JPS61228684A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To prevent position deviation due to the diffusion of impurities at a P-N junction and to make it possible to obtain high speed response and a high-power emitted light output, by setting the carrier concentration of an active layer, which is formed between a first clad layer in an N-type region, and a second clad layer formed in a P-type region, at a value larger than those of the first and second clad layers. CONSTITUTION:An active layer is made to be an N-type region. The carrier concentration of the active layer is made larger than the carrier concentration of first and second clad layers 2 and 4. For example, on an N-type InP substrate 1 having a concentration of Te 1X10<18>cm<-3>, the following layers are sequentially formed by a liquid phase epitaxial growing method: an N-type InP clad layer 2 having a concentration of Te 1X10<18>cm<-3>; an N-type InGaAsP active layer 3 having a concentration of Te 5X10<18>cm<-3>; a P-type InP clad layer 4 having a concentration of Zn 1X10<18>cm<-3>; and a P-type InGaAsP contact layer 5 having a concentration of Zn 3X10<18>cm<-3>. In this way, Te, which is the N-type impurities, is added in the active layer 3, and the P-N junction is formed at an interface between the active layer 3 and the P-type clad layer 4. The carrier concentration of the P-type clad layer 4 is decreased to 1X10<18>cm<-3>. Thus the occurrence of a tunnel phenomenon is prevented.

Description

[Detailed description of the invention] 11↓Ω Kozuki! The present invention relates to a semiconductor light emitting device having a double heterojunction.

BACKGROUND OF THE INVENTION With the recent development of optoelectronics, research on light emitting diodes including semiconductor lasers is progressing. Light-emitting diodes are small, have a long lifespan, and have high reliability, but for optical communication purposes, they are required to have even higher light output and faster response speed, so they are being used as semiconductor materials. A high-quality epitaxial crystal with an emission wavelength in the low-loss region of silica-based optical fiber is used, and the 0.7
In the ~0.9μm band, GaA 1^s/GaAs system,
InGaAsP/InP in the 1-1.7μm band
system is mainly used.

Communication light emitting diodes made of these materials generally have a double heterojunction structure in order to increase light emission output. In a double heterojunction, an active layer with a small bandgap is sandwiched between two cladding layers with a large bandgap, and electrons injected into the active layer are transferred to the valence band by a potential barrier created in the conduction band. The diffusion of these carriers into the cladding layer is suppressed by being confined by the potential barrier formed in the cladding layer, so even a small amount of current increases the concentration of injected carriers and increases the rate of radiative recombination per unit time.
In other words, the luminous efficiency is improved and the luminous output is also increased.

On the other hand, the response speed is determined by the recombination lifetime τ of carriers injected into the active layer region, and the cutoff frequency fe is determined by the following formula % Formula % It is also known that the carrier lifetime τ becomes smaller as the concentration of impurities added to the active layer increases. It is being therefore,(
In order to increase the response speed, that is, to improve the cutoff frequency f, as seen from equation 1), it is sufficient to increase the impurity concentration and decrease the carrier lifetime τ.

Note that Zn, Mg, etc. are most commonly used as impurities added to the active layer because they are easily diffused and have little toxicity.

Problems to be Solved by the Invention A cross-sectional view of a conventional InGaAs P/In P light emitting diode is shown in FIG. A heterojunction is formed between the active layer 7 and the cladding layers 2 and 4, respectively.

Now, in order to provide this light emitting diode with high-speed response, it is assumed that the impurity concentration of the active layer 7 is increased by adding impurities to each layer at a concentration as shown in FIG. 8 during crystal growth of each layer. Zn as an impurity added to the active layer 7
is used, and as a result, the active layer 7 becomes an n-type region, and n
The purpose is to form a pn junction with the mold cladding layer 2.

However, since the p-type impurity Zn (or Mg) is easily diffused, Zn is deposited at a high concentration (5×IO”
cm-'), Zn easily diffuses into the n-type cladding layer 2 below, resulting in a Zn diffusion profile as shown by the broken line in FIG.

As a result, the vicinity of the boundary between the n-type cladding layer 2 and the active layer 7 becomes an n-type region, and the pn junction that was intended to be formed at the boundary between the active layer 7 and the n-type cladding layer 2 actually becomes an n-type region in the vicinity of the boundary between the n-type cladding layer 2 and the active layer 7.
will be formed inside. Therefore, the energy band diagram of this light emitting diode becomes as shown in FIG. The carriers injected into the active layer 7 flow out of the active layer 7, and the carrier density decreases.

That is, the luminous efficiency deteriorates, the luminous output decreases, and the initial objective of increasing the response speed cannot be achieved.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a semiconductor light emitting device that enables high speed response and high light output.

Problems and Means for Solving The semiconductor light emitting device of the present invention forms an active layer in the n-type region between a first cladding layer in the n-type region and a second cladding layer in the n-type region. Furthermore, the carrier concentration of the active layer is set higher than that of the first and second cladding layers.

Note that the second cladding layer is a two-layer structure consisting of a first layer formed immediately above the active layer and a second layer formed further above the first layer and having a larger carrier concentration and thickness than the first layer. It may be a structure.

In a preferred embodiment of the present invention, the active layer is made of InGaAs P with a carrier concentration of 1xlQI8-5x10''cm-' and a thickness of 0.1-2.0 μm;
The craft layer has a carrier concentration of 1 xlQl? ~2XI
It is made of InP with a thickness of 0.2 to 2.0 μm.

In general, n-type impurities are difficult to diffuse, so by creating this structure, a p-n junction is formed at the interface between the n-type active layer and the p-type second cladding layer, and the p-n junction is formed by diffusion of the impurity. The position will not shift.

By the way, it is known that when both p-type and n-type carrier concentrations are high in a pn junction, the width of the potential barrier of the depletion layer becomes small and the probability of tunneling phenomenon increases. If tunnel current appears as dark current and causes tunnel breakdown, it will no longer be useful as a light emitting diode, so it is necessary to prevent this tunneling phenomenon from occurring. For this purpose, it is necessary to set the carrier concentration on the low concentration side of the pn junction, that is, the second craft layer, to be low.

Furthermore, when the second cladding layer is formed on top of the active layer, the thickness of the second cladding layer is adjusted to prevent damage to the active layer due to impurity diffusion during processing of the light emitting device. It needs to be set large.

However, if the second cladding layer with a low carrier concentration is made thicker, the electrical resistance will increase and the characteristics as a light emitting element will deteriorate.

Therefore, the second cladding layer has a two-layer structure of the first layer and the second layer, and first the thin first layer with low carrier concentration is placed on top of the active layer.
If a thick second layer with a high carrier concentration is formed on the first layer, the second layer has a thickness that does not damage the active layer during processing and has a low electrical resistance. cladding layer can be realized.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the semiconductor light emitting device of the present invention, and FIG. 2 is a carrier concentration distribution diagram in each layer of this embodiment. The illustrated semiconductor light emitting device is Te I
It has an n-type 1nP substrate 1 with a concentration of 18cm-', and on the substrate 1 there is a 5μ thick layer of TEL XIO with a concentration of 5μcm-'.
An n-type InP cladding layer 2 of m is formed, and further Te5
1.um thick n-type 1nGaA with xlo''Cm-' concentration
An sP active layer 3 is formed. On the active layer 3, a Zn I
p-type 1nP cladding layer 4, further Zn 3
1 μm thick p-type 1nGaAs P with C,11-3 concentration
A contact layer 5 is formed.

The layers from the n-type cladding layer 2 to the contact layer 5 were sequentially formed by liquid phase epitaxial growth. That is, in this embodiment, instead of the p-type impurity Zn added to the active layer 7 in the conventional example shown in FIG. It is formed at the interface with the cladding layer 4 and further reduces the carrier concentration of the p-type cladding layer 4 to IXIO"cl" to prevent the occurrence of tunneling.

When an electrode was provided on each of the n-type substrate 1 and the p-type contact layer 5 in this example, and an electric field was applied from the p-type contact layer 5 toward the n-type substrate 1, the interruptions shown in FIGS. 3 and 4, respectively, were obtained. Frequency characteristics and light emission output characteristics were obtained. The broken line in the figure shows the characteristics of the conventional example shown in Figure 7, and the light emitting diode of this example has a higher cutoff frequency and light emission output than the conventional example at each current value, that is, faster response and higher output. It can be seen that this has been achieved.

A cross-sectional view of the second embodiment and carrier concentration distribution maps in each layer are shown in FIGS. 5 and 6. This second embodiment is similar to the embodiment of FIG. A type 1nP cladding layer 6 is provided to prevent the active layer 3 from being damaged during processing, and its cutoff frequency and light emission output exhibit characteristics similar to those of the first embodiment.

