mutual heat between each laser element is transferred. The influence of heat is reduced, and durability against heat is improved.

Conventional inorganic insulators such as 5in2 and Si3N4 require layer formation by vacuum processes (sputtering, plasma CVD, etc.), but organic insulators can be formed using simple and short-term processes such as spin coating and dip methods. The process can easily form a layer of desired thickness. Furthermore, the pattern can be formed by either dry or wet etching process, and the etching solution and gas provide selectivity with respect to the substrate, so the process is simple.

Examples of organic insulators used in the array of the present invention include polyimide, organic silicon compounds, and the like. Note that the thermal expansion coefficients of the materials constituting each element of a semiconductor laser generally vary, and it is important to appropriately adopt an organic insulator that has a thermal expansion coefficient of the same order of magnitude as the thermal expansion coefficient of those materials. This is desirable because problems such as cracking, peeling, warping, and distortion caused by stress are less likely to occur.

For example, GaAs (thermal expansion coefficient 6.6x 1010-
For semiconductor lasers that are mainly composed of polyimide (thermal expansion coefficient of about 5 x
1010-5de') is undesirable because the coefficients of thermal expansion of the two are different by one order of magnitude. Therefore, the coefficient of thermal expansion is 4, which is the same as or lower than that of GaAs.
It may be adjusted within the range of X 10-7 to 2 X 10-'deg-'. Especially within the above range.

1 x 10-6 to 9 x 1010-6 de' is preferred.

〔Example〕

Hereinafter, the present invention will be explained in detail by examples with reference to the drawings.

FIGS. 1(a) to (C) are diagrams showing one embodiment of the semiconductor laser array of the present invention, in which (a) is a plan view, and (b) is a plan view taken along line AA' shown in (a). (C) is a cross-sectional view of the BB' portion shown in the plan view (a).

In this laser array, the tops of five striped ridges serve as current injection regions for each element, and ohmic electrodes 7 are formed in the injection regions. It is separated by 11. That is,
This is a semiconductor laser array in which each element has a common layer below the ohmic electrode 7. Note that each semiconductor laser element may be formed independently without having a common part. Further, an extraction electrode 9 is laminated on each ohmic electrode i7 via an organic insulating layer 10, and the electrical contact between the electrode 7 and the electrode 9 is made using the organic insulating layer IO.
This is done by a through hole 12 provided in the. Furthermore, each electrode separation region 11 and each ohmic voltage Vi above it
The gap 7 is also filled with an organic insulating layer IO, which is a feature of the present invention.

Next, an example of a method for manufacturing the semiconductor laser array of the present invention will be described.

First, n with a thermal expansion coefficient of 6.6x lo-6deg-'
n-type GaAs substrate 1 as a buffer layer 2.
1μ of As, 2μ of n-type AjGaAs as cladding layer 3
-, 2 scales of n-type AjO, 4GaO, 6As as the cladding layer, non-doped GaAs as the active layer 4 10
0 person, A j O, 2G a O, 8A S 30 people were repeated four times, and finally Ga A s 100 people were stacked to form an active region with a multi-quantum well structure. Next, 15p of p-type A10.4 Ga0.8 As is used as the cladding layer 5.
The cap layer 8 was formed using GaAs of 0.5 u+ by molecular beam epitaxy.

Subsequently, the cap layer 8 right side and the cladding layer 5 are replaced with the active layer 4.
Five stripe-like ridges were formed by partially etching up to about 0.4 scales. Next, a silicon nitride film 6 is formed on the entire surface on which the striped ridge is formed by plasma CVD, and then only the electrified silicon film 6 at the top of the ridge is etched to have a width of 3 μm.
An injection zone was formed. Note that the same effect can be obtained even if p and n are replaced among the methods for producing the five stripes described above.

Next, a Cr--Au ohmic electrode 8i7 was formed as an upper electrode, and electrode separation regions 11 were formed by etching to form five independent electrodes.

Next, as the interlayer organic insulating film 10, the thermal expansion coefficient is about the same as that of the substrate 1, cladding layer 5, etc. (5x 10-'deg).
-' ) polyimide (product name PIX-L100, manufactured by Hitachi Chemical Co., Ltd.) is applied to the entire surface to a slightly thick layer (approximately 2 to 3 μm), heat treated to imidize (polymerize), and then etch-backed. The surface was flattened.

