Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2000-04-20
2002-01-08
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S013000, C257S021000, C257S080000, C257S083000, C257S461000, C257S918000, C257S094000, C257S096000
Reexamination Certificate
active
06337493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nitride semiconductor (for example, In
X
Al
Y
Ga
1−X−Y
N, 0≦X, 0≦Y, X+Y≦1) device for use in a light-emitting or light-receiving device such as a light-emitting diode (LED), a laser diode (LD), a solar cell, an optical sensor, or an electronic device such as a transistor or a power device.
2. Description of the Prior Art
Nitride semiconductors are put into practical use as a material for a highly bright blue LED or a purely green LED in various light sources such as a full-color LED display, a traffic signal lamp, or an image scanner light source. Basically, these LED devices have a structure in which a buffer layer made of GaN, an n-side contact layer made of Si-doped GaN, an active layer of a single quantum well (SQW) structure made of InGaN or a multi-quantum well (MQW) structure having InGaN, a p-side cladding layer made of Mg-doped AlGaN, and a p-side contact layer made of Mg-doped GaN are successively laminated on a sapphire substrate, and show extremely excellent characteristics, namely, 5 mW with an external quantum efficiency of 9.1% in the case of a blue LED having a light-emission wavelength of 450 nm at 20 mA, and 3 mW with an external quantum efficiency of 6.3% at 20 mA in the case of a green LED having a light-emission wavelength of 520 nm.
However, although the aforesaid LED devices disclosed by the applicant of the present invention have a high output to be fully applicable for practical use and are applied to various products such as a signal, a LED device capable of reducing the consumed power without decrease in the light-emission output is desired in accordance with the requirement of energy saving and others in recent years. In order to reduce the consumed power of the LED device, reduction in the forward bias voltage of the LED device may be considered.
For example, Japanese Laid-open Patent Publication No. 8-97471 discloses a light-emitting device in which a p-type contact layer has a two-layer structure including, from the electrode side, a first layer doped with Mg at 1×10
20
to 1×10
21
/cm
3
and a second layer doped with Mg at a lower concentration than the first layer and within the range from 1×10
19
to 5×10
20
/cm
3
. However, since the value of Vf attained by the technique of the aforesaid publication is 4V, a further reduction is desired.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a nitride semiconductor device capable of reducing the value of Vf.
Namely, the object of the present invention can be achieved by the following construction (1) to (9).
(1) A nitride semiconductor device comprising;
a substrate,
an n-type nitride semiconductor layer formed on the substrate,
an active layer formed on the n-type nitride semiconductor layer and,
a p-type nitride semiconductor layer formed on the active layer,
wherein said active layer has a quantum well structure including a well layer made of a nitride semiconductor containing In and,
said p-type nitride semiconductor layer has a p-type contact layer, a p-type high concentration doped layer interposed between said active layer and said p-type contact layer and a p-type multi-film layer interposed between said active layer and said p-type high concentration doped layer,
said p-type multi-film layer formed by laminating alternately first nitride semiconductor layers containing Al and second nitride semiconductor layers having a different composition from said first nitride semiconductor layer, at least ones of said first nitride semiconductor layers and said second nitride semiconductor layers containing a p-type impurity,
said p-type contact layer having a p-type impurity concentration higher than that of said p-type multi-film layer and lower than that of said p-type high concentration doped layer.
(2) A nitride semiconductor device as set forth in (1), characterized in that the nitride semiconductor device further comprises;
a p-type low concentration doped layer interposed between said p-type multi-film layer and said p-type high concentration doped layer, said p-type low concentration doped layer having a p-type impurity concentration lower than that of said p-type multi-film layer.
(3) A nitride semiconductor device comprising;
a substrate,
an n-type nitride semiconductor layer formed on the substrate,
an active layer formed on the n-type nitride semiconductor layer and,
a p-type nitride semiconductor layer formed on the active layer,
wherein said active layer has a quantum well structure including a well layer made of a nitride semiconductor containing In and,
said p-type nitride semiconductor layer has a p-type contact layer, a p-type high concentration doped layer interposed between said active layer and said p-type contact layer and a p-type single film layer made of Al
b
Ga
1−b
N (0≦b≦1) containing a p-type impurity interposed between said active layer and said p-type high concentration doped layer,
said p-type contact layer having a p-type impurity concentration higher than that of said p-type single film layer and lower than that of the said p-type high concentration doped layer.
(4) A nitride semiconductor device as set forth in (3), characterized in that the nitride semiconductor device further comprises;
a p-type low concentration doped layer interposed between said p-type single film layer and said p-type high concentration doped layer, said p-type low concentration doped layer having a p-type impurity concentration lower than that of said p-type single film layer
(5) A nitride semiconductor device as set forth in (1) or (2), characterized in that said p-type multi-film layer has a p-type impurity concentration in a range from 5×10
17
to 1×10
21
/cm
3
.
(6) A nitride semiconductor device as set forth in (3) or (4), characterized in that said p-type single film layer has a p-type impurity concentration in a range from 5×10
17
to 1×10
21
/cm
3
.
(7) A nitride semiconductor device as set forth in any one of (1) to (6), characterized in that said p-type high concentration doped layer has a p-type impurity concentration in the range from 5×10
18
to 1×10
22
/cm
3
.
(8) A nitride semiconductor device as set forth in any one of (1) to (7), characterized in that said p-type contact layer has a p-type impurity concentration in a range from 1×10
18
to 5×10
21
/cm
3
.
(9) A nitride semiconductor device as set forth in any one of (2) and (4) to (8), characterized in that said p-type low concentration doped layer has a p-type impurity concentration less than 1×10
19
/cm
3
.
Further, the present invention can make an improvement in the electrostatic breakdown voltage as well as reduction in Vf by the following construction (10) to (12), thereby advantageously increasing the reliability of the device.
(10) A nitride semiconductor device as set forth in any one of (1) to (9), characterized in that said n-type nitride semiconductor layer has an n-type first multi-film layer made by successive lamination of at least three layers including a lower layer made of an undoped nitride semiconductor, a middle layer made of a nitride semiconductor doped with an n-type impurity, and an upper layer made of an undoped nitride semiconductor.
(11) A nitride semiconductor device as set forth in any one of (1) to (10), characterized by having an undoped GaN layer and an n-type contact layer containing an n-type impurity that are successively formed on said substrate.
(12) A nitride semiconductor device as set forth in (11), characterized in that said n-type first multi-film layer is formed on said n-type contact layer, and further the combined thickness of said undoped GaN layer, said n-type contact layer, and said n-type first multi-film layer is 2 to 20 &mgr;m.
In other words, according to the present invention, at least three p-type impurity containing layers having different p-type impurity concentrations, i.e. a p-type multi-film layer doped at a low concentration or a p-type si
Mitani Tomotsugu
Narimatsu Hiroki
Sakai Tomoaki
Tanizawa Koji
Lee Eddie
Lee Eugene
Nichia Corporation
Volentine & Francos, PLLC
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