JPH07297448A - Light emitting device - Google Patents

Abstract

PURPOSE:To highly suppress the light emitting intensity of a light emitting device by connecting in series light emitting elements and electronic elements having negative resistance. CONSTITUTION:An n-type GaAs layer 302, AlGaAs layer 303, InGaAs layer 304, AlGaAs layer 305, and n-type GaAs layer are successively formed on an n-type GaAs substrate by epitaxial growth so that the layers 302, 303, 304, 305, and 306 can constitute a resonance tunnel diode. The layers 303 and 305 are barrier layers and a quantum level is formed in the 304 between the layers 303 and 305. A current-voltage characteristic having a negative resistance is obtained, because, when a bias voltage is applied across the diode 10, an electric current flows when the energy position of the quantum level coincides with the lower end of the conductive zone of one AlGaAs layer, but, when the bias voltage is higher or lower, no electric current flows. The electrons flowing in the layer 308 from the layer 307 are re-coupled with holes flowing in the layer 308 from the layer 309 and, when the electrons are re-coupled with the holes, light is generated.

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 such as a light emitting diode and a laser, and more particularly to a light emitting device which facilitates control of light emission intensity by an external voltage and enables light emission at a plurality of wavelengths.

[0002]

2. Description of the Related Art Light emitting diodes (hereinafter referred to as LEDs) and lasers (hereinafter referred to as LDs) have been known as solid-state light emitting elements, and are used in optical communication, optical disks, lamps, displays and the like. Widely used in the field.

Known lamps and displays using solid-state light-emitting elements include color lamps and color displays in which LEDs capable of emitting red, green, and blue light are combined (for example, Jun Usami et al., IEICE Technology). Research report EID 90-100). Further, a radiation type display using a laser as a light source is also known.

[0004]

The conventional solid-state light-emitting device is a two-terminal device, which emits light by applying a voltage between the terminals to energize it. In the LD, when the applied voltage was increased and the current reached a certain threshold value, laser oscillation occurred and laser light was obtained. Further, the current also sharply rises at a certain voltage in the LED, and the light emission intensity increases. As described above, in the conventional solid-state light emitting device, there was a lower limit to the voltage applied to the two terminals in order to obtain light of desired intensity, but at a large voltage, light emission always occurred unless the device was destroyed. In other words, it causes light emission only in a certain applied voltage range,
It was not possible to suppress light emission at a voltage above and below that.

As described above, in the conventional solid-state light emitting device, the light emission cannot be freely controlled by the applied voltage. For this reason, there is a limitation in the method of combining a plurality of light emitting elements or in combination with an electronic element. For example, in a lamp or a display, when light emission of a plurality of wavelengths is mixed to obtain light emission of a desired color, it is necessary to separately adjust the voltage and current applied to the solid-state light emitting element having each light emission wavelength.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new light emitting device capable of controlling emission intensity higher than ever before in order to overcome the above problems.

[0007]

The object of the present invention is achieved by connecting in series a light emitting element which emits light when energized and an electronic element having a negative resistance.

The object of the present invention is also achieved by connecting in parallel two or more elements in which at least one light emitting element and an electronic element having a negative resistance are connected in series.

The object of the present invention is also achieved by forming a light emitting region made of a semiconductor layer and a conductive region having a negative resistance on the same substrate, and connecting the semiconductor layer and the conductive layer in series.

The object of the present invention is also achieved by forming two or more light emitting regions made of a semiconductor layer and a conductive region connected in series to at least one of these light emitting regions on the same substrate.

The object of the present invention is also to provide the above semiconductor layer III.
This can be achieved by using a semiconductor selected from the group of semiconductors consisting of -V group semiconductors and II-VI group semiconductors.

The object of the present invention is also achieved by constructing the semiconductor layer and the conductive layer using a semiconductor selected from the group consisting of III-V semiconductors and II-VI semiconductors.

[0013]

1 is a block diagram of an embodiment of the present invention.
An electronic element 101 having a negative resistance is connected in series to the light emitting element 100. A voltage is applied between the terminals 102 and 103 to energize the light emitting element 100 and the electronic element 101 to cause the light emitting element to emit light.

