JPH03292778A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To obtain an end face light emitting LED which does not start a laser oscillation in a practical range of temperature lower than 0 deg.C by a method wherein an active layer, a second clad layer, and a first clad layer are so set in refractive index as to satisfy a formula, an active layer > a second clad layer > a first clad layer, and the the active layer and the first clad layer are so set in thickness as to satisfy cutoff conditions under which an optical waveguide layer is not given the fixed value of guide type. CONSTITUTION:A double hetero structure where an active layer is sandwiched between first clad layers 20 and 30 is provided onto a semiconductor substrate 60, and the double hetero structure concerned is sandwiched between second clad layers 40 and 50. At this point, the refractive indexes, n1, n2, and n3, of the active layer 10, the first clad layers 20 and 30, and the second clad layers 40 and 50 are so set as to satisfy a formula, n1>n2>n3. As a current is required to be injected into an active layer as constricted, a current blocking layer 70, a cap layer 80, and an electrode 90 are provided. A semiconductor light emitting element of this design has almost the same structure with a semiconductor laser, so that it can be made to operate as a semiconductor laser under a certain condition.

Description

[Detailed Description of the Invention] 7. Industrial Application Fields] The present invention relates to an edge-emitting device (edge-emitting LED).

[Conventional technology] Conventional edge-emitting LEDs have a layer structure similar to that of semiconductor lasers, and the reflectance at the edge is reduced by some method to suppress laser oscillation, or the laser oscillation is suppressed by reducing the reflectance at the edge in some way. Most of them suppress laser oscillation by inserting a region with high loss.

[Problems to be solved by the invention] However, with conventional technology, laser oscillation often occurs easily at temperatures below 0°C, and complicated manufacturing processes are required to reduce end face reflectance and form loss regions. It is said that

The ninth object of the present invention is to provide an edge-emitting LED that can be easily manufactured without adding new manufacturing steps such as reducing the reflectance of the end face or forming a loss region, and that does not cause laser oscillation in a practical temperature range of 0°C or less. It is about providing.

[Means to solve the problem]

In order to achieve the above object, the semiconductor light emitting device of the present invention has an active layer with a thickness of 11 μm on a semiconductor substrate, and a first layer with a thickness of 12 μm made of a semiconductor crystal whose forbidden band width is larger than that of the active layer.
It has a double heterostructure sandwiched between two cladding layers, and further has an optical waveguide structure in which the double heterostructure is sandwiched vertically between second cladding layers, and the refractive index n1 of the active layer and the first cladding layer are refractive index n2 and the second
The relationship between the refractive index n3 of the cladding layer is larger in the order of active layer, second cladding layer, and first cladding layer (nl>13>n2), and the relationship between the thickness tl of the active layer and the first cladding layer is The thickness t2 of the optical waveguide is set to a thickness under a cutoff condition that does not give an eigenvalue of the waveguide configuration to the optical waveguide.

For specific materials, the thickness of each layer that satisfies the above conditions is:
The electromagnetic field distribution within each layer is calculated using Maskwell's equation. Specifically, the journal of the Institute of Electronics and Communication Engineers (T
rans, IEcE' 7315vol, 5
Calculated according to the analysis method described in 6-CNα5, p277).

For example, when only the TE mode is considered, the electric field distribution in each layer is determined by setting the coordinates as shown in Figure 1(b). Here, γ', ``k?-β2 1: wave number in each layer If we connect this matrix at the boundaries of each layer and consider the exponential attenuation in the outermost layer, we get γN γ0 γN γO where the suffixes O and N refer to the outermost layer (corresponding to the layer with refractive index n3). show.

d, (i=1.2..., N): The layer thickness of each layer.

Since a waveguiding state exists when the propagation constant β is a solution to equation (1), each layer thickness tt2 such that β does not satisfy equation (1) is a layer thickness that satisfies the conditions of the present invention.

[Effect]

The operation of the present invention will be explained using the drawings.

FIGS. 1(a) and 1(b) show a schematic cross-sectional view (FIG. 1(a)) and a refractive index distribution (FIG. 1(b)) perpendicular to the emission direction of the edge-emitting LED of the present invention. It includes a tuple heterostructure in which the active layer 10 is sandwiched between first cladding layers 20 and 30 on a semiconductor substrate 60, and further has a structure in which a sonodouble heterostructure is sandwiched between second cladding layers 40.50. At this time, there is a relationship of nt>n3>n2 between the refractive index n of the active layer 10, the refractive index n2 of the first cladding layer 20.30, and the refractive index n3 of the second cladding layer 40.50. A current flow kink layer 70 is used to narrowly inject current into the active layer. and a cap layer 80 and an electrode 90. This structure is almost the same as that of a semiconductor laser. Naturally, there are conditions under which it can be operated as a semiconductor laser.

