JPS58197784A - Light emitting diode - Google Patents

Abstract

PURPOSE:To produce LED made of InGaAsP with high efficiency and output by a method wherein an active layer with narrow forbiden band width is held by P- and N-layers successively changing the concentration of the active layer in the direction of layer thickness. CONSTITUTION:In a LED where N type In1-xGaxAs1-y active layer 32 is held by P-InP layer 33 and N-InP layer 31, the donor density of the active layer 32 is successively changed in the direction of layer thickness. When LED is supplied with forward bias voltage, if an active layer 12 is doped to increase donor density from a layer 11 to another layer 13 in a energy band diagram, the lower end of conduction band of active layer and the upper end of valency electron band are lowered in the direction of layer thickness generating an accelerating electric field for the electrons and hole injected into the active layer. Consequently the thickness of active layer almost equivalent to the conventional hole diffusion length may be increased producing LED made of InGaAsP with high efficiency and output as well as inconspicuous saturation characteristic.

Description

[Detailed description of the invention] The present invention relates to high efficiency light emitting diodes.

Highly efficient light emitting diodes with a simple structure, superior economy and reliability are suitable for optical communications! In the 1 μm wavelength band, which exhibits low dispersion and low loss, the light is required as a variety of light sources (Currently, InGaA
A double telojunction type light emitting diode made of sP mixed crystal material has been developed, but this light emitting diode has the characteristic that the luminous efficiency decreases in the high current injection region and the output saturates. Since this is a major obstacle to increasing efficiency, it is particularly desired to develop a light emitting diode that does not reduce efficiency.

FIG. 1 is a band diagram when a forward bias voltage is applied to a conventional double-terojunction type light emitting diode. In the same figure, 11 is a first semiconductor 1 made of N-type InP. 12 is a 5yPl- containing In1-xGax.
y, 13 is a second semiconductor 1'lte made of P-type InP, and Int-xGaxAsyPt-y1.2 serves as an active layer. However, xtl satisfies 0<4≦1.0<χ≦1. Electrons 14 injected from N-type InP 11 and P-type I
Letter hole 15 it Ins − injected from nP 13
xGaxAsyPt, y Recombine in the internal f of 12, of which the radiatively recombined component contributes to the conversion of optical energy, and a small amount of non-radiatively recombined component reduces the internal quantum efficiency of the light emitting diode. This non-radiative recombination component increases rapidly as the injected carrier density increases, compared to the radiative recombination component. For this reason, the light emitting output does not increase with the rate of increase in the injection current and does not exhibit saturation characteristics, and the internal quantum efficiency decreases significantly in the high injection current region. In order to prevent this decrease in efficiency and obtain a high-efficiency, high-output light emitting diode, even if a large current is injected, the
It is desirable to have a structure in which the density is not too high, and in that case, the electric field C1 in the Qll thickness direction in the active layer is small, so the injected carriers spread and accumulate inside the active layer by diffusion. The region n is determined by the diffusion length. Normally, the diffusion length of holes is smaller than the diffusion length of electrons, and even if the active e storage is greater than the diffusion length of holes, holes will only be accumulated in a region about the diffusion length.

Therefore, is the internal quantum efficiency equal to 111? Therefore, the active layer thickness is 5: Even if the active layer is depleted, it is only effective up to a thickness approximately equal to the hole diffusion length. I with a composition whose emission wavelength is 1.3 sm
In the example of n 1-xGaxAsyPt -y, the hole expansion i
The length is about 2 μm in the hole density of lXl0'', which is about 1/10 of the electron diffusion length.In the conventional structure, the active layer thickness was increased to improve the internal quantum efficiency. Even if we did not try to do so, we could not obtain a light-emitting diode with high efficiency and high output due to the limit of active thickness.

The present invention aims to eliminate the above-mentioned drawbacks and to improve the efficiency and output of a light emitting diode. In order to achieve this objective, the light emitting diode of the present invention has a structure in which a semiconductor 1 and a second semiconductor layer having different conductivity types sandwich an active layer 1 having a narrower sideband width than the semiconductor layer. Equipped and more! 81N Ki Activation Dice Book Supplement? 11 degrees gradually increases or decreases from the side in contact with the first semiconductor layer toward the semiconductor @2 in the layer thickness direction.

FIG. 2 is a band diagram when a forward bias voltage is applied to the light emitting diode according to the present invention.

In the same figure, ◆Choli! The active layer of the cubs is the active shoulder.

