JPS60128691A - Semiconductor light-emitting device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor light-emitting device having structure, in which the rise of threshold currents is inhibited and differential quantum efficiency and temperature characteristics are improved, by forming a semiconductor layer, forbidden band width thereof is smaller than those of a substrate, a buffer layer and a current inhibiting layer, between the substrate or the buffer layer and the current inhibiting layer while being separated from a striped groove. CONSTITUTION:A layer such as an N type InGaAsP layer 22 is grown on an N type InP substrate 21, and a P type InP current inhibiting layer 23 is grown. A striped groove extending in the <011> direction of a crystal is formed through etching by a hydrochloric acid solution. The InGaAsP layer 22 is etched selectively up to a section exposed to the base of the groove and the lower layer section of the P type InP layer 23 in the vicinity of said section by using a sulfuric acid solution. A base body is thermally treated for approximately thirty min at a temperature of 600 deg.C in a hydrogen atmosphere, and N type InP grown in an air gap section from which the InGaAsP layer 22 is removed and the bottom of the groove. An N type InP clad layer 25, a non-doped InGaAsP active layer 26, a P type InP clad layer 27 and a P type InGaAsP contact layer 28 are grown in succession. A P side electrode 29 and an N side electrode 30 are formed to the base body, and cleavage is executed, thus completing an aimed element.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a semiconductor light emitting device, particularly to improving the differential efficiency and temperature characteristics of a semiconductor light emitting device in which an active region is grown embedded in a stripe groove.

(b) Background of the technology Semiconductor light emitting devices are the most important component in systems that use light as an information signal medium, such as optical communications, and are essential for realizing the required wavelength band or for producing a stable single fundamental zero. Contributing to the advancement of the system are the repeated improvements in basic characteristics such as second-order transverse mode oscillation, single longitudinal mode oscillation, improved linearity of current-optical output characteristics, improved quantum efficiency, and increased output power. .

(C1 Prior Art and Problems Many structures have already been provided for semiconductor light emitting devices, one of which is VSB (V-grOovedSub
Strate Buried double hete
ro-structure) lasers.

Figure 1 is a cross-sectional view showing an example of a VSB laser. In the figure, 1 is an n-type indium phosphorus compound (InP) substrate, 3 is a p-type InP current blocking sound, 4 is a stripe groove, and 5 is a cross-sectional view showing an example of a VSB laser.
is an n-type InP layer grown at the same time as the cladding layer 5.

6 is a non-doped indium-gallium-arsenic-phosphorus compound (InGa, AsP) active layer; 5
a indicates an InGaAsp layer grown at the same time as the active layer 6, 7 indicates a p-type ■Hl) cladding layer, 8 indicates a p-type ■I]GaAsP contact layer, 9 indicates a p-side electrode, and 10 indicates an nlll1l tolerance pole.

In the VS, B laser like this conventional example, the stripe groove 4 has a τ
Since the lt1 surface is the (111)B plane, the cladding layer 5. The double heterojunction structure of the active layer 6 and cladding layer 7 can be easily grown, and the shape and dimensions of the active layer 6 are stable. It is smooth and has the advantages of characteristics such as no diffuse reflection of light from this part and smooth light intensity distribution.

The conventional example of the VSB laser described above has the following problems. That is, if we look at the conductivity type of the semiconductor layer outside the stripe groove of the VSB laser with the above structure, (a)
l 11 Q a A s P contact layer 8 and I
p-type head region consisting of nP cladding layer 7, (b) InP/
(iii) a p-type head region consisting of the i n p current blocking layer 3; It is known that a pHpn junction is formed between both electrodes. This VSB laser is provided with a p-type inP cladding layer 7-) I) denoted by 1g in FIG.
Due to the flow of leakage current in the path of the P current blocking layer 3-・n 壓In1) substrate 1, the p Tagawa structure has a current Ig.
7. Operates as a sirisk that increases the gate current. The T6 current 1a corresponding to the anode 1 specific current is sequentially turned on, increasing the reactive current and causing a decrease in the temperature characteristics of the laser.

Regarding the operation of the thyristor using the p'n I) n41G structure, first, an active region and a double diode junction semiconductor layer are grown on the semiconductor substrate, and then a mesa-shaped layer is left on the striped part, and both sides thereof are etsonized. And fat
Embedment 6 to form a semiconductor layer and grow a semiconductor layer to embed it.
It is already known that in a laser with a p n p 11 structure, the active layer left outside the buried layer has the effect of suppressing the anode current of the p n p 11 structure.

However, in order to obtain the same effect in a laser having a structure in which the active region is grown within the stripe groove, such as the VSB laser, it is necessary to
As shown below, under the pmInPmIn upper layer 3, there is a JnGaASP layer 2 with a smaller manufacturing energy band gap than InP.
If you set up.

