JPS59165480A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To enable to reduce the size and to modulate at a high speed by alternately laminating P type semiconductor layers having a thickness of the degree equal to de Broglie's wave length of electron and hole or less and N type semiconductor layers to form a multilayer thin film and providing a light modulator in part thereof. CONSTITUTION:P type semiconductor layers 3a-3d made of P type In0.53Ga0.47 As and N type semiconductor layers 4a-4d made of N type In0.53Ga0.47As are alternately laminated on a clad layer 32 to form a multilayer thin film. The film is isolated to left and right regions via a slot 38. The right side 39 of the slot 38 is a light emitting unit which operates as a semiconductor laser, and the left side 40 is a light modulator in which the end face opposed to the slot 38 is formed vertically to the optical axis by a reactive ion etching method. The light emitted from the unit 39 reflected on both end faces of the modulator 40, and again returned to the unit 39 to unstabilize the oscillation is avoided by slightly inclining the both end faces of the modulator 40 from the direction perpendicular to the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting device that integrates a semiconductor laser and a modulator and can externally modulate the output light of the semiconductor laser at high speed by varying the absorption peak wavelength of the modulator. .

Semiconductor lasers that can be modulated at high speeds are considered important in the field of optical communications as they enable high-speed, large-capacity transmission of information, but they are also used in other fields, such as optical computing and optical information processing. The importance of 1 is likely to increase in the future.

Conventionally, a direct modulation method has been used to modulate semiconductor lasers. This method directly modulates the current flowing through the laser and is simple, but the upper limit of the modulation speed is determined by the resonant frequency, and in practical terms it is about several GHz.

Furthermore, in the direct modulation method, since the laser has the characteristic of oscillating in multi-axis modes during modulation, the spectrum is broadened, and when used as a light source for optical communication, the problem arises that the transmission band is degraded due to the dispersion effect of the fiber. On the other hand, such a problem does not occur with the external modulation method. Conventionally, LiNbO3 and L are used as modulators for external modulation of semiconductor lasers.
This has been carried out experimentally by utilizing the characteristics of strong electric materials such as iTaO5, mainly its electro-optic effect. However, in order to obtain sufficient modulation, the modulator requires a few pulses, so it has a large capacity, and a high applied voltage of several tens of V is required. Complicated adjustments such as axis alignment were required.

The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a semiconductor light-emitting element that is compact and capable of high-speed modulation by monolithically forming a light-emitting section and a light modulating section on a semiconductor substrate. That is, the semiconductor light emitting device according to the present invention has a multilayer thin film formed by alternately stacking P-type semiconductor layers and N-type semiconductor layers each having a thickness of about the de Broglie wavelength of electrons and holes or less. The invention is characterized in that a light emitting part is provided in a part of the light emitting part, and a light modulating part that modulates the intensity of light from the light emitting part in another part by an applied voltage. An example will be explained in detail.

FIG. 1 is a band diagram of a light emitting section and a light modulating section showing the operating principle of a semiconductor light emitting device according to the present invention.

In the figure, Ia, Ib, 1c and 1d are P-type semiconductor layers. Further, 2a, 2b, 2c and 2d are n-type semiconductor layers. Black circles indicate electrons and white circles indicate holes. The thickness of each semiconductor layer is about the de Broglie wavelength of electrons and holes,
Or less. Here, the de Broglie wavelength and td are i, using Blank's constant and carrier momentum P.
A quantity defined by d=h/p, for example, in InP, the length d;
This is about 300 A, which is a small value compared to the carrier diffusion length. In such a thin semiconductor layer, the kinetic energy of carriers in the thickness direction is quantized. 11.12 and 13 schematically show the discrete energy levels of electrons appearing in the conduction band. Further, 21 and 22 are the energy levels of holes in the valence band. The spacing between energy levels directly depends on the thickness of the semiconductor layer, and increases as the thickness decreases. Assume that a voltage is applied to the multilayer thin film shown in FIG. 1 so that the P-type semiconductor layer 1a becomes positive with respect to the N-type semiconductor layer 2d.

In this state, the P-type semiconductor layer 1a and the N-type semiconductor layer 2a are in a forward bias state. On the other hand, when the adjacent n-type semiconductor layer 2a (!: P-type half-type conductor layer 1b is in a reverse bias state, the thickness of the depletion layer formed at the junction increases. As a result, the n-type semiconductor The effective thickness felt by the electrons existing inside the layer 2a decreases9, and the spacing between the energy levels of the conductor increases.The same thing applies to the energy levels of the conduction bands of the other n-type semiconductor layers 1b11C and 1d. It also occurs for the P-type semiconductor layer 2''% 2 bs
It will also be appreciated that the spacing between the energy levels of the 2c and 2d valence bands increases. Consider the case where light is incident on a semiconductor layer having the above band structure. The absorption coefficient of light depends on the spacing between the energy levels of the semiconductor layer, so the amount of light absorbed changes depending on the externally applied voltage.
It can be seen that this becomes a modulator. Furthermore, if a resonator is made using the above semiconductor layer as an active layer, it becomes a laser. Recombination of electrons and holes occurs at the junction between the forward biased semiconductor layers, thereby allowing lasing to occur. Since each semiconductor layer is as thin as the de Broglie wavelength, the injected carriers can tunnel through the potential barrier generated in the reverse biased portion of the semiconductor layer.