The semiconductor wE2 is doped with impurities that increase the donor zone spacing in the layer thickness direction from the side in contact with the semiconductor 1 of @1. As a result, the lower end of the active conduction band,
As shown in @2 Figure 1, the upper end of the valence band decreases as it advances toward the semiconductor layer of @2 in the thickness direction, and an accelerating electric field is applied to the electrons and holes injected into the active layer. will occur.

Therefore, carriers injected into the active layer can quickly move into the active layer. Therefore, while the active layer thickness of a conventional light emitting diode could only be increased to the extent of the hole diffusion length, in the present invention, the active layer thickness of a light emitting diode can be made much thicker. , light emitting diode Q) It has a structure that is advantageous for high efficiency and high output.

FIG. 3 shows an embodiment of the present invention, and 30 is an NWInP
The substrate, 31 GJ @l semiconductor layer made of Nu InP, 32 was made by gradually changing the donor interstitial space in the layer thickness direction. ll Ir*-*GaxAsyP1-y active layer, 33 is P-type 1nP, 34 is P-type Int-xGaxAs
yPt-w.

35 is 81, 36 is A1GeNi/Au electrode, 37
is a Ti, y′Pt/Au electrode. However, 0≦Z≦1,
0≦W≦l. The crystal growth uses the molecular beam epitaxial growth method, and the active layer is N-type InxGar-xAs.
yPl-y 32 is doped by 8n% and donor density 1 is N-type I
P-type InP33 at about xxlo/d on the side in contact with nP31
It increases continuously in the direction of 1 thickness and reaches about 1×10 2 in the part in contact with the P-type IflP 33. Also N11InP@board 31 and N11InP32
The donor spacing of P-type InP33 is about xxlo/cII, and the acceptor spacing of P-type InP33 is about xxlo/cII.
The total layer thickness of at-xGaxAsyPl-y 32 is about 6 μm.According to the actual example, the active layer thickness is 3 times thicker than the conventional one, so the carrier density is 1/1 even with the same injection electric value.
3, the optical output is nearly twice that of the conventional one, and a high-efficiency, high-output InGaAsP light-emitting diode with mild saturation characteristics can be obtained.

FIG. 4 shows another embodiment of the present invention, in which the donor density due to 8n doping is approximately 1x1n/d. In
I-xGaxAsyPt -y 321 , approximately 5X1
0/? 71f N @ In t -xGaxAsyP
N-type In1 with t −y 322 and about lXl0/Cld
-vGaxAsyPx -y 3230) 311 When active layers are formed, each thickness is approximately 2μ
It is m. The parts other than the active llI are the same as in the previous example. As shown in the figure, the structure is such that the donor density of the active layer is changed functionally, and it is effective for materials in which it is difficult to create the active layer 111 by continuously changing the donor density.

As described above with the specific examples, according to the present invention, it is possible to realize a light emitting diode which has high internal electron efficiency and is particularly effective for increasing the efficiency and output of a light emitting diode using InGaAsP mixed crystal.

[Brief explanation of drawings]

FIG. 1 is a band diagram when a voltage is applied in the forward direction to a light emitting diode according to the conventional, conventional, and FIG. 2 is a light emitting diode according to the present invention. Further, FIG. 3 is a sectional view of a light emitting diode showing one embodiment of the present invention, and FIG. 4 is a sectional view of a light emitting diode showing another embodiment. 11 and 31 are N-type InP, 12 is Int-xGaxA
syPI-7, 13 and 33 are pHTnP%? , 32
, 321° 322 and 323 are NWInl-xGaxA
syPx-y, 30 is N11InP substrate, 34 is PWInt-zGazAswPt-w. 35 is 8i0 fable, 36 is AuGeNi /Au Dentsubaki 1a
7 is T i /P t /Au Ill 纺, 14 is an electron, and 15 holes. Base 1 Mouth A Tei 3 Figure 7

Claims (2)

[Claims] (1) It has a structure in which an active # made of a semiconductor having a narrower forbidden band width than the first and second semiconductor layers is sandwiched between a semiconductor layer of @1 and a second semiconductor layer having different conductivity types. ,
Furthermore, the impurity concentration in the active layer is such that the impurity concentration in the first semiconductor f
1. A light emitting diode characterized in that the number increases or decreases sequentially from the side in contact with $1 toward the second semiconductor layer in the one thickness direction. of (2) The active layer has a structure in which a plurality of semiconductors 11N whose impurity concentrations are slightly different from each other are stacked;
The light emitting diode according to claim 11@, characterized in that: