Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2001-06-25
2002-10-08
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S013000, C257S082000
Reexamination Certificate
active
06462356
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a light-emitting device using electroluminescence (EL).
BACKGROUND OF ART
Semiconductor lasers have been used as a light source for optical communications systems. Semiconductor lasers excel in wavelength selectivity and can emit light with a single mode. However, it is difficult to fabricate the semiconductor lasers because many stages of crystal growth are required. Moreover, types of light-emitting materials used for semiconductor lasers are limited. Therefore, semiconductor lasers cannot emit light with various wavelengths.
Conventional EL light-emitting devices which emit light with a broad spectral width have been used in some application such as for displays. However, EL light-emitting devices are unsuitable for optical communications and the like, in which light with a narrow spectral width is required.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a light-emitting device which can emit light having a remarkably narrow spectral width in comparison with conventional EL light-emitting devices and exhibiting directivity, and can be applied not only to displays but also to optical communications and the like.
First Light-emitting Device
A first light-emitting device according to the present invention comprises a substrate and a light-emitting device section,
wherein the light-emitting device section comprises:
a light-emitting layer capable of emitting light by electroluminescence;
a pair of electrode layers for applying an electric field to the light-emitting layer;
a light-propagation section for propagating light emitted in the light-emitting layer;
an insulation layer disposed between the pair of electrode layers, having an opening formed in part, and capable of functioning as a current concentrating layer for specifying a region through which current to be supplied to the light-emitting layer flows through the opening; and
an optical section for light propagated through the light-propagation section,
wherein the optical section forms photonic band gaps in one dimension or two dimension and has a defect section which is set so that an energy level caused by defects is within a specific emission spectrum, and
wherein the light emitted in the light-emitting layer is emitted with spontaneous emission in one dimension or two dimension inhibited by the photonic band gap.
According to this light-emitting device, electrons and holes are injected into the light-emitting layer respectively from the pair of electrode layers (cathode and anode). Light is emitted when the molecules return to the ground state from the excited state by allowing the electrons and holes to reconnect in the light-emitting layer. At this time, light with a wavelength in the photonic band gap cannot be propagated through the optical section. Only light with a wavelength equivalent to the energy level caused by the defects is propagated through the optical section. Therefore, light with a very narrow emission spectrum width with spontaneous emission inhibited in one dimension or two dimensions can be obtained with high efficiency by specifying the width of the energy level caused by the defects.
In the present invention, the light-propagation section is part of the light-emitting device section and supplies light obtained in the light-emitting layer in the light-emitting device section to a waveguide section. The light-propagation section includes at least the optical section and a member (one of the electrode layers, for example) which is connected with a core layer in the waveguide section. This is also applicable to a second light-emitting device as described later.
According to the first light-emitting device, since the insulation layer functions as a current concentrating layer in the light-emitting device section, the region through which current supplied to the light-emitting layer flows can be specified. Therefore, current intensity and current distribution can be controlled in the region from which it is desired to emit light, whereby light is emitted with high emission efficiency.
In the case where the insulation layer functions as cladding, assuming that the waveguide formed of a light-emitting layer as a core and an insulation layer as cladding, the guide mode of light propagated toward the waveguide section through the light-propagation section can be controlled by specifying the opening of the insulation layer. Specifically, the guide mode of light propagated through the light-emitting layer (core) can be set at a specified value by specifying the width of the region in which light is confined (width perpendicular to the direction in which light is transmitted) by the insulation layer (cladding) The relation between the guide mode and the waveguide is generally represented by the following equation.
Nmax+1
≧K
0
·a
·(
n
1
2
−n
2
2
)
½
/(&pgr;/2)
where:
K
0
: 2&pgr;/&lgr;,
a: half width of waveguide core,
n
1
: refractive index of waveguide core,
n
2
: refractive index of waveguide cladding, and
Nmax: maximum value of possible guide mode.
Therefore, if the parameters of the above equation such as the refractive indices of the core and cladding have been specified, the width of the light-emitting layer (core) specified by the width of the opening of the current concentrating layer may be selected depending on the desired guidemode. Specifically, the width (2a) of the light-emitting layer corresponding to the core in a desired guide mode can be calculated from the above equation by substituting the refractive indices of the light-emitting layer provided inside the current concentrating layer and the insulation layer (current concentrating layer) for the refractive indices of the core and cladding of the waveguide, respectively. It is appropriate to determine the suitable width of the core layer of the waveguide section to which light is supplied from the light-emitting device section while taking into consideration the resulting width of the light-emitting layer, calculated value obtained from the above equation based on the desired guide mode, and the like. Light with a desired mode is propagated from the light-emitting device section toward the waveguide section with high combination efficiency by appropriately specifying the width of the light-emitting layer, width of the core layer, and the like. In the light-emitting device section, the light-emitting layer in the current concentrating layer formed using the insulation layer may not uniformly emit light. Therefore, it is appropriate that the designed values for each member such as the light-emitting layer, light-propagation section, and waveguide section be suitably adjusted based on the width (2a) of the core (light-emitting layer) determined using the above equation so that each member exhibits high combination efficiency.
The guide mode of the light-emitting device is preferably 0 to 1000. In particular, when used for communications, the guide mode is preferably about 0 to 10. Light with a specific guide mode can be efficiently obtained by specifying the guide mode of light in the light-emitting layer in this manner.
As described above, according to the present invention, a light-emitting device which can emit light having a remarkably narrow spectral width in comparison with conventional EL light-emitting devices and exhibiting directivity, and can be applied not only to displays but also to optical communications and the like can be provided.
Second Light-emitting Device
A second light-emitting device according to the present invention comprises a light-emitting device section, and a waveguide section which transmits light from the light-emitting device section, the light-emitting device section and the waveguide section being integrally formed on a substrate,
wherein the light-emitting device section comprises:
a light-emitting layer capable of emitting light by electroluminescence;
a pair of electrode layers for applying an electric field to the light-emitting layer;
a light-propagation section for propagating light emitted in the light-
Kaneko Takeo
Koyama Tomoko
Nelms David
Oliff & Berridg,e PLC
Seiko Epson Corporation
Tran Long K.
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