JP2000349332A - Edge light emitting element and self-scanning light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an edge light emitting element whose outside light emitting efficiency is improved. SOLUTION: In an edge light emitting thyristor, NPNP structures 12, 14, 16, and 18 are laminated on an N type substrate 10, and an insulating film 19 and an anode electrode 20 are formed on the anode layer 18. It is desired that the anode electrode 20 is connected with the anode layer 18 only in the neighborhood of the edge so that the outside light emitting efficiency of the edge light emitting thyristor can be improved. Then, the insulating layer 19 is set at a position separated from the edge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for enhancing the external luminous efficiency of an edge emitting device, and a self-scanning light emitting device using such an edge emitting device.

[0002]

2. Description of the Related Art Conventionally, an edge emitting LED array has been known in order to increase the definition of a light emitting diode (LED) array and improve the coupling efficiency with a lens due to the directivity of emitted light. The basic structure of the edge emitting LED is IEEE Tran
s. Electron Devices, ED-2
6, 1230 (1979).

However, in order to drive an LED array, since each LED is connected to a driving IC by wire bonding or the like, it has been difficult to achieve high definition, compactness, and low cost.

In response to this problem, the present inventors have already filed a patent application for a self-scanning edge light emitting element array having a PNPN structure in which a driving circuit and a light emitting element array are integrated (Japanese Patent Laid-Open No. 9-85885). Gazette).

FIG. 1 shows an edge light-emitting thyristor used in the edge light-emitting device described in Japanese Patent Application Laid-Open No. 9-85885. (A) is a plan view, and (b) is an XY cross-sectional view of (a).

As shown in FIG. 1B, the edge emitting thyristor includes an N-type semiconductor layer 12, a P-type semiconductor layer 14, an N-type semiconductor layer 16, and a P-type semiconductor layer 16 formed on an N-type semiconductor substrate 10.
The semiconductor device includes a P-type semiconductor layer 18 and an anode electrode 20 formed to be in ohmic contact with the P-type semiconductor layer 18. Although not shown, an insulating coating (made of an insulating material that transmits light) is provided on the entire structure, and an Al wiring (not shown) is provided on the structure. A contact hole (not shown) for electrically connecting the electrode and the Al wiring is formed in the insulating film. A cathode electrode (not shown) is provided on the back surface of the N-type semiconductor substrate 10.

In such an edge-emitting thyristor, light is emitted from the edge surfaces of the gate layers 14 and 16.

[0008]

In the conventional edge emitting thyristor, since the injection current from the anode electrode also flows to a location away from the end face as shown by an arrow in FIG. It is difficult to take out the light emission at the end, and the external light emission efficiency from the end face is not good.

Accordingly, it is an object of the present invention to provide an edge light emitting device with improved external light emitting efficiency.

Another object of the present invention is to provide a self-scanning type light emitting device using such an edge light emitting element.

[0011]

According to a first aspect of the present invention, there is provided an edge light emitting device having an electrode for injecting a current into a light emitting layer on an anode layer. In addition, an insulating film is provided so that a current flows therethrough, so that external luminous efficiency is enhanced.

[0012] The insulating film may be provided below the electrode portion remote from the end surface, or the insulating film may have an opening in a portion in contact with the end surface, and the electrode portion other than the electrode portion corresponding to the opening. It is provided below.

The present invention can provide an edge light emitting diode or an edge light emitting thyristor having the above structure.

A second aspect of the present invention is a self-scanning light-emitting device using the edge light-emitting element having the above-described structure.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to an edge light emitting thyristor. The present invention can be generally applied to an edge light emitting device including not only an edge light emitting thyristor but also an edge light emitting diode. .

FIGS. 2A and 2B are a plan view and an XY sectional view of a first embodiment of the edge emitting thyristor of the present invention.

This edge emitting thyristor is an N-type substrate 10
This shows a structure in which NPNP structures 12, 14, 16, and 18 are stacked on top of each other, and an insulating film 19 and an anode electrode 20 are formed on the anode layer.

In order to improve the external luminous efficiency of the edge emitting thyristor, it is desirable that the anode electrode 20 is connected to the anode layer 18 only near the edge face.
The insulating film 19 is provided at a position away from the end face. Here, the magnitude of the current connected to the anode layer 18 is important for improving the external luminous efficiency. As the connection area of the anode electrode 20 to the anode layer is smaller, the distribution of the current flowing from the anode electrode is narrowed, and the current distribution of the light emitting section can be concentrated near the end face, so that the external luminous efficiency is improved.
For example, as shown in FIG. 2A, when the length of the electrode portion connected to the anode layer is L and the width is W, L = 5 μm
m, W = 10 μm (case 1), L = 10 μm, W =
Comparing with 10 μm (Case 2), the light emission amount in Case 1 was able to be increased by 50% compared to Case 2.

