JPS6018988A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To enable to oscillate at a lower threshold value and a higher efficiency and to realize a large beam output oscillation by a method wherein each stripe-shaped excited region is independently provided at plural stripe regions, wherein all of the boundary surfaces between mutually adjoining stripe regions become a total reflection angle to laser beams, and a current injection mechanism is provided at the excited regions. CONSTITUTION:A boundary surface between stripe regions 31 and 32 and a boundary surface between stripe regions 32 and 33 all become a total reflection angle to laser beams. An impurity compensation is performed in an active layer of the region 32 with impurities having a reverse conductivity to that of the active layer and a first stripe- shaped excited region is formed in the longitudinal direction of the resonator, while an impurity compensation is performed in an active layer of the stripe region 33 with impurities and a plural number of second stripe-shaped excited regions, which are mutually parallel, are formed in the longitudinal direction of the resonator. These excited regions are adjacent to P-N junction faces, which are grown between the active layers at both ends of a semiconductor laser and the excited regions; and P-N junction faces, which are formed on the boundary surfaces between the guide layers and the excited regions, electrons are flowed in form these P-N junction faces and a gain distribution is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser, and more particularly to a source output semiconductor laser.

Recently, visible light semiconductor lasers using crystalline materials such as AlGaAs/GaAs are capable of continuous oscillation at room temperature with low threshold and high efficiency, making them ideal as sources for original digital audio disks (DAD). Now, devices using this visible light semiconductor laser are being put into practical use.

Demand for this visible conductor laser is increasing as a light source for use in printers, etc.
In order to meet this requirement, efforts are underway to develop a semiconductor laser that can withstand fire source output oscillations. Further, for this aJ view semiconductor laser, it is desirable to increase the coupling efficiency with the optical system, and a V-thesis is required in which the horizontal and vertical deviations of the active layer are desirable.

Among such semiconductor V-za, Tsukada published an article in the American magazine “Journal of Applied Physiology”.
BH (Buried Heterostructure
e) The v-za is ah, but this HH laser has an activeness of 1mf.
f1 Kuhnod + 117 C and υ〃Ivy pn combination has a structure τ that can be effectively used as a carrier only for active 1-same, and the horizontal and vertical spread of the active layer is equal. The light source has a nearly circular shape, and the laser oscillates with low threshold current. However, the spot size of Zoei's BHv-The is 2~
Since it is extremely small, about 3 μm in size, it is capable of room temperature continuous @ oscillation (CW).
) Optical output is 2 to 3 mW, pulse operation (100 ns width) Optical output has an operating limit of about 10 mW, and if more optical output is emitted, the reflective surface will be easily destroyed. This phenomenon is known as carbon damage, and the limiting power density of CW operation is around 1 MW/d. On the other hand, as a method to prevent optical damage and obtain fire source power, a structure BOG (Buried
Japanese Journal
of Applied Physics''.

It is reported in Volume 19, pages L591-L594.

The structure of this laser is such that the active layer and the guide layer are buried in a cladding layer, and a part of the original active layer is allowed to seep into the adjacent guide J→, thereby increasing the level of optical damage. Although this configuration depends on the original amount seeping into the guide layer, its maximum optical output was limited to around 10 mW.

In addition, impurity compensation is performed by diffusing the opposite type of impurity to the active layer in the central portion of the D H structure resonator having a highly concentrated active layer, which is separated from the longitudinal radiation plane by more than the carrier diffusion length. Hayashi et al. have proposed a semiconductor laser that has an excitation region with an effectively reduced bandgap and a window structure with an effectively wide bandgap near both emission surfaces, making it possible to oscillate the source output. 53-56781 (referred to as 'subservient order'). In the semiconductor laser of this earlier application, a DH structure in which the active layer is sandwiched between two cladding layers 1 and 2 is processed into a mesa shape, and a third cladding 11 is formed around the active layer.
The structure is such that the pn junction surface formed by burying the active layer and then diffusing impurities is within the third cladding layer of the buried layer or within the second cladding layer between the active layer and the substrate. . In this structure, when a large current is injected to perform the dog light output 1a, the current flows exceeding the pn junction breakdown voltage of each cladding layer, but all of this current becomes a reactive current, so it is part of the injected current. The ratio that effectively contributes to oscillation decreases, the external differential quantum efficiency deteriorates, and a phenomenon occurs in which the optical output is quickly saturated. Therefore, it is conceivable to use the II8 edge layer as the buried layer, but it is extremely difficult to do so using ordinary liquid crystal technology, and it is unlikely to be realized.

