JP2000228561A - Field-effect light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an element configuration of a quantum well field-effect light emitting element placed in an optical resonator and a method for driving it. SOLUTION: This light emitting element contains an light emitting active layer 5 composed of a quantum structure. From a substrate 1, at least a first conductive semiconductor emitter layer 2, a second conductive semiconductor base layer 4, a light emitting quantum well layer 5, an insulation semiconductor barrier layer 6 having a band gap larger than that of the quantum well layer 5, and a first conductive semiconductor collector layer 8 are laminated in this order. Further, light reflectors having high reflective for the light emitted from the light emitting quantum well layer 5 are provided above and below the light emitting quantum well layer 5 so as to surround it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to light-emitting devices such as light-emitting devices for use in optical communication, particularly for parallel and large-capacity optical transmission between devices constituting an electric circuit, and light-emitting devices for use in an optical neural network. The present invention relates to a field-effect light emitting device including a quantum well layer.

[0002]

2. Description of the Related Art A technique of wiring between electronic circuits by light is expected as a technique for overcoming a wiring capacity delay of a signal in an electrical wiring in an LSI or the like. Conventionally, as a light emitting element for such a purpose, it has been considered to integrate a large number of surface emitting semiconductor lasers on the same substrate.

However, a semiconductor laser generally requires a large current density for laser oscillation, and has a non-linear optical output characteristic with respect to current. That is,
There is a problem that a threshold value is provided, and the threshold value varies greatly depending on the device temperature.

[0004] Due to these problems, when a large number of semiconductor lasers are integrated on the same substrate, the oscillation characteristics such as the threshold value of the laser are greatly changed due to heat generated by the semiconductor laser. There are drawbacks. In addition, there is also a problem that the heat generated by itself accelerates the deterioration of the element.

Therefore, it is considered that integrating a large number of surface emitting semiconductor lasers on the same substrate is not particularly suitable as a light emitting element for optical transmission between adjacent electric circuits which does not require a large optical output. Can be

On the other hand, a method of using a light emitting element that does not cause laser oscillation, that is, a normal light emitting diode for light transmission between adjacent electric circuits, is different from a method of using a semiconductor laser.
It is considered that the method is not affected by heat. But,
In general, ordinary light-emitting diodes have a disadvantage that the ratio of the number of light-emitting photons to the number of injected carriers, that is, the external quantum efficiency, is low because the proportion of light that is emitted to the outside of the light that has re-combined within the semiconductor is small. There is.
For this reason, the element generates heat due to carriers that do not contribute to light emission, thereby deteriorating the element characteristics. To avoid this, the number of light emitting elements integrated on the same substrate must be reduced. In addition, ordinary light-emitting diodes have poor luminous efficiency, so that even if the fluctuation of the current flowing through the light-emitting diodes is suppressed, quantum fluctuations occur in the emitted light.

[0007] In addition, a normal light emitting diode generally has a low light emission intensity modulation speed, and is considered to be unsuitable for transmitting a large amount of data.

On the other hand, a quantum well field effect type light emitting device has been proposed (JJAP, vol. 22, pp. 139-143).
L22-L24 (1982)). To modulate the output light, the conventional light emitting element basically modulates the number of carriers. However, in the present quantum well field effect element, the modulation of the number of carriers is not performed at all and the quantum well is not modulated. This is a light emitting element that modulates the light emission rate itself by applying an electric field in the vertical direction to the light emitting element. In this device, as a result, a high speed (ultimately 1 unit) does not depend on the carrier recombination time, which has limited the switching time of the conventional light emitting device.
The switching of the light emission intensity (about 0 ps) is realized, and it is considered that the light emitting element is suitable as a light emitting element for optically transmitting a large amount of data at high speed.

However, this quantum well field effect type light emitting device also has a drawback that the luminous efficiency is generally low and a drawback that the extinction ratio during light modulation cannot be made too large.

A light emitting device for solving this drawback is disclosed in Japanese Patent Application Laid-Open No. Hei 4-96389. This light emitting device has a configuration in which a minute optical resonator of a wavelength order is arranged so as to surround the quantum well field effect light emitting device. In the present light emitting device, the emitted light is efficiently extracted to the outside by the minute optical resonator of the order of the wavelength, so that the light emitting efficiency is very good. Further, a method of modulating the light emission amount of the microcavity light emitting element is described in JJAP, vo.
l. 22, pp. L22-L24 (1982), it not only changes the matrix element of the Hamiltonian of the electric dipole interaction but also reduces the spectral shape of the excited electronic system and the minute shape. By changing the degree of overlap of the spectral shapes of the electromagnetic fields in the resonator, the recombination time of spontaneous emission can be changed more greatly, and at the same time, the emission pattern can be changed.