FIGS. 3 (a) and 3 (b) show the edge emission according to the present invention.
FIG. 3 shows a plan view and an XY cross-sectional view of a second embodiment of the thyristor.
You. This embodiment further reduces the current distribution in the width direction.
It is made to be able to. That is, the insulating film 3
0 indicates an opening (width W _O, Length L_O) 32 provided
Through this opening, a part of the anode electrode 20 is formed.
Is connected to the anode layer 18. Therefore the electrodes to connect
Area width (W_O× L_O) Can be selected.
According to such a structure, the width W of the opening of the insulating film is obtained. _OIs the electrode
Can be made smaller than the width of
External luminous efficiency by increasing current density
Up.

In the first and second embodiments, the semiconductor layers are stacked on the N-type semiconductor substrate in the order of NPNP. However, the semiconductor layers are stacked on the P-type semiconductor substrate in the order of PNPN. Needless to say, the present invention can be applied to the structure. In this case, the electrode provided on the uppermost N-type semiconductor layer is a cathode electrode, and the electrode provided on the back surface of the P-type semiconductor substrate is an anode electrode.

In the above embodiment, the semiconductor layer of the same conductivity type as that of the semiconductor substrate is laminated immediately above the semiconductor substrate, for the following reason. That is, generally, when a PN (or NP) junction is formed directly on the surface of a semiconductor substrate, the characteristics of the device tend to deteriorate due to poor crystallinity of the formed semiconductor layer. That is, when the crystal layer is epitaxially grown on the substrate surface, the crystallinity of the layer near the substrate surface is worse than the crystallinity after the crystal layer has grown to a certain degree or more. Therefore, once the same semiconductor layer as the semiconductor substrate is formed,
This is because the above-mentioned problem can be solved by forming a PN (or NP) junction. Therefore, it is preferable to interpose this semiconductor layer.

Three basic structures of a self-scanning light-emitting device to which the above-described edge-emitting thyristor can be applied will be described.

FIG. 4 is an equivalent circuit diagram of the first basic structure of the self-scanning light emitting device. Light emitting thyristors T (−2) to T (+2) are used as light emitting elements,
(−2) to T (+2) have gate electrodes G _{−2 to} G _{+2 respectively.}
Is provided. Each gate electrode has a load resistance R
_A power supply voltage V _GK is applied via _L. Each of the gate electrodes G _{-2 to} G ₊₂ is connected to a resistor R _I to create an interaction.
Are electrically connected via Also, three transfer clock lines (φ1, φ2, φ3) are connected to the anode electrode of each single light emitting thyristor every third element (as if repeated).

In operation, first, the transfer clock φ ₃
Becomes high level, and the light-emitting thyristor T (0) is turned on. At this time, from the characteristics of the three-terminal thyristor,
The gate electrode G ₀ is lowered to zero volts nearby. Assuming that the power supply voltage V _GK is 5 volts, the gate voltage of each light emitting thyristor is determined from the network of the load resistance R _L and the interaction resistance R _I. Then, the light emitting thyristor T (0)
, The gate voltage of the element close to
As the distance from (0) increases, the gate voltage increases. This can be expressed as:

V _G0 <V _G1 = V _G−1 <V _G2 = V _G−2 (1) The difference between these voltages is the load resistance R _L and the interaction resistance R _I
Can be set by appropriately selecting the value of.

It is known that the turn-on voltage V _ON on the anode side of the three-terminal thyristor is higher than the gate voltage by the diffusion potential V _dif .

V _ON ≒ V _G + V _dif (2) Therefore, if the voltage applied to the anode is set higher than the turn-on voltage V _ON , the light emitting thyristor is turned on.

[0028] Now a state where the light-emitting thyristor T (0) is turned on to apply a high-level voltage V _H to the next transfer clock pulse phi _1. This clock pulse φ ₁ is simultaneously applied to the light emitting thyristors T (+1) and T (−2),
When the value of the high level voltage V _H is set in the following range, only the light emitting thyristor T (+1) can be turned on.