FIG. 2 is a current-voltage characteristic (IV characteristic) diagram for explaining the operating principle of the device shown in FIG. Figure 2
The curve 110 in the inside represents the characteristics of the electronic device. When the voltage is increased, the current increases once and then decreases, and it has a so-called negative resistance. Curves 111, 112, 11
3 is a load curve when the light emitting element is regarded as a load on the electronic element. This load curve is also the current-voltage characteristic of the light emitting element, and is represented by a straight line here for simplicity. Here, the value of the current flowing through the light emitting element necessary to obtain the emission intensity determined according to each application is Ith.
And When the light emitting element is an LD, Ith may be regarded as a threshold value of a current required for laser oscillation. As shown in FIG. 2, when the voltage between the terminals 102 and 103 in FIG. 1 is V1 or more and V2 or less, the current becomes Ith or more and a desired light emission intensity is obtained. On the other hand, when V1 or less or V3 or more, the emission intensity becomes less than the desired intensity. As described above, desired light emission can be caused only in a certain voltage range.

FIG. 3 is an IV characteristic diagram for explaining another operation principle of the device shown in FIG. Reference numeral 114 in this figure is a load curve obtained from the IV characteristic of the light emitting element. In FIG. 3, the load curve 114 intersects the IV characteristic of the electronic device at two points. This indicates that the device of Figure 1 has two stable states. Of these two states,
The emission intensity is high when the current value is high, and the emission intensity is low when the current value is low. For example, as a light emitting element, L
When D is used, if the low current value is equal to or lower than the oscillation threshold value, these two states are substantially light on / off states. As long as there is no disturbance from the outside, the transition between these two states does not occur, and it has a so-called memory function. Further, as a disturbance from the outside, if a pulse voltage is applied in combination with a DC bias, it is possible to easily cause a transition between the two states.

FIG. 4 shows a case where two or more light emitting devices shown in FIG. 1 are connected in parallel.

Reference numerals 201, 202 and 203 denote light emitting elements, and 20
Reference numerals 4, 205 and 206 are electronic elements having negative resistance. If each combination of the light emitting device and the electronic device follows the operation principle described in FIG. 2, and if the IV characteristics of the light emitting device and the electronic device are adjusted so that light emission of each light emitting device can be obtained in different voltage ranges, Each light emitting element can be made to individually emit light only by the voltage value applied between the terminals 210 and 211. For example, if a light emitting element that emits the three primary colors of light, red, green and blue, is used, it can be applied to a color display. In the conventional color display, it is necessary to individually control the light emitting elements that generate lights of different wavelengths, but according to the present invention, there is an advantage that the control circuit becomes simpler because it can be controlled only by the voltage value.

The light emitting device and the electronic device are III-V group semiconductors or
These devices can be formed on the same substrate by using a II-VI group semiconductor. Since the lattice constant of the II-VI group semiconductor is close to the lattice constant of the III-V group semiconductor, a high quality II-VI group semiconductor can be epitaxially grown on the III-V group semiconductor substrate. Moreover, II-VI semiconductors and III-
Group V semiconductors have band gaps of various values, and cover the ultraviolet to infrared region in the wavelength range. For this reason,
It is suitable for applications such as displays. Furthermore, since a heterojunction with a large band discontinuity at the junction surface can be obtained, a quantum well with high energy can be created, and by utilizing resonant tunneling through the quantum well level, an electronic device with a large negative resistance can be created. can do. This can increase the ratio of the emission intensity when the light emitting element is on and when it is off.

[0019]

【Example】

<First Embodiment> A first embodiment of the present invention will be described with reference to FIG. In this example, GaA, which is one of the III-V semiconductors, is used.
3 is an example of a light emitting device manufactured on a substrate made of s. n
N-type GaAs layer 302, Al on the n-type GaAs substrate 301
GaAs layer 303, InGaAs layer 304, AlGaAs layer 3
05, the n-type GaAs layer 306 is sequentially epitaxially grown. This epitaxial growth may be performed by molecular beam epitaxy, chemical vapor deposition, or the like. The layers 302 to 306 form a resonant tunneling diode. AlGaAs layer 303, InGaAs layer 304, A
Each of the lGaAs layers 305 has a thickness of about several nm. AlGaAs layers 303 and 305 are barrier layers,
Quantum levels are formed in the InGaAs layer 304 sandwiched between them.

