JPS59112671A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a laser which operates in high efficiency and up to high temperature in a striped semiconductor laser by forming a buried region which hardly becomes ON without forming a channel, thereby extremely reducing the leakage current. CONSTITUTION:A buried region such as an active layer 6 is formed on an N type InP substrate 1, and when the region is surrounded by a semiconductor layer, an N type InGaAsP layer 8 which is the same as or smaller in a forbidden band width than the layer 6 is grown on the substrate 1. Then, an N type InP layer 1a, an undoped InGaAsP active layer 6 and a P type InP layer 7 are laminated at the center on the surface of the layer 8, P type and N type layers 2, 3 for forming a reverse bias junction for blocking a current are laminated and grown while disposing the exposed side surface on the layer 8. Thereafter, a P type InP layer 4 and an InGaAsP cap layer 5 are laminated and grown on the entire surface including the surface of the exposed layer 7, and a P type region 9 which is intruded into the layer 4 corresponding to the layer 6 is diffused and formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in striped semiconductor lasers, and particularly to striped semiconductor lasers that have low leakage current and operate with high efficiency.

Buried type (BH) semiconductor lasers are important as light sources for high-quality optical fiber communications because they have a low threshold and operate in a fundamental mode.

FIG. 1 shows an example of a conventional BH laser using an InGaAsP crystal. In the figure, 1 is an n-type InP substrate, 2 is a p-type InP substrate, and 2 is a p-type InP substrate.
type InP layer, 3 is n-type InP layer, 4 is p-type InP layer, 5
is n-type or p-type InGaAsP camp layer, 6 is n
1 nGaAsP active layer; 7 is a p-type InP layer forming an INN junction with active layer 6; 9 is a Zn diffusion region for guiding current to the stripe region; to and 11 are electrodes.

Current is supplied to the electrode IO through the ■ pole and the electrode 11 through the ○ pole. Further, the region including the active layer 6 is called a stripe region I3, and the other region is called a buried region A. In the buried region A other than the strife region B, a structure is adopted that includes layers 1, 2.3 and 1-channel npnp type reverse bias junction (thyristor structure) in order to target the current. There is. However, in an embedded structure composed of a pass-through homozygote, the leakage current shown by the solid line 20 in the figure easily turns on the thyristor in the embedded region A, and a large leakage current flows as shown by the double arrow 30. I did it.
There was a drawback.

Therefore, as an example to improve this problem, as shown in FIG. 2, a DC-P BH (double chame
l planar buried heterostr
ucture) L/-The ga Electronics
It was published in Letters magazine, volume 18, page 953, in 1982. In DC-P BH laser (arrow 2
Even if there is a leakage current of 0, the embedded region A,
flows into the InGaAs p layer 6a, which has a small forbidden band width, and the presence of this InGaAsP layer 6a increases the main voltage of the thyristor in the buried region A1.
OJ is capable of suppressing the leakage current flowing outside the stripe region B to an extremely low level, and as a result, high efficiency and high temperature operation are reported. However, DC-
In a PBH laser, a channel called a buried region A2 must be provided, and when the channel is turned on, a large leakage current flows. Inset area A1
．． A2 also becomes an obstacle in terms of effective utilization of the wafer surface4.
Think about the drawback of being 0.

In view of the above-mentioned drawbacks, the present invention provides a striped semiconductor laser in which a buried region is formed so that it is difficult to turn on without providing a Tetonel.

The present invention will now be described in detail using the drawings.

An example using the InGaAsP thread crystal of the present invention is shown in FIG. 1ban type InP substrate (or n type InP layer),
2 and 3 are p-type and n-type InP layers, respectively, forming reverse bias junctions for blocking current; 4 are p-type InP layers; 5
is an InGaAsP cap layer, 1a is an n-type InP layer, 6
7 is an undoped InGaAsP active layer, 7 is a p-type InP layer, 9 is a Zn diffusion region, and 11 is an electrode. The feature of the present invention is that the p-type InP layer 2, the n-type InP layer 1a and the n-type I
This is because an n-type 1nGaASP layer 8 having a forbidden band width comparable to or smaller than that of the active layer is provided between the nP substrate 1 and the nP substrate 1. That is, the n-type InGaAsP layer 8 does not have any effect on the current in the stripe region, or the n-type InGaAsP layer 8 and the p-type InP layer 8 do not affect the current in the buried region.
Due to the difference in the forbidden band width of the layer 2, the electron flow flowing through the interface can be made significantly smaller than the hole flow, so that the thyristor is difficult to turn on, and the current flowing through the buried region can be made extremely small.

