GB2154059A - Light emitting chip and communication apparatus using the same - Google Patents
Light emitting chip and communication apparatus using the same Download PDFInfo
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- GB2154059A GB2154059A GB08501482A GB8501482A GB2154059A GB 2154059 A GB2154059 A GB 2154059A GB 08501482 A GB08501482 A GB 08501482A GB 8501482 A GB8501482 A GB 8501482A GB 2154059 A GB2154059 A GB 2154059A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/20—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate
- H01L33/24—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular shape, e.g. curved or truncated substrate of the light emitting region, e.g. non-planar junction
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/42—Coupling light guides with opto-electronic elements
- G02B6/4201—Packages, e.g. shape, construction, internal or external details
- G02B6/4202—Packages, e.g. shape, construction, internal or external details for coupling an active element with fibres without intermediate optical elements, e.g. fibres with plane ends, fibres with shaped ends, bundles
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/24—Means for obtaining or maintaining the desired pressure within the vessel
- H01J61/26—Means for absorbing or adsorbing gas, e.g. by gettering; Means for preventing blackening of the envelope
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/96—Lamps with light-emitting discharge path and separately-heated incandescent body within a common envelope, e.g. for simulating daylight
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J7/00—Details not provided for in the preceding groups and common to two or more basic types of discharge tubes or lamps
- H01J7/14—Means for obtaining or maintaining the desired pressure within the vessel
- H01J7/18—Means for absorbing or adsorbing gas, e.g. by gettering
- H01J7/186—Getter supports
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01K—ELECTRIC INCANDESCENT LAMPS
- H01K1/00—Details
- H01K1/52—Means for obtaining or maintaining the desired pressure within the vessel
- H01K1/54—Means for absorbing or absorbing gas, or for preventing or removing efflorescence, e.g. by gettering
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
- H01S5/227—Buried mesa structure ; Striped active layer
- H01S5/2275—Buried mesa structure ; Striped active layer mesa created by etching
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0225—Out-coupling of light
- H01S5/02251—Out-coupling of light using optical fibres
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
- H01S5/2201—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure in a specific crystallographic orientation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
- H01S5/2205—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers
- H01S5/2222—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special electric properties
Abstract
A light emitting chip having a buried hetero-structure has a laser region consisting of a buffer layer (2), an active layer (3) and a cladding layer (4) formed on a body (1). Contact layers (8, 9) form a neck (7) in the laser region (2, 3, 4). At least a part of the active layer (3) lies between the neck (7) and the body (1), and in contact with the plane (B) of the contact layers (8, 9) on which no atoms of light impurity elements are found; a better contact is made and leakage is reduced. An improved current optical output characteristic is achieved and the threshold current is reduced. <IMAGE>
Description
SPECIFICATION
Light emitting chip and optical communication apparatus using the same
The present invention relates to a light emitting chip and to an optical communication apparatus using such a light emitting chip.
The words 'light' and 'optical' will be used to refer to electromagnetic radiation of any suitable wavelength and are not confined to the visible region.
Semiconductor lasers have been used as the light emitting source in devices such as audio discs, video discs or in optical communications.
A buried-hetero structure (hereinafter abbreviated to "BH") has been developed as one of the structures of the semiconductor laser chip of the type described above. For example, the magazine "Electronics Materials", published by Industrial Research Association, April, 1979, pages 26-28 describes a GaAs-GaAIAs system BH semiconductor laser, and the same magazine also describes in the April issue, 1983, page 92 InF-lnGaAsP system BH semiconductor laser. A visible light band semiconductor laser (wavelength between 0.7 and 0.9 m) formed by the GaAIAs system has substantially the same BH laser chip structure as that of a long wave band semiconductor laser (wavelength between 1.2 and 1.6 ym) formed by the InP-lnGaAsP system.
Now, a long wave band semiconductor laser will be explained by way of example.
Figure 1 of the accompanying drawings illustrates the structure of the BH type semiconductor laser developed by the inventors of the present application prior to the making of the present invention. A buffer layer 2 consisting of low concentration n-type InP, an active layer 3 (d = 0.15 ym) consisting of undoped
InGaAsP, a clad layer 4 consisting of p-type
InP and a cap layer 5 consisting of p-type
InGaAsP are sequentially formed by a liquid phase epitaxial process on an n-type InP single crystal substrate 1 having a (100) crystal plane on its main surface.The total thickness of these four epitaxial layers is from approximately 3 to 4 ,um. Thereafter, this multilayered grown layer is removed by a standard photolithographic process with an etching solution such as bromoethanol so that the cap layer 5 is left in a striated form having a width of from 5 to 6 ym. This striated part extends in the direction of < 110 > axis of the crystal so that the edge surface of the active layer 3 becomes a (110) cleavage. This improves the light emitting efficiency of the device. In consequence, the crystal exhibits anisotropy with respect to the etching solution described above, and the part extending over the active layer 3, the clad layer 4 and the cap layer 5 has an inverted truncated triangle cross-section, that is, an "inverted mesa" structure.
The side plane forming this inverted mesa structure (hereinafter referred to as the "inverted mesa plane") becomes a (111) crystal plane on which In atoms appear.
The lower part of the inverted mesa structure of the strip portion continues a forward mesa structure described by gentle curves B and C as shown in Figure 1, and the boundary between the inverted mesa structure and the forward mesa structure defines a part of the laser region having the smallest width (hereinafter called a "neck 7" for the sake of description). The portion 6 encircled by a dotted line will be called a "double hetero structure" for the sake of description, and the term "laser region" will be used to refer to the buffer layer 2, active layer 3 and clad layer 4.
In Figure 1 symbol B represents the (111) plane on which P (phosphorus) atoms appear, and symbol C represents the (100) plane or the plane in the proximity of the former. The active layer 3 is formed above this neck portion (see "Electronics Materials", published by Industrial Research Association,
April, 1983, page 92, Figure 7).
After the mesa etching, the part which has been etched and which has become recessed is buried by laminating and a blocking layer 8 covering the side surface of the active layer 3 and consisting of p-type InP, a buried layer 9 consisting of n-type InP and a cap layer 10 consisting of n-type InGaAsP. Zinc (ZN) atoms are diffused into the mesa portion 9 so as to reach the intermediate portion of the clad layer 4, and a p + -type ohmic contact layer 11 is thereby formed. Furthermore, electrodes 12 and 13 are provided at predetermined positions on the mesa portion and on the reverse of the substrate 1, respectively. The substrate 1 is then divided in a predetermined manner into laser chips 14 of several hundred ym square. Also shown in Figure 1 is an insulating film (SiO2 film) 15.
When used as the light source for optical fibre communication, a semiconductor layer chip must have a low operating current, a large optical output which can be sent into the optical fibre, the possibility of modulation up to a high frequency, à small spectral width, and a small change of the optical characteristics with temperature. The BH laser chip has been employed so as to satisfy these requirements.
The inventors of the present invention have made intensive studies in order to develop a laser chip which is operative at a low operating current (low threshold current Itch) and has high performance. These studies will be described briefly.
It was believed that the threshold current (Ith) of the semiconductor laser depended only upon the width and thickness of the active layer. Therefore, the position of the active layer at the mesa-like double hetero junction was regarded merely as a parameter deciding the width of the active layer.
However, in the BH laser chip described above, a problem is encountered in that, since it is difficult to control the position (i.e. height) and width, of the active layer 3 and the width of the neck 7, they tend to deviate from the predetermined values so that the threshold current (Ith) increases while the output drops.
The applicant assumed that the reason was that since the active layer is arranged at the position close to the neck, where the laser region has the smallest width, the width will change drastically if the position of the active layer moves only slightly upward from the neck.
To cope with this problem, the applicant produced the BH laser chip by arranging the centre position of the active layer 3 above the neck 7 so that the change of the width was not significant even if the position of the active layer varied in the vertical direction to some extent.
However, many BH laser chips produced in this manner still exhibited greater threshold current values (Ith) than the rated value In the course of their investigations, the inventors have developed a technique to make the width of the active layer lie in a desired range (e.g. from 1.1 to 1.9 #m) with a high yield, and to locate the centre position of the active layer having a thickness of 0. 15 im within a range extending from a position deviating by 0.5 ym towards the upper side from the neck (hereinafter called the "positive side") to a position deviating by 0.2 ym towards the lower side from the neck (hereinafter called the "negative side").
