JPH02192785A - Semiconductor light-emitting device - Google Patents

Abstract

PURPOSE:To realize a laser having high oscillation efficiency by providing multiple well layers within a semiconductor layer structure such that widths of the wells are decreased gradually from the electron injected side and that the wells have the same quantum units. CONSTITUTION:A semiconductor layer is produced by forming a clad layer 2 of one conductivity type, multiple quantum well layers 5-7, a clad layer 8 of the opposite conductivity type and a contact layer 9 on a substrate 1 sequentially in that order. The well layers 5-7 are formed such that widths of the wells are decreased gradually from the electron injected side towards the center of the device. Further, the wells 5-7 have different compositions from each other so as to align quantums of the wells with each other. Accordingly, injected electrons are stored uniformly in the quantum wells 5-7 and a laser presenting a high oscillation efficiency can be realized. Such laser is accomplished by forming electrodes on the lower face of the substrate and on the upper face of the contact layer 9 and cleaving the substrate 1 at a length of a resonator.

Description

DETAILED DESCRIPTION OF THE INVENTION (Summary) The present invention relates to a semiconductor light emitting device using a multiple quantum well (MQW) structure, and aims to realize a laser exhibiting high oscillation efficiency using the multiple quantum well structure.

- It has a semiconductor layer structure in which a conductivity type cladding layer, a multiple quantum well layer 1 and an opposite conductivity type cladding layer are laminated in order, and the multiple quantum well layer has a well width that is successively thinner from the side into which electrons are injected, and each well The composition is sequentially changed so that the quantum levels of the two are the same.

[Industrial application field]

The present invention relates to a semiconductor light emitting device using a multiple quantum well structure.

Semiconductor lasers are important as light sources essential to optical transmission systems. In recent years, the modulation speed of optical transmission systems has increased to about gigabit. For such high-speed modulation, semiconductor lasers are also required to have high performance, and in particular, a small wavelength shift (chirping) during modulation is strongly required.

An appropriate way to suppress this chirping is to increase the differential gain of the semiconductor laser.

Quantum well structures are seen as promising as a way to achieve this goal.

[Conventional technology]

Conventional quantum well lasers include a multiple quantum well structure in which a plurality of well layers each having a width of several tens to hundreds of well layers are stacked, and a single quantum well structure.

It has been predicted that 3 to 5 layers would be best in order to oscillate at a low threshold.

Although such multiple quantum well lasers have been manufactured, sufficient effects have not been obtained at present.

1) Note 1: For example.

■, 8 to akawa and A, Yariv, E
enhanced modulation performance
mance and reduced quantum
noise 1nquantu+n well 1a
sers'CLEO'851tH5,Baltimo
re (1985).

The reason for this is that if the composition width of the quantum well varies, the quantum level formed within the quantum well fluctuates, making it impossible to obtain a quantum effect.

The reason why good oscillation characteristics cannot actually be obtained is considered to be that the electrons pass through the well layer before being accumulated in the well due to the relationship between the relaxation time and drift time of the electrons injected into the well layer. As a result, electrons accumulate in the well on the side into which electrons are injected, while more electrons accumulate in the later wells, causing non-uniform distribution of electrons within the well and impairing the characteristics of the laser.

To prevent this, conventional GR has a single quantum well and gently changes the energy gap of the barrier layers on both sides of the well.
An INSCH single quantum well structure 2' is adopted.

2) S, P, Hersee, b, de Cremoux
and J., P., Duckemin.

8pp1. Phys, Letters, 44
p476 (1,984).

However, in order to make full use of the quantum effect, a three to four multi-quantum well structure is still superior.

In order to sufficiently relax electrons injected into the quantum well layer into the well, it is sufficient to simply widen the well width.

However, if the well width is widened in consideration of electron diffusion and drift time, quantum effects cannot be obtained. Therefore, multiple quantum wells are effective, and high characteristics can be achieved by sequentially changing the width of the wells. That is, the width of the first well into which one electron is injected is wide, and the width of the last well is the narrowest.