Therefore, carriers can reach the semiconductor layer at the other end, making it possible to inject and supply carriers to the entire multilayer thin film. As a result, the laser gain becomes larger than when the n-type semiconductor layer and the P-type semiconductor layer are each made of stronger layers.

FIG. 2 is a cross-sectional view in the direction perpendicular to the optical axis of one embodiment of the present invention, and FIG. 3 is a cross-sectional view in the optical axis direction of 0InGaA
On a semiconductor substrate 61 made of n-type InP made of sP-based mixed crystal, a layer thickness of 1 μm is doped with Sn, n=I.
A null cladding layer 62 is formed of n-type InP with a thickness of 10"/'6n3. On this layer 62, a Be
A P-type semiconductor layer made of P-type Ino, 5aGaatyAs doped with P ``I
17/c1n3 n-type I no, 5aGa a4y,
A multilayer thin film is formed by alternately stacking four n-type semiconductor layers each made of As. 3JL, 3b,
3c and 3d are p-type semiconductor layers, and 4as 4b, 4c, and 4d are n-type semiconductor layers. Molecular beam epitaxial growth is used to form each layer. 66 and 34 are layers 111 [
A cladding layer made of P-type InP doped with 1 μm of Be and P=1×1018/cm3 and P-type In asaGa
Contact layer consisting of o, 4yAs, 35.66 and 3
7 is an electrode. The multilayer thin film is separated into two regions, left and right, by a groove 68. In FIG. 6, the right side 39 of the third groove is a light emitting section that operates as a semiconductor laser, and the left side 40 is a light modulating section.

The lengths of the light emitting section 69, the groove 38, and the light modulating section 40 in the optical axis direction are 300 μm, 120 μm, and 150 μm, respectively.

The end face of the light emitting part 39 facing the groove 38 is formed perpendicular to the optical axis by reactive ion etching. Moreover, the end face on the opposite side is a cleavage plane. 6th
In the figure, Po indicates light that passes through the light modulation section 40 and is modulated there and output. Both end surfaces of the light modulator 40 are perpendicular to the optical axis in order to prevent the light emitted from the light emitting section 9 from being reflected by both end surfaces of the light modulating section 40 and returning to the light emitting section 9, making the oscillation unstable. It is formed at a slight angle from the opposite direction. The wavelength of the laser light is approximately 1.5 μm. Therefore, according to the present invention, by simply changing the voltage applied to the electrode 40 by a few volts, the light modulating section 4 can be
The zero absorption edge wavelength can be changed in the range of 1.4 μm to 1.5 μm, and speed modulation of 1 GHz is possible with an extinction ratio of 100%.

Further, in the above embodiment, since laser light is emitted from the light emitting section 39 in the opposite direction to the light modulating section 40, if a light modulating section is provided symmetrically with the same structure on the opposite side, each can be modulated independently. Two signal lights can be sent, resulting in an economical light source.

[Brief explanation of the drawing]

FIG. 1 is a band diagram of a light emitting section and a light modulating section showing the operating principle of a semiconductor light emitting device according to the present invention, and FIG. 2 is a cross-sectional view in a direction perpendicular to the optical axis of an embodiment according to the present invention. ■－■
FIG. 6, which shows a line sectional view, is a sectional view in the optical axis direction. 1B11b, 1c, 1ds 3a13b, 3c and 6d
are P-type semiconductor layers, 7a, 2b% 2c, 2d14a, 4
b, 4c and 4d are n-type semiconductor layers, 11.12.13.
21 and 22 are energy levels, 61 is a semiconductor substrate, 32 and 33 are CLA and RAD layers, 64 is a contact layer,
35, 36 and 67 are electrodes, 58 is a groove, 39 is a light emitting part,
40 is a light modulation section. Patent applicant: NEC Corporation

Claims (1)

[Claims] (1) A multilayer thin film is formed by alternately stacking P-type semiconductor layers and N-type semiconductor layers having a thickness of about the de Broglie wavelength of electrons and holes or less, and a part of the layer emits light. What is claimed is: 1. A semiconductor light emitting device, comprising: a light modulating section that modulates the intensity of light from the light emitting section in accordance with an applied voltage.