JPH03239385A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To make it possible to control an oscillation state with voltage or a light inlet signal by separating electrodes into two or more in a high resistance region, injecting electric current by way of one or more segment electrodes and applying voltage by way of one segment electrodes. CONSTITUTION:An N type semiconductor substrate 1 is provided with a semiconductor laminated layer 6 where an N type semiconductor layer 2 which serves as a clad layer, a semiconductor layer 3 which serves as a superlattice structural layer, a P type semiconductor 4, and a P type semiconductor layer 5 which has high conductivity and forms a metal and ohmic alloy layer are laminated thereon in this order. The semiconductor laminated layer 6 is provided with an electrode 7 connected with an N type semiconductor substrate 1 for current injection and an electrode metal layer 8 connected with the P type semiconductor layer 5. It further divides the semiconductor layers 4 and 5 and the electrode metal layer 8 into two and more segments electrically separated and applies a constant voltage source 23 to the segment of one party and a constant current source 16 to the segment 15 of the other party. The constant voltage 23 forms a partially mixed crystal of a superlattice section of a voltage-applied saturable absorption region 21, thereby controlling an oscillation state with voltage or a light input signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bistable semiconductor laser device that can be the most basic element as an optical functional element used in optical exchange, optical information processing, etc.

(Prior Art) Bistable semiconductor laser devices have an important function for optical information processing including optical storage devices, and the development of such devices has been actively promoted. Among these devices, research and development has been conducted on a simple bistable semiconductor laser configuration that enables bistable operation by providing a non-excited region with a saturable absorption effect within the semiconductor laser resonator. There is. (Reference 1, asher
・5solidState Electron, 7(
1964) 707) However, the saturable absorber of a bistable semiconductor laser having a non-excited region is often created accidentally due to deterioration of the end facets, etc., and there are problems with reproducibility and controllability. Because the stability region is narrow and the degree of freedom in design is small, it has not been put to practical use as a device.

In order to eliminate these drawbacks, a semiconductor laser device with a superlattice structure in the active layer and an electrode layer with electrically separated segments is used, which is tunable with low power consumption and capable of high-speed operation. A composite type bistable semiconductor laser device has been proposed (Patent Application Publication No. 1988-296573).

This will be explained using FIGS. 3 to 5. For example, on an N-type semiconductor substrate 1 made of single-crystal GaAs, a cladding layer of, for example, single-crystal Al
-x A s (0<x<1) N-type semiconductor layer 2
For example, Ga, As/A1. Ga+-, As(0<z
<1) A semiconductor layer as the superlattice structure layer 3 and a single crystal A1. A P-type semiconductor layer 4 made of Ga+-AS (0<X<]) and a P-type semiconductor layer made of, for example, single crystal GaAs, which has high conductivity and can form an ohmic alloy layer with metal. 5 has a semiconductor layer 6 laminated in this order. In this case, the semiconductor stack 6 has an electrode layer 7 bonded to the N-type semiconductor substrate 1 and an electrode metal layer 8 bonded to the P-type semiconductor layer 5 for current injection. The semiconductor layers 4, 5 and the electrode metal layer 8 are divided into two or more electrically separated segments, one segment 17 is connected to a constant voltage source 23, and the other segment I5 is connected to a constant current source 1G.
Apply.

At this time, by injecting a large number of carriers into the region 19 of the active layer 3 under the segment 15, the region 2o of the active layer 3 under the segment 17 is used as a region for generating optical gain for laser oscillation. is used as a region of saturable absorption that can be controlled by the principle described in FIG. 4 below.

For example, GaAs/A1. It is known that in a superlattice structure based on a Ga+1As heterostructure, an electron-hole bound state called an exciton exists stably even at room temperature, and it has a large light absorption peak, compared to a normal semiconductor. ing. It is known that this exciton absorption exhibits a larger absorption saturation than normal optical absorption between bands, and that the peak can be shifted to longer wavelengths by applying a voltage to the superlattice structure (quantum confined Stackle effect). It is being

FIG. 4 shows the spectrum of exciton absorption in the saturable absorption region 20 observed in the semiconductor laser device as shown in FIG. 3, and the voltage V2 applied to the segment 17.
This diagram schematically shows the dependence. The peak indicated by C in the figure is an exciton absorption peak when no electric field is applied. This peak shifts toward longer wavelengths as V2 changes. The wavelength indicated by B in the figure indicates the laser oscillation wavelength caused by the optical gain generation region 19 in the semiconductor laser device shown in FIG. Therefore, the amount of light absorbed at the wavelength of B, which causes relay laser oscillation, changes as the applied voltage changes.