The threshold current 1th (hereinafter called also "It,"') of the device of Figure 1 exhibits a change such as shown in the diagram of
Figure 2 of the accompanying drawings with the position of the active layer relative to that of the neck. When the active layer is positioned on the positive side (or when the centre position of the active layer 3 is located on the side of the clad layer 6 on the upper side) from the neck position, the threshold current 1th increases drastically. In the diagram, the threshold current (It,) [unit: mA] at room temperature is plotted on the ordinate and the position (L) of the active layer with respect to the neck (the position of the centre portion of the active layer) [unit: ym ] is plotted on the abscissa.The dashed line represents a line based on the theoretical value when the position of the active layer is nothing but a parameter deciding its width. As shown in the diagram, the threshold current value 1th decreases as the active layer is positioned towards the negative side from the neck (that is, the centre position of the active layer 3 is between the neck 7 and the body 1) and 1th attains a minimal value of about 24 mA at the position of - 0.3 ,um, and becomes thereafter gradually higher.With the position (L) of the active layer being in the range of from - 0.6 ym to - 0.7 jum, 1th at that position becomes substantially equal to 1th at L = 0, and the I th value is from 32 mA to 33 mA. When the position (L) of the active layer becomes positive, 11h increases drastically. Figure 4 of the accompanying drawings shows the relationship between the voltage applied to a laser diode and the current flowing through it. In
Figure 4 the dotted line represents theoretical characteristics, but it has been found that the practical characteristics are not in agreement with the theoretical characteristics described above but exhibit those represented by the solid line.
When the position of the active layer is on the positive side with respect to the neck as shown in Figure 3 of the accompanying drawings, this difference between the theoretical characteristics and the practical characteristics is believed to result from the existence of a leakage path 17 in parallel with the laser diode 16.
The difference between the positive and negative positions of the active layer is that both side surfaces of the active layer may be in contact with the inverted mesa plane (A plane) formed by etching the inverted mesa portion or in contact with the forward mesa plane (B plane) formed by etching the forward mesa portion. The forward mesa plane (B plane) close to the neck is the (111) plane on which phosphorus atoms (P atoms) appear, and the inverted mesa plane (A plane) is the (111) plane on which the In atoms appear. It is therefore believed that on the (111) plane (B plane) on which P atoms appear, bonding of the interface between the side surface of the active layer and this plane is high, while on the (111) plane (A plane) on which the In atoms appear, bonding of the interface is low so that the leakage paths may occur.
Two leakage paths are believed to occur.
The first is a path through which surface current flows along the (111) plane (A plane) on which the In atoms appear, from the clad layer 4 to the buffer layer 2. The other is a path which occurs because the height of the junction barrier of the pn junction formed by the block layer 8, which is in contact with the (111) plane (A plane) on which the In atoms appear, and the buffer layer 2, is lower than that of the active layer.
The inventors of the present invention have confirmed that atoms of light elements other than In seem to exist on the X-ray photograph of the (111) plane (A plane) on which In atoms appear. However, it has not been clarified yet whether the lighter atoms are contamination that has been deposited on the interface during etching and has remained unremoved by washing, or foreign matter that has been deposited during epitaxial growth of the blocking layer, buried layer 9 and cap layer 10.
Therefore, the present invention provides a buried heterostructure laser in which at least part of the active layer lies between the neck and the body. Thus, both side surfaces of the active layer 3 come into contact with the B plane which is the stable plane and a device which has a low threshold current may then be achieved. It will be appreciated that although the above discussion relates specifically to an InP-lnGaAsP system chip, the invention may have embodiments in the form of a GaAs-GaAIAs system chip; no limitation is implied.
Furthermore, embodiments of the present invention may allow the provision of an optical communication apparatus ensuring stable and highly reliable optical communication by incorporating therein a light-emitting chip having a low driving current and high stability.
In a light-emitting chip according to the present invention, the side surface of an active layer which emits the laser light from its end surface may be a (111) plane (B plane) having an interface state which is stable and on which phosphorus (P) atoms appear. The width of the active layer is preferably between 1.6 to 2.0 ,um. Therefore, no leakage path occurs because the side surface of the active layer is in contact with the (111) plane having a stable interface side. Therefore, both leakage current and threshold current value can be reduced.
Since the threshold current may be made small, the driving current may also be small, the heat output of the chip is less and laser light emission can be effected in a stable manner. Since the occurrence of the kink in the current-optical output characteristics may be prevented, a laser chip according to the invention, when assembled in an optical communication apparatus. may reduce noise and stabilize optical coupling with an optical fibre, thereby accomplishing optical communication having high reliability.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a sectional view of the BH laser chip which was developed by the applicant prior to this invention and has already been discussed;
Figure 2 is a diagram showing the correlation of the threshold current with the change of the position of the active layer in the BH laser chip of Fig. 1;
Figure 3 is an equivalent circuit diagram at the double hetero junction of the BH laser chip of Fig. 1;
Figure 4 is a diagram showing the V-l characteristics of the BH laser chip of Fig. 1;
Figure 5 is a sectional view of a wafer used for producing a first embodiment of a BH laser chip in accordance with the present invention;;
Figure 6 is a sectional view of the wafer after mesa etching in the production of the first embodiment of BH laser chip in accordance with the present invention;
Figure 7 is a sectional view of the wafer used in the production of the first embodiment of BH laser chip after burying and growing treatment;
Figure 8 is a sectional view of the wafer used in the production of the first embodiment of BH laser chip after an ohmic contact layer has been formed in accordance with the present invention;
Figure 9 is a sectional view of the wafer used in the production of the first embodiment of BH laser chip after electrodes have been formed in accordance with the present invention;
Figure 10 is a sectional view of the first embodiment of BH laser chip according to the present invention;;
Figure 11 is a sectional view of an oscillator for optical communication (light emitting electronic appliance) which incorporates therein an embodiment of BH laser chip of the present invention;
Figure 12 is a sectional view of a second embodiment of BH laser chip when a blocking layer is not in contact with a substrate in the present invention; and
Figure 13 is an enlarged sectional view of principal portions of a third embodiment of the present invention.
Figures 5 to 10 are sectional views of production steps of a BH laser chip in accordance with a first embodiment of the invention. Figure 11 shows an example when the laser chip is assembled into a box-like package, and is a sectional view of an oscillator for optical communication (light emitting electronic appliance).
First of all, the structure of the laser chip will be described step-by-step with reference to the production steps thereof.
Although this embodiment relates to a BH laser chip of a long band InP-lnGaAsP system by way of example, it is to be understood that the present invention can likewise be applied to a BH laser chip of a GaAs-Ga-AIAs system of a visible band. The ratio of each mixed crystal is not described in particular, because it is well known in the art.
The laser chip of this embodiment can be produced in the following manner. First, a wafer (semiconductor thin sheet) 18 shown in
Figure 5 is prepared. The wafer 18 consists of 200 #m (d = 200 lim) single crystal substrate 1 made of n-type InP, having an impurity concentration of 5 x 1018 atomscm-3; and a multi-layered grown layer which is epitaxially grown on the (100) crystal plane of the substrate 1 as its main surface.The multilayered grown layer consists of a buffer layer 2 (d = 1 - 2 item) made of n-type InP, an
active layer 3 made of undoped InGaAsP (d
= 0.15 yam), a clad layer 4 made of p-type
InP (d = 3.5 - 4 ym) and a cap layer 5 made of p-type InGaAsP (d = 0.1 - 0.2 #m), from the lower layer to the upper in the
order named. The active layer 3 has hetero junctions on its upper and lower surfaces to form a double hetero junction, and is 0.15 jum thick.
Next, a plurality of etching masks 19 con
sisting of about 5 to 6 ym wide belt-like SiO2 films or the like are formed in parallel with one another on the main surface of this wafer
18. The semiconductor layers exposed from the masks 19 are etched by an etching solution such as bromoethanol. Etching is made till the surface layer portion of the substrate
be terminated at an intermediate depth of the
buffer layer 2. In this case, a laser chip such as shown in Figure 2 can be obtained. The
resulting chip is different from the laser chip of this embodiment only in that the etching thickness of the buffer layer is different, and the buffer layer of the laser chip shown in
Figure 2 is thicker.