V _G−2 + V _dif > V _H > V _{G + 1} + V _dif (3) The light emitting thyristors T (0) and T (+1) are simultaneously turned on. When the cut high-level voltage of the clock pulse phi _3, so that the light-emitting thyristor T (0) is able to transfer it becomes ON state and OFF.

As described above, in the self-scanning light-emitting device, the light-emitting thyristors can have a transfer function by connecting the gate electrodes of the respective light-emitting thyristors with a resistance network. From the above-described principle, if the high-level voltages of the transfer clocks φ ₁ , φ ₂ , and φ ₃ are set so as to slightly overlap each other in order, the ON state of the light-emitting thyristor is sequentially transferred. That is, the light emitting points are sequentially transferred, and a self-scanning edge light emitting element array can be realized.

FIG. 5 is an equivalent circuit diagram of the second basic structure of the self-scanning light emitting device. This self-scanning light emitting device
A diode is used as a method of electrically connecting the gate electrodes of the light emitting thyristor. Light emitting thyristor T (-2)
ＴT (+2) are arranged in a line.
G _{-2 to} G ₊₂ are light-emitting thyristors T (−2) to T (+2)
Represents the respective gate electrodes. R _L represents the load resistance of the gate electrode, and D _{−2 to} D ₊₂ represent diodes that perform electrical interaction. V _GK represents a power supply voltage. Two transfer clock lines (φ1, φ2) are connected to the anode electrode of each single light emitting thyristor every other element.

The operation will be described. Transfer clock phi ₂ becomes high level first, and the light-emitting thyristor T (0) is turned on. At this time, due to the characteristics of the three-terminal thyristor, the gate electrode G ₀ is lowered to near zero volt. Assuming that the power supply voltage V _GK is 5 volts, the gate voltage of each light emitting thyristor is determined from the network of the resistor R _L and the diodes D _{-2 to} D ₊₂ . Then, the gate voltage of the element close to the light emitting thyristor T (0) decreases most, and thereafter the gate voltage increases as the distance from T (0) increases.

However, due to the unidirectionality and asymmetry of the diode characteristics, the effect of lowering the voltage works only to the right of T (0). That is, the gate electrode G ₁ is set to a voltage higher than G ₀ by the forward rise voltage V _{dif of the} diode, and the gate electrode G ₂ is set to a voltage higher than G _{1 by} the forward rise voltage V _{dif of the} diode. Is done. On the other hand, the gate electrode G on the left side of T (0)
_{At -1,} no current flows because the diode D _-1 is reverse-biased, and therefore has the same potential as the power supply voltage V _GK .

The next transfer clock pulse φ ₁ is transmitted to the nearest light emitting thyristors T (1), T (−1), and T (3).
And T (−3), among which:
The element with the lowest turn-on voltage is T (1),
Turn-on voltage of about G ₁ of the gate voltage of the T (1) + V
_dif , which is about twice V _dif . The element with the next lowest turn voltage is T (3), which is about four times V _dif . The ON voltage of T (-1) and T (-3) is about V _GK +
V _dif .

[0035] From the above, the high-level voltage of the transfer clock pulse by setting between about 4 times the V _dif about twice the V _dif, it is possible to turn on only the light-emitting thyristor T (1), A transfer operation can be performed.

FIG. 6 is an equivalent circuit diagram of the third basic structure of the self-scanning light emitting device. This self-scanning end face light emitting element array includes switch elements T (-1) to T (2) and light emitting elements for writing L (-1) to L (2). The configuration of the switch element portion shows an example using diode connection. The gate electrodes G _{−1 to} G ₁ of the switch element are also connected to the gate of the light emitting element for writing. A write signal S _in is applied to the anode of the light emitting element for writing.

The operation of the self-scanning light emitting device will be described below. Now, assuming that the transfer element T (0) is in the ON state, the voltage of the gate electrode G ₀ falls below V _GK (here, 5 volts) and becomes almost zero volt. Therefore, if the voltage of the write signal S _in is equal to or higher than the diffusion potential of the PN junction (about 1 volt), the light emitting element L (0) can be made to emit light.

[0038] In contrast, the gate electrode G _-1 is about 5 volts, the gate electrode G ₁ is about 1 volt. Therefore, the writing voltage of the light emitting element L (-1) is about 6 volts,
The write voltage of the light emitting element L (1) is about 2 volts.
Now, the voltage of the write signal S _in which can write only in the light emitting element L (0) is a range of about 1 to 2 volts. When the light emitting element L (0) is turned on, that is, when the light emitting element enters a light emitting state, the voltage of the write signal S _in line is fixed at about 1 volt, so that an error that another light emitting element is selected can be prevented. it can.