However, in this microcavity light-emitting device, due to the structure of the device, a current is injected from the emitter side arranged above the substrate and the potential on the collector side arranged below the device is changed. The light emission amount and the light emission pattern were changed. Generally, the modulation speed of light emission of this element is a speed at which the potential on the collector side can be modulated, that is,
Although it is determined by the CR time constant of the electric circuit on the collector side, in such an element configuration, the area of the pn junction on the collector side must be increased, and the CR time constant, that is, the emission modulation There is a disadvantage that the switching time increases.

Further, when many light emitting elements are integrated on the same substrate, in order to separately connect to the collector side (modulation electrode) of each light emitting element, if the collector is on the substrate side, wiring is required. However, there is a disadvantage that the method of obtaining the electrodes is complicated.

On the other hand, the structure in which the collector is arranged above the element is also a Physical Review A48.
pp. Although it is proposed in R2534-R2537 (1993), a specific method for manufacturing a device and a structure are not specified. Furthermore, in this conventional proposal, a current confinement structure is provided below the Bragg reflector, but in such a structure, the Bragg reflector generally has a thickness of a wavelength order and a material having a different refractive index. Are alternately stacked in multiple layers, so that the distance between the current confinement structure and the light emitting layer disposed thereon is increased.
Therefore, there is a disadvantage that the current spreads in the light emitting layer, and the reactive current that does not contribute to light emission at all increases. If the collector electrode is increased in order to reduce the reactive current, the capacity of the collector electrode is increased as described above, so that there is a disadvantage that the modulation speed is reduced.

[0014] The object of the present invention, in view of the situation described above,
An object of the present invention is to provide a new device configuration of a quantum well field effect type light emitting device arranged in an optical resonator and a driving method thereof. In particular, an electrode on a collector side serving as a modulation electrode is arranged on an upper portion of the device. It is another object of the present invention to provide a new element configuration and a driving method thereof.

[0015]

According to the present invention, there is provided a light-emitting device having a light-emitting active layer having a quantum structure, comprising:
A semiconductor layer of a first conductivity type (called an emitter layer or a current injection layer), a semiconductor layer of a second conductivity type (called a base layer),
A light-emitting quantum well layer, an insulating semiconductor layer having a band gap larger than the quantum well layer (called a barrier layer), and a semiconductor layer of the first conductivity type (called a collector layer or a modulation current layer) are sequentially formed. A light reflector (typically in the order of the emission wavelength) having a high reflectance for light emitted from the light-emitting quantum well layer, which is stacked and surrounds the light-emitting quantum well layer. (Which is an optical resonator).

Based on this basic structure, the following more specific structures are possible. The light reflector is a conductive light reflector having a high reflectance of 90% or more with respect to light emitted from the light emitting quantum well layer, or has a thickness on the order of the wavelength of light emitted from the quantum well layer. An optical resonator with
A Bragg reflector in which semiconductors having different refractive indices are alternately and periodically arranged, and at least the Bragg reflector arranged on the emitter side is partially oxidized to become an insulator, forming a current confinement structure. I do.

Further, since the semiconductor collector layer is provided on the upper portion, the semiconductor collector layer can be easily processed and can have a small area. Further, the electrodes of the semiconductor collector layer may be formed in a ring shape to reduce the capacitance.

Further, the light emitting element is formed on the same substrate so that the base layer and the emitter layer each have a common electrode (for all the light emitting elements, a constant current may be passed between them). Many may be laminated and arrayed.

In addition, the light emitting elements are stacked in large numbers on the same substrate and are two-dimensionally arrayed. The electrodes of the collector layer are connected in a column and the column wiring is connected, and the electrodes of the base layer are connected in a row. Row wiring, and the electrode of the emitter layer may be made a common electrode.

Further, in the method for driving a light emitting device of the present invention, which achieves the above object, the present invention provides a method for driving a light emitting device. It is characterized in that the intensity of light emitted from the collector layer side is modulated by modulating the reverse voltage applied between the electrodes of the collector layer.

With the quantum well field effect light emitting device of the present invention having the above-described structure, it is possible to manufacture a light emitting device capable of reducing the capacitance of the upper modulation electrode (collector side electrode) which is easy to process. In addition to the quantum well field effect type, higher-speed light modulation becomes possible. In addition, it is possible to manufacture a light-emitting element having a configuration in which a modulation electrode is arranged above the element. When a large number of light-emitting elements are arranged on the same substrate, each element is separately (completely independent). Alternatively, the modulation can be performed semi-independently such as in a matrix.

Furthermore, since the current can be confined to a narrow region, the reactive current which does not contribute to light emission at all can be greatly reduced, and the quantum efficiency of the light emitting device can be greatly improved.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a cross section of a first embodiment of a microresonator quantum well field effect light emitting device according to the present invention. In FIG. 1, 1 is a p-GaAs substrate, 2 is 20
Period 571５７ thickness Al _{0 . 2} Ga _0.8 As / 690Å
A Bragg reflector made of a thick AlAs layer (also functioning as an emitter layer);
An insulating layer (functioning as a current confinement structure) formed by oxidizing the layer, 4 is a 1135 ° thick n-Al
_0.2 Ga _0.8 As layer (functioning as a base layer),
Reference numeral 5 denotes an i (intrinsic) -GaAs quantum well light emitting layer having a thickness of 100 °, 6 denotes an i-AlAs layer having a thickness of 100 ° (functioning as a barrier layer), and 7 denotes an i-Al layer having a thickness of 1050 °.
_0.2 Ga _0.8 As layer (functioning as a spacer layer for adjusting the length of the resonator), 8 is a 20-period 571Å thickness pA
a Bragg reflector composed of l _0.2 Ga _0.8 As layer / 690ｌ thick AlAs layer (also functioning as a collector layer),
9 and 11 are Au / C of the p-side emitter and collector, respectively.
An r electrode 10 is an n-side base AuSn electrode. Reference numeral 12 is a schematic diagram of a light emission pattern.

Next, a method for manufacturing the light emitting device of this embodiment will be described with reference to FIGS. First, p-type GaAs
A GaAs buffer layer (not shown), 2
0-period 571 ° thick p-Al _0.2 Ga _0.8 As / 6
Laminated structure 2 of 90 ° thick AlAs layer, n-thickness of 1135 °
Al _0.2 Ga _0.8 As layer 4, 100 ° i-GaAs
s quantum well layer 5, i-AlAs layers 6, 10
I-Al _{0 . 2} Ga _0.8 As layer 7, 20 periods of 571Å thick p-Al _0.2 Ga _0.8 As layer / 69
A laminated structure 8 of a 0 ° thick AlAs layer and a 100 ° GaAs cap layer 13 are produced by a molecular beam epitaxial method (FIG. 2A).

Next, in order to form a light emitting element portion on the GaAs substrate 1, after patterning the light emitting element portion by photolithography, etching is performed to the lower portion of the Bragg reflector layer 2 by reactive ion etching. (FIG. 2 (b)).

Subsequently, the etched element is held in an electric furnace, and heated at 450 ° C. while flowing steam to thereby remove the AlA contained in the Bragg reflector layer 2.
By oxidizing the outer periphery of the s layer to Al ₂ O ₃ ,
An insulating layer 3 is formed (FIG. 2C).

Next, in order to form a modulation electrode portion (collector electrode portion), after patterning by photolithography, etching is performed halfway through the i-Al _0.2 Ga _0.8 As layer 7 by reactive ion etching. After that, AlAs is selectively etched by an HF solution.
Only the layer 6 is removed (FIG. 2D).

Further, the AuSn electrode 10 is vapor-deposited in a ring shape on the quantum well light emitting layer 5 while leaving the etching mask. And a modulation electrode (collector electrode) with an open window
11 is formed by evaporating Au / Cr on the cap layer 13, and the current injection electrode (emitter electrode) 9 is
Au / Cr is formed on the back surface of the substrate 1 by vapor deposition.

Finally, the electrodes 9, 10, and 11 are made ohmic by heating while flowing H ₂ in an electric furnace to complete the device (FIG. 2E).

In this embodiment, the band structure near the quantum well light emitting layer 5 is as shown in FIG. 5 (this shows a state where an appropriate reverse voltage is applied between the base and the collector). Therefore, it is possible to reduce the CR time constant by reducing the area on the modulation electrode 11 side to enable high-speed modulation, and to control the inclination of the band structure of the quantum well light emitting layer 5 as shown in FIG. Is controlled, further high-speed modulation can be performed. That is, as shown in FIG. 5, the energy interval between quantum levels and the spatial separation in the stacking direction between the wave functions of both carriers are controlled by controlling the inclination of the band structure of the quantum well light emitting layer 5 (see FIG. 5). The light emitting rate can be controlled at high speed and efficiently, as shown in the quantum well light emitting layer 5). Further, the light emission amount can be largely modulated by voltage control, the extinction ratio can be increased, and the light emission pattern can be changed.