Furthermore, in this structure, unless the width of the mesa-shaped active layer region is narrowed, spatial hole burning will occur in the carrier distribution as well as source output oscillation, easily allowing negative mode oscillation. However, when the width of the active C1 region is narrowed, the spot size becomes narrower, the oscillation source output decreases, and the source output oscillation becomes difficult. In addition, with this structure, it is possible to shoot with a certain degree of fire source density cw, but 5 normal A I Ga A
This only increased the level of damage to the reflective surface by several times when the S/core aAs semiconductor laser was subjected to CW oscillation with source power density.

Furthermore, when using a semiconductor laser as the original writing light source, it is necessary to perform iPCM operation using the semiconductor laser.
In order to perform PCM operation on a conventional semiconductor laser, a direct modulation method is used in which pulse driving is performed while a constant current near a threshold current is flowing to cause source output oscillation.

However, this method tends to require setting a bias current for each element due to variations in threshold current in each element, complicates the driving device, and is difficult to integrate. In this case as well, it is necessary to have a semiconductor laser that has excellent dynamic characteristics, which has a fundamental transverse mode emission over a wide range of current operation, and suppresses relaxation oscillations, as well as excavating the source output.

Furthermore, when using a semiconductor laser as a light source, it is necessary to overlook the single-axis mode.

To achieve this purpose, H, C, Ca5ey, etc. published the magazine “
Applied Physics Letters”
As stated in Vol. 27, p. 142 (1975), di
distributed-feedback (D F B
) v-the has been proposed and developed. This is intended to periodically provide irregularities in the original traveling region and to cause oscillation in a single-axis mode determined by the original reflection by the irregularities. To make this DFB laser,
It is necessary to form irregularities that are the same as the oscillation wavelength in the length direction of the resonator, which requires large-scale equipment and requires a complex process with poor reproducibility. In addition, in DFBV-Z, oscillation occurs with the original interference between the unevenness, so not only does the threshold current generally become high, but also the dislocation near the interface that occurs when the unevenness is buried and grown.
Therefore, it has drawbacks such as severe deterioration, and there are various problems in putting it into practical use.

On the other hand, when two laser beams with similar wavelengths are coupled, only the same emission wavelengths of the semiconductor lasers compete with each other, resulting in a monotonous mode, as reported by Lang and Kobayashi in the American magazine “IEgE The Jo.”
Urnal of Quantum Elect-ro
nics'' magazine, QE-11, page 515 (1'975).As a method of obtaining single-mode oscillation from a single semiconductor laser by fully utilizing this effect, it is usually Attempts have been made to perform compres- sion using an oscillation source guide layer.

However, with this method, complete original coupling is not possible, single-axis mode oscillation is uncertain, and there is a risk of carrier leakage into the guide layer, which increases the threshold current. It had

The purpose of the present invention is to eliminate these drawbacks, to not only oscillate with high efficiency at a low drive value, but also to be able to generate high-speed C output through fundamental transverse mode oscillation and single-axis mode oscillation.
It is an object of the present invention to provide a semiconductor V-zer which suppresses relaxation oscillations, exhibits RC and FC dynamic characteristics, can change h1 at high speed, can be manufactured with relative ease, and has excellent reproducibility and reliability.