When a bias is applied, a current flows when the energy level of the quantum level coincides with the lower end of the conduction band of one AlGaAs layer, but no current flows in the bias before and after the current band. The characteristics are obtained. Further on the n-type GaAs layer 306, n-type Al
GaAs layer 307, GaAs layer 308, p-type AlGaAs
The layer 309 and the p-type GaAs layer 310 are grown.

The layers 307 to 310 form a light emitting device. 307, 308 and 309 form a so-called pin junction, and light is emitted from the GaAs layer 308 which is an i layer. 311 and 312 are ohmic electrodes. The electrons flowing from the n-type AlGaAs layer 307 into the GaAs layer 308 are recombined with the holes flowing from the p-type AlGaAs layer 309, and at this time, light is emitted. Light may be extracted in a direction parallel to or perpendicular to the semiconductor layer. When light is extracted in the direction parallel to the semiconductor layer, laser oscillation can be caused by using two parallel crystal planes obtained by cleaving the semiconductor on a plane perpendicular to the semiconductor layer as reflection surfaces for light.

Next, the case where the present light emitting device is used according to the principle shown in FIG. 2 will be described. A positive voltage is applied to the terminal 313 as compared with the terminal 314. When the positive voltage is gradually increased, the current between the two terminals increases, and when a certain voltage is reached, a desired light emission intensity can be obtained. When the voltage is further increased, it enters the negative resistance region of the resonant tunneling diode,
The current gradually decreases. When the voltage exceeds a certain level, light emission hardly occurs. In the case where the light emitting portion is created so as to oscillate, a current equal to or higher than the threshold current for laser oscillation flows only in a certain voltage region, and laser oscillation occurs. By adjusting the current-voltage characteristics of the resonant tunneling diode by changing the thickness of the semiconductor layers 303 to 305, the voltage region in which substantial light emission is obtained can be adjusted. From the above, a light emitting device that emits light only in a certain specific voltage range can be obtained.

The light emitting device of this embodiment can also be used in the operating principle of FIG. 3 by adjusting the current-voltage characteristic of the resonant tunnel diode. In this case, even if the voltage between the two terminals is constant, a bistable state corresponding to the on / off state of light emission is realized. To shift from the off state to the on state, a negative pulse voltage may be applied so as to be superposed on a constant voltage between the two terminals. Further, it is possible to shift from the ON state to the OFF state with a positive pulse voltage.

In the present embodiment, both the light emitting element and the negative resistance element are made of III-V group semiconductors, but they may be made of other semiconductors. In particular, a device having a wide range of emission wavelength can be obtained by making it in combination with a II-VI group semiconductor. Moreover, since a large negative resistance is obtained, it becomes easy to design a voltage value that can obtain an on / off state of light emission.

Although the resonance tunnel diode is used as the negative resistance element in the above, other electronic elements such as Esaki diode may be used.

The light-emitting device shown in this embodiment can be applied to a light-emitting device used in a display device, optical communication, etc., which makes the control of light emission intensity much easier than in the past. Further, when it is used in the operation principle having a bistable state, it can be applied to a logic circuit or a memory circuit.

<Second Embodiment> FIG. 6 shows a second embodiment of the present invention.
Will be explained. This embodiment is an embodiment of a light emitting device capable of emitting light with two different wavelengths. On the n-type GaAs substrate 401, the n-type GaAs layer 402 and the AlGaAs layer 40
3, InGaAs layer 404, AlGaAs layer 405, and n-type GaAs layer 406 are sequentially epitaxially grown. An n-type AlGa layer is further formed on the n-type GaAs layer 406.
An As layer 407, a GaAs layer 408, a p-type AlGaAs layer 409, and a p-type GaAs layer 410 are grown.

The layers 402 to 406 form a resonant tunneling diode, and the operating principle thereof is as described in the first embodiment. AlGaAs layer 403, InG
The thickness of each of the aAs layer 404 and the AlGaAs layer 405 is about several nm. The layers 407 to 410 form the first light emitting element.