Since the masks 19 are disposed so as to extend in the direction of the < 110 > axis of the crystal, the portions of the double hetero structure remaining below the masks 19 to extend over the cap layer 5 and the clad layer 4 has an inverted mesa cross-section. On the other hand, the buffer layer 2 and the upper layer portion of the substrate 1 have a forward mesa structure which describes a parabola from above to below. The inverted mesa plane becomes the (111) crystal plane (A plane) on which the In atoms appear, and the upper end portion of the forward mesa portion becomes the (111) plane (B plane) on which the
P atoms appear. The most contracted portion of the double hetero structure 6, that is, the neck 7, is formed at the boundary between the forward mesa portion and the inverted mesa portion.In this embodiment, the neck width is prescribed to be from 0.9 to 1.5 ,um, for instance. This means that since the inverted mesa plane becomes the (111) plane of the crystal, it can be formed with high reproducibility by setting in advance the size of each layer and the mask width. The active layer 3 which is 0. 1 5 ,um thick is formed so that the position of the surface coming into contact with the buffer layer 2 (that is, the lower surface) is lower (negative) than the position of the neck 7. The position of the active layer 3 is between 0 and 0.6 ,um (at the center position of the active layer) as can be seen from the diagram of Figure 2, for example.As a result, the laser chip produced by this method has a low threshold current value (I,h) ranging from about 24 to 30 mA, and the maximum width of the active layer 3 is up to 2 ym.
Next, after the masks 19 have been removed from the main surface of the wafer 18, a blocking layer 8 (d = 0.5 ELm) of p-type
InP, a buried layer 9 (d = 3.5 - 4 ,um) of n-type Inp and a cap layer 10 (d = 0.1 - 0.2 ym) of n-type InGaAsp are sequentially formed by liquid phase epitaxial technique in the recessed portion formed by etching, as shown in Figure 7.
Then, a mask 20 is formed on the main surface of the wafer 18 so that the upper surface of the mesa portion 8 is exposed, and
Zn is thereafter diffused. The mask 20 may consist of an insulating film such as a CVD
PSG film (phosphosilicate glass film formed by chemical vapor deposition) or a two-layered structure of this insulating film and a photoresist film used for patterning this insulating film. This Zn diffusion forms a p±type ohmic contact layer 11 in the mesa portion which layer 11 reaches the intermediate depth (0.5
- 0.8 ,um) of the clad layer 4.
Next, the mask 20 is removed as shown in
Figure 9, and an electrode 12 having a lower surface layer consisting of Cr (d = 0.7 ttm) and an upper surface layer consisting of Au (d
= 1 ,um) is formed on the main surface side of the wafer 18. The portion of the substrate 1 of the wafer 18 is ethced. After the substrate 1 becomes about 100 ym thick, Au
GeNi (d = 0.3 ELm), Pd (d = 0.2 lim) and
Au (d = 1.2 ,um) are sequentially evaporated on the reverse of the wafer 18, forming another electrode 13. However, the state of lamination of these electrodes 12 and 13 is not shown in the drawing.
Next, the wafer 18 is divided in the desired manner, and a large number of BH laser chips 14 such as shown in Figure 10 can be produced.
The present invention is not particularly limited to the embodiment described above, but may have a structure such as shown in
Figure 12 or Figure 13.
In Figure 12 the blocking layer 8 is not in contact with the body 1, but instead lies entirely above the buffer layer 2. This embodiment is otherwise similar to that of Figure 10.
In the embodiment of Figure 13 only a part of the active layer 3 is below the neck 7, but since the principal portions of the side surfaces of the active layer are in contact with the B plane [ (111) plane], which is the stable plane, so it is possible to prevent the passage of the leakage current. The embodiment of
Figure 13 may otherwise be similar to the embodiment of Figure 10 or of Figure 12.
A laser chip 14 produced as described above has a light emitting wavelength in the 1.3 ym band, and is incorporated as a light source in an oscillator 21 for optical communication as shown in Figure 11. In the oscillator, the laser chip 14 is fixed to a bed 23 at the centre of the recess of a metallic stem 22 (kovar) via a silicon carbide (SiC) submount 24. A fibre guide 25 made of kovar is inserted through the peripheral wall of the stem 22 and is hermetically fixed to the stem 22 by silver brazing 26. A fibre cable 27 is inserted into this fibre guide 25.The jacket is peeled off from the inner end portion of the fibre cable 27 to form an optical fibre (diameter = 135 !lem) consisting of a core (diameter = 10 ym) and a clad (diameter = 125 ym) in such an arrangement as to oppose the light emitting surface of the laser chip 14 and to take the laser light into the optical fibre 28 efficiently. The tip of the optical fibre 28 is held in place by a fixing member 29 so that its position relative to the light emitting surface of the laser chip 14 does not change.