The semiconductor laser of the present invention has an impurity-doped active layer and a guide layer adjacent to the active layer made of a material having the same conductivity as the active layer and a lower refractive index than the active layer 111 on the semiconductor substrate. This guide layer has the same conductivity as the active layer and is also sandwiched between first and second cladding layers made of a material with a small refractive index. A first stripe-like region having a narrow width, a second stripe-like region having a wider width than this region, and a third stripe-like region having a width even wider than this region are formed in order from the vicinity of one reflective surface in the direction. , the interface between the first and second striped regions and the second and third striped regions.
A stripe-like structure whose interface with the stripe-like region is at a total reflection angle with respect to the laser source, and a third cladding layer embedded on the substrate on both sides of this stripe-like structure A first stripe-like excitation region is formed in the active layer of the second stripe-like region in the direction along the length of the resonator by impurity compensation with an impurity having a conductivity opposite to that of the active layer. , a plurality of second stripe-like excitation regions formed in the active layer of the third stripe-like region in parallel with each other in the longitudinal direction of the resonator by impurity compensation with the impurity; The present invention is characterized in that each of the second excitation regions has a current injection 1N groove independently provided therein.

The present BljJ will be explained in detail using page 11 below.

Figure 1 shows implementation 1 of the present invention! ' Perspective view of 211. 31'', Figures 4 and 5 are A-A' and B-B of Figure 1.
'.

CC' sectional view and top view, Figure 846, Figure 7, Figure 8
The figure shows a side view, a perspective view, and a plan view of this embodiment 1j in the middle of manufacturing.
As shown in the figure, n-type GaA with (100) plane as the plane
lcn type AIo on s substrate lo, +20ao6sAs first
The cladding layer 11 has a thickness of 1.5 μm and an n-type concentration n””I
AI of XI o”Cm-3 0.2 sGa o, r
sAs guy Tono 112e0.5μm, n type concentration n
= 3 X 10” cm-3 of AI O, 1sGa
o, e 5 active layer 13 0.08Jim, n-type AI0
．． 4GaO, 6As second cladding layer 14tl-1,0μ
m grow. In this case, the high concentration n-type AlGaAs layer is 5nTe.

Alternatively, it can be formed by doping with an impurity such as Te.

Next, the entire surface is coated with a 5i02 film 15, and then photoresist method and etching arrow are used to coat the resonator in the longitudinal direction (0
11) In the vicinity of the reflective surface on one side, a width of 3 μm and a length of 1
0 μm first striped region 31. This is followed by a second striped region 32 with a width of 8 μm and a length of 200 μm.
．． Subsequently, etching is performed until the S io 2 film 15 is left in each of the third stripe-like regions 33 having a width of 20 μm and a length of 100 μm until reaching the in-type GaAs substrate 10 in the pond region.

(Broom diagram 7). At this time, the centers of each striped region are made to coincide in the length direction of the resonator, and the boundaries between the first striped region 31 near the reflecting surface and the second striped region 32 adjacent thereto, and the second striped region At the boundary between the region 32 and the adjacent striped region 33, the angle θ (Fig. 8) that each slope makes with the longitudinal direction of the resonator is (
−10) is set so that the critical angle and shi are also large. That is, the critical angle ψ is expressed by the following equation, where nl is the refractive index of the buried layer and n2 is the refractive index of the guide layer or active layer.

nl 5in ψ=- 2 In this example, the angle θ<14
It is desirable to do so at a certain time. In this way, among the sources that emit light from the first and second excitation regions and propagate in the cavity length direction within the active layer and the guide layer, those that hit the slope will
It is totally reflected by this slope and travels within a narrow stripe-shaped area near the plane of incidence.

Next, while leaving the 5iOz film 15, a striped double heterojunction (DH) structure made of a material with a lower refractive index than the guides 1→12 and a p-type film with different impurity types were added.
-Form-AI O,3sGa o,s sAs embedded/i
! (Third cladding layer) Filled with 16 layers. At this time 5iOz
Since no crystal is grown on the film 15, only both sides of the striped DH junction structure can be filled. This embed i1
It is preferable that 6 be of the p-type, which has a high specific resistance. next,
Remove the 5iOz film 15.5i0211〦1
A window 34 with a width of 3 μm and a length of 180 μm is opened in the center of the second striped region 32, and a window 34 with a width of 8 μm and a width of 3 μm and a length of 80 μm in the resonator length direction is formed in the third striped region 33. Two windows 35 and 36fc are opened in parallel, and zinc at a concentration of s x i ot8ctY3 is diffused into the active layer by a low concentration diffusion method such as an embedding method or a two-zone method (zinc diffusion region 18).