The second section shows the relationship between the thickness tl of the active layer and the vertical radiation angle of the emitted beam when operating as a semiconductor laser. In this calculation, the first cladding layer thickness t2 is 03 μmη. The case where n 2 = n h = 3.26 is the most commonly used tuple heterostructure semiconductor laser, which exhibits the well-known tendency that the vertical emission angle gradually increases as the active layer thickness increases from 0. . On the other hand, rz=
If the value is 3.31, the vertical radiation angle is calculated by closing the active layer at 0.06 μm or more. This indicates that no waveguide moat exists in this waveguide below 0.06 μm.

In other words, laser oscillation is extremely suppressed. Actually, since the active layer is a gain medium, the wave is guided by its gain, but since it coexists with the radiation mode, even if laser oscillation occurs, the oscillation threshold becomes extremely high. That is, below the oscillation threshold, it operates as an edge-emitting LED, and operates equivalent to a conventional edge-emitting LED with reduced edge reflectance or loss. In terms of manufacturing, since it is composed of a multilayer semiconductor laminated structure, no special manufacturing process for suppressing oscillation is required, so it can be manufactured more easily than in the past.

〔Example〕

Hereinafter, the present invention will be explained in detail using the embodiment shown in FIG. After stacking a GaAs buffer layer on a GaAs substrate, Si-doped (A Ilo, s Ga o, s
) A 1.0 μm thick second cladding layer 40 made of o5Ino,sP. Si-doped (A no,s
A first cladding layer 20 with a thickness of 0.3 μm made of Ga 0.4) 0.5 Ino, s P. Non-doped Ga
Active layer 10 with a thickness of 0.04 μm made of 5Ino5F
．． Zn doped (A n O, 8G ao, < ) o
, s I n o, sP with a thickness of 0.3 μm.
．． 5) Thickness 1.0 consisting of 0.5 I n 0.5 P
A second cladding layer 50 with a thickness of μm is grown in this order by metal organic vapor phase epitaxy, and a thin film of GaI nP
Through the layer, a layer of Si-doped GaAs with a thickness of 0.
A current blocking layer 70 of 7 μm was laminated. Next, the current blocking layer 70 was partially removed by photolithography and etching, and then a 2 μm thick cap layer made of Zn-doped GaAs was deposited again by metal organic vapor phase epitaxy to produce an edge-emitting LED wafer. . Thereafter, the GaAs substrate side was polished to form a 100 μm thick wafer, electrodes 90 were formed, and the wafer was divided into individual chips to form edge-emitting LEDs. The prototype edge-emitting LED maintained its LED operation without oscillation even at temperatures of -30°C.

〔Effect of the invention〕

According to the present invention, it is possible to obtain an edge-emitting LED that can be easily manufactured and does not cause laser oscillation even at a practical temperature of 0° C. or lower.

In the example, we considered plastic fiber transmission and showed a system using Aj7Ga I nP material that has an emission wavelength in the visible range.
It can also be implemented in nGaAsP based materials.

[Brief explanation of drawings]

Figures 1 (a) and (b) are schematic cross-sectional views and diagrams showing the refractive index distribution of the semiconductor light emitting device of the present invention, and Figure 2 shows the activity of the vertical radiation angle when the device of the present invention operates as a semiconductor laser. FIG. 3 is a diagram showing the dependence on layer thickness and also shows the active layer thickness at which the waveguide becomes cutoff. In the figure, lO... active layer, 20.30... first cladding layer, 40.50... second cladding layer, 60...
・Semiconductor substrate, 70...Current flow, kink layer,
80... Cap layer, 90... Electrode.

Claims (1)

[Claims] An active layer with a thickness of t_1 μm is formed on a semiconductor substrate by a semiconductor crystal with a thickness of t_2 μm and a forbidden band width larger than that of the active layer.
m has a double heterostructure sandwiched between first cladding layers, and further has an optical waveguide structure in which the double heterostructure is sandwiched vertically between second cladding layers, and the refractive index n_1 of the active layer and the first The refractive index n_ of the cladding layer of
2 and the refractive index n_3 of the second cladding layer is the order of the active layer, the second cladding layer, and the first cladding layer (n_3).
1>n_3>n_2), and the thickness t_ of the active layer
1 and the thickness t_2 of the first cladding layer are set to thicknesses under a cutoff condition that does not give an eigenvalue of a waveguide configuration to the optical waveguide.