JPS6035590A - Planar type semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To simplify the manufacture and further facilitate the control of the luminous efficiency of laser and the luminous position of light emitting mode characteristic by a method wherein an electrode and a control electrode in which driving current is injected are formed on the same plane. CONSTITUTION:A double hetero-junction structure 15 consisting of the lower clad layer 13, an active layer 12, and the upper clad layer 14 is formed on a substrate crystal 11, and P type and N type impurities are diffused and ion-implanted respectively to depths reaching at least the active layer 12 in parallel at fixed intervals in the longitudinal direction of the layer 14, resulting in the formation of a P type region 16 and an N type region 17 in the active layer 12 on both sides of a light emitting region 18 constituting the active layer. Metallic electrodes 19 and 20 are evaporated on respective regions, and a metallic stripe-form electrode 21 is provided as the control electrode between the P type region 16 and the N type region 17 of the layer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting device, such as a planar light emitting diode or a semiconductor laser, which has drive current injection electrodes on the same plane.

Semiconductor lasers have a double heterojunction structure, which reduces the threshold current and enables continuous oscillation at room temperature. One embodiment of the basic structure of this double heterojunction semiconductor laser is as shown in FIG.
ctAa layer 3, GaAs layer 3 as an active layer, and P AlGaAs N I as an upper cladding layer on top of it.
It is constructed by sequentially forming I by liquid phase or vapor phase epitaxial growth. The p-AlGaAs layer of such a double heterojunction structure S is made into a glass, and the n
1 When the GaAs layer 3 is made negative and a forward bias current is applied, electrons and holes are injected into the active layer, and the injected electrons and holes are created by the heterojunction between the active layer and both cladding layers. Diffusion is suppressed by the potential barrier and efficiently confined within the active layer, where electrons and holes recombine to generate light. The oscillation threshold mainly depends on the thickness of the active layer, that is, the carrier density and the density of light, and since the active layer can now be formed with control on the order of submicrons, the active layer can be formed with a small amount of current. The density of electrons and holes within can be increased. On the other hand, the refractive index of the active layer with a small bandgap is larger than that of the LAD layer with a large bandgap. Therefore, a dielectric waveguide is formed with the active layer as the core, and electrons and holes within the active layer are formed. The light generated by the recombination propagates within the active layer, and is amplified by repeating the guided emission action in a resonator constructed using the open plane of the crystal, resulting in laser oscillation. .

As mentioned above, light-emitting diodes or semiconductor lasers are being put into practical use due to the double heterojunction structure, and devices on the micron order have appeared, and photo-electronic devices have been combined with electronic devices such as field-effect transistors. Attempts to construct integrated circuits are also represented.

However, in the above-mentioned light emitting diode or semiconductor laser, the drive current flows in a direction perpendicular to the active layer of the double heterojunction, so the field effect transistor's ↓
Therefore, when forming an opto-electronic integrated circuit, it is inevitable that the manufacturing process becomes very complicated.

The object of the present invention is to provide a planar type light emitting diode or semiconductor laser, in which a drive current injection electrode and a control electrode are provided on the same plane so that luminous efficiency, luminous mode characteristics, luminous position, etc. can be easily controlled. An object of the present invention is to provide a semiconductor light emitting device.

The semiconductor light emitting device according to the present invention will be explained with reference to an embodiment shown in FIG.
A semi-insulating semiconductor crystal layer /3 having a lattice constant equal to that of the substrate crystal and having a large forbidden band energy width is provided as a lower cladding layer on top of the substrate crystal, and a semiconductor crystal having a small forbidden band energy width is provided on top of this as an active layer. A crystal layer /2 is provided, and a semi-insulating semiconductor crystal layer /V having a large forbidden band energy width is further provided in a laminated manner on top of the crystal layer /2.

This multilayer structure 15 is the same as the double Peter junction structure of a semiconductor laser device, and is formed by a vapor phase epitaxial growth method or a molecular beam epitaxial growth method with good film thickness controllability, but it is formed by using a known liquid phase epitaxial growth method. You can also do that.