With such a multi-quantum well structure, the energy of injected electrons relaxes while traveling on the quantum well and gradually descends to the vicinity of the conduction band, so a wide initial well width means that the injected electrons with high energy However, the electrons are sufficiently relaxed within the well, and the fact that the latter well is narrow means that the energy of the electrons is low, so even if the well is narrow, the electrons are sufficiently relaxed.

(Problem to be solved by the invention) However, in the above conventional example, the quantum level that easily causes laser oscillation is dependent on the well width, so if this continues, the quantum level of each well will be different, and high oscillation characteristics can be expected. Can not.

An object of the present invention is to realize a laser that does not exhibit high oscillation efficiency using a multiple quantum well (11 structures).

(Means for Solving the Problems) The above problems are solved by having a semiconductor layer structure in which a -conductivity type cladding layer, a multiple quantum well layer 1 and an opposite conductivity type cladding layer are laminated in this order, and the multiple quantum well layer has the following.

This is achieved by a semiconductor light-emitting device characterized in that the well width is successively thinner from the side into which electrons are injected, and the composition is successively changed so that the quantum (V) of each well becomes the same.

[Function] The present invention realizes a multi-quantum well laser that is optimal as a quantum well laser by matching the quantum level of each well by changing the composition of each well.

In multi-quantum well lasers, it has been conventional practice to aim for high performance by matching the quantum levels. However, by changing the well width and matching the quantum units as in the present invention, the injected electrons can be uniformly distributed to each quantum well. It will accumulate in the well, and it will prevent the characteristics from becoming bad due to non-uniform accumulation as in the past.

FIG. 1Q) and (2) are diagrams of the principle of the present invention, including a band structure diagram and an electron distribution diagram within a well.

FIG. 1(1) is a diagram of the present invention, and FIG. 1(2) is a diagram of a conventional multiple quantum well structure.

In the figure, r Ec is the bottom of the conduction band + EV is the valence band, and the first quantum unit is indicated by a dotted line. Also, n is the number of electrons,
is the distance perpendicular to the well.

Conventionally, each well has the same width and composition, so the electrons injected from the n side have the distribution shown in the figure, and if enough electrons are not accumulated in the well, there will be a loss. Therefore, the characteristics could not be improved.

On the other hand, in the present invention, the width of each well is variable,
In addition, since the composition is changed and the quantum levels are matched, the injected electrons have an even distribution and a -like gain can be obtained, resulting in high characteristics.

Here, how to change the composition of the multiple quantum well and the well width is as follows.

First, let's focus on electrons. Holes are ignored because their quantum level difference is small.

In order to sufficiently relax electrons into the well, the distribution of the well width W(x) is changed exponentially as shown in the following equation.

W(x) −Wo exp(x/L), ...(1
) Here, the initial well width -6 is less than the thickness at which the quantum effect can be obtained and is sufficiently thick (for example, 200 people), and L is determined by the electron relaxation time τ and the diffusion constant, and M#(Dτ )1
” is a guideline.

Further, the width B of the barrier layer may be constant, for example.

Have 50-100 people.

Next, in order to match the quantum level in the well, the composition is determined according to the following 2.

(αL, /2) tan (αLz/2) - ten (βL2/
2) (m"/m*').

(αL, /2) cot (αL, /2) −1 (βL, /2) (m”/m”), =42) However, +: when the number of wells is odd.

: When the number of wells is odd It is.

here.

α” = 2 m” E,, /h/2π.

β" = 2 m"' (C E,, > /h/2π.

L2 is the well width 1m'' is the effective quality of electrons L, m'' is the effective quality of holes L, E is the quantum level, and V is the depth of each well (
h is Planck's constant.

3) For example Hideo Kanazawa, Quantum Mechanics, Asakura Shoten (1965).

In order to match the quantum units in the well, if E9 is the band gap (determined by the composition) of each well, then E, +
It is sufficient to keep E, , constant. Since E of each well is a variable and the width L2 of each well is a fixed value given in advance,
By solving the above equation, E9 can be determined so that E, + En is constant for each well. Once E is determined, the corresponding composition is determined.

Embodiment C] FIG. 2 is a sectional view of a main part of an embodiment of a semiconductor light emitting device using a p-type 1nP M plate.

In the figure, 1 is a p-type (p-Hnp substrate).

