JPS6066893A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To contrive to reduce the threshold value by enabling the reduction of the reactive current flowing through an active layer on both sides of a stripe groove part by a method wherein a p type inversion layer is formed in an n type clad layer. CONSTITUTION:An n type clad layer 12, active layer 13 and a p type clad layer 14 are successively grown on an n type compound semiconductor substrate 11, resulting in the formation of a double hetero junction. Besides, an n type current block layer 15 grown and formed on the clad layer 14 and provided with the stripe groove reaching the clad layer 14 and a p type coat layer 16 grown and formed on the block layer by including the groove are furnished. Then, the part of the clad layer 12 except for the region immediately under the stripe groove and in contact with the active layer is inverted into p type.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor laser technology, and relates to a semiconductor laser device (1) with a low threshold current at tPH and a method for manufacturing the same.

[Technical background of the invention and its problems]

Dinotal Audio Disc (DAD).

2. Description of the Related Art As semiconductor lasers are increasingly being used as optical disk devices for video disks, document files, etc. and as light sources for optical communications, techniques for mass production of semiconductor lasers are becoming necessary. Conventionally, the liquid phase epitaxial growth method (LPE method) using the sliding shade method has been used as a manufacturing technology for HD'A multilayer heterojunction crystals for semiconductor lasers, but the LPE method has limitations in increasing the wafer area. There is. For this reason, crystal growth techniques such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), which have excellent uniformity and control over large areas, are attracting attention.

A semiconductor laser as shown in FIG. 1 is an example of a wave path laser that takes advantage of the characteristics of the MOCVD method. In the figure, 1 is an N-GaAs substrate, 2 is an N-GaAtA3 cladding layer, 3 is a GaAtAa active layer, and 4 is a P-GaAt
As cladding layer, 5 is N GaAs 'it, 'z flow stop layer, 7 and 8 are metal electrodes. In a laser with such a structure, when looking at a cross section perpendicular to the electrode plane, ' current While there is only a simple PN junction in the striped part where the blocking layer is missing, PNPN junctions are formed on both sides of the striped part. A reverse bias will be applied to the PN junction, so that almost no current will flow through the PNPN junction, and current will flow only through the 0-stripe portion.

The laser with the above structure is obtained by first crystal growth from the substrate 1 to the current blocking layer 5 and by etching a part of the current blocking layer 5 into a zero-stripe shape.(7) Covering layer 6 and contact layer It is produced by a two-stage crystal growth process called the second crystal growth to form 7. Here, the second
The growth of the cladding layer 7 at the start of crystal growth in phase () is on the GaAtAs surface whose surface has been exposed to the air.For this reason, growth is difficult using the conventional LPE method. MOC with easy upward growth
, which became possible to manufacture with good controllability for the first time using the VD method.

By the way, the laser with the structure shown in Fig. 1 has a current confinement structure called an internal stripe structure, but its current confinement effect is insufficient compared to a laser with a so-called buried structure (BH laser). It's hard to say. In other words, the threshold current of a typical RH lede is 2
0 CmA) or less, whereas in the +1q laser shown in FIG. 1, the minimum is about 41 CmA).

This difference in threshold current between the two is due to the following reason.

(1) In the BH laser, the active layer in the part where no current is injected is removed, and the active layer left in a stripe shape is uniformly excited. On the other hand, in the Rade shown in FIG. 1, the active layer exists in a planar shape, and the transverse mode is emitted only up to the active layer where the excitation is relatively weak. Therefore, the internal loss of the laser resonator becomes larger than that of the BH radar.

(2) In the case of a BH laser, a high-resistance buried layer or PN
A buried layer of a PN junction is formed, and the structure is such that almost no current flows outside the active region. On the other hand, in the laser shown in Fig. 1, the current narrowed by the striped groove also spreads laterally through the P-shaped rad layer, and the stripe-shaped groove is 0.
flows through the active layer on both sides of the body. Therefore, a reactive current is generated, leading to an increase in the threshold current. [Objective of the Invention] An object of the present invention is to minimize the reactive current flowing outside the striped light emitting region in an internal stripe structure. The object of the present invention is to provide all semiconductor laser devices capable of lowering the threshold voltage.

Another object of the present invention is to provide a semiconductor laser device that can easily realize all of the above semiconductor laser devices! ! Our goal is to provide a method for creating power.

[4 Summary of the Invention] The gist of the present invention is to form a P-type inversion layer in the N-type cladding layer having the structure shown in FIG. 1 to reduce the reactive current flowing in the active layer on both sides of the strino groove. It is in.