The semiconductor layer constituting this double heterojunction is made of Ga.
Alks/GaAs, I? LG(LAIIP/I?
Examples include LP, InGaAsP/Gaps, etc.
The oscillation wavelength changes depending on the constituent material. In the double heterojunction structure/S, cladding layers 1.3 above and below the undoped active layer 12. Regarding /II, it is different from a normal double heterojunction structure semiconductor laser device, and it does not need to be conductive, and it is necessary to have one cladding layer of n-type and the other of p-type, which is a different conductivity type. It is made of a highly insulating semiconductor.

If the insulation of this cladding layer is low, it will not only cause leakage current parallel to the lateral excitation current, but also leakage current to the field effect control electrode, which will be detailed later. It is necessary that For this reason, especially if the insulation of the upper cladding layer/da is insufficient, an additional 5s
An insulating film such as Ot*5ZN4 is provided to improve insulation. In this way, it is convenient for the cladding layer to have high insulating properties when field effect transistors are formed on the same plane.

As mentioned above, once a double heterojunction structure IS is formed on the substrate crystal using crystal layers having approximately the same lattice constant and different forbidden band energy widths, a predetermined interval is formed in the length direction of the upper cladding layer. p-type impurities and n-type impurities are diffused or ion-implanted in parallel to each other to a depth that reaches at least the active layer/U to form a p-type region/6 and an n-type region/7. Metal electrode on the area/9. ．． 20 is deposited. - As an example, using Sz as the n-IJ impurity and Be as the 7) type impurity, the ion implantation concentration is 10" to 10"
When ion implantation is performed with an acceleration energy of 120 KgV at cm-", the impurity doping concentration is 10'?-10
An ion implantation region of the required concentration of about 111 cm-'' is obtained.

Therefore, the active layer /J has an undoped semiconductor crystal layer (light emitting region) ig constituting the active layer as the center, and a p-type region /6 and an n-type region /i are arranged on both sides of the p-i-n layer.
A bond will be formed. Note that when the semiconductor light emitting device constitutes a semiconductor laser, a double heterojunction structure/
A reflector (
resonator).

In the above embodiments, an undoped semiconductor crystal layer was used as the active layer, but the active layer does not necessarily have to be an intrinsic semiconductor.
A similar effect can be obtained with the configuration -p++$+-n-p+.

Between the p-type region/ro and the n-type region 17 of the upper cladding layer lq, a gold nine-striped electrode, 2/, is provided as a control electrode.

In the above configuration, a hole current is injected from the p-type region /A and an electron current is injected from the n-type region /7 by applying a potential to both regions. 10I10L required for laser oscillation
The high electron/hole pair density on the order of 8t does not depend on carrier confinement in the p-n direction in conventional double heterojunction lasers, but rather on the narrow carrier injection surface on the sides of the thin layer of the active layer. Achieved by current density injection.

Specifically, the injection current density is determined by the thickness of the active layer, from the p subregion to the n
When a low forward voltage is first applied between the p region 16 and the n region/7, which is determined by the distance to the mold region, the injected electrons and holes become countercurrents in the narrow light emitting region 7g of the active layer. They repeatedly collide and scatter each other, but because the density of electrons and holes is low, most of them pass through the light-emitting region without recombining, and the electrons reach the p region and the holes reach the n region, where they undergo n regeneration. Join. At this time, since the upper and lower claddings have high insulation properties, almost no leakage of the injected current occurs. However, there are many crystal defects in both the p region and the n region, and the luminous efficiency due to recombination is low.

When the applied forward voltage is increased, the injection current density of electrons and holes increases, and the density of electrons and holes passing through the light emitting region increases. When the electron density reaches about 10'δcIn-'', the recombination time of electrons and holes, that is, the carrier lifetime, decreases, and the probability of radiative recombination occurring within the light emitting region increases.

The recombination of electrons and holes within the light emitting region has high luminous efficiency.
The strength of the light field also increases. When the strength of the light field exceeds a threshold, stimulated emission of light by the light field occurs in addition to spontaneous light emission, and finally a racing state occurs, and laser light oscillates on both end faces of the light emitting region. do. Once lacing occurs, this laser light oscillates most strongly and emits light because the recombination of electrons and holes occurs mainly in the center of the crystalline light-emitting region, rather than in the ion-implanted defect-rich region. Double heterojunctions can sufficiently confine light at the top and bottom of the region, and in the lateral direction, the p subregion and n subregion
A degree of light confinement is provided by the mold region. The injected current density that produces the above-mentioned racing state is called the threshold current density, and the threshold current density at which racing actually occurs is as high as 10'4/i or more, and its value with respect to the applied voltage varies due to the space charge effect. suppressed.