The optical fibre 28 and the fibre guide 25 are hermetically sealed by silver brazing to prevent moisture from entering the stem 22 through the optical fibre.
A monitor fiber guide 31 made of kovar is fixed to the other side wall of the stem 22, and a monitor optical fiber 32 at its inner end (having a diameter of 1 mm) faces the other laser light emitting surface of the laser chip 14. The monitor fiber guide 31 is fixed to the stem 22 by silver brazing 33 so as to keep the interior of the stem 22 air-tight. The monitor fiber guide 31 and the monitor optical fiber 32 are hermetically fixed by low melting glass (not shown). The recess of the stem 22 is also maintained air-tight by a metallic cap 35.
When a voltage is applied across the oscillator described above and a lead not shown in the drawing, the laser chip 14 emits laser light. The laser light is transferred to a desired position through the optical fiber 28 as the transmission medium. The optical output of the laser light is constantly monitored by the monitor optical fiber 32 so that the optical output becomes constant.
The embodiment of the invention described above provides the following effects.
(1) In the BH laser chip obtained in accordance with the present invention, the position of the active layer is on the negative side from the neck position of the mesa-like double hetero structure portion, and the side surface of the active layer are out of contact with the (111) plane having an interface which is believed to be incomplete and on which the In atoms appear. In addition, the width of the active layer is as small as from 1.8 to 2,us.
For these reasons, the threshold current value (It) becomes as small as from 24 to 30 mA.
(2) Due to the effect described in item (1), transverse mode oscillation becomes stable.
the occurrence of kink in the current-optical output characteristics can be prevented. and the movement of the near field image and the deflection of the remote field image can be prevented.
(3) Since the position of the active layer is below the neck in the laser chip of the present invention, it can be easily identified so that it serves as a guide when discriminating the chips and carrying out intermediate inspection, thus making them easier to produce.
(4) Since 1th becomes smaller in the laser chip of the present invention, the driving current becomes lower and the exothermy of the chip can be restricted to a low level.
Therefore, the temperature characteristics, the optical output and screening yield can be improved .
(5) Since the temperature characteristics can be improved as described in item (3), the service life of the chips can be extended.
(6) The cost of production of the laser chips having excellent characteristics can be reduced due to the effects described in items (1) through (5) described above.
(7) The optical communication apparatus incorporating therein the laser chip of the present invention has a low threshold current value and a small driving current. Therefore, the occurrence of the kink, the movement of a near field image and the deflection of a remote field image can be prevented so that high optical coupling efficiency can be kept at low power and with less noise, and optical communication can be effected with a high level of reliability and stability.
Claims (11)
1. A light emitting chip having a laser region on a body of the first conductivity type, the laser region having a first semiconductor layer of the first conductivity type contacting the body, a second semiconductor layer of the second conductivity type, and an active layer between the first and second semiconductor layers, side surfaces of the laser region being contacted by at least one further semiconductor layer, wherein the laser region has a neck at which it has minimum width and at least a part of the active region is between the neck and the body.
2. A light emitting chip according to claim 1 wherein one further semiconductor layer contacts the side surfaces of the first semiconductor layer, the second semiconductor layer and the active layer.
3. A light emitting chip according to claim 2 wherein the one further semiconductor layer is of the second conductivity type.
4. A light emitting chip according to claim 2 or claim 3, wherein a second further semiconductor layer contacts the one further semiconductor layer and side surfaces of the second semiconductor layer.
5. A light emitting chip according to claim 4, wherein the one further semiconductor layer and the second further semiconductor layer are of opposite conductivity type.
6. A light emitting chip according to any one of the preceding claims wherein the at least one further semiconductor layer contacts the body.
7. A light emitting chip according to any one of the preceding claims, wherein all the active layer is between the neck and the body.
8. A light emitting chip according to any one of the preceding claims wherein the semiconductor layers are made of an indium-phosphorus material.
9. A light emitting chip according to any one of the preceding claims wherein the active layer has a thickness between 0.1 #m and 0.2 jim and a width between 1.6 itm and 2 run
10. A light emitting chip substantially as described herein, with reference to and as illustrated in Figures 5 to 10 or Figure 12 of
Figure 13 of the accompanying drawings.
