JPS60133777A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To oscillate the titled device by a single wavelength over a wide range of temperatures by a method wherein the carrier density is controlled by passing forward directional currents to a reflection region having a diffraction grating. CONSTITUTION:A laser is composed of an N type InP substrate 1', an N type InP clad layer 2', an undoped InGaAsP active layer 3', a P type InP clad layer 4', a P type InGaAsP contact layer 5', an InGaAsP undoped photo waveguide layer 6', an insulation region 7', a driving P type electrode 8', a wavelength control P-side electrode 9' and an N-side electrode 10'. Light emission is obtained in a region A by passing forward idrectional current between the electrodes 8' and 10'. Injecting current to the reflection region B varies the refractive index in accordance with the number of injected carriers, thus enabling the wavelength capable of selective reflection to be controlled within a distribution of gain; accordingly, the enlargement of the temperature region of single vertical mode oscillation can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor light emitting device, and particularly to a distributed reflection semiconductor laser having a diffraction grating.

(Prior Art) FIG. 1 shows a cross-sectional view of a semiconductor light emitting device having a diffraction grating made of a conventional Inp/InGaAsP thread material. ? , in the figure, l is n-type indium metal (In
P) substrate and cladding layer, 2 is undoped indium gallium arsenide e-phosphorus (JnGaAsP) active layer,
3 is a p-type InGaAsP waveguide layer, 4 is a p-type InP cladding layer, 5 is a p-type InQaAsp-x cladding layer, 6
7 is a p-side electrode, 7 is an n-side electrode, A is a light emitting region, and B is a reflective region.

Here, the following relationship exists between the band width Ea of the active layer 2, the band width Eg of the waveguide layer 3, and the band width Ec of the cladding layer 1.4.

Ea(Eg(Ec) In the reflective region of the optical waveguide layer 3,
(b) A folded lattice is formed periodically. The operation of a semiconductor laser having such a structure is as follows: p 9jll electrode 6 has positive and n
A negative voltage is applied to the side electrode 7, a current is injected into the light emitting region A of the active layer 2, and light emission is obtained by recombination. This light is guided by the active layer 2 and the optical waveguide layer 3, but is reflected by the diffraction grating formed in the reflective area B of the optical waveguide layer 3.
The light is amplified in the light emitting region A, and the laser oscillates at a wavelength determined by the period of this diffraction grating. In order to oscillate with a single wavelength, the configuration of the reflection region must satisfy the following condition (1).

λ= A m 2mn ft , , , , , , (
1) In equation (1), λ is the oscillation wavelength, m is an integer, nef
t is the oscillation wavelength, the effective refractive index determined by the active layer, the optical waveguide layer, and the cladding layer, and A is the period of the diffraction grating. λ must be within the gain distribution of the active layer. However, in semiconductor light emitting devices with the above structure, the gain distribution determined by the band width energy changes greatly due to temperature changes, and the temperature range for single oscillation is narrow because the gain distribution changes significantly beyond the range of wavelengths that can be selected by the diffraction grating. There was a problem.

(Purpose of the invention) The invention was proposed to eliminate these drawbacks, and its purpose is to always maintain selectable wavelengths in the reflection region in response to changes in the gain distribution due to temperature changes. It is an object of the present invention to provide a structure of a semiconductor light emitting device with a diffraction grating in which the single wavelength oscillation temperature range is widened by controlling the temperature within the range.

(Structure of the Invention) In order to achieve the above object, the present invention provides a semiconductor substrate having an electrode at the bottom thereof, a cladding layer formed on the semiconductor substrate and having a band width of Ec, and a cladding layer formed on the cladding layer. , an active layer having a band width Ea and forming a light emitting region; an optical waveguide layer formed on the cladding layer, having a band width Eg, having a diffraction grating, and forming a reflection region;
(3) Formed on the active layer and optical waveguide layer, with a band width of E.
a cladding layer c; an insulating region formed in a portion of the cladding layer where the active layer and the optical waveguide layer are in contact with each other; The main electrode is formed on the reflective region, and the wavelength control electrode is formed on the reflective region, and the band width is Ea+E.
There is a relationship of Ea<Eg<EC with g+EC, and a forward current is passed through the pn junction formed through the reflective region to adjust the refractive index according to the injected carrier concentration. In particular, the gist of the invention is to provide a semiconductor light emitting device characterized in that the oscillation wavelength can be controlled and the temperature range of single-longitudinal mode oscillation can be expanded.

To summarize, the present invention provides a wavelength control electrode in the reflective region that is electrically separated from the driving electrode for injecting carriers into the light emitting part, and injects forward current into the reflective region through this electrode. The oscillation wavelength is controlled by adjusting the effective refractive index of this portion.