The leakage current 1g as described above near the stripe groove
significantly increases, resulting in an increase in threshold current. There is a need for a structure in which the thyristor operation due to the pnl)n structure can be suppressed without such an increase in threshold current.

(dl Purpose of the Invention The present invention aims to provide a structure for a semiconductor light emitting device in which an active region is embedded and grown in a stripe trench, in which the increase in threshold current is suppressed and the differential quantum efficiency and temperature characteristics are improved. purpose.

tel Structure of the Invention The object of the present invention is to provide a first conductivity type semiconductor substrate or a first conductivity type semiconductor substrate.
A second semiconductor layer of a second conductivity type is provided in contact with a semiconductor layer of the second conductivity type, a stripe-shaped groove penetrating the second semiconductor layer is formed, and a third semiconductor layer of the first conductivity type is formed in the groove. a semiconductor layer;
a fourth semiconductor layer that is in contact with the third semiconductor layer and has a smaller forbidden band width than the third semiconductor layer and serves as an active region;
a fifth semiconductor layer of a second conductivity type whose forbidden band width is narrower than that of the fourth semiconductor layer in contact with the semiconductor layer, and a region extending outside the groove of the fifth semiconductor layer; A sixth semiconductor layer of the first conductivity type is interposed between the semiconductor layer and the second semiconductor layer, and has a smaller forbidden band width than the second semiconductor layer, the semiconductor substrate, or the first semiconductor layer. achieved by a semiconductor light emitting device in which the second semiconductor layer is separated from the semiconductor substrate or the first semiconductor layer by the seventh semiconductor layer, except in the vicinity of the groove, that is, the semiconductor of the present invention In each of the light emitting devices, a current blocking layer of the second conductivity type is provided between the semiconductor substrate or buffer layer of the first conductivity type and the sixth semi-integrated layer grown simultaneously with the first cladding layer outside the two-stripe groove. It is similar to the conventional VSB laser in that there is a sixth semiconductor layer on top of the second semiconductor layer, an extended portion of the second layer of the 24th voltage type, and a pnpn structure.

The semiconductor light emitting device of the present invention is characterized in that the seventh semiconductor layer is provided between the semiconductor substrate or the buffer layer and the current blocking layer (where the forbidden band width is smaller than that of the seventh semiconductor layer), spaced apart from the stripe groove. shall be.

Note that the conductive turtle type of this seventh semiconductor layer may be either p or n.

Since the seventh semiconductor layer is sandwiched between the first and second semiconductor layers having a larger forbidden band width, electrons or holes are confined in this seventh semi-integrated layer and the turn-soon of the silice operation is caused. thwarted.

However, if the seventh semiconductor layer is in contact with the striped groove, the distance from the active region to the seventh semi-integrated layer is small, and therefore the distance between the seventh semiconductor layer and the first or second semiconductor layer is small. Since the resistance present up to the pH junction is low, the leakage current passing through this pn junction, that is, the threshold current increases significantly. In order to suppress this increase in threshold current, the seventh semiconductor layer is separated from the stripe trench. A pn junction formed between the seventh semiconductor layer and the first or second semiconductor layer, which preferably has a small forbidden band width, is formed between the first semiconductor layer and the second semiconductor layer. Compared to a pn junction, the ratio Δ■/Δ■ of the current increase ΔI to the voltage increase ΔV in the second cladding layer decreases. It has the effect of suppressing an increase in leakage current, and the effect of suppressing saturation of optical output when the current is increased and deterioration of characteristics when the temperature rises can be obtained.

(f) Embodiments of the Invention The present invention will be specifically described below by way of embodiments with reference to the drawings.

FIG. 3 is a sectional view showing the first embodiment of the present invention. In the figure, 21i is an Ln-type InP substrate, 22 is an InGaASP layer of Ltn-type or pm, 23 is a p-type (nP) current blocking layer, 25 is an n-type InP cladding layer, and 25a is also an n-type InP layer.
P starvation 26 is a non-doped 1nGaA8P active layer, 2
6a is also the same r, zInGaASP layer.

27 is p-type 111P re, 28 is p-type nQaAs
The p-contact layer, 29 is a p-side electrode, and 30 is an n-side electrode.

In this example, 7, for example, impurity concentration 1jt2 x 10is
(m-3) On the n mI n P substrate 21 of about 100 nm, for example, an active layer 26 made of a material having a smaller energy bandgap than InP constituting the substrate and the current blocking layer 23 is formed.
InGaASP with a composition ratio equivalent to
The thickness is 0.2 as an n-type of about 10"(,x-").
The layer 22 shown in FIG. 3 is formed by selectively removing the area near the area where the stripe grooves are to be formed, and further growing the layer 23. It can be manufactured by the same manufacturing method as the conventional example described in . However, InGaABP layer 22
The conductivity type may be p-type, and there is a large degree of freedom in terms of impurity concentration and thickness.

