JPH06151958A - Light emitting device - Google Patents

Abstract

PURPOSE:To obtain a stable light emitting output by installing a resistor for light emitting output controller controlling light emitting output which is connected in parallel to an electrode at a position near the electrode formed on the surface of a second conductive type layer thereby controlling the fluctuation of light emitting output accompanying the temperature change in individual light emitting element. CONSTITUTION:A light emitting diode 8 and a resistor 6 for light emitting output controller are combined in parallel on a light emitting element 10, and a constant current supply circuit 9 for supplying a constant current to the light emitting element 10 is connected to one end of said parallel circuit. When this parallel circuit is driven by a constant current, the resistance value of the resistor 6 for light emitting output controller rises together with temperature increase, and the proportion of a current flowing to the resistor 6 for light emitting output controller decreases. On the other hand, this circuit has a constant current drive, so that the proportion of the current flowing to the light emitting diode 8 increases. Therefore, the resistance value of the resistor 6 for light emitting output controller changes in response to the changes in the light emitting element 10 and ambient temperature and thus the proportion of a current flowing to the light emitting diode 8 is controlled and thus a predetermined light emitting output is always obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, and more particularly to a light emitting device having a surface emitting type light emitting element.

[0002]

2. Description of the Related Art A light emitting device having a small and light emitting element is widely used in various fields. In recent years, a light emitting device has been used in an optical printer that records information by light irradiation, an image reader that reads an image or barcode data by using reflection intensity of light, or an optical communication device that uses an optical signal. There is.

FIG. 7 is a schematic sectional view showing the structure of a light emitting device using gallium arsenide phosphide which has been used conventionally.

In the light emitting device shown in FIG. 7, a gallium arsenide phosphide semiconductor containing tellurium forms an N-type semiconductor 1. Zinc is diffused into the N-type semiconductor 1 to form a P-type gallium arsenide phosphide semiconductor 2 (hereinafter referred to as P-type semiconductor 2). When zinc is diffused into the N-type semiconductor 1, the upper surface of the N-type semiconductor 1 is masked by a selective diffusion film 5 having a diffusion window, and diffusion is performed from the diffusion window. 2 can be formed.

A positive electrode 3 is formed on the upper surface of the P-type semiconductor 2.
And the negative electrode 4 is formed on the back surface of the N-type semiconductor 1. Then, a constant current supply circuit (not shown) that is provided near the light emitting element and supplies a current to the light emitting element causes a forward current to flow to the joint surface between the P-type semiconductor 2 and the N-type semiconductor 1 and is injected. Electric energy is converted into light energy by the diffusion of the carriers, and light is emitted.

In the light emitting device as described above, most of the injected current is converted into heat and self-heats from the light emitting portion. The temperature of the light emitting section rises due to the self-heating and the rise in the ambient environment temperature due to the heat emitted from the entire apparatus such as an optical printer including the light emitting element. It is known that in a general light emitting element, when a constant current flows through the light emitting element, the light emission output decreases as the temperature rises, as shown in FIG. Therefore,
The light-emission output of the light-emitting element fluctuates due to self-heating and a temperature change accompanying a change in ambient environment temperature.

The existence of the fluctuation of the light emission output due to the temperature change is due to the LE of an electrophotographic system for recording an image by light irradiation.
In a D-array printer or the like, this is a serious problem when obtaining high gradation print output. That is, if a temperature change occurs during operation, the light emission output of the light emitting element fluctuates, the intended gradation cannot be reproduced, and high quality print output cannot be obtained.

As a means for correcting the deterioration of print quality caused by the variation of the light emission output due to such temperature change, the temperature near the light emitting portion is detected by a temperature sensor or the like, and the detected temperature information is fed back to the light emitting element drive circuit. do it,
The voltage and current are controlled to control the light emission output to be constant.

[0009]

However, in order to accurately control the light emission output by detecting the temperature change and controlling the voltage and current according to the temperature information, a temperature sensor is provided for each light emitting element. It is necessary to provide it. However, the light emitting element used in the LED array printer or the like is a light emitting element array in which a plurality of light emitting elements are arranged in a line, and providing a temperature sensor for each light emitting element is practical in terms of space and cost. Not. Therefore, in many cases, temperature sensors are arranged at both ends of the light emitting element array or at several places to detect and control the temperature of the entire light emitting element array. Therefore, the entire light emitting device is controlled only by the temperature information about the limited light emitting elements in the vicinity of the temperature sensor, the control corresponding to the temperature change of each light emitting element cannot be performed, and the print quality such as print spots is not controlled. There is a problem that the deterioration cannot be completely corrected.

Therefore, an object of the present invention is to provide a simple and inexpensive light emitting device capable of obtaining a desired stable light emission output by controlling the fluctuation of the light emission output due to the temperature change of each light emitting element. To do.

[0011]

In order to solve the above-mentioned problems, the present invention provides, as a first object, a first conductivity type substrate and a second conductivity type substrate formed on a part of the first conductivity type substrate. A conductive type layer; and a current supply circuit that supplies a current between a pair of electrodes formed on the surfaces of the first conductive type substrate and the second conductive type layer, respectively. In a light emitting device having a light emitting element that causes a current to flow in a forward direction to emit light at a bonding surface between the first conductivity type substrate and the second conductivity type layer, in the vicinity of an electrode formed on the surface of the second conductivity type layer. A light emission output control resistor that is connected in parallel to the electrode at a position and that controls the light emission output by increasing or decreasing the resistance value according to changes in the light emitting element and the ambient temperature, and controlling the current flowing through the light emitting element; Resistor for controlling light emission output and light emission And characterized in that to drive the entire child at a constant current, as the second, the light emission output control resistor is provided in the interior of the current supply circuit, the second
It is characterized in that it is connected in parallel with an electrode formed on the surface of the conductivity type layer. Thirdly, the light emission output control resistor is provided between the light emitting element and the current supply circuit. , And is connected in parallel with the electrode formed on the surface of the second conductivity type layer.

[0012]

In the light emitting device of the present invention, when the light emitting device is driven with a constant current, the surface of the second conductivity type layer of each light emitting element,
Alternatively, the resistance value of the light emission output control resistor connected in parallel with the electrode formed in the vicinity thereof changes according to the self-heating of the light emitting element and the fluctuation of the ambient temperature. That is, when the temperature of the light emitting element rises, the resistance value of the light emission output control resistor rises according to the temperature, and the amount of current flowing into the light emission output control resistor among the supplied constant current decreases. .
On the contrary, the amount of current flowing into the light emitting element increases. Therefore, the amount of current flowing into the light emitting element increases or decreases according to the amount of increase or decrease in resistance of the light emission output control resistor due to temperature change, the light emission output that changes with temperature is corrected, and the light emission output is controlled according to temperature change. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings.

In the light emitting device of the light emitting device according to the present invention, the gallium arsenide phosphide semiconductor containing tellurium forms the N-type semiconductor 1 as shown in the schematic sectional view of FIG. 1 and the schematic plan view of FIG. Zinc is diffused into the N-type semiconductor 1,
A P-type gallium arsenide phosphide semiconductor 2 (hereinafter referred to as P-type semiconductor 2) is formed. When diffusing zinc into the N-type semiconductor 1, the upper surface of the N-type semiconductor 1 is masked by a selective diffusion film 5 having a diffusion window, and diffusion is performed from the diffusion window to a desired range. The P-type semiconductor 2 can be formed. A positive electrode 3 is formed on the upper surface of the P-type semiconductor 2 and a negative electrode 4 is formed on the back surface of the N-type semiconductor 1.

A feature of the present invention is that the light emission output control resistor 6 is provided on the upper surface of the selective diffusion film 5 and the positive electrode 3 is formed.
It is being provided in a state of being connected in parallel with.

The light emitting element drive current is supplied from the constant current supply circuit (not shown) to the light emission output control resistor 6 and the positive electrode 3 through the pads 7a and 7b. At this time, the current supplied to the positive electrode 3 flows in the forward direction to the junction surface between the P-type semiconductor 2 and the N-type semiconductor 1, and the injected majority carriers are diffused to convert the electric energy into light energy. Light is emitted.

The operation state of the light emitting element having the light emission output control resistor formed as described above will be described. FIG. 3 shows an equivalent circuit of the first embodiment of the light emitting device according to the present invention. The light emitting diode 8 and the light emission output control resistor 6 are installed in parallel on the light emitting element 10, and a constant current supply circuit 9 for supplying a constant current to the light emitting element 10 is connected to one end of this circuit. When the temperature of the light emitting element rises due to self-heating and changes in ambient temperature, the light emitting diode 8 has a temperature characteristic that the light emission output decreases as the temperature rises, as shown in FIG. On the other hand, the light emitting output control resistor 6 connected in parallel with the light emitting diode 8 has a temperature characteristic in which the resistance value increases as the temperature rises. When the parallel circuit of the light emitting diode 8 and the light emission output control resistor 6 is driven by a constant current, the light emission output control resistor 6 rises as the temperature rises.
Resistance value increases, and the ratio of the current flowing into the light emission output control resistor 6 decreases. On the other hand, since this circuit is driven by constant current, the ratio of the current flowing into the light emitting diode 8 increases.

Therefore, the resistance value of the light emission output light emission output control resistor 6 changes in response to changes in the light emitting element 10 and the ambient temperature, and the ratio of the current flowing into the light emitting diode 8 is controlled. A light emission output can be obtained.

Next, a method of selecting the light emission output control resistor 6 will be described.

As described above, the light emission output L of the light emitting element is
It is proportional to the current I ₂ flowing into the light emitting element and changes according to the ambient temperature T. Further, the current I ₂ flowing into the light emitting element changes according to the ambient temperature T. That is, let L _{0 be} the change in the light emission output due to the ambient temperature T, g (T) be the function with the temperature at that time as a variable, and h (T) be the function with the temperature as a variable for the change in the current I ₂ . The following three expressions are obtained.

L = L ₀ I ₂ (Equation 1) L ₀ = g (T) (Equation 2) I ₂ = h (T) = L / g (T) (Equation 3) Further, as shown in FIG. , If the light emitting output control resistor 6 and the light emitting diode 8 are connected in parallel and driven by a constant current I,
When the current flowing into the light emitting output control resistor 6 is I ₁ and the current flowing into the light emitting diode 8 is I ₂ , the relationship is I = I ₁ + I ₂ (Equation 4). At this time, the resistance value R of the resistor 6 for controlling the light emission output
Is R = R ₀ (1 + mT) (Equation 5), where R ₀ is the specific resistance value and m is the temperature coefficient. Further, at this time, the flowing current I ₁ is I when the voltage applied to the circuit is V ₁ = V / R = V / {R ₀ (1 + mT)} (Equation 6) Further, since the voltage across the light emitting diode 8 is V, assuming that the current flowing through the light emitting diode 8 is I ₂ and the ambient temperature is T, the function of V indicating the voltage across the light emitting diode 8 is V = f (I ₂ , T) ( It is given by Equation 7). From the above (Equation 1) to (Equation 7), L = g (T) {If (h (T), T) / R ₀ (1 + mT)} (Equation 8) is obtained, and the light emission output is determined as the ambient temperature. It can be represented by T.

Next, using (Equation 8), a simulation is carried out on changes in the light emission output when the ambient temperature is changed.

For example, in a light emitting device using a gallium arsenide phosphide semiconductor, the function g (T) and the function f (h (T)
, T) can be derived from the measured data.

G (T) = 2.88 10 ⁻⁴ exp (−0.0062T) f (h (T), T) = f (I ₂ , T) = (7.7 10 ⁻⁵ I ₂ −0.0022) T + (0.016 I ₂ +1.60) Using these data, the combination of the values of I, R ₀ , and m which makes the light emission output of the light emitting diode almost constant with respect to the ambient temperature including the self-heating amount is simulated from the equations (3) and (8). Get by. For example, in the case of the light emitting element using the gallium arsenide phosphide semiconductor, the values of I, R ₀ , and m at which the optical output-ambient temperature graph becomes substantially horizontal can be selected. In this case, the temperature change of the light output is suppressed to 0.1% / ° C. or less in the temperature range of 0 ° C. to 80 ° C.

I = 9 (mA) R ₀ = 310 (Ω) m = 0.027 (/ ° C.) Here, the resistance of the values of R ₀ and m is determined by the sintered body of metal oxide (thermistor material). It can be easily obtained by using.

In a light emitting device using a double hetero type aluminum gallium arsenide semiconductor, the function g (T)
The function f (h (T), T) can be derived from the actually measured data.

G (T) = 1.17 10 ³ exp (−0.0064T) f (h (T), T) = f (I ₂ , T) = (− 0.0024 I ₂ −0.0033) T + (0.34 I ₂ +1.51 ) Using these data, as in the case of the gallium arsenide phosphide semiconductor, I, R ₀ that makes the light emission output of the light emitting diode substantially constant with respect to the ambient temperature including the self-heating amount according to equations (3) and (8). , M are obtained by simulation. For example, in the case of the light emitting device using the aluminum gallium arsenide semiconductor, the values of I, R ₀ , and m at which the optical output-ambient temperature graph becomes substantially horizontal can be selected. In this case, the temperature change of the light output is suppressed to 0.1% / ° C. or less in the temperature range of 0 ° C. to 80 ° C.

I = 0.9 (mA) R ₀ = 3140 (Ω) m = 0.03 (/ ° C.) The resistance of the values of R ₀ and m is obtained by using a metal oxide sintered body (thermistor material). It is easily available.

Therefore, as shown in FIG. 4, a predetermined light emission output can always be obtained even when the temperature of the light emitting portion and the ambient temperature change. The rate of change of the resistance value of the light emission output control resistor 6 with respect to temperature can be adjusted by the material and shape of the resistor.
In particular, by further short-circuiting the light emission output control resistor 6 by trimming so as to have a shape having a short-circuit path capable of finely adjusting the resistance value, further excellent light emission output control becomes possible. Further, the light emission output control resistor 6 is a light emitting element 10
Since it is provided on the surface of the light emitting element, that is, in the vicinity of the light emitting portion, it can quickly react to the temperature change of the light emitting portion and can always perform a predetermined light emission output control.

Next, an equivalent circuit of the second embodiment is shown in FIGS.
The equivalent circuit of the embodiment is shown in FIG. In the second embodiment, the light emission output control resistor 6 is provided inside the constant current supply circuit 9, and in the third embodiment, the light emission output control resistor 6 is provided in the constant current supply circuit 9 and the light emitting element 10. It is provided between the two. In any case, it can be provided near the light emitting element 10 which generates a large amount of heat or near the constant current supply circuit 9.
The same effect as that of the embodiment can be obtained.

Although the light emitting device in which the P-type semiconductor is formed on the N-type semiconductor has been described in the above embodiment, the light-emitting device having the same structure as the light-emitting device in which the N-type semiconductor is formed on the P-type semiconductor is also described. Can be made. Further, instead of the diffusion type light emitting device, the junction may be formed by epitaxial growth added with impurities.

Further, the junction portion of the light emitting diode is also 1
Not only one PN junction but also a single hetero, a double hetero, or a quantum structure may be used. Further, the light emitting element is not limited to the light emitting diode and may be a laser diode. Further, for simplification, one light emitting diode is shown in the above embodiment, but a light emitting diode array combining two or more may be a laser diode array. Further, in the present embodiment, in constant current driving, a combination of a light emitting element whose light emission output decreases with temperature rise and a resistor whose resistance value rises is shown, but like a light emitting diode using a silicon carbide, A combination of resistors in which the light emission output increases and the resistance value decreases with increasing temperature may be used. In addition, although the gallium arsenide phosphide semiconductor containing tellurium is used as the N-type semiconductor in the above-described embodiment, a gallium arsenide phosphide semiconductor containing tin, selenium, sulfur, germanium, silicon or the like may be used. Also,
The case where a gallium arsenide phosphorus semiconductor containing zinc is used as the P semiconductor has been described, but a gallium arsenide phosphorus semiconductor containing magnesium, manganese, gadnium or the like may be used.

Further, although gallium arsenide phosphorus is used as the P-type semiconductor and the N-type semiconductor in this embodiment, other compound semiconductors such as gallium arsenide, aluminum arsenide phosphorus, gallium-phosphorus, indium-gallium-phosphorus, etc. are used. It is also possible.

In the above embodiment, the method of diffusing the impurities to form the P-type semiconductor has been described. However, the method of diffusing the impurities is not limited to the above-mentioned method. For example, the P-type semiconductor is formed by the ion implantation method. You may form.

Further, in the above-mentioned embodiment, the present invention has been described by using the light emitting device having the PN junction.
The invention is not limited to joining, but for example, PIN joining,
It can also be used for MIS junction and Schottky junction.

[0036]

According to the light emitting element of the present invention, the light emitting element emits light even when the ambient temperature changes rapidly due to self-heating of the light emitting element and heat generation of the entire apparatus such as an optical printer having the light emitting element. Since the current supplied to the part can be controlled according to the change of the light emitting element and the ambient temperature, a predetermined light emission output can be always obtained.

Therefore, when the light emitting device of the present invention is used as an exposure light source for an optical printer or the like, a predetermined light emission output can be obtained irrespective of changes in the ambient temperature during the operation of the optical printer, so that the intended gradation can be obtained. Can be reproduced and high quality print output can be obtained. That is, it is possible to obtain high print quality without print spots. Further, since the light emission output can be controlled only by the resistor, it is inexpensive and the light emitting device can be downsized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view illustrating a first embodiment of a light emitting element of a light emitting device according to the present invention.

FIG. 2 is a schematic plan view illustrating a first embodiment of a light emitting element of a light emitting device according to the present invention.

FIG. 3 is an equivalent circuit illustrating a first embodiment of a light emitting element of a light emitting device according to the present invention.

FIG. 4 is a characteristic diagram showing a light emission output-ambient temperature characteristic when a light emitting element of a light emitting device according to the present invention is driven with a constant current.

FIG. 5 is an equivalent circuit illustrating a second embodiment of the light emitting element of the light emitting device according to the present invention.

FIG. 6 is an equivalent circuit illustrating a third embodiment of the light emitting element of the light emitting device according to the present invention.

FIG. 7 is a schematic sectional view illustrating a light emitting element of a conventional light emitting device.

FIG. 8 is a characteristic diagram showing a light emission output-ambient temperature characteristic when a light emitting element of a conventional light emitting device is driven with a constant current.

[Explanation of symbols]

 1 N-type semiconductor (first conductivity type substrate) 2 P-type semiconductor (second conductivity type layer) 3 Positive electrode 4 Negative electrode 5 Selective diffusion film 6 Light emission output control resistor 9 Constant current drive circuit

Claims (3)

[Claims] 1. A first-conductivity-type substrate, a second-conductivity-type layer formed on a part of the first-conductivity-type substrate by implanting impurities, and each of the first-conductivity-type substrate and the second-conductivity-type layer. A current supply circuit that supplies a current between a pair of electrodes formed on the surface,
A light emitting device including a light emitting element that causes a current to flow between the electrodes in a forward direction by the current supply circuit to cause light to be emitted at a bonding surface between the first conductivity type substrate and the second conductivity type layer, It is connected in parallel to an electrode formed on the surface of the mold layer in parallel with the electrode, and the resistance value is increased / decreased according to the change of the light emitting element and the ambient temperature to control the current flowing through the light emitting element to control the light emission output. A light emitting device comprising a resistor for controlling light emission output, and driving the resistor for light emission output control and the entire light emitting element with a constant current. 2. A first conductivity type substrate, a second conductivity type layer formed on a part of the first conductivity type substrate by impurity implantation, and each of the first conductivity type substrate and the second conductivity type layer. A current supply circuit that supplies a current between a pair of electrodes formed on the surface,
A light-emitting device including a light-emitting element that causes a current to flow between the electrodes in a forward direction by the current supply circuit to emit light at a bonding surface of the first conductivity type substrate and the second conductivity type layer, And is connected in parallel with the electrode formed on the surface of the second conductive type layer, and controls the current flowing through the light emitting element by increasing or decreasing the resistance value according to the change of the ambient temperature. A light emitting device comprising a light emission output control resistor for controlling light emission output, wherein the light emission output control resistor and the entire light emitting element are driven by a constant current. 3. A first conductivity type substrate, a second conductivity type layer formed on a part of the first conductivity type substrate by implanting impurities, and each of the first conductivity type substrate and the second conductivity type layer. A current supply circuit that supplies a current between a pair of electrodes formed on the surface,
A light-emitting device having a light-emitting element that causes a current to flow in a forward direction between the electrodes by the current supply circuit to cause light to be emitted at a bonding surface between the first-conductivity-type substrate and the second-conductivity-type layer, A current that is provided between the current supply circuits and is connected in parallel with an electrode formed on the surface of the second conductivity type layer, and that increases or decreases the resistance value according to changes in the light emitting element and the ambient temperature and flows through the light emitting element. A light emitting device, comprising: a light emission output control resistor for controlling a light emission output by controlling the light emission output, and driving the light emission output control resistor and the entire light emitting element with a constant current.