That is, the present invention provides an N-type compound semiconductor substrate, a double heterojunction formed by sequentially growing an N-type cladding layer, an active layer, and a P-type cladding layer on this substrate, and a double heterojunction formed on the P-type cladding layer. an N-type current blocking layer formed with a stripe-like groove having a depth reaching the P-type cladding layer;
In the semiconductor laser device, a portion of the N-type cladding layer in contact with the active layer is inverted to P-type, except for a region under the striped groove.

In addition, the present invention, when manufacturing a semiconductor laser device having the above structure, sequentially grows an N-type cladding layer, an active layer, and a P-type cladding layer on an N-type compound semiconductor substrate to form a double heterojunction; An N-type current blocking layer is grown on the P-type cladding layer, and then the current blocking layer is selectively etched to a depth up to the P-type cladding layer to form striped grooves, and then in an As atmosphere at high temperature. By heat treatment, the portion of the N-type cladding layer in contact with the active layer except for the region under the striped groove is inverted to P-type, and then a P-type covering layer is grown on the current blocking layer including the groove portion. This is the method used to form it.

〔Effect of the invention〕

According to the present invention, a striped 0-shaped groove 1ll in which a part of the N-type cladding layer is inverted to P-type (in the regions on both sides, a PN junction is formed in the N-type cladding layer. In the region below the trench, a current barrier is formed inside the active layer or on the side of the cladding layer in contact with the active layer. ? is determined by the bandgap of the semiconductor layer, especially the narrower bandgap of the P-type and N-type semiconductor layers. However, although it also depends on the carrier concentration of the semiconductor layer, cropping depends largely on the size of the potential barrier.On the other hand, the bandgap of the semiconductor layer forming the cladding layer is smaller than that of the active layer. Normally, it is set to be large by about 100 to 200 (meV).For this reason, when creating a PN junction formed in the cladding layer, the potential barrier size is set in the active layer or between the active layer and the cladding layer. It is 100 to 200 [meV] thicker than that of a PN junction formed in .

Therefore, if the same forward voltage is applied to both PN junctions, the density of the current flowing through the PN junction in the cladding layer is 1 compared to that of the PN junction in the active layer or between the active layer and the cladding layer. It becomes smaller by more than an order of magnitude. Therefore, the proportion of current flowing through the PN junctions under the striped grooves becomes extremely large compared to the case where the PN junctions on both sides of the striped grooves are not formed in the N-type cladding layer.

In other words, the current confinement effect is much more effective than in the structure shown in FIG. 1, and the Rede excavation threshold current can be significantly reduced.

Note that in order to sufficiently obtain the above effects, the PN junction formed in the N-type cladding layer needs to be formed optically separated from the active layer. This measure is the diffusion length of electrons, which are minority carriers in the P-type layer, injected from the N-type cladding layer, and the larger the diffusion length, the more the dog-like effect can be obtained. P-type Ga 055At1M5A”
When the carrier concentration in the layer is 1 (118Cz-'),
The diffusion length of the minority gearbox is about 05 [μm] 11! Met.

The FiPN junction is connected to the active layer directly under the striped groove.
A method of forming a PN junction between the cladding layers and forming a PN junction on both sides of the striped groove in the N-type cladding layer at a position with a diffusion length of a minority gearier than the active layer is to form a doped P-type junction in the half-half). The fact that impurities are easily diffused at high temperatures and also easily diffused into the gas phase can be utilized. For example, in the case of Zn doped as a P-type impurity in a Ga 055AtO, 45As layer, 750 [
At a high temperature of [degrees Celsius], several cμm] per hour diffuses through one molten phase, and furthermore, it becomes safer in the gas phase than on the crystal surface. Using this effect, a desired structure can be obtained extremely easily. That is, according to the first growth slope: I) After growing up to the N-type current blocking layer, a part of the N-type current blocking layer is etched away in a stripe shape, and then a high temperature treatment is performed in a -vapor phase.

In this case, since the P-type cladding layer is exposed to the gas phase surface in the region directly under the striped groove, the P-type impurity doped in the P-type cladding layer evaporates, and the P-type impurity in the P-type cladding layer concentration decreases.

Therefore, the P-type impurity in the P-type cladding layer diffuses into the active layer and even into the N-type cladding layer, but since the P-type impurity concentration in the P-type cladding layer decreases, the P-type impurity concentration and the N-type impurity concentration decrease.
By setting the N-type impurity concentration of the N-type cladding layer in an appropriate relationship, it is possible to prevent the N-type cladding layer from inverting to the P-type conduction'1[i-type. On the other hand, since the N-type current blocking layer exists in contact with the P-type cladding layer in the regions on both sides of the striped groove, the diffusion of P-type impurities in the P-type cladding layer is caused by the N-type current blocking layer. It is significantly suppressed compared to the case where it does not exist.