According to the manufacturing method described above, the growth of the semiconductor layer is divided into three steps, but according to the manufacturing method whose step-by-step cross-sectional views are illustrated in FIGS. Same as (possibly twice).

That is, in the second embodiment, for example, an n-type InGaASP layer 22 is grown on an n-type inP substrate 21,
Continuation°? The l-p type InP current blocking layer 23 is grown to, for example, an impurity concentration of 2×10 Ccm and a thickness of about 1.5 (μm). Next, stripe grooves extending in the <011> direction of the crystal are formed by etching with a hydrochloric acid (ltic) solution. The cross-sectional shape of this stripe groove is an inverted trapezoid, and the slope is a (111) B plane. (Figure 4 (
(See a)) Next, using a sulfuric acid (H2SO4) solution, remove only the portion exposed on the bottom of the C2 groove and the vicinity thereof.
■ nGaASP layer 2 up to the lower layer of 23
Select 2 and spend about 22 minutes. (See FIG. 4(b)) Next, the semiconductor substrate is subjected to heat treatment in a hydrogen (H2) atmosphere at a temperature of about 600 Co for about 30 minutes.

Mass transfer due to this heat treatment
rt ) phenomenon, I n GaAsPIt first
n-type InP grows in the void where j 22 has been selectively removed and in the bottom of the groove. This n-type InP region is designated as 24. (See Figure 4 (C1)) After that, by using the conventional technology, the impurity concentration is reduced to 2, for example.
N-type np cladding layer 25 of about XlO (tM)
and the thickness is, for example, 0.15 Cμm] Chengho's non-doped l
The n Ga As P active layer 26 and the p-type Ir1P cladding layer 27 with an impurity concentration of, for example, 5×10 (-+++J), the impurity concentration of, for example, 1×10 [α]
; 1UcJpWInGaAsP contact layer 28 is sequentially grown.

By this conventional technology, 1) the side electrode 29
, the n-side electrode 30 is installed (by force opening, etc., the device of this example is completed. (See FIG. 4(d)). FIG. 5 illustrates the current-optical output characteristics of a conventional VSB laser in which the structure does not include a layer with a narrow forbidden band width, which is a feature of the present invention.

however.

The solid line A represents the present embodiment, and the broken line B represents the conventional example for comparison, and the ambient temperature of 25 ('O) or 50 ('O) is shown in parentheses.

As explained above, in the conventional example, when the applied voltage is increased and the current is increased, the ratio of the reactive current is gradually increased, and the optical output characteristic curve is curved downward. A major factor in this increase in reactive current is the operation of the thyristor of the pnpH structure, but if the ambient temperature rises, this decrease in quantum efficiency will become significant.

According to the present invention, the threshold current increases compared to the conventional example, but when the current is increased, the increase in reactive current is small, the differential quantum efficiency is large, and the optical output characteristic curve becomes almost a straight line, which is better than the conventional example. A significant increase in power output is achieved. This effect is particularly strong when the ambient temperature is still low.

(g) As described in detail, the present invention improves the differential quantum efficiency and temperature characteristics of a semiconductor light emitting device in which an active region is buried and grown in a striped trench.

An increase in light output is achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional example of a V'SB laser. Fig. 2 is a cross-sectional view showing an example of an improvement plan, Fig. 3 is a cross-sectional view showing an embodiment of the present invention, and Fig. 4 (a) to (1) are process steps showing other embodiments of the present invention. The forward sectional view and FIG. 5 are diagrams showing an example of 'current resistance-light output characteristics. In the figure, 21 is an n-type Jnp substrate, 22 is an InQa
ASP layer, 23 is a p-type InP layer, 25 and 25a are n-type InP layers, 26 is an InGaASP active layer, 27 is a p-type I
28 is a p-type Ir1GaASPI layer, 29 is an n-side electrode, and 30 is an n-side electrode. Fig. 1 Fig. 9 Fig. 3 Fig. 2.9 Fig. 4 Fig. 4 (shi) Fig. 5 (katsu [n A]

Claims (1)

Claims: A second semiconductor layer of a 24th voltage type is provided in contact with a semiconductor substrate of a 14th voltage type or a first semiconductor layer f. A striped groove penetrating the second semiconductor layer is formed, and a third semiconductor layer of the first conductivity type is formed in the groove.
a fourth semiconductor layer that is in contact with the semiconductor layer and has a smaller forbidden band width than the third semiconductor layer and serves as an active region; is provided with a fifth semiconductor layer of a 24th conductivity type, and a fifth semiconductor layer of a first conductivity type is provided between a region of the fifth semiconductor layer extending outside the groove and the second semiconductor layer. A sixth semiconductor layer is interposed between the second semiconductor layer and a seventh semiconductor layer whose forbidden band width is smaller than that of the semiconductor substrate or the first semiconductor layer. A semiconductor light emitting device characterized in that a second semiconductor layer is separated from the semiconductor substrate or the first semiconductor layer.