On the p-type GaAs layer 410, a p-type ZnSe layer 411, a p-type ZnMgSSe layer 412 and a p-type ZnS layer are further formed.
Se layer 413, ZnCdSe layer 414, n-type ZnSSe
Layer 415, n-type ZnMgSSe layer 416, n-type GaAs
Layer 417 is grown by molecular beam epitaxy.
The layers 411 to 417 form the second light emitting element. The ZnCdSe layer 414 mainly emits light. 418,
Reference numerals 419 and 420 are ohmic electrodes. The first light emitting element emits red light, while the second light emitting element emits blue light.

Next, a method of operating the light emitting element will be described. The terminals 421 and 422 have the same potential, and a negative voltage is applied as compared with the terminal 423. In this case, the first light emitting element and the second light emitting element are connected in parallel. However, a negative resistance is connected in series to the first light emitting element. Here, the operation principle of the portion including the first light emitting element and the negative resistance element connected in series with the first light emitting element follows the principle described in FIG. In this case, the first light emitting element emits light only in the voltage range in which the current supplied by the negative resistance element is a certain value or more.
On the other hand, the voltage value at which the second light emitting element emits light is larger than the voltage value at which the first light emitting element emits light. Therefore, only one of the first light emitting element and the second light emitting element can emit light only by the voltage value.

When the light emitting device according to the present embodiment is applied to a multi-wavelength lamp or display, the emission wavelength can be controlled by a control circuit simpler than the conventional one. Moreover, since a plurality of light emitting elements can be formed by stacking them, higher integration can be achieved. In addition, when used as a light source of a radiative display, it is possible to generate light with a plurality of wavelengths from a spatially close portion, unlike the conventional method in which a plurality of light emitting elements are used side by side, so that a higher definition radiation can be obtained. Mold display is obtained.

Various applications other than the display-related application are possible. For example, application to an optical memory is also possible. Regarding materials that generate light by light stimulation,
Solid State Technology, August 1986, pp. 135-138. Using the light-emitting device of this example, first, light having a shorter wavelength (blue) than the second light-emitting element is irradiated to this material to trap carriers for writing, and when reading, read from the first light-emitting element. It is possible to emit light by irradiating long-wavelength (red) light to excite trapped carriers. As a result, signal writing and reading can be performed only by adjusting the voltage applied to one light emitting device.

[0033]

According to the present invention, the ON / OFF operation of the light emitting element can be easily controlled by the value of the applied voltage or the pulse voltage. Further, in the case of having a plurality of light emitting elements, it can be specified by the value of the voltage applied to the light emitting element to emit light. When applied to lamps and displays,
The emission wavelength can be controlled with a simpler control circuit than the conventional one. Moreover, since a plurality of light emitting elements can be formed by stacking them, higher integration can be achieved.

[Brief description of drawings]

FIG. 1 is a block diagram of a light emitting device of the present invention.

FIG. 2 is an explanatory diagram of an operation principle of the light emitting device of the present invention.

FIG. 3 is an explanatory diagram of an operation principle of the light emitting device of the present invention.

FIG. 4 is a block diagram of a light emitting device of the present invention.

FIG. 5 is a cross-sectional view of a light emitting device that is a first embodiment of the present invention.

FIG. 6 is a cross-sectional view of a light emitting device that is a second embodiment of the present invention.

[Explanation of symbols]

100 ... Light emitting element, 101 ... Electronic element, 102, 103
... terminal, 104 ... current, 105 ... light.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi Shiiki 1-280, Higashi Koikekubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (6)

[Claims] 1. A light emitting device comprising a light emitting element which emits light when energized and an electronic element having a negative resistance, which are connected in series. 2. A plurality of light emitting elements are connected in parallel,
A light emitting device, wherein at least one of the light emitting elements is connected in series with an electronic element having a negative resistance. 3. A light emitting device, wherein a light emitting region made of a semiconductor layer and a conductive region having a negative resistance are formed on the same substrate, and the semiconductor layer and the conductive layer are connected in series. 4. A light emitting device comprising: a plurality of light emitting regions made of a semiconductor layer; and a conductive region serially connected to at least one of the light emitting regions on the same substrate. 5. The light emitting device according to claim 3, wherein the semiconductor layer is composed of either a III-V group semiconductor or a II-VI group semiconductor or both. 6. The light emitting device according to claim 3, wherein the semiconductor layer and the conductive layer are made of either or both of a III-V group semiconductor and a II-VI group semiconductor.