Therefore, the amount of decrease in the P-type impurity concentration in the P-type cladding layer is small. Therefore, the P-type impurity can be sufficiently diffused into the N-type conductor. By making the P-type impurity concentration in the P-type cladding layer a certain amount higher than the N-type impurity concentration in the N-type cladding layer, the side of the N-type cladding layer in contact with the active layer can be inverted into a P-type conductive layer. It becomes possible.

[Embodiment of the Invention] FIG. 2 is a sectional view showing a schematic Nl'J structure of a semiconductor laser according to an embodiment of the invention. 11 in the figure is N-GaA
s substrate, 12 is N-GaO, 5sAtO, 45As
13 is Ga 1185A"0.15A8 active layer 114 is P-Ga (1,55Ato, 45AS cladding layer, 15 is N-GaAs 11i flow 1511 stop layer, 16 is P-GaAs covering layer (contact layer 9. 17
, J8 is a metal 11i pole layer, J9 is a P-type anti-i1'i l
ff1 f are shown respectively.

The laser with the above structure is realized by the steps shown in Figures 3(a) to 3(dJ).As shown in Figure 3 (aJ), an N-GaAs substrate 11 (Si-doped 2 x 1018 cm) with a plane orientation of (100) is used. -3) N with a thickness of 2 [μm] on top
-GaO, 55Ato, 45As cladding layer 12, (S
undoped GaoB5 AtO, 15As active layer-13 with a thickness of 0.1 [μm], P-GaO,s5A"0.45As cladding layer z4 with a thickness of 2 [μm] (Zn-doped 7' An N-GaAs current blocking layer 15 (Se layer 5×10 18 α-3) with a thickness of 4×10 on ) and a thickness of 2 μm was successively grown.
The MOCVD method was used for the second crystal growth, and the growth conditions were: substrate temperature 7 s o [°C:], v/711 = 2
0, Carrier JJ” (H2) flow rate ~10
(4/m1n), the raw stone is trimethyl gallium (TMG)
: (CFI)3Ga) ,)limethylaluminum (TMA: (CH3)3At), aluminum (,A
sn5) r p dopant dinoethyl zinc (DEZ)
:(C2H3)2Zn) rn dopant: Hydrogen selenide (H2Se), growth rate is 0.25 Cμm/m
1n). Although it is not necessarily necessary to use the MO-CVD method for the first crystal growth, the use of the MO-CVD method, which allows crystal growth with good uniformity over a large area, is better than the LPE method when considering mass production. It is advantageous and necessary compared to.

Next, as shown in FIG. 3(b), a photoresist 2 is coated on the current blocking layer 15, and the photoresist 21 is coated with a width [μm].
Form a striped window and use this as a mask to block current 1? The grooves 15 are selectively etched to form striped grooves 22. Next, after removing resist 2 and performing surface cleaning treatment, prior to the second crystal growth,
It was heat-treated at 50 [° C.] for 90 minutes at a high temperature of 11Y1 in an As positive pressure atmosphere.

As a result, the P-type impurity in the P-type cladding layer 14 is diffused into the N-type cladding layer 12, and as shown in FIG. The portion in contact with is inverted to P-type, and a P-type inversion layer 19 is formed. Here, the reason why the p jQ layer 19 is not formed in the region under the striped groove 61 is that the P-type N substance in the P-type cladding layer 14 is diffused into the gas phase under the striped groove. This is to do so. After this, a second crystal growth was performed using the MOCVD method. In other words, Fig. 3 (C
) with a roughness of 2 [μm] on the entire surface to be struck.
(155Az (IA5As covered 1 wheat m 1 6 (Se
Dawg l X J, 018tm-3) and thickness 8 [μ
m] N-GaAs contact layer 17 (Se dodo 1
×1018) were sequentially grown and formed.

From this point on, normal electrical bonding is done by contact layer 1.
A Cu-Ar electrode layer 18 is formed on the substrate 11, and an Au electrode layer 18 is formed on the lower surface of the substrate 11.
A -Ge electrode 19 was deposited to obtain the structure shown in FIG. The sample thus obtained was cleaved to create a resonance chamber length 2.
The characteristics of the device cut into a 50 [μm] Fabry-Perot laser were extremely low, with a threshold current of 30 [mA].