On the right, InGaA forming the active layer 3 and contact layer 5
sP is lattice matched to InP, and in order to facilitate ohmic contact with the electrode metal, it has a mixed crystal ratio with a band gap of about 0.75 eV to 1.2 eV.
InGaAs P is preferred.

Further, in the above two examples, only one example was shown for the thickness and carrier concentration of each layer, and the same effect can be obtained as long as the thickness and carrier concentration of each layer are within the ranges shown in Table 1.

Table 1 However, the carrier concentration of the n-type cladding layer 4 must be lower than that of the active layer 3 and the second n-type cladding layer 6, as in the distribution diagram of FIG. Further, when the n-type cladding layer 4 is relatively thick, the second n-type cladding layer 6 is not necessary.

Further, in this embodiment, the n-type cladding layer 2 is located below the active layer 3, and the n-type cladding layer 4 is located above the active layer 3, but the reverse may be used. That is, on a p-type substrate, an n-type cladding layer, an n-type active layer, an n-type cladding layer,
Similar effects can be obtained by sequentially forming n-type contact layers.

Furthermore, as a semiconductor material, InGaAs of the above embodiment is used.
P/In In addition to the P system, InGaA is also used for communication.
sSb/InSb system, GaAlAsSb/GaSb
system, InGaAs P /GaAs system, GaAsAs
Quaternary, ternary, binary, including P/GaAs system■
- Group compound semiconductors or other semiconductors may be used.

Furthermore, although a liquid phase epitaxial method was used as a crystal growth method, a molecular beam epitaxial growth method or a metal organic pyrolysis vapor deposition method (MOCVD method) may also be used.

Furthermore, similar effects can be obtained by using Sn, Se, or S instead of Te added to the substrate 1, cladding layer 2, and active layer 3 as n-type impurities, and Instead of Zn added to the cladding layer 6 and contact layer 5, Mg5Cd or the like may be used. however,
Regarding n-type impurities, Se is preferable to S etc.
, Te, and other substances with large atoms are more difficult to diffuse. Therefore, Se.

The use of large atoms such as Te is more effective in preventing diffusion.

As explained above, according to the present invention, an active layer with a high carrier concentration can be formed without shifting the position of the pn junction surface, so a semiconductor light emitting device with a fast response speed and a large light emitting output can be realized. be done.

Therefore, it is very effective to apply the semiconductor light emitting device according to the present invention to optical communication equipment.

[Brief explanation of drawings]

1 and 2 are a cross-sectional view and a carrier concentration distribution diagram of a semiconductor light emitting device according to an embodiment of the present invention, respectively. FIGS. 3 and 4 are a cut-off frequency characteristic diagram and a carrier concentration distribution diagram of the embodiment of the present invention, respectively. Figures 5 and 6 are cross-sectional views and carrier concentration distribution diagrams of other embodiments, and Figures 7, 8, and 9 are cross-sectional views and carrier concentration distribution diagrams of conventional examples, respectively. , is an energy band diagram. (Main reference numbers) 1... n-type 1nP substrate, 2... n-type 1nP cladding layer, 3... n-type 1nGaAs P active layer, 4... p-type 1nP cladding layer,

Claims (6)

[Claims] (1) The first cladding layer in the n-type region and the second cladding layer in the p-type region.
cladding layer and an active layer formed between the first and second cladding layers, wherein the active layer is an n-type region, and further the carrier concentration of the active layer is equal to 1. A semiconductor light emitting device characterized in that each carrier concentration is higher than that of a second cladding layer. (2) The second cladding layer includes a first layer formed on the active layer and a second layer formed on the first layer and having a carrier concentration and thickness larger than that of the first layer. A semiconductor light emitting device according to claim 1. (3) the active layer is made of InGaAsP;
3. The semiconductor light emitting device according to claim 1, wherein the second cladding layer is made of InP. (4) The carrier concentration of the active layer and the second cladding layer is 1×10^1^8 to 5×10^1^9, respectively.
cm^-^3, 1 x 10^1^7 to 2 x 10^1^8c
The semiconductor light emitting device according to claim 3, which is in the range of m^-^3. (5) The semiconductor light emitting device according to claim 4, wherein the active layer and the second cladding layer have thicknesses in the range of 0.1 to 2.0 μm and 0.2 to 2.0 μm, respectively. . (6) The semiconductors constituting the active layer and the first and second cladding layers are InGaAsSb/InSb-based,
GaAlAsSb/GaSb system, InGaAsP/Ga
The semiconductor light emitting device according to claim 1 or 2, which is either As-based or GaAlAsP/GaAs-based.