At this time, the active layer 13 becomes p-type with impurity compensation, but on the other hand, the n-type concentration of the guide layer 12 adjacent to the active layer 13 is higher than the zinc diffusion concentration, so there is no need to control the depth of zinc diffusion. A pn junction is formed at the boundary between the active layer 13 and the guide layer 12. Next, p-type ohmic contacts 19 and 20 are formed independently on the diffusion light surfaces of the zinc-diffused regions in the first and second striped regions, while an n-type ohmic contact 21 is formed on the substrate 10 side. The semiconductor laser of the present invention can be obtained by forming a current injection mechanism independently in each p-type ohmic contact (19, 20). In this embodiment, as shown in FIG. 4, a pulsed laser cutting edge can be obtained by supplying all pulse signals between the pulse drive source 3o and the geogeometric contacts 19 and 21. In addition, ohmic contact 20
A resistor 29 is connected between the angles 210 and 210 for stable operation.

In the structure of the present invention, zinc is deeply diffused into the n-type active layer in the second striped region 32 and the third striped region 33, and the p shadow region (3
4 to 36) become the first to third excitation regions by current injection. In this structure, the excitation region formed in the second and third striped regions is formed at the pn junction surface between the excitation region and the active layer at both ends of the excitation region and at the interface between the guide layer and the active layer. Carriers (electrons) are injected from these pn junction surfaces adjacent to the pn junction surfaces, forming a gain distribution. In particular, in the structure of the present invention, unlike the previous application, carriers are injected from the pn junction plane on three sides to form a gain distribution, resulting in a flat and nearly rectangular gain distribution, which increases the gain necessary for fundamental transverse mode oscillation. This enables low-threshold laser oscillation.

Furthermore, the effective bandgap of the active region formed by impurity compensation by zinc diffusion is reduced due to the pantothiyl, but the active layer in the non-excited region becomes an n-shaded region with a high f% degree. Therefore, due to the Burstein shift, the Fermi level enters the congregation band and the effective band gap is widened. According to the experimental results of the inventor, in this example, the bandgap of the excitation region is reduced by 50 me'V compared to the n-type active layer of the non-excitation region.

Therefore, the laser beam emitted in the excitation region propagates within the n-type active layer with almost no absorption. In particular, in the structure of this embodiment, since the boundary surface between the two-stripe region and the third stripe-like region forms a total reflection angle with respect to the laser source advancing toward the resonator. Of the light emitted from the excitation region within the three-stripe region, those that are incident on this interface are reflected and enter the second stripe-like region without loss. In addition, the laser source re-excited in the excitation region within the second striped region travels in the cavity length direction, but the boundary between the first striped region and the second striped region near the reflective surface also resonates. Since it is at a total reflection angle with respect to the laser source traveling in the longitudinal direction of the device, the laser source enters the first stripe-shaped region without loss, and the narrow first stripe-shaped region formed near the reflecting surface. propagates without being absorbed.

Furthermore, this striped region is not just sandwiched between cladding layers in the vertical direction of the active layer, but also in the horizontal and lateral directions of the active layer, both ends of which are sandwiched between buried layers (third cladding layer). A heavy optical wave path is formed with respect to the beam. Therefore, the laser source travels the entire length of this optical waveguide, which is nearly transparent to the laser source, without leaking. Furthermore, the source reflected by the reflecting surface passes through this source waveguide again and enters the wide second waveguide. The light returns to the third striped region and is re-excited in the excitation region of each region, contributing to oscillation without loss.

By making the vicinity of the sub-reflecting surface transparent to the laser source in this way, the level of optical loss that occurs can be raised all the way, and oscillation from the source can be performed. In other words, in a normal semiconductor laser, the end face of the active layer, which becomes the excitation region, is exposed as a reflective surface due to carrier injection, and surface recombination occurs there, forming a depletion layer and creating a state with a small band gap. When the source power is increased, the source is absorbed due to this reduced bandgap, causing local heat generation and rising to near the melting point, causing optical damage.

