Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Compound semiconductor
Reexamination Certificate
2002-08-26
2003-05-13
Ghyka, Alexander (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Compound semiconductor
C438S044000, C438S047000
Reexamination Certificate
active
06562649
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compound semiconductor light emitting device, and in particular to a compound semiconductor light emitting device which can be suitably applied to an InP-semiconductor laser having a BH structure (Buried Hetero-structure); and a process for producing the same.
2. Description of the Related Art
Hitherto, a device having the following structure has been known as an InP-semiconductor laser having a BH structure. This device will be described referring to FIG.
4
.
FIG. 4
is a schematic light-emitting end face of an InP-BH structure type semiconductor laser in the prior art.
This device has an InGaAsP active layer
103
in a stripe form over an n-type InP substrate
101
. On the upper and lower surfaces of the active layer
103
, InGaAsP guide layers
105
are formed which have such a composition that the guide layers
105
have larger band gaps than the active layer
103
. On the n-type substrate portions
101
a
at both sides of the active layer
103
, there are formed a p-type InP sub-layer
107
having a carrier concentration of 5×10
17
cm
−3
, and an n-type InP sub-layer
109
having a carrier concentration of 1×10
18
cm
−3
, in this order from the lower to the upper. A p-type InP cladding layer
111
having a carrier concentration of 1×10
18
cm
−3
is formed over/on the active layer
103
and the n-type InP sub-layer
109
. On the p-type InP cladding layer
111
, a p-type InGaAs contact layer
113
is deposited. Electrodes
115
and
117
are formed on the upper surface of the p-type InGaAs contact layer
113
and the lower surface of the n-type InP substrate
101
, respectively.
In this semiconductor laser, a current path narrowing layer, that is, a current blocking layer composed of the p-type sub-layer
107
and the n-type sub-layer
109
is formed at both sides of the active layer
103
. The p-type cladding layer
111
over the active layer
103
, the n-type sub-layer
109
, the p-type sub-layer
107
and the n-type substrate
101
constitute a pnpn structure. By this structure, the current injected to the device does not flow into other than the active layer
103
.
In the p-type cladding layer
111
on/over the n-type sub-Layer
109
and the active layer
103
in such a conventional semiconductor laser, its carrier concentration is raised to 1×10
18
cm
−3
, in order to lower the resistance of the semiconductor laser. However, when the p-type cladding layer
111
is formed, Zn, which is a p-type dopant and may be introduced as DMZn: dimethylzinc (Zn(CH
3
)
2
), is diffused to the n-type sub-layer
109
. As a result, in the n-type sub-layer
109
holes are generated. The holes and electrons, which are n-type carriers, are combined and extinguished so that the number of the n-type carriers in the n-type sub-layer
109
is reduced. Therefore, the function as the n-type of the n-type sub-layer
109
is deteriorated. Namely, carriers are canceled out. Thus, the performance as the current blocking layer, that is, the performance of injecting currents efficiently into the active layer
103
is deteriorated, resulting in a problem that the light emission efficiency of the semiconductor laser falls.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a compound semiconductor light emitting device which makes it possible to keep the effect of confining carriers into an active layer and improve light emission efficiency. Another object of the present invention is to provide a process for producing a compound semiconductor light emitting device.
Therefore, the compound semiconductor light emitting device of the present invention comprises an active layer disposed on/over a first conductive type substrate; a second conductive type sub-layer and a first conductive type sub-layer, in this order from the lower to the upper, disposed on/over the first conductive type substrate and at both sides of the active layer; a second conductive type cladding layer disposed on/over the active layer and the first conductive type sub-layer; a second conductive type contact layer disposed on/over the second conductive type cladding layer; and a second conductive type diffusion barrier layer disposed between the first conductive type sub-layer and the second conductive type cladding layer.
The second conductive type sub-layer and the first conductive type sub-layer form a current blocking layer, and, accordingly, have the function of injecting a current efficiently into the buried active layer. Therefore, each of the sub-layers may also be called as a current block layer. The second conductive type diffusion barrier layer is disposed between the first conductive type sub-layer and the second conductive cladding layer. Therefore, when the light emitting device of the present invention is produced, the diffusion of the second conductive type dopant from the second conductive type cladding layer can be confined into the second conductive type diffusion barrier layer. For this reason, the second conductive type dopant is not incorporated into the first conductive sub-layer. Thus, the first conductive type carrier in the first conductive type sub-layer does not become extinct, so that its carrier concentration does not fall. Thus, the first and second conductive type sub-layers can cooperate to keep the function as the current blocking layer, and consequently the efficiency of injecting the current into the active layer can be improved, as compared with the prior art.
Preferably, each of the first conductive type substrate, the second conductive type sub-layer, the first conductive type sub-layer, the second conductive type cladding layer and the second conductive type diffusion barrier layer may be made of InP; and each of the active layer and the second conductive type contact layer may be made of InGaAs or InGaAsP.
When the semiconductor compound light emitting device is made of the aforementioned materials, Zn (zinc) is used as the second conductive type dopant for forming any second conductive type layer. If the second conductive type cladding layer contacts the first conductive type sub-layer, it is feared that Zn is diffused from the second conductive type cladding layer to the first conductive type sub-layer during the formation of the second conductive type cladding layer. Therefore, if the second conductive type diffusion barrier layer is beforehand formed between the second conductive type cladding layer and the first conductive type sub-layer, the diffusion barrier layer can take therein Zn. Accordingly, the diffusion of Zn to the first conductive type sub-layer can be restrained. Thus, the dopant concentration in the first conductive type sub-layer is not reduced during the formation of the device, so as to result in the value as designed. As a result, the carrier concentration in the first conductive type sub-layer also results in the value as designed.
Preferably, the second conductive type diffusion barrier layer may be a layer formed as follows. Namely, this layer is firstly formed as a preparatory (or provisional) layer having a lower carrier concentration than the carrier concentration in the second conductive type cladding layer. In the subsequent steps of forming the second conductive type cladding layer, the second conductive type dopant is diffused from the second conductive type cladding layer to the preparatory layer. By this diffusion, the preparatory layer is finally turned into a layer having the same or substantially the same carrier concentration as in the second conductive type cladding layer.
According to the above, the second conductive type diffusion barrier layer becomes a layer-substantially functioning as a part of the second conductive type cladding layer in the compound semiconductor light emitting device. As a result, the first conductive type sub-layer can keep the effect as the current blocking layer. Since the second conductive type diffusion barrier layer becomes a part of the second conductive type c
Kashima Yasumasa
Munakata Tsutomu
Ghyka Alexander
Oki Electric Industry Co. Ltd.
Volentine & Francos, PLLC
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