This value is extremely low compared to the structure shown in FIG. 1, and it can be seen that the present invention has a remarkable effect of reducing reactive current.

Note that the present invention is not limited to the embodiments described above. For example, the step of inverting a portion of the N-type cladding layer to P-type is not limited to the embodiment and can be modified as appropriate. As an example, in the first crystal growth stage of the N-type current blocking layer, the N-type impurity concentration does not exceed 6 degrees.
There is a method in which P-type impurities are also doped within lrll. In this case, in the regions on both sides of the striped groove, N
Since the P-type impurity in the type current blocking layer suppresses the diffusion of the P-type impurity from the P-type cladding layer, the diffusion of the impurity from the P-type cladding layer to the N-type cladding layer in the heat treatment process is more effectively achieved. It can be carried out. Furthermore, as another example, there is a method in which the region of the N-type cladding layer in contact with the active layer is sufficiently doped with P-type impurities in advance, and a P-type inversion layer is formed at the time of the first crystal growth. be. In this case, during the heat treatment process prior to the second crystal growth, the P-type impurity passes through the striped grooves 17 and evaporates into the gas phase, so that the degree of P-type impurity under the striped grooves increases. As a result, the galvanic type of the N-type cladding layer doped with P-type impurities is also reversed to the original N-type.

It goes without saying that the same effects as in the above embodiment can be obtained even with the two methods described above.

Further, as the N-type current blocking layer, N-GaAtAs f may be used instead of N-GaAs0, and N-type l
It may be a two-layer structure or a multi-layer structure including x and j.

Furthermore, the double heterojunction structure containing the active layer has a symmetry of 3
The structure is not limited to a layered structure, and may be an asymmetrical structure or a multilayered structure of three or more layers. Further, as the P-type impurity, not only Zn but also any impurity that can be implanted by thermal diffusion at high temperature can of course be applied to the present invention as a reverse process of implantation by diffusion. Further, the constituent material is not limited to GaAtAs, and compound semiconductor materials such as InGaAsP and GaAtInP may be used.

In addition, as a crystal growth method, MB is used instead of MO-CVD.
It is also possible to use the E method. Other modifications may be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a schematic structure of a conventional semiconductor laser, FIG. 2 is a sectional view showing a schematic structure of a semiconductor laser according to an embodiment of the present invention, and FIGS. 3(a) to (d) 1 is a cross-sectional view showing the manufacturing process of the laser according to the above embodiment. 11-N-GaAs substrate, 12-N-cao5
5At045A8 cladding layer, 13 ・=Andoso c
a085At[115””active layer, 14-P-c'
ao, 55AtO, 45A" cladding layer, 15---
N-GaAs current blocking layer, 16-P-GaO,5
5AtO, 45A, 8 covering layers (contact l1Vi),
17, 18... Metal electrode layer, 19... P-type inversion layer,
22...Striped groove. Voice agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Figure 3

Claims (3)

[Claims] (1) In a semiconductor radar device made of a compound semiconductor material and having a double heterojunction structure, an N-type semiconductor substrate and an active layer are grown on the substrate with the active layer sandwiched between an N-type cladding layer and a P-type cladding layer. a double heterojunction, an eclipse-type current blocking layer grown on the P-shaped rad layer and having a striped groove extending to the cladding N''i!, and including the groove. a P-type cladding layer grown on the current blocking layer, and a portion of the N-type cladding layer in contact with the active layer except for a region under the striped groove is inverted to P-type. Features of the semiconductor laser device. (2) In a method for manufacturing a semiconductor laser device made of a compound semiconductor material and having a double heterojunction structure, an N-type cladding layer, an active layer, and a P-type cladding layer are grown one-by-one on an N-type semiconductor substrate. a step of forming a heterojunction, a step of growing an N-type current blocking layer I- on the P4 layer, and then a step of growing an N-type current blocking layer I- on the P4 layer,
A process of selectively etching the grooves leading to the type cladding layer to form striped grooves, and then performing a high temperature heat treatment under an As pressure atmosphere to remove the area under the striped grooves and remove the active part of the N-type cladding layer. P71 for the part that touches the layer! l
and then including the groove portion and said '?'. 15□ A method for manufacturing a semiconductor laser device, which is specialized in that it comprises a step of growing a P-type staged layer on a flow blocking layer. (3) As the step of growing and forming the P-type coating layer, MO
- A method for using a semiconductor laser device KP according to claim φi, characterized in that a CVD method is used.