. (4) Next, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

FIG. 2 shows a cross-sectional view of an embodiment of the present invention using an InP/InGaA8P crystal system, in which 1' is an n-type InP substrate, 7 is an n-type InP cladding layer, and 3
′ is an undoped InGaAsP active layer, 4′ is a p-type In
P cladding layer, 5' is p-type InGaAsP contact layer, 6' is InGaAsP undoped optical waveguide layer, 7
' is an insulating region formed by proton irradiation, 8' is a p-side electrode for laser driving, g is a p-side electrode for wavelength control, 10
' is the n-side electrode.

Here, the following relationship exists between the band width Ea of the active layer 3', the band width Eg of the optical waveguide layer 6', and the band width EC of the cladding layers 2' and 4'. Ea<Eg<Ea Further, A indicates a light emitting region and B indicates a reflective region. It is necessary that the InGaA8P quaternary crystal has lattice alignment with the InP single crystal.

Next, the operation will be described. A current in the desired direction is caused to flow between the laser driving p-side electrode 8' and the nl1111 electrode l()', and light emission is obtained by carrier recombination in the A region. This light is guided to the anti-kR region B by a double heterostructure waveguide including the active layer 3'. At this time, selective reflection occurs due to periodic changes in the refractive index due to the diffraction grating provided in the reflection region B, and laser oscillation in a single longitudinal mode occurs.

If a current is injected into the reflective region B at this time, the refractive index changes depending on the number of injected carriers. The refractive index change △n is expressed as follows from the plasma oscillation equation: -6,7Xl0-'' (c
J) ,ε0
is the dielectric constant and e is the electron charge. In this way, the effective refractive index "eff" can be adjusted to a desired value by the current injected into B, making it possible to selectively reflect changes in the gain distribution of the active region due to changes in band width due to temperature changes. By controlling the wavelength within the gain distribution, it is possible to expand the temperature range of single-longitudinal mode oscillation.

FIG. 3 shows another embodiment of the present invention, and unlike the case of FIG. 2, FIG. 3 shows an asymmetric type.

The symbols shown in the figure are the same as in FIG. 2.

Note that the end face on the main electrode 8' side needs to be vertical. The end face on the control electrode 9' side may be a slope.

In this example, an example using InP/InGaAsP-based materials is described, but %GaA3/AffiaA8
Other materials may also be used.

Further, although the present invention does not refer to the striped structure of the light emitting device, it is obvious that any striped structure can be applied. It is also obvious that a structure in which the p and n types are reversed from that of this embodiment is also conceivable.

(Effects of the Invention) As explained above, according to the present invention, the effective refraction of the reflection region can be improved by flowing a forward current through the reflection region where the diffraction grating is located and adjusting the transmission density. By adjusting the reflectance ratio (ef), adjusting the reflectable wavelength, and always controlling the oscillation wavelength within the gain distribution determined by the band width, it is possible to realize single wavelength oscillation over a wide temperature range. It has the following.

[Brief Description of the Drawings] Fig. 1 is a sectional view of a conventional semiconductor light emitting device, Fig. 2 is a sectional view of a semiconductor light emitting device according to an embodiment of the present invention, and Fig. 3 is a sectional view of another embodiment. show. l...N-type InP substrate and cladding layer 2...
...Undoped InGaA8P active layer 3...p
Type InGaA8P optical waveguide layer 4...P type InP
Cladding layer 5...p-type InGaAsP contact layer 6...
...P-side electrode 7...N-side electrode 1'...N-type InP substrate 2'...N-type InP cladding layer 3'...
・Undoped InGaA8P active layer (8) 4'...P-type InP cladding layer 5'...
・P-type InGaA8P contact layer 6'... Undoped InGaAsP optical waveguide layer 7'... Insulating region 8'... Laser driving p-side electrode 9'...
・Wavelength control p-side electrode 10'...N-side electrode patent applicant Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] a semiconductor substrate having an electrode at the bottom; a cladding layer formed on the semiconductor substrate and having a PC band in the band; an active layer formed on the cladding layer and having an Ea band and forming a light emitting region; an optical waveguide layer formed on the cladding layer and having Eg in the band and having a diffraction grating and forming a reflective region; a cladding layer formed on the active layer and the optical waveguide layer and having EC in the band; and an insulating region formed in a portion of the cladding layer where the active layer and the optical waveguide layer are in contact with each other, and separated by the insulating region,
The main electrode is formed on the light emitting region through the contact layer, and the wavelength control electrode is formed on the reflective region.
g < Ec (7) By setting the relationship M, a forward current is caused to flow through the pn junction formed through the reflective region, and the refractive index is adjusted according to the injected carrier concentration, thereby changing the oscillation wavelength. A semiconductor light emitting device characterized by being able to control and expand the temperature range of single-longitudinal mode oscillation.