Next, to explain the action of the control electrode 2/ provided between both impurity regions, first, when no potential is applied to the control electrode from the outside, the gap between the control electrode 2/ and the p-region 16 is dpX or the n-type region/ If the gap is dn and both electrodes are located exactly between the p sub-region and the n-type region, the potential of the control electrode and the p-subregion and the n-type region are located exactly between the p-subregion and the n-type region.
Since it is kept at a potential intermediate between the potential of the sub-region and the potential of the n-type region, the distance between the control electrode and each region dp, d
By reducing n, there is an effect of simultaneously promoting frost, child injection, and hole injection.

In the active layer under this control electrode, there is no external electric field due to the influence of the metal conductor, and there is also no space charge effect of the injected carriers themselves, and the thermal movement of electrons and holes is mainly due to the diffusion of the carriers' own concentration gradient. It is in a state. Compared to the drift state in which carriers flow at high speed under an electric field, the flow is in a stagnant state, and therefore the carrier density in the active layer under the control electrode increases relatively, promoting recombination.

This control electrode is sufficiently effective if it has a width equivalent to the carrier diffusion length, and in the case of a GaAs laser device, it is on the order of several microns. Chills at about 2 microns.

When a positive potential is further applied to this control electrode, electron injection is promoted, hole injection is suppressed, and the recombination position of electrons and holes is brought to the p-group region side of the light-emitting region. Furthermore, when a negative potential is applied, electron injection is suppressed and hole injection is promoted, so that the recombination position is on the n-type region side, and the position is determined by the magnitude of the applied voltage. Therefore, by adjusting the width of the control electrode, the distance to the impurity implantation region, the applied potential, the polarity, etc., the emission efficiency and emission mode characteristics of the laser can be improved.
Light emitting position etc. can be controlled.

FIG. 5 shows an embodiment in which two control electrodes are provided, one in the vicinity of the p-type region between the p-type region/A and the n-type region/7 in the upper cladding layer /G, and the other in the vicinity of the n-type region. A pair of metal control electrodes 21 are provided at the positions along the respective regions by vapor deposition or the like.

The control electrode 21b provided on the n-type region/7 side forms a Schottky electrode on the upper cladding layer/da of the semi-insulating semiconductor, and when a positive potential is applied to the n-type region, the control electrode 21b is activated. 03< in the direction of pushing up the potential of the active layer directly under the electrode to a positive value with respect to the t-n type region and promoting injection of electrons from the n-type region to the light emitting region of the active layer. In particular, in the case of high current density injection such as in a semiconductor laser device, the injection current density is suppressed by the space charge effect, so applying a positive potential to the control electrode 21b increases the amount of electron injection, resulting in a racing state. It has the effect of promoting. Conversely, when a negative potential is applied to the control electrode and the 2ybKn type region, the injection current is suppressed and the racing state is stopped or suppressed.

The control electrode 21α provided on the p-group region side has ? The control electrode 2/l) on the Lm region side has the same effect on electrons, and when a negative potential is applied to the control @electrode 2/α with respect to the p region, the potential of the active layer directly under the control electrode increases. is pushed down negatively relative to the p-genus region. This reduces the space charge effect that inhibits hole injection and promotes high-density hole injection. Conversely, when a positive potential is applied to the control electrode 2/(L), the injection of holes is suppressed, resulting in the effect of stopping or suppressing the racing state.

When a constant voltage is applied to the p-type region electrode /9 and the n-type region electrode 0, a positive potential is applied to the control electrode 21b, and a negative potential is simultaneously applied to the control electrode 21b, the voltage from each region increases. In addition to promoting electron injection and hole injection, the drift electric field in the center of the light emitting region of the active layer is reduced.

Therefore, the drift speed of electrons and holes decreases, and as a result, the density of electrons and holes in the center of the light emitting region increases, promoting radiative recombination. When the voltage applied to both control electrodes is further increased, the drift electric field at the center of the light emitting region becomes zero or negative. Therefore, the flow of carriers becomes extremely stagnant here, and the carrier density further increases. That is, a kind of carrier trapping is performed by the potential applied to the control electrode.

