Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Groove formation
Reexamination Certificate
2002-09-26
2004-09-07
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Groove formation
C438S039000, C438S022000, C438S602000, C438S046000, C438S047000, C438S455000, C438S035000, C257S102000, C257S097000, C257S099000, C257S079000, C257S085000, C257S081000, C257S098000
Reexamination Certificate
active
06787383
ABSTRACT:
RELATED APPLICATIONS
This application claims the priority of Japanese Patent Applications No. 2001-297927 filed on Sep. 27, 2001 and No. 2002-259396 filed on Sep. 4, 2002, which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting device and a method for manufacturing thereof.
2. Related Art
A light-emitting device whose light emitting layer section is composed of (Al
x
Ga
1-x
)
y
In
1-y
P alloy (where 0≦x≦1 and 0≦y≦1, which may simply be expressed as AlGaInP alloy, or more simply as AlGaInP, hereinafter) can be provided as a high-luminance device when it employs a double heterostructure in which a thin AlGaInP active layer is placed between an n-type AlGaInP cladding layer and a p-type AlGaInP cladding layer, both of which having a larger band gap than that of the AlGaInP active layer. Recent efforts have also succeeded in putting a blue light-emitting device into practical use, which device having formed therein a similar double heterostructure using In
x
Ga
y
Al
1-x-y
N (where 0≦x≦1, 0≦y≦1 and x+y≦1).
Referring now to an AlGaInP light-emitting device, a light emitting layer section thereof having the double heterostructure is formed by stacking an n-type GaAs buffer layer, an n-type AlGaInP cladding layer, an AlGaInP active layer and a p-type AlGaInP cladding layer, all of which layers are grown in this order on an n-type GaAs substrate by hetero epitaxial growth process. Current supply to the light emitting layer section is effected through metal electrodes formed on the surface of the device. The metal electrodes are typically formed so as to cover only a center portion of the main surface of the light emitting layer section since it can otherwise serve as a light interceptor, which allows the light to be extracted from the peripheral area having no electrode formed therein.
An area of the metal electrode as small as possible in this case can ensure a larger area for light leakage around the electrode, which is advantageous in that improving the light extraction efficiency. Previous efforts have been made in increasing the amount of extracted light by modifying shape of the electrode so as to effectively spread electric current throughout the device. This strategy is, however, still suffering from an inevitable problem of increasing area of the electrode, which raises a dilemma such that decreased area for light leakage undesirably limits the amount of extracted light. There is now another proposal of raising the light extraction efficiency by covering the main surface of the light emitting layer section with an ITO (indium tin oxide) electrode layer having a high conductivity in place of using the metal electrodes, which is typically disclosed in Japanese Laid-Open Patent Publication No. 6-188455 or No. 1-225178.
Investigations by the present inventors, however, revealed that contact resistance with a compound semiconductor layer on the device side tends to become high by using the ITO-made transparent electrode layer as it is, which inevitably degrades the emission efficiency due to increase in series resistance. One typical method to reduce contact resistance is proposed in Japanese Laid-Open Patent Publication No. 1-225178, according to which an electrode contact layer composed of an InGaAs layer is provided between the ITO electrode layer and a semiconductor layer on the device side so as to be corresponded to the entire surface of the ITO electrode layer. It is, however, essential for this case that the electrode contact layer is made of InGaAs or the like having a low band gap energy in order to ensure ohmic contact, so that even an extremely small thickness thereof will inevitably result in degradation in the light extraction efficiency due to absorption of the light. Even for the case where the transparent electrode is used, a problem will still remain in a phase of manufacturing devices in that a metal bonding pad to which a wire for current supply is bonded must be arranged on the transparent electrode. This, however, tends to concentrate drive voltage to the areas where the highly-conductive metal bonding pad is formed, and tends to lower the light extraction efficiency due to poor current supply in the area around the pad, which serves as a light extraction area, so that it may not be always sure that using the transparent electrode promises effects to a sufficient degree.
SUMMARY OF THE INVENTION
Accordingly, the present invention is to provide a light-emitting device having an oxide transparent electrode layer as an electrode for driving light emission, and being capable of enhancing effect of improving the light extraction efficiency exhibited by such oxide transparent electrode layer, and also is to provide a method for manufacturing such light-emitting device.
The light-emitting device of the present invention premises that it has a light emitting layer section which comprises a compound semiconductor layer, and an oxide transparent electrode layer for applying drive voltage for light emission to the light emitting layer section, and that it is composed so that the light from the light emitting layer section can be extracted through the oxide transparent electrode layer, where a feature of the device resides in that an electrode contact layer for reducing contact resistance of the oxide transparent electrode layer is arranged between the light emitting layer section and the oxide transparent electrode layer so as to contact with such oxide transparent electrode layer, where on a contacting interface of such oxide transparent electrode layer, occupied areas and unoccupied areas for the electrode contact layer are arranged in a mixed manner. The electrode contact layer preferably comprises a compound semiconductor.
As has been described in the above, an oxide transparent electrode layer typically composed of ITO cannot always ensure a desirable ohmic contact even though a trial is made on bringing such layer into direct contact with a compound semiconductor layer on the device side, which may result in degraded emission efficiency due to increased series resistance based on the contact resistance. Whereas, the light-emitting device of the present invention is successful in reducing contact resistance of the oxide transparent electrode layer by placing the electrode contact layer for reducing contact resistance of the oxide transparent electrode layer so as to be brought into contact with the device side of such oxide transparent electrode layer. Further, the occupied areas and unoccupied areas for the electrode contact layer are arranged in a mixed manner on the contacting interface of the oxide transparent electrode layer, so that the light absorption by the electrode contact layer can successfully be reduced even when such electrode contact layer is, by nature, very likely to absorb the light from the light emitting layer section, since the light generated just under the occupied area for the electrode contact layer can leak through the non-occupied area adjacent thereto. Such formation of the electrode contact layer can successfully raise the light extraction efficiency of the device as a whole.
The electrode contact layer formed so as to cover the entire portion of the contact plane on the device side of the oxide transparent electrode layer will, however, result in the problems below:
(1) contact resistance of the oxide transparent electrode layer is reduced even in an area just under the bonding pad used for wire bonding, but this undesirably tends to concentrate the drive current, and consequently light emission, within such area, where much portion of the emitted light is shielded by the bonding pad and thus light extraction efficiency will be degraded; and
(2) the electrode contact layer may serve as a light absorber depending on material species of compound semiconductor used therefor, which will similarly result in degradation of the light extraction efficiency.
To solve these problems, a feature of the light-emitting device
Ikeda Shun-ichi
Morisaki Hiroshi
Noto Nobuhiko
Nozaki Shinji
Uchida Kazuo
Anya Igwe U.
Shin-Etsu Hanotai Co., Ltd.
Smith Matthew
Snider Ronald R.
Snider & Associates
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