2 is a p-1nP buffer layer, and 3 is an active layer.

fnGaAsP/InP MQW layer, 4 is n type (n-)
The InPn quad layer 15 is a p-rnl' buried layer, and 6 is an n-
1nP buried layer, 7 is p-[nP buried layer, 8 is n-InP
They are a cladding layer and a 9ban-1nGaAsP contact layer.

Further, the cladding layer 4, the active layer 3, and the buffer layer 2 constitute a mesa stripe 10.

Next, the structure of the example will be explained below, including the outline of the manufacturing method.

For continuous growth including the MQIQ layer, metal organic vapor phase epitaxy (MOVPIE) is suitable because it grows a thin film having a quantum effect.

First, on the +p-1nP substrate 1.

p-1nP buffer layer 2 (Cd doped, carrier concentration 6X10"cm-'thickness ~
0.5 .mu.m) 7 InGaAsl'/InP MI layer 3.n4nP cladding layer 4 (Sn doped, carrier concentration I.times.10"cm" thick ~ 0.5 .mu.m) 8 are grown sequentially.

Here, the InGaAsP/InP MQW layer 3 is made by alternately laminating 4N InGaAsP well layers having a thickness of 50 layers and 5 layers of InP barrier layers whose surface layer thickness and composition vary.

The InGaAsP well layer has the following composition and thickness derived from the above equations (1) and (2) sequentially from the electron injection side (n side).

No, Mi thickness (μm) (included) 1 1.450 200 2 1.462 150 3 1.496 100 4 1.550 50 However, for 2 compositions, the peak wavelength of the photoluminescence spectrum is used instead of the band gap E9. displayed.

Next, a 5iOz stripe mask is formed, and mesa etching is performed using this as a mask to form a mesa stripe IO.
form.

Next, leave the SiO□ stripe mask on.

As a buried layer by liquid phase epitaxial growth (LPE) method.

p-1nP layer 5 (Cd doped, carrier concentration 5X10"cm-').

n-InP layer 6 (Sn doped, carrier concentration lXl018cm-3)
.

p-1nP second buried layer 7 (Zn doped, carrier concentration I x 10'!1c
m-3) are grown sequentially.

Furthermore, after removing the SiO□ stripe mask, n-1n
P cladding layer 8 (Sn-doped, carrier concentration 1×10I810l8 thickness ~0.3 μm) + n-1nGaAsP contact layer 9 (Sn-doped, carrier concentration 2.4X1018cm-'
Grow to a thickness of ~0.2 μm).

After this, although not shown, ohmink contact electrodes are formed on the lower surface of the substrate 1 and the upper surface of the contact layer 9, and the side surfaces of the substrate are separated at the resonator length (in the mesa stripe direction) to complete the laser.

Furthermore, in the embodiments, an InGaAsP/InP-based laser was described, but the present invention applies to other compound semiconductors.

For example, AlGaAs/GaAs system, AlGa1nP
/GaAs-based lasers can also be applied.

The device of the example has a frequency characteristic of about 1.0% compared to the conventional example.
In the figure, there is a 5x improvement and an approximately 30% reduction in threshold current.

1 is p-1nP substrate 2 is p-1nP buffer layer 3 is an InGaAsP well layer M (IW layer).

4 is an n-In22971 layer.

5.6.7 is InP Rikome Shukomi The layer is an n-In22971 layer.

9 is an n-InGaAsP contact layer.

10 is a mesa stripe [Effects of the Invention] As explained above, according to the present invention, a laser exhibiting high oscillation efficiency using a multiple quantum well structure could be realized.

[Brief explanation of the drawing]

Figures 1 (1) and (2) are diagrams of the principle of the present invention, including a band structure diagram and an electron distribution diagram within a well. FIG. 2 is a sectional view of a main part of an embodiment of a semiconductor light emitting device using a p-type 1nP M plate. (2) is low) Click here for the present invention's Kori diagram diagram

Claims (1)

[Claims] It has a semiconductor layer structure in which a cladding layer of one conductivity type, a multiple quantum well layer, and a cladding layer of an opposite conductivity type are laminated in this order. A semiconductor light emitting device characterized in that the composition of the semiconductor light emitting device is sequentially changed so that the quantum levels of the semiconductor light emitting devices are the same.