In the above explanation, we talked about applying a predetermined voltage to both control electrodes at the same time to promote laser oscillation and stopping.
If a positive potential is applied only to the control electrode 21b on the mold region side, electron injection is promoted and hole injection is suppressed, so that recombination of electrons and holes is inevitably caused on the p-type region side of the light emitting region. It happens. On the other hand, if a negative potential is applied only to the control electrode 2/α on the p-type region side, hole injection in the p-type region is promoted.
, recombination occurs on the n-type region side, and the luminescence level is determined by the magnitude of the applied voltage. Therefore, in order to control the magnitude of the potential applied to both control electrodes, it is necessary to control the laser oscillation position in the light emitting region between the p-type region and the n-type region, rather than simply promoting laser oscillation. It can be moved and set, making it easy to adjust the incidence of laser light into the optical fiber.

An example of a semiconductor light emitting device according to the present invention is a GaA4As-GIZA8- crystal having a length of 100 μm, an active layer thickness of 0.1 μm, a distance between an n-type region and a p-type head region, that is, a width of a light-emitting region of the active layer of 6 μm. In a GaAlks double heterostructure semiconductor laser device, metal stripe-like electrodes each having a width of 1 μm are deposited along the n-type region and the p-type head region on the upper cladding layer with an interval of 1 μm, and the n-type region and 2 in the p-type head area. When a voltage of Ov is applied, the current density is only about 10 2 fiy'ad and no excitation occurs. In this state, if you apply the same potential as the p-type region to the control electrode on the n-type region side and the same potential as the n-type region to the control electrode on the p-type region side, a drive current of about 105 A/m will be generated. flows, and the electron/hole density becomes 10"crn-" or more in the region where the drift electric field is low at the center of the active layer, resulting in a racing state.

In the embodiment of the light emitting device shown in the drawings, a single semiconductor structure is shown as the active layer, but the active layer has a thickness of 50 to 50 nm.
A multilayer quantum well structure may also be provided in which three or more ultrathin films of two types of compound semiconductors having different compositions of 1ooX are alternately laminated. By forming the active layer into a quantum well structure, the oscillation threshold current density is low and changes little due to temperature changes, and oscillation can be achieved by changing the thickness of the ultra-thin semiconductor film that makes up the multilayer. This is a planar semiconductor light-emitting device that also has the features of a C1 device with a quantum well structure, such as being able to change the wavelength of laser light and improving the confinement effect of injected carriers.

As is clear from the above description, in the semiconductor light emitting device according to the present invention, the electrode for injecting a driving current and the control electrode are formed on the same plane, so that manufacturing is simple when forming an integrated circuit. In particular, opto-electronic integrated circuits combined with electronic elements such as field effect transistors can be easily constructed on the same plane. In addition, the light emitting region has a double heterojunction structure, which allows for sufficient light confinement in the two downward directions, and light confinement in the horizontal direction as well, which is made up of the p-type head region and the n-type region. This makes it possible to realize a semiconductor laser device that has low light propagation loss, and also allows control of laser light emission efficiency, light emission mode characteristics, and light emission position, and is suitable for use in optical communications, information processing, and the like.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically showing a known semiconductor laser device with a double heterojunction structure, FIG. 2 is a perspective view showing an embodiment of a planar semiconductor light emitting device according to the present invention, and FIG. FIG. 7 is a perspective view showing another example of the semiconductor light emitting device. //... Substrate crystal, 12... Active layer, 13... Lower cladding layer, /4'... Upper cladding layer, /, 5-
...double heterozygous structure, /6...p-type head region, /
R...n type region, /Ir...light emitting region 1.2/...
・Control electrode 3,

Claims (1)

[Claims] In a semiconductor light emitting device having a double heterojunction structure in which an active layer is clad from above and below with compound semiconductor layers having a larger forbidden band energy width than the active layer, at least the active layer is kept at a predetermined interval in the length direction of the upper cladding layer. 1. A Brainer type semiconductor light emitting device, characterized in that a p-type impurity ion implantation region and a l-type impurity ion implantation region are provided with a depth that reaches the depth of the layer, and a control electrode is provided between both knee ion implantation regions.