The operation of this embodiment having the above structure will be described with reference to FIG. As shown in FIG. 3, the device is held in a cryostat 18 and a 77K
The carrier was injected into the quantum well light emitting layer 5 by applying a voltage between the current injection electrode (emitter electrode) 9 and the base electrode 10. At the same time, a reverse voltage was applied between the base electrode 10 and the current modulation electrode (collector electrode) 11.
Further, a photodetector 15 having the same diameter as that of the collector electrode portion 11 was disposed immediately above the element. In this figure,
19 is a constant current source, 14 is a pulse voltage application power supply, 16 is a current amplifier, and 17 is an oscilloscope.

FIG. 4 shows a high-speed modulation characteristic of the light emitting device of the first embodiment of the present invention measured by the apparatus shown in FIG. In a sample in which the diameter of the current modulation electrode 11 was 10 μm, the CR time constant when the light modulation electrode 11 was driven by a 50 ohm transmission line was about 10 ps, and the light intensity modulation speed was the light emission lifetime (this element). In case of about 1
High-speed modulation of 1 ns or less, which is not limited to about 00 ns, is possible.

In the light emitting device according to the first embodiment of the present invention, the emission quantum efficiency, that is, the external quantum efficiency in which the number of emitted photons with respect to the number of injected electrons is very high was achieved. As a result, when this device is driven by a constant current source in which fluctuation is suppressed, quantum fluctuation of emitted light can be suppressed to be small.

In this embodiment, a resonator having a length of about a wavelength is used as the minute optical resonator, but, of course, the present invention is not limited to this. It can be used from a resonator having a length of about 1/10 wavelength to a resonator having a length of about 10 times the wavelength. Further, in this embodiment, a Bragg reflector in which semiconductors having different refractive indexes are alternately stacked is used as the light reflector, but a Bragg reflector made of a dielectric material or a metal mirror may be used. Further, as disclosed in JP-A-4-96389, a Bragg reflector in which materials having different refractive indexes are alternately laminated three-dimensionally may be used. An effect peculiar to a minute resonator light-emitting element is generated, and further improvement in modulation of light-emission recombination time and increase in light-emission efficiency are expected.

In the present embodiment, a one-dimensional quantum well is used as the light emitting portion. However, the present invention is not limited to this, and the luminous efficiency may be reduced as disclosed in Japanese Patent Application Laid-Open No. Hei 4-96389. In order to further increase the above, a light emitting element having a quantum wire as a two-dimensional well or a quantum box as a three-dimensional well as a light emitting part may be used.

(Second Embodiment) An example in which a large number of light emitting elements of the present invention are integrated on the same substrate is shown in FIG. The structure and manufacturing method of each element are the same as those in the first embodiment. (In this embodiment, as shown in FIG. 6B, the space between the individual elements is filled with an insulating material 27 such as polyimide. ). FIG. 6 is a structural view in which the light emitting device of the present invention is integrated ((b) is a cross-sectional view along (a) in the left-right direction). In this figure, reference numeral 25 denotes a column wiring connected to a collector electrode (modulation electrode) 21 (this is, for example, wired on an insulating layer formed on a base electrode 22), and reference numeral 20 denotes a wiring to the base electrode 22. The row wiring 23 is an emitter electrode (current injection electrode), which is arranged on the entire rear surface of the substrate 26.

In this embodiment, the emitter electrode 23 is common to all elements integrated on the same substrate 26. When this element is driven in a matrix, a base electrode 22 and an emitter electrode 23 connected to a certain row wiring 20 are used.
The current is injected by applying a constant voltage during the period, and the voltage of the modulation electrode (collector electrode) 21 connected to a certain column wiring 25 is changed. The amount and emission pattern can be modulated.

For this reason, unlike the conventional example, it becomes possible to control the amount of light transmitted from each light emitting element integrated on the same substrate to the photodetector semi-independently (modulation electrode (collector electrode)). 21 can be controlled completely independently.

Further, as compared with the case where the surface-emitting type semiconductor laser is integrated on the same substrate, the amount of current to be injected is always constant irrespective of the on / off state of the signal. Irrespective of this, the calorific value becomes constant, and a stable signal can be transmitted.

