Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2002-04-25
2004-08-24
Lee, Eddie (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S101000, C257S102000, C257S094000, C257S095000, C257S096000, C257S097000, C257S011000, C257S012000, C257S013000, C257S745000
Reexamination Certificate
active
06781158
ABSTRACT:
RELATED APPLICATION
This application claims the priority of Japanese Patent Application No. 2001-133247 filed on Apr. 27, 2001, which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a light emitting element using compound semiconductor and a method for manufacturing thereof.
DESCRIPTION OF THE BACKGROUND ART
General method for manufacturing light emitting diodes or semiconductor laser elements is such that forming a plurality of compound semiconductor layers on a compound semiconductor singlecrystalline substrate to thereby obtain a multi-layered compound semiconductor wafer having formed therein a p-n junction, and fabricating such wafer into elements. Among these, light emitting diode made from III-V compound semiconductor, and in particular, gallium arsenide phosphide GaAs
1-a
P
a
-base (where a relation of 0.45≦a≦1.0 is satisfied) light emitting diode can be fabricated by forming a plurality of gallium arsenide phosphide GaAs
1-a
P
a
(or gallium phosphide GaP) epitaxial layers on a gallium phosphide GaP or gallium arsenide GaAs singlecrystalline substrate, and by diffusing a p-type impurity such as Zn in the uppermost layer of such epitaxial layers, where selecting mixed crystal ratio a will result in light emission at wavelength region covering red, orange and yellow regions. The reason why the range of the mixed crystal ratio a is defined as 0.45≦a≦1.0 resides in that enhancing indirect transition emission using nitrogen as an isoelectronic trap, which will be described in the next paragraphs.
GaAs
1-a
P
a
-base compound semiconductor has a band structure responsible for indirect transition and is not advantageous in obtaining excellent light emission property in the intact state, so that it is a general practice to dope nitrogen (N) to thereby raise the emission efficiency. Nitrogen can raise the emission efficiency since it forms an isoelectronic trap which acts as a luminescent center in the compound semiconductor, to thereby restrict motion of electrons and widen the distribution range of the electron momentum in a wave number vector-momentum space, which successfully increases direct transition components.
Of the entire nitrogen doped in the GaAs
1-a
P
a
-base compound semiconductor, only a portion thereof residing in a restricted area in the vicinity of the p-n junction portion, where most of emissive recombination of the carrier occur, is contributable to improve light emission efficiency, whereas excessive nitrogen doped in the other area may adversely lower the emission efficiency since it can act as a photo-absorbing center. Japanese Laid-Open Patent Publication No. 2000-312032 thus proposes a structure of light emitting element in which an area having a nitrogen concentration lower than that in the p-n junction is formed on the p layer side, to thereby suppress the emission loss due to light absorption.
The light emitting element of the foregoing publication however suffers from the problems below.
(1) An extremely wide numerical range of 0.3×10
18
atoms/cm
3
to 9×10
18
atoms/cm
3
is disclosed as the concentration of nitrogen to be doped to the p-n junction portion, which is far from being a numerical range for optimizing the emission luminance. There is no consideration on effects on the optimum nitrogen concentration depending on the emission wavelength, that is, exerted by the mixed crystal ratio of a compound semiconductor used.
(2) Too much emphasis on the emission luminance described in the above (1) may not always yield best results in view of long-term sustainment of the element performance.
(3) The improved emission output is ascribable to the constitution in which the n-type layer side of the p-n junction portion is a low-carrier-concentration layer, whereas the p-type layer side has a lowered nitrogen concentration so as to suppress the light absorption. However in such constitution, the light emission is essentially ascribable to hole injection to the n-type layer side, so that the lowered nitrogen concentration in the p-type layer side is not so effective in suppressing the light absorption.
It is therefore a first object of the present invention to provide a GaAsP-base light emitting element capable of sustaining an excellent light emission property for a long period, and a method for manufacturing thereof. It is a second object to provide a GaAsP-base light emitting element having a high luminance and further capable of suppressing light absorption more effectively than in the previous constitution.
SUMMARY OF THE INVENTION
To solve the foregoing problems, the light emitting element of the present invention is characterized in that comprising:
a p-n junction portion responsible for light emission formed between a p-type GaAs
1-a
P
a
layer (where a represents mixed crystal ratio and satisfies a relation of 0.45≦a≦1.0) and an n-type GaAs
1-a
P
a
layer (where a represents mixed crystal ratio and satisfies a relation of 0.45≦a≦1.0); and
a first nitrogen-doped zone formed in a portion including the p-n junction interface between such p-type GaAs
1-a
P
a
layer and n-type GaAs
1-a
P
a
layer,
wherein nitrogen concentration of such first nitrogen-doped zone is set higher than the nitrogen concentration whereat the emission luminance of the light emitting element reaches maximum.
A method for manufacturing a light emitting element is characterized in that manufacturing a light emitting element which comprises a p-n junction portion responsible for light emission formed between a p-type GaAs
1-a
P
a
layer (where a represents mixed crystal ratio and satisfies a relation of 0.45≦a≦1.0) and an n-type GaAs
1-a
P
a
layer (where a represents mixed crystal ratio and satisfies a relation of 0.45≦a≦1.0); and a first nitrogen-doped zone formed in a portion including the p-n junction interface between such p-type GaAs
1-a
P
a
layer and n-type GaAs
1-a
P
a
layer,
and such method comprises the steps of:
fabricating a plurality of light emitting elements by varying nitrogen concentration Y of the first nitrogen-doped zone while keeping a mixed crystal ratio a of the p-type GaAs
1-a
P
a
layer and n-type GaAs
1-a
P
a
layer constant;
finding an emission luminance
itrogen concentration relationship by measuring emission luminance of the individual light emitting elements;
finding from such relationship a nitrogen concentration Y
p
whereat the emission luminance of the light emitting element will become maximum; and
forming the first nitrogen-doped zone so as to have a nitrogen concentration larger than the nitrogen concentration Y
p
.
It should now be noted that notation “GaAs
1-a
P
a
” hereinafter is to express a concept covering both of gallium arsenide phosphide and gallium phosphide unless otherwise being specifically noted.
The light emitting element having formed therein the p-n junction between the n-type GaAs
1-a
P
a
layer and p-type GaAs
1-a
P
a
layer (referred to as GaAsP-base light emitting element hereinafter, which includes GaP-base light emitting element having mixed crystal ratio a of the n-type GaAs
1-a
P
a
layer and p-type GaAs
1-a
P
a
layer of 1) will be successful in raising the emission efficiency as described in the above by virtue of doped nitrogen which functions as an isoelectronic trap, but the element is also known to cause gradual decrease in the emission luminance with time of current supply as indicated by curve {circle around (
1
)} in FIG.
3
. As is known from
FIG. 3
, the luminance decreases with the elapse of cumulative current supply time t from an initial luminance B
1
measured immediately after start of the constant current supply. Length of time necessary for the luminance to reach a predetermined limit luminance B
s
, or ratio of the initial luminance and luminance attained after the elapse of predetermined time period typically 1,000 hours (referred to as element life L, hereinafter), can provide an index for assessing the element life.
Examination by the present inventors revealed the following facts. As shown in
FIG.
Endo Masahisa
Nakamura Akio
Shinohara Masayuki
Gebremariam Samuel A
Lee Eddie
Shin-Etsu Handotai & Co., Ltd.
Snider Ronald R.
Snider & Associates
LandOfFree
Light emitting element and method for manufacturing thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light emitting element and method for manufacturing thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light emitting element and method for manufacturing thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3286241