This can be explained as follows. That is, FIG. 4 shows an energy band structure diagram when the layered structure as shown in FIG. 3 is formed, with the horizontal axis representing the energy level and the vertical axis representing the y-axis of FIG.

n-type InGaAspH\', 8 is stripe region B
As shown in FIG. 4(c), the electrons and holes recombine in the active layer 6 without affecting the current, contributing to light emission efficiently. On the other hand, in embedded area A,
The egg Lugie band at thermal equilibrium is shown in FIG. 4(a), but changes as shown in FIG. 4(b) when voltage is applied. At this time, p-, In
The current flowing through the buried region A is blocked by the zero bias state between the P layer 2 and the n-InP layer 3, but this reverse bias junction causes avalanche multiplication or minute leakage current f) T, (from C Even if it is turned on, n −I
Due to the difference in forbidden band width between the nGaAsP layer 8 and the p-InP layer 2, the electron flow J0 flowing through this heterojunction can be made significantly smaller than the hole flow Jp. i.e. j/j
<p 1. Under this condition, n InP layer 1, n
-InGaAsP layer 8, p-InP layer 2. n-InP
When considering layer 3 as an n-p-n type heterojunction transformer/star, the current amplification factor can be kept very small, so even if the thyristor is turned on, the current flowing through the entire can be made significantly smaller.

Therefore, the injected current flows efficiently through the stripe region, resulting in highly efficient laser characteristics. In addition, n-type 1nP
If the height of the layer 1a is set to about 2 to 3 μm, the active layer 6V
The c-confined light is not absorbed by the n-type InGaAsP layer 8. In addition, the n iJ InGaAsP layer 8
Since it is formed over the entire blood of the element (sea urchin...), it is possible to suppress leakage current in any buried region A within the element.

The structure of the present invention can be fabricated by two rounds of crystal growth. 1. In the first crystal growth, an n-type InGaAsP layer 8, an n-type 1nP layer 1a, an anodoped active layer 6, and a p-type InP layer 7 are sequentially grown on the n-type InP substrate 1. next,
Only the portions to be left as stripes are masked by photosonography, and the other portions are removed by etching up to just above the n-type InGaAsP layer. By using selective etching, the etching can be stopped directly above the n-type InGaAsP layer 8. Next, a second crystal growth process is performed to form p-type InP that will become the buried region A.
Layer 2, n-type InP layer 3, p-type InP layer 4, n-type InGa
Grow an AsP cap layer 5. Zn diffusion is performed on the stripe region B to form a Zn diffusion region 9, and p 1+1
11. The device is fabricated by forming n-side electrodes 10°11. Note that in this example, n-type I
A structure in which an n-type 1nP layer is interposed between the nP substrate l and the n-type InGaAsp layer 8 as a buffer layer for alleviating the influence of the substrate may also be used.

The above embodiments are PBH (planar buried).
Although a typical BH groove structure as shown in FIG. It is also applicable to internal stripe type lasers that have a reverse bias junction in the current blocking region.1.Although the above example uses an n-type InP substrate, it is also possible to use a p-type InP substrate and change the conductivity type. It can also be applied to structures inverted from n-type to p-type and from p-type to 11-type.

It goes without saying that the present invention can also be applied to a DFB laser in which periodic irregularities are provided near the active layer, a structure in which a low-loss waveguide is provided on the extension of the active layer in the optical axis direction, and the like.

As explained in detail below, according to the present invention, since leakage current can be extremely reduced, a semiconductor laser that is highly efficient and operates at high temperatures can be obtained. It can be used as a light source.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an example of the structure of an embedded laser for hunting, FIG. 2 is a vertical cross-sectional view showing the element structure of a DC-PBH laser, and FIGS. B of
FIG. 4 is a vertical sectional view showing an embodiment applied to an H-groove structure and an internal stripe structure, respectively. FIG. 4 is an energy band structure diagram for explaining the operation of the embodiment of FIG. 3. 1- n-type InP substrate, 1a... n-type InP layer (first semiconductor crat layer), 2... p-type InP layer (second semiconductor layer), 3... n-type InP layer, 4・
・・p-type InP layer, 5 ・=n-type or type InQ
aAsP kiya. 6.6a-n-type InGaAsP active layer, 7.
...p-type InP layer, 8...n-type InGaAsP layer (third semiconductor layer), 9...Zn diffusion region, 10.1
1... Electrode. Patent Applicant: International Telegraph and Telephone Corporation Representative: Inuzuka, 1 person from outside the university

Claims (1)

[Scope of Claims] (Jl A band-shaped active layer that generates light emission is surrounded by a semiconductor cladding layer that has a smaller forbidden band width and a smaller refractive index than the active layer, and the semiconductor cladding layer In a buried semiconductor laser, a buried structure including a reverse bias junction for blocking current in a buried region on a side surface of the active layer is disposed in a semiconductor substrate. 10) Disposed uniformly on the substrate so as to be in contact with both a first semiconductor cladding layer of a conductivity type and a second semiconductor layer of a second conductivity type forming a reverse bias junction in the buried region. A semiconductor laser comprising a third semiconductor layer of a first conductivity type having a narrower forbidden band width than the second semiconductor layer. (2) The semiconductor laser according to claim 1, wherein a buffer layer of a first conductivity type is disposed on the substrate. (3) InP is used for the substrate and InGaA is used for the active layer.
2. The semiconductor laser according to claim 1, characterized in that sP is used.