[0041]

As described above, the quantum well field effect type light emitting device of the present invention makes it possible to manufacture a light emitting device having a small capacitance of the modulation electrode (collector).
Higher-speed light modulation becomes possible. Furthermore, it is possible to manufacture a light emitting element having a configuration in which a modulation electrode is arranged above the element. When a large number of the light emitting elements are arranged on the same substrate, each element has a degree corresponding to the case. It is now possible to modulate with independence.

Further, since the current can be confined to a narrow region, the reactive current which does not contribute to light emission at all can be greatly reduced, and the light emission quantum efficiency of the light emitting device can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a sectional configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a process chart illustrating a method of manufacturing a light emitting device according to a first embodiment of the present invention.

FIG. 3 is a configuration diagram of an apparatus for measuring a light emitting device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a high-speed modulation characteristic of the light emitting device according to the first embodiment of the present invention.

FIG. 5 is a band structure diagram of the light emitting device according to the first embodiment of the present invention.

FIG. 6 is a configuration diagram of an example in which the light emitting device of the present invention is integrated on the same substrate.

[Explanation of symbols]

1 p-GaAs substrate 2 20-period 571 ° thick p-Al _0.2 Ga _0.8 A
Brass reflector composed of s layer / 690６ thick AlAs layer 3 Insulating layer 4 1135Å thick n-Al _0.2 Ga _0.8 As layer 5 100Å i-GaAs quantum well light emitting layer 6 100Å thick i-AlAs layer 7 1050 ° thick i-Al _0.2 Ga _0.8 As layer 8 20 periods of 571 ° thick p-Al _0.2 Ga _0.8 A layer
Brass reflector composed of s layer / 690６ thick AlAs layer 9 Emitter electrode composed of Au / Cr electrode 10 Base electrode composed of AuSn electrode 11 Collector electrode composed of Au / Cr electrode 12 Schematic diagram of light emission pattern 13 Cap layer 14 Pulse voltage application Power supply 15 Photodetector 16 Current amplifier 17 Oscilloscope 18 Cryostat 19 Constant current source 20 Row wiring 21 Collector electrode (modulation electrode) 22 Base electrode 23 Emitter electrode (current injection electrode) 25 Column wiring 26 Common substrate 27 Polyimide

Claims (10)

[Claims] In a light emitting device having a light emitting active layer having a quantum structure, at least a semiconductor emitter layer of a first conductivity type, a semiconductor base layer of a second conductivity type, a light emitting quantum well layer, An insulating semiconductor barrier layer having a band gap larger than that of the quantum well layer and a semiconductor collector layer of the first conductivity type are sequentially stacked, and are vertically arranged so as to surround the light emitting quantum well layer. A field-effect light-emitting device comprising a light reflector having a high reflectance for light emitted from a light-emitting quantum well layer. 2. The light reflector according to claim 1, wherein the light reflector is a conductive light reflector having a high reflectance of 90% or more with respect to light emitted from the light emitting quantum well layer. Light emitting element. 3. The light reflector according to claim 1, wherein at least a part disposed on the side of the emitter layer is made of an insulator, and a current flowing from the emitter layer to the base layer is narrowed. The light emitting device according to claim 1, wherein the light emitting device is a light emitting device. 4. The light reflector according to claim 1, wherein the light reflector comprises a Bragg reflector in which at least two types of semiconductors having different refractive indexes are alternately and periodically arranged. Light emitting element. 5. At least a part of the Bragg reflector on the emitter layer side is made of a semiconductor containing aluminum as a component, and a part of the semiconductor containing aluminum is oxidized to be an insulator. 5. The light-emitting device according to claim 4, wherein a current flowing from the emitter layer to the base layer is narrowed by the insulating portion. 6. A light emitting device according to claim 1, wherein said semiconductor collector layer has a reduced area. 7. The light emitting device according to claim 1, wherein the electrode of the semiconductor collector layer is formed in a ring shape. 8. The light-emitting device according to claim 1, wherein a plurality of the light-emitting elements are stacked and arrayed on the same substrate so that the base layer and the emitter layer each have a common electrode. The light-emitting element according to any one of the above. 9. The light emitting device according to claim 1, wherein a plurality of the light emitting elements are stacked on the same substrate and are two-dimensionally arrayed. The electrodes of the collector layer are connected in a column, and the electrodes of the base layer are connected in a row. 8. The light emitting device according to claim 1, wherein the electrodes are arranged in a row, and the electrode of the emitter layer is made a common electrode. 10. A reverse voltage applied between a base layer electrode and a collector layer electrode is modulated while applying a constant voltage between a base layer electrode and an emitter layer electrode to cause a current to flow.
The method according to claim 1, wherein the intensity of light emitted from the collector layer is modulated.