On the other hand, in the structure of the present invention, the laser source has a band gap of 5QmeV in the laser traveling region near the sub-reflection surface.
Since the light is generated from the reduced area, the original absorption near the reflecting surface is small and the level of optical damage is significantly increased.

In the structure of the present invention, the t light emitted from the excitation region of the nif in the striped region of ε53 enters the striped region of Ki2 without leaking, but this incident light is The property of concentrating light on a region causes complete coupling in the excitation region. As a result, of the oscillation wavelengths from the two excitation regions, those whose oscillation wavelengths match are strengthened and become the oscillation axis mode.

Normally, the oscillation axis modes of the two excitation regions do not necessarily match, but as a result, the oscillation modes become almost one.
Axis mode oscillation can be achieved.

Further, in the structure of the present invention, the excitation regions in the second and third striped regions are each independently provided with current injector grooves. A constant current is injected into the excitation region within this third striped region to bring it into an excited state,
When no current is injected into the excitation region in the second striped region and the excitation region is kept in a non-excited state, there is an absorption loss 'f! of about 150 Crn-1 for the propagating light. : Since it has,
The propagating source is absorbed and laser oscillation is blocked. On the other hand, when a current is injected into the excitation region within the second striped region to convert it into an excited state, the propagated source is re-excited and the laser oscillation is immediately started. Therefore, a constant full current is always injected into the excitation region within the three striped regions, and the excitation region within the second striped region is easily PCized by repeating current injection on and off.
M operation can be performed, and by controlling the amount of current injected, it is possible to obtain an oscillator with an arbitrary large optical output.

Furthermore, the structure of the present invention has the following advantages because it has a guide layer adjacent to the active layer, which is different from the above-described order. Firstly, the optical loss novel can be completely improved. That is, during laser oscillation, a part of the source seeps out from the active layer to the adjacent guide layer and oscillates, but the leaked source passes through the guide layer 1c, which has a wide bandgap relative to the oscillation wavelength, and therefore suffers no absorption loss. Passes through without incident. By the way, in the active layer, the band gap is reduced in the excitation region formed by deeply diffusing zinc and compensating for impurities.
When the element emitted in this excitation region travels through the highly concentrated n-type active layer, it is absorbed by the element, albeit slightly, and the absorption coefficient was found to be approximately 3 Q Cm' according to experiments. . In this case, when a large current is fully injected without the guide layer gold, the optical output damage is normal for AlGaAs and /GaAs.
This occurs due to the optical output being 5 to 6 times smaller than that of a semi-conductor laser, but if the amount of the element in the active layer is reduced by allowing the element to seep into the guide layer as in the structure of the present invention, optical damage can be reduced. The light output level produced can be increased, making it possible to produce dog light output.

In addition, in the structure of the present invention, the source traveling within the guide layer is also the third one.
Total reflection occurs at the striped region, the interface between the band and the second striped region, and the interface between the second striped region and the first striped region, and within the first striped region adjacent to these reflective surfaces. is incident without loss. In this region, both the guide layer and the guide layer have a low refractive index.
Since the waveguide is entirely embedded in the cladding layer, the waveguide can travel within the guide layer without leaking and can oscillate without loss.

Furthermore, in general semiconductor lasers, the vertical spread angle of the active layer is 40 degrees to 50 degrees or more, and the active layer horizontal spread angle θI is around 10 degrees to 15 degrees, so the spot Although the size is flat, the structure of the present invention can narrow the vertical spread angle θ□ of the active layer to 25 to 30 degrees by seeping into the original guide 1. Since the surface is sandwiched between the buried layer (and therefore the active layer in the horizontal and lateral directions), the active horizontal and lateral spread angle θ9 is 15 degrees to 20 degrees.
Since it is around 100 degrees, it is possible to obtain a nearly equicentric light source.

