Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-08-23
2004-06-01
Porta, David (Department: 2878)
Coherent light generators
Particular active media
Semiconductor
Reexamination Certificate
active
06744798
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a surface-type light amplifier device usable as a surface light emitting laser etc. when a resonator is disposed outside the device and to a method for the manufacture thereof. The “surface-type” light amplifier device referred to herein is a device comprising a light function portion for amplifying and emitting light and a substrate for physically supporting the light amplification function portion, wherein the emitted light rises with a specific angle relative to the surface of the substrate, generally in the direction of intersecting the substrate surface at right angles (in the normal direction).
DISCUSSION OF THE BACKGROUND
As for surface-type light amplifier devices of this type, there is the one disclosed in Reference Literature 1: “Electrically pumped mode-locked vertical-cavity semiconductor lasers” (W. Jiang, M. Shimizu, R. P. Mirin, T. E. Reynolds and J. E. Bowers, Optics Letters, Vol. 18, No. 22, pp. 1937-1939, 1993). As shown in
FIG. 2
, the prior art surface-type light amplifier device
30
structurally comprises an n-type GaAs substrate
31
on which a multilayer reflecting mirror of n-type semiconductor
32
, an n-type cladding layer
33
, an n-type GaAs active layer
34
, a p-type cladding layer
35
, a p-type AlGaAs layer
37
and a p-type GaAs contact layer
38
are deposited in the order mentioned. The p-type AlGaAs layer
37
and p-type GaAs contact layer
38
are partially cut off into a shape having a shape having a predetermined surface area. An antireflection coating
39
is deposited onto the top surface of the p-type GaAs contact layer. A surface electrode
40
is formed on the p-type cladding layer
35
, with an insulating film
36
sandwiched therebetween, so as to surround the cut-off portions and come into contact with the top peripheral part of the p-type GaAs contact layer
38
. A substrate electrode
41
is deposited on the bottom surface of the n-type substrate
31
.
Injection of carriers into the n-type GaAs active layer
34
is attained by current injection, i.e. by applying voltage between the surface electrode
40
and the substrate electrode
41
.
Holes are injected from the surface electrode
40
into the n-type GaAs active layer
34
sequentially via the p-type GaAs contact layer
38
, p-type AlGaAs layer
37
and p-type cladding layer
35
. Electrons are injected from the substrate electrode
41
into the n-type GaAs active layer
34
sequentially via the n-type GaAs substrate
31
, multilayer reflecting mirror of n-type semiconductor
32
and n-type cladding layer
33
.
When the prior art device
30
is used as a light amplifier device or particularly as a surface-emitting laser, the associated resonator comprises the multilayer reflecting mirror of n-type semiconductor
32
built in the device and an external reflecting mirror (not shown). Between the external reflecting mirror not shown and the antireflection coating
39
there is generally disposed a lens (not shown). It goes without saying that the antireflection coating
39
is used for reducing the resonator loss and obtaining the light gain. For the same reason, the layers
33
to
35
,
37
and
38
are subjected to treatments such as for suppressing the impurity concentration etc. to a low degree so that the optical absorption loss can be lowered.
FIG. 3
shows another prior art surface-type light amplifier device
50
. This device is disclosed in Reference Literature 2: “High single-transverse-mode output from external-cavity surface-emitting laser diode” (M. A. Hadley, G. C. Wilson, K. Y. Lau and J. S. Smith, Appl. Phys. Lett., Vol. 63, No. 12, pp. 1607-1609, 1993) and comprises a GaAs substrate
51
not of n-type but of p-type, on which a multilayer reflecting mirror
52
of p-type semiconductor, a p-type multi-quantum well active region
53
and a multilayer reflecting mirror
55
of n-type semiconductor are deposited in the order mentioned. Voltage is applied between a substrate electrode
57
deposited on the bottom surface of the substrate
51
and a bonding pad
56
disposed on an insulating film
54
and brought into contact with the top peripheral surface of the multilayer reflecting mirror of n-type semiconductor
55
to inject an electric current (carriers) into the multi-quantum well active region
53
, thereby obtaining excited light. Holes are injected from the side of the substrate electrode
57
into the multi-quantum well active layer
53
via the p-type GaAs substrate
51
and the multilayer reflecting mirror of p-type semiconductor
52
, whereas electrons are injected thereinto from the opposite side, i.e. from the bonding pad
56
, via the multilayer reflecting mirror of n-type semiconductor
55
.
This device
50
is, by nature, not a device for an external resonator. However, in the case that a resonator is composed only of the multilayer reflecting mirror of n-type semiconductor
55
and the multilayer reflecting mirror of p-type semiconductor
52
embedded in the device, it inevitably poses a substantial problem that the transverse mode does not become a single lobe when the diameter of the device is made large. In order to solve the problem it is necessary to provide an external reflecting mirror not shown. Single-lobe beams can be obtained by deliberately lowering the reflecttivity of the multilayer reflecting mirror of n-type semiconductor
55
, then providing a suitable reflecting mirror outside the device on the side of the multilayer reflecting mirror of n-type semiconductor
55
, and adjusting the position of a lens disposed in an optical path toward the external reflecting mirror, for example. In any event, the resonator has a composite construction comprising a first resonator composed of the multilayer reflecting mirror of p-type semiconductor
52
and the multilayer reflecting mirror of n-type semiconductor
55
which are provided in the device and a second resonator composed of the multilayer reflecting mirror of p-type semiconductor
52
and the external reflecting mirror.
In the device
30
shown in
FIG. 2
, however, it is particularly difficult to obtain laser beams having a large diameter. This is because, if the effective area of the n-type GaAs active layer
34
, i.e. the area coated with the antireflection coating
39
and actually contributing to oscillation, is made large for enlarging the device diameter, it will become impossible to uniformly inject holes into that area. This results solely from the fact that each of the p-type semiconductor layers
38
,
37
and
35
has high electrical resistance. In order to inject holes into the neighborhood of the center of the effective area of the n-type GaAs active layer, it is necessary to cause the holes first to flow through the p-type semiconductor layers
38
,
37
and
35
in the in-plane direction from the surface electrode
40
in contact with the peripheral edge of the antireflection coating
39
and then to be injected into the center of the n-type GaAs active layer
34
. In the actual course of operation, however, this cannot be attained because the majority of holes are injected into the peripheral edge of the p-type GaAs contact layer
38
from the surface electrode
40
and then advance straightforward without being well spread laterally and reach the n-type GaAs active layer
34
.
In order to actually secure the state of uniform hole injection into the n-type GaAs active layer
34
in the conventional device
30
fabricated in accordance with such structural principle, it is required to reduce the diameter of the effective area of the n-type GaAs active layer
34
to not more than tens of &mgr;m. That is to say, when a large output power is required, it is necessary to adopt a method of arraying a plurality of devices, resulting in sacrifices of singleness and uniformity of optical beams.
In the conventional device
50
shown in
FIG. 3
, however, since holes can be injected from the substrate electrode
57
in surface contact with the back surface of the p-type GaAs substrate
51
, the uniformity in the in-plane d
Agency of Industrial Science and Technology
Monbleau Davienne
Porta David
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