The light emission intensity is determined by the amount of current flowing _{in the} write signal _Sin , and it is possible to write an image at an arbitrary intensity. Further, in order to transfer the light emitting state to the next element, it is necessary to once lower the voltage of the write signal S _in line to zero volt and turn off the light emitting element once.

As described above, the self-scanning type light emitting device constituted by using the edge emitting thyristor of the present invention can be applied to an optical print head and the like. When used in an optical print head, high-quality printing can be realized because the external luminous efficiency of each light emitting element is improved.

[0041]

According to the present invention, the insulating film is provided under a part of the electrode so that the current injection electrode is connected to the anode layer only near the end face. This makes it difficult for a current to flow at a location distant from the end face, thereby suppressing light emission.
Since the current easily flows near the end face, light emission can be limited to the vicinity of the end face. Since light emission near the end face can be easily taken out, external light emission efficiency can be improved.

Further, according to the present invention, it is possible to provide a self-scanning light-emitting device in which external light-emitting efficiency is increased by arraying edge light-emitting elements and adding a self-scanning function.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a conventional edge emitting thyristor.

FIG. 2 is a diagram showing a structure of an edge emitting thyristor according to a first embodiment of the present invention.

FIG. 3 is a diagram showing a structure of an edge emitting thyristor according to a second embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram of a first basic structure of the self-scanning light emitting device.

FIG. 5 is an equivalent circuit diagram of a second basic structure of the self-scanning light emitting device.

FIG. 6 is an equivalent circuit diagram of a third basic structure of the self-scanning light emitting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 N-type semiconductor substrate 12 N-type semiconductor layer 14 P-type semiconductor layer 16 N-type semiconductor layer 18 P-type semiconductor layer 19 Insulating film 20 Anode electrode 22 Al wiring 24 Contact hole 30 Insulating film 32 Opening

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Seiji Ohno 3-5-11, Doshumachi, Chuo-ku, Osaka-shi, Osaka Inside Nippon Sheet Glass Co., Ltd. (72) Inventor Nobuyuki Komaba 3-chome, Doshucho, Chuo-ku, Osaka-shi, Osaka No.5-11 Nippon Sheet Glass Co., Ltd. F term (reference) 2C162 FA17 FA20 FA23 5F041 AA03 CA14 CA93 CA98 CB22 CB31 CB33

Claims (7)

[Claims] 1. An edge light emitting device having an electrode for injecting a current into a light emitting layer on an anode layer, wherein an insulating film is provided under a part of the electrode so as to allow a current to flow in the vicinity of the end face, thereby improving external luminous efficiency. An edge light emitting device characterized by being enhanced. 2. The edge light emitting device according to claim 1, wherein said insulating film is provided below an electrode portion on a side farther from the end face. 3. The end face according to claim 1, wherein the insulating film has an opening at a portion in contact with the end face, and is provided below an electrode portion other than the electrode portion corresponding to the opening. Light emitting element. 4. An edge light emitting diode comprising the edge light emitting element according to claim 1. 5. An edge light-emitting thyristor comprising the edge light-emitting element according to claim 1. 6. A light-emitting device having a plurality of control electrodes for controlling a threshold voltage or a threshold current is arranged, and the control electrode of each light-emitting device is connected to the control electrode of at least one light-emitting device located in the vicinity thereof by an electric resistance. Or in a self-scanning light emitting device in which a plurality of wirings for applying a voltage or a current from the outside are connected to an electrode for controlling light emission of each light emitting element, which is connected through an electric element having electric unidirectionality. A self-scanning light emitting device, wherein the light emitting element is the edge light emitting thyristor according to claim 5. 7. A plurality of switch elements having control electrodes for threshold voltage or threshold current for switching operation are arranged, and control of at least one switch element located near the control electrode of each switch element is performed. Connected to the electrodes via electrical resistance or an electrical element having electrical unidirectionality, a power line is connected to each switch element using electrical means, and a clock line is connected to each switch element. A self-scanning switch element array formed, and a light emitting element array in which a plurality of light emitting elements having threshold voltage or threshold current control electrodes are arranged, wherein each control electrode of the light emitting element array is a control electrode of the switch element. A self-scanning light-emitting device provided with a line for applying a current for light emission to each light-emitting element by being electrically connected to the light-emitting element. Light-self-scanning light-emitting device which is a edge-emitting thyristor as described in claim 5.