11. An optical communication apparatus including a light emitting chip according to any one of the preceding claims.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59010008A JPS60154689A (en) | 1984-01-25 | 1984-01-25 | Light emitting element and lighr communication equipment using the same |
| US57622184A | 1984-02-02 | 1984-02-02 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8501482D0 GB8501482D0 (en) | 1985-02-20 |
| GB2154059A true GB2154059A (en) | 1985-08-29 |
| GB2154059B GB2154059B (en) | 1987-10-28 |
Family
ID=26345157
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08501482A Expired GB2154059B (en) | 1984-01-25 | 1985-01-21 | Light emitting chip and communication apparatus using the same |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2154059B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0301826A2 (en) * | 1987-07-28 | 1989-02-01 | Nec Corporation | A semiconductor laser of a refractive index-guided type and a process for fabricating the same |
| CN102544425A (en) * | 2010-12-28 | 2012-07-04 | 株式会社杰士汤浅国际 | Electric storage device |
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| GB1502953A (en) * | 1974-03-04 | 1978-03-08 | Hitachi Ltd | Semiconductor device and a method of fabricating the same |
| EP0007730A1 (en) * | 1978-07-10 | 1980-02-06 | Hitachi, Ltd. | Semiconductor laser device |
| GB2031644A (en) * | 1978-09-20 | 1980-04-23 | Hitachi Ltd | Semiconductor laser device |
| EP0026062A1 (en) * | 1979-09-12 | 1981-04-01 | Xerox Corporation | A heterojunction semiconductor laser |
| EP0033137A2 (en) * | 1980-01-23 | 1981-08-05 | Hitachi, Ltd. | Semiconductor laser device |
| EP0038085A1 (en) * | 1980-04-15 | 1981-10-21 | Nec Corporation | Buried heterostructure laser diode and method for making the same |
| EP0042484A2 (en) * | 1980-06-25 | 1981-12-30 | Northern Telecom Limited | High radiance LED's |
| EP0044571A2 (en) * | 1980-07-23 | 1982-01-27 | Hitachi, Ltd. | Semiconductor laser device |
| EP0069563A1 (en) * | 1981-07-03 | 1983-01-12 | Hitachi, Ltd. | Semiconductor laser device |
| GB2105100A (en) * | 1981-08-24 | 1983-03-16 | Hitachi Ltd | Laser diode |
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1985
- 1985-01-21 GB GB08501482A patent/GB2154059B/en not_active Expired
Patent Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1502953A (en) * | 1974-03-04 | 1978-03-08 | Hitachi Ltd | Semiconductor device and a method of fabricating the same |
| EP0007730A1 (en) * | 1978-07-10 | 1980-02-06 | Hitachi, Ltd. | Semiconductor laser device |
| GB2031644A (en) * | 1978-09-20 | 1980-04-23 | Hitachi Ltd | Semiconductor laser device |
| EP0026062A1 (en) * | 1979-09-12 | 1981-04-01 | Xerox Corporation | A heterojunction semiconductor laser |
| EP0033137A2 (en) * | 1980-01-23 | 1981-08-05 | Hitachi, Ltd. | Semiconductor laser device |
| EP0038085A1 (en) * | 1980-04-15 | 1981-10-21 | Nec Corporation | Buried heterostructure laser diode and method for making the same |
| EP0042484A2 (en) * | 1980-06-25 | 1981-12-30 | Northern Telecom Limited | High radiance LED's |
| EP0044571A2 (en) * | 1980-07-23 | 1982-01-27 | Hitachi, Ltd. | Semiconductor laser device |
| EP0069563A1 (en) * | 1981-07-03 | 1983-01-12 | Hitachi, Ltd. | Semiconductor laser device |
| GB2105100A (en) * | 1981-08-24 | 1983-03-16 | Hitachi Ltd | Laser diode |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0301826A2 (en) * | 1987-07-28 | 1989-02-01 | Nec Corporation | A semiconductor laser of a refractive index-guided type and a process for fabricating the same |
| EP0301826A3 (en) * | 1987-07-28 | 1990-03-21 | Nec Corporation | A semiconductor laser of a refractive index-guided type and a process for fabricating the same |
| CN102544425A (en) * | 2010-12-28 | 2012-07-04 | 株式会社杰士汤浅国际 | Electric storage device |
| CN102544425B (en) * | 2010-12-28 | 2015-09-23 | 株式会社杰士汤浅国际 | Electrical storage device |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8501482D0 (en) | 1985-02-20 |
| GB2154059B (en) | 1987-10-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19990121 |