Furthermore, a thicker photoresist (1,
5 to 2)) was coated on the entire surface. Next, the through hole 12 and the embedded groove for the extraction electrode 10 (interlayer insulation cover)
A resist pattern was formed.

The pattern formation method involves masking the through-hole area and applying a silicon-containing coupling agent (hexamethyldisilazane) to the other areas in order to differentiate the etching grade between the through-hole and the other areas. , made by Chisso Corporation) and heat treated (120°C) to form silylation (Si
(containment)). As a result, the Si-containing coupling agent diffuses to the surface except for the through-hole pattern.
02RIE durability is improved, and a difference occurs in the etching rate between the silylated portion and the unsilylated portion.

Subsequently, reactive ion etching using O2 was performed to open a window for the through hole 12 and to form a groove for embedding the extraction electrode.

Furthermore, with the photoresist remaining, Cr-Au was deposited as an extraction electrode material using a resistance heating method, and the substrate was heated to 90°C with a photoresist stripping solution (trade name: Microposit Remover 140, manufactured by Silapray). Soaked in. As a result, the photoresist was removed and at the same time the deposited layer above it was also removed, forming separate and independent extraction electrodes 9 for each laser element.

Next, the lower surface of the GaAs substrate 1 is wrapped 1
After polishing to a thickness of 00 μs, the n-type ohmic electrode 15
Then, an Au-Ge electrode was deposited.

Subsequently, after heat treatment for diffusion, the resonant surface 13
．． I gave up on 14.

In the semiconductor laser array of the present invention manufactured as described above, the extraction electrodes 9 can be extended sufficiently widely on the array, so that bonding can be easily performed.

Although an example of the method for manufacturing the semiconductor laser array of the present invention has been described above, the manufacturing method is not limited to this example. For example, the number of semiconductor laser elements and the oscillation wavelength may be determined according to the specifications. .

Furthermore, in the above example, when forming through holes and buried grooves, the organic insulating layer IO was partially silylated with hexamethyldisilazane produced in collaboration with silicon to give different etching grades. The method for forming the through holes and buried grooves in the method is not limited to the above method, and other silicon-containing chemicals or aromatic compounds such as chlorobenzene and xylene may be used to give different etching grades.

Further, although the electrode separation region 11 was formed by etching in the above example, it can also be formed by high resistance ion implantation using, for example, a focused ion beam or a focused ion beam.

Furthermore, although the resonant surfaces 13 and 14 in the above example were formed by cleaving, they may be formed by etching one or both surfaces in a wet process or dry process, depending on the convenience of mounting, for example.

Further, the structure of the semiconductor laser in the above example is made of GaAs.
, An-based material or a ridge wave structure was used, but BH
It may be a refractive index waveguide type laser such as a CPS structure, or a gain waveguide type laser such as a stripe electrode type or proton bobbard type laser.

In addition, materials for semiconductor lasers include GaAs, AjGa
In addition to As-based, InP, InGaAs, i, Aj! Ga
InP-based materials can be used, and the present invention is not limited to the type of material.

〔Effect of the invention〕

As explained above, the semiconductor laser array of the present invention has
An organic insulating layer is provided between each electrode for insulation, so even though the array has a fine laser pitch, the reliability of the insulation between each electrode is high, and the mutual contact between each laser element is high. This array allows for precise control of laser characteristics because there is little thermal influence. Furthermore, the formation of the organic insulator is easy.

The semiconductor laser array of the present invention having such useful properties can be widely applied as a light source in various information fields and industrial fields.

[Brief explanation of the drawing]

FIGS. 1(a) to (C) are diagrams showing one embodiment of the semiconductor laser array of the present invention, in which (a) is a plan view, and (b) is a plan view taken along line AA' shown in (a). (C) is a cross-sectional view of the BB' portion shown in the plan view (a).

Claims (1)

[Scope of Claim] A semiconductor laser array having a plurality of semiconductor laser elements arranged in a plane and a plurality of electrodes arranged to enable independent driving of each of the laser elements, comprising: A semiconductor laser array characterized in that an organic insulating layer is used for insulation.