The structure of the present invention differs from the previous structure in that an excitation region is formed in a wide striped region of the central fan by compensating for impurities. By the way, semiconductor crystals such as GaAs have different refractive indexes depending on the type of n-type and p-type impurities and the impurity concentration. The refractive index of the excitation region was increasing in the direction. In this way, the refractive index difference is sufficiently smaller than the value formed by the heterojunction of a normal Bll laser, large enough to enable transverse mode control, and the pn junction at the boundary between the guide layer and the active layer. Since carriers are mainly injected from , a nearly rectangular carrier distribution is maintained in lma. For this reason, if the width of the stripe near both incident surfaces, that is, the width of the optical waveguide, is made as wide as in this example, spatial hole burning will occur in the carrier distribution. This suppresses the increase in gain required for this, and allows stable fundamental transverse mode detection to be maintained even during large optical output oscillation.

Further, the structure of the present invention is as follows. In the second cladding layer of the third striped region, a pn junction is also formed between this second cladding layer and the region in which zinc is diffused. The rate at which carriers leak from this layer due to current injection is small, and making the second cladding layer thinner reduces thermal resistance, so it is effective for producing large optical output.

As explained above, in the semiconductor laser according to the present invention, compared to a normal semiconductor laser in which the excitation region is directly exposed to the reflective surface, chemical reactions with the outside are less likely to occur, and deterioration due to optical reactions on the reflective surface is prevented. Furthermore, it can be manufactured in the same manufacturing process as a normal buried heterojunction (BH) laser, it can be easily driven by high-speed PCM, and it can realize single-axis mode excavation.

Although this example describes the AI GaAs/GaAs double heterojunction crystal material, other crystal materials such as InGaAsP/InGaP, InGaP/
AlIn1'.

InGaAsP/InP, AlGaAs8b/(JaA
It can also be applied to many crystalline materials such as sSb.

[Brief explanation of the drawing]

Figure 1 is a perspective view of an embodiment of the present invention, Figures 2, 3, and 4.
The figure is each cross-sectional view of A-λ, B-B', and CC' in Fig. 1,
FIG. 5 is a top view of FIG. 1, FIG. 6 is a cross-sectional view of a double heterojunction crystal grown in the process of manufacturing this example, and FIG. 7 is a top view of the double heterojunction crystal grown in the process of manufacturing this example. Figure 8 is a perspective view when both sides of the bonded crystal are etched off leaving the entire striped region. In the figure, 10... - n-type GaAs substrate, 11... -...n
Type Alo, azGa O, 6sAs first cladding layer, 1
2 ・=・n-type AI0.25Gao, tSAS guide layer, l 3 ・---n-type Al o, t sQa O
, 85AS active layer, 14-- n-type Al o, 4 Gao
, sAs WJ2: 9 layer) layer, 15...
・5i02 film, 16...p-type AI0.35G
ao, 5sAs jili inclusion layer, 17-・-・-8r
OzfJi,is...Zinc diffusion region, 19
・・・・P type ohmic contact, 20・・・・
...p-type ohmic contact, 21...n-type ohmic contact, 29...resistance, 30.
...Hals [V.4.31, 32. 33...
...Stripe area% 34,35.36...
...It's a window. Enemy 3 Figure 4 - Figure left

Claims (1)

[Claims] A semiconductor substrate is provided with an impurity-doped active layer and a guide layer adjacent to the active layer made of a material having the same conductivity as the active layer and a lower refractive index than the active layer. A double heterojunction semiconductor multilayer structure sandwiched between first and second o-clad layers made of a material with the same 6TIE properties as the active layer and a refractive index lower than that of the guide layer is formed on one side in the longitudinal direction of the resonator. A first stripe-like region having a narrow width, a second stripe-like region having a wider width than this region, and a third stripe-like region having a width even wider than this region are formed in order from the vicinity of the reflecting surface, and A striped structure in which the interface between the first and second striped regions and the interface between the second and third striped regions are at total reflection angles with respect to the laser source, and this striped structure. and a third cladding layer embedded on the substrate on both sides of the substrate, and impurity compensation is performed in the active layer of the @2 striped region with an impurity having a conductivity opposite to that of the active layer to achieve the resonance. a first stripe-shaped excitation region formed in the direction of the length of the vessel; a plurality of second stripe-like excitation regions formed in the active layer of the third stripe-like region in parallel with each other in the longitudinal direction of the resonator by impurity compensation with the impurity; 2. A semiconductor laser characterized by having a current injection mechanism independently provided in each excitation region.