Led with alternated strain layer

Abstract

The present invention relates to light omitting diodes having an AlGaInP active layer disposed between two cladding layers of AlGaInP, with a strain layer grown on the second cladding layer and comprising a superlattice structure in the form of a plurality of thin alternated AlGaInP layers with preselected composition. In one embodiment, the composition of the alternated AlGaInP layers is an ohmic n-electrode on a rear surface of a GaAs substrate: a distributed AlGaAs Bragg reflecting layer in the form of a multi-layer lamination; a first, lower AlGaInP cladding layer grown on the reflecting layer; an AlGaInP active layer grown on the lower cladding layer; a second, upper AlGaInP cladding layer grown on the active layer; a strain layer grown on the second cladding layer, the strain layer comprising a superlattice structure in the form of a plurality of thin alternated AlGaInP layers with the composition: (AlxGa1-x)1-yInyP/(AlnGa1-n)1-hInhP, where 0.5≦x≦1; 0.4≦y≦0.6/0≦a≦0.4; 0≦b≦0.4.

Description

BACKGROUND OF THE INVENTION

The present invention relates to light-emitting diodes (LEDs).

SUMMARY OF THE INVENTION

The present invention relates to light omitting diodes having an AlGaInP active layer disposed between two cladding layers of AlGaInP, with a strain layer grown on the second cladding layer and comprising a superlattice structure in the form of a plurality of thin alternated AlGaInP layers with preselected composition. In one embodiment, the composition of the alternated AlGaInP layers is an ohmic n-electrode on a rear surface of a GaAs substrate; a distributed AlGaAs Bragg reflecting layer in the form of a multi-layer lamination; a first, lower AlGaInP cladding layer grown on the reflecting layer; an AlGaInP active layer grown on the lower cladding layer; a second, upper AlGaInP cladding layer grown on the active layer; a strain layer grown on the second cladding layer, the strain layer comprising a superlattice structure in the form of a plurality of thin alternated AlGaInP layers with the composition: (Al x Ga 1-x ) 1-y In y P/(Al a Ga 1-a ) 1-h In h P, wherein 0.5≦x≦1; 0.4≦y≦0.6/0≦a≦0.4; 0≦b≦0.4.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing, which constitutes a part of the specification, an exemplary embodiment exhibiting various objectives and features hereof is set forth. Specifically, the FIGURE constitutes a somewhat diagrammatic view of a light omitting diode constructed according to one embodiment of the present invention, shown in elevation.

According to the present invention, there is provided a LED having an alternated AlGaInP strain layer.

The present invention will now be described, by way of example, with reference to the accompanying drawing, which is a section through an example of an LED according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawing, a light-emitting diode comprises: an ohmic n-electrode 1 on a rear surface of a GaAs substrate 2 ; a distributed AlGaAs Bragg reflecting layer 3 to improve the luminous efficiency (the Bragg reflector layer being in the form of a multi-layer lamination); a first, lower AlGaInP cladding layer 4 grown on the layer 3 ; an AlGaInP active layer 5 grown on the layer 4 ; a second, upper AlGaInP cladding layer 6 grown on the layer 5 ; an AlGaInP alternated strain layer 7 grown on the layer 6 ; a window layer 8 grown on the layer 7 ; and an ohmic p-electrode on the layer 8 .

A double hetero-junction or multi-quantum well structure could replace active layer 5 .

The alternated strain layer 7 is a structure consisting of thin alternated mismatched multi-layers. Also this structure can be described as a strain layer superlattices structure (SLS). It uses different compositions of (Al x Ga 1-x ) 1-y In y P thin layers as dislocation traps to reduce the induced defect density from upper cladding layer 6 changing to window layer 8 . Also it is useful for modifying the band structure from high band gap upper cladding layer 6 to low band gap window layer 8 by changing the periodicity of (Al x Ga 1-x ) 1-y In y P thin layers, so the forward voltage becomes smaller and more stable.

Compositions of a typical example are set out below.

1. Distributed Bragg layer 3

Al x Ga 1-x As/Al y Ga 1·y As

where 0≦x≦1; 0≦y≦1; x≠y

2. Cladding layers 4 and 6

(Al x Ga 1-x ) 1·y In y P

where 0.5≦x≦1; 0.4≦y≦0.6

Thickness 0.5 μm≦D≦1.5 μm

3. Alternated (superlattice structure) strain layer 7

(Al x Ga 1-x ) 1-y In y P/(Al a Ga 1-a ) 1-b In b P

where 0.5≦x≦1; 0.4≦y≦0.6/0≦a≦0.4; 0≦b≦0.4

Thickness D≦20 nm

4. Multi-quantum well

(Al x1 Ga 1·x1 ) 1-y1 In y1 P/(Al x2 Ga 1-x2 ) 1-y2 In y2 P

where 0.5≦x1≦1; 0.4≦y1≦0.6/0≦x2≦0.4; 0≦y2≦0.4

Thickness D≦20 nm

5. Window layer 8

Ga x In 1-x P

where 0.9≦x≦1

Thickness 5 μm≦D≦15 μm

Claims

1. A light emitting diode comprising:an ohmic n-electrode on a rear surface of a GaAs substrate; a distributed AlGaAs Bragg reflecting layer in the form of a multi-layer lamination; a first, lower AlGaInP cladding layer grown on the reflecting layer; an AlGaInP active layer grown on the lower cladding layer; a second, upper AlGaInP cladding layer grown on the active layer; a strain layer grown on the second cladding layer, the strain layer comprising a superlattice structure in the form of a plurality of thin alternated AlGaInP layers with the composition; (AlxGa1-x)1-yInyP/(AlaGa1-a)1-bInbP where 0.5≦x≦1; 0.4≦y≦0.6/0≦a≦0.4; 0≦b≦0.4; a window layer grown on the strain layer; and an ohmic p-electrode on the window layer.

2. A light-emitting diode according to claim 1, wherein the distributed Bragg layer has the composition:AlxGa1-xAs/AlyGa1-yAs where 0≦x≦1; 0≦y≦1; x≠y.

3. A light-emitting diode according to claim 1, wherein each of the cladding layers has the composition:(AlxGa1-x)1-yInyP where 0.5≦x≦1; 0.4≦y≦0.6.

4. A light-emitting diode according to claim 1, wherein the active layer has the composition:(AlxlGa1-xl)1-ylIny1P/(Alx2Ga1-x2)1-y2Iny2P where 0.5≦x≦l; 0.4≦yl≦0.6/0≦x2≦0.4; 0≦y2≦0.4.

5. A light-emitting diode according to claim 1, wherein the window layer has the compositionGaxIn1-xP where 0.9≦x≦l.