Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – Using an energy beam or field – a particle beam or field – or...
Reexamination Certificate
1998-10-27
2001-03-27
Chaudhuri, Olik (Department: 2814)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
Using an energy beam or field, a particle beam or field, or...
C438S479000
Reexamination Certificate
active
06206962
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light emitting device having a structure in which an n-type cladding layer, an active layer and a p-type cladding layer, respectively made of a Group II-VI compound semiconductor, are sequentially stacked and to a method of manufacturing same.
2. Description of the Related Art
In recent years, a demand for the high density, high resolution of recording and reproduction of an optical disc and a magneto-optic disc rises. There is also a marked tendency to develop a high brightness display device and a low-loss optical fiber communication device as well as an optical analytic device for DNA and a particular chemical substance. In response to them, the development of semiconductor light emitting devices capable of emitting green or blue light has been demanded as their light sources.
As materials for composing the green or blue light emitting semiconductor devices, Group II-VI compound semiconductors each of which comprises at least one element of Group II elements of zinc (Zn), magnesium (Mg), beryllium (Be), cadmium (Cd), mercury (Hg) and manganese (Mn) and of at least one of elements of Group VI of oxygen (O), sulfur (S), selenium (Se) and tellurium (Te) hold great promise.
To obtain a semiconductor light emitting device having high luminous efficiency, it is necessary to improve the crystallinity of the Group II-VI compound semiconductors. Among the Group II-VI compound semiconductors, mixed crystal of ZnMgSSe, in particular, can lattice-match with a substrate comprising GaAs or ZnSe which is excellent in crystallinity and easy to obtain, which enables it to improve crystallinity. The ZnMgSSe mixed crystal is, therefore, particularly known as a material for the guiding layer and the cladding layer of a semiconductor light emitting device (as shown in, for example, Electronic Letters 28 (1992), page 1,798).
The Group II-VI compound semiconductors are, however, generally difficult to have high carrier concentrations even if p-type impurities are added thereto. The mixed crystal of ZnMgSSe, for example, has a low carrier concentration of only about 1×10
17
to 2×10
17
cm
−3
. Among materials which lattice-match with GaAs, ZnSSe mixed crystal can have a higher carrier concentration than ZnMgSSe, however, at most, it is only about 7×10
17
cm
−3
. For that reason, even if a p-side electrode is formed through a ZnSSe layer above a cladding layer made of ZnMgSSe mixed crystal, it is difficult to maintain an ohmic contact with the p-side electrode, thereby causing a rise in operating voltage. Due to this, power consumption increases and, at the same time, heat is generated disadvantageously resulting in a deterioration in device.
In the prior art in consideration of these disadvantages, Group II-VI compound semiconductor layers capable of obtaining high carrier concentrations without lattice-matching with GaAs are formed above the ZnSSe layer to lower operating voltage. A ZnSe layer, for example, capable of obtaining a carrier concentration of about 1×10
18
cm
−3
is formed on the ZnSSe layer and a ZnTe layer capable of obtaining a carrier concentration of about 1×10
19
cm
−3
is formed on the ZnSe layer.
The conventional semiconductor light emitting device can maintain an ohmic contact between the ZnTe layer and the p-side electrode. The carrier concentration of the ZnSe layer is, however, low and it is impossible to sufficiently lower operating voltage. As a result, the conventional device is disadvantageous in that sufficiently longer life time cannot be expected. The reason is considered to be the influence of the ZnTe layer.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-stated disadvantages. It is therefore an object of the present invention to provide a semiconductor light emitting device capable of lowering operating voltage by increasing the carrier concentrations of Group II-VI compound semiconductor layers provided between a p-side electrode and a p-type cladding layer, and to provide a method of manufacturing same.
A semiconductor light emitting device according to the present invention has a structure in which at least an n-type cladding layer, an active layer, a p-type cladding layer and a cap layer including Group II-VI compound semiconductors comprising at least one element of Group II elements of zinc (Zn), magnesium (Mg), beryllium (Be), cadmium (Cd), manganese (Mn) and mercury (Hg) and at least one element of Group VI elements of oxygen (O), sulfur (S), selenium (Se) and tellurium (Te), respectively, are sequentially stacked, in which a p-side electrode is formed in contact with the cap layer, wherein the cap layer has a thickness of less than 10 nm.
Another semiconductor light emitting device according to the present invention is provided in which at least an n-type cladding layer, an active layer, a p-type cladding layer and a contact layer comprising Group II-VI compound semiconductors consists of at least one element of Group II elements of zinc (Zn), magnesium (Mg), beryllium (Be), cadmium (Cd), manganese (Mn) and mercury (Hg) and at least one element of Group VI elements of oxygen (O), sulfur (S), selenium (Se) and tellurium (Te) are respectively stacked in this order, wherein p-type impurities in concentration of 1×10
18
cm
−3
or more and 2×10
18
cm
−3
or less are added to the contact layer.
A yet another semiconductor light emitting device according to the present invention is provided in which at least an n-type cladding layer, an active layer, a p-type cladding layer, a backing layer and a contact layer comprising Group II-VI compound semiconductors comprising at least one element of Group II elements of zinc (Zn), magnesium (Mg), beryllium (Be), cadmium (Cd), manganese (Mn) and mercury (Hg) and at least one element of Group VI elements of oxygen (O), sulfur (S), selenium (Se) and tellurium (Te), are respectively stacked in this order, wherein p-type impurities in concentration of 1×10
18
cm
−3
or more and 3×10
18
cm
−3
or less are added to the backing layer.
A method for manufacturing a semiconductor light emitting device according to the present invention, comprises the steps of:
growing a plurality of Group II-VI compound semiconductor layers comprising at least one element of Group II elements of zinc (Zn), magnesium (Mg), beryllium (Be), cadmium (Cd), manganese (Mn) and mercury (Hg) and at least one element of Group VI elements of oxygen (O), sulfur (S), selenium (Se) and tellurium (Te), by irradiating corpuscular beams onto a substrate, respectively; and
thereby manufacturing the semiconductor light emitting device comprising at least an n-type cladding layer, an active layer, a p-type cladding layer, a backing layer and a contact layer sequentially stacked on the substrate, wherein
a growth temperature in a growth step in which Group II-VI compound semiconductor layers are grown after the backing layer is formed, is set lower than the growth temperature of the formation of the preceding layers in the growth step.
Another method for manufacturing a semiconductor light emitting device according to the present invention comprises the steps of:
growing a plurality of Group II-VI compound semiconductor layers comprising at least one element of Group II elements of zinc (Zn), magnesium (Mg), beryllium (Be), cadmium (Cd), manganese (Mn) and mercury (Hg) and at least one element of Group VI elements of oxygen (O), sulfur (S), selenium (Se) and tellurium (Te), by irradiating corpuscular beams onto a substrate, respectively; and
thereby manufacturing the semiconductor light emitting device comprising at least an n-type cladding layer, an active layer, a p-type cladding layer, a backing layer and a contact layer stacked in this order on the substrate, wherein
a growth temperature in the growth step of growing Group II-VI compound semiconductor layers after formation of the backing layer is set lower than a temper
Kijima Satoru
Okuyama Hiroyuki
Chaudhuri Olik
Sonnenschein Nath & Rosenthal
Sony Corporation
Wille Douglas A.
LandOfFree
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