It is well known that exciton absorption in a superlattice structure easily saturates depending on the light intensity.

FIG. 5 shows GaAs/A1. An experimental example of the saturable absorption characteristics of Ga, +, As superlattices is shown. In the absorption spectrum, as the light intensity increases from Wl to W2 to W3, significant absorption saturation is observed on the ultra-exciton absorption wavelength side.

When the absorption peak of the saturable absorption region is shifted by the applied voltage v2 and matches the laser oscillation wavelength of the optical gain region, it functions as an effective saturable absorber and causes optical bistable operation.

The reason why optical bistable can be configured stably and with good controllability in such a laser device is that the wavelength at which laser oscillation is achieved by injected carriers in the optical gain region is 2
This is because the exciton absorption peak is on the low energy side of about 0 meV, and the exciton absorption peak can be further shifted to the long wavelength side by an externally applied voltage.

Such conditions apply to GaAs/A1. Ga, , As-based superlattices are generally satisfied.

For example, regarding the relationship between the exciton absorption peak and the laser oscillation wavelength, Ta, Rucha et al. Jpn, J. Appl.
, Phys.

=5 221] p, I, 182 (1983), etc.
Regarding the applied voltage dependence of the exciton absorption peak, Tar
ucha et al. Jpn.

J, Appl, Phys, 24 pp, L442
(1985) et al.

However, in optical communication applications, 1.5 μm is more important.
The situation is different in the belt. The wavelength of laser oscillation with respect to the exciton absorption peak does not always have a low energy of about 20 meV in a superlattice structure, but it is due to the competition between the band edge shrinkage effect due to carriers and the band filling effect.

InGaAs(P)/InP or InGaAs, which is expected to be a material system for 1.5 μm band MQW lasers
In the (P)/InA IAs-based superlattice, material-specific properties (injected carriers cause Auger absorption effects, intraband absorption, etc.), and saturation of the gain coefficient occurs at relatively lower implantation levels than in the GaAs-based superlattice. ), the laser oscillation wavelength is the same or a few meters away from the exciton absorption peak.
The saturable absorption coefficient at the laser oscillation wavelength increases at a few thousand cm', and even if the exciton absorption peak is shifted to longer wavelengths by an electric field, the absorption efficiency remains low. The change is slight and corresponds to the change in the absorption effect at wavelength C in FIG. As an electric field-controlled bistable element, the adjustment range is small, making it difficult to create devices and multiple stages.

(Problems to be Solved by the Invention) The present invention provides an electrode for a semiconductor laser device including a double heterojunction as a useful functional element for optical calculation, optical exchange, optical pulse shaping, etc. in optical information processing and optical communication. is separated into two or more by a high resistance region, a current is injected through one or more segment electrodes, a voltage is applied through one or more segment electrodes, one or more voltages or one or more An object of the present invention is to provide a semiconductor laser device whose oscillation state can be controlled by an optical input signal.

(Means for Solving the Problems) The present invention provides the above-mentioned semiconductor laser device in which a superlattice is partially mixed crystallized in an active region under two or more segment electrodes electrically separated from each other by a resistance region. (by interdiffusion),
By utilizing the nonlinear absorption of excitons existing in a superlattice structure in which the quantization level is shifted to the short wavelength side as a saturable absorption medium, and further controlling the nonlinear absorption of the excitons with a voltage, it is possible to Two or more stable states are obtained for three or more pre-initial horn signals.

The exciton structure of the conventional normal superlattice structure has the saturable absorption region, which utilizes the optical nonlinearity of exciton absorption and the electric field effect (quantum confined Stark effect), shifted to the short wavelength side by partial mixed crystallization. It differs in its basic configuration from a bistable semiconductor laser that utilizes saturable absorption characteristics and electric field effects.

(Embodiment) FIG. 1 is a diagram showing the structure of an embodiment of the present invention. However, since the effects of the present invention are mainly noticeable in bistable lasers in the 1.5 μm band, examples will be described using the case of an InGaAsP/InP superlattice as an example. For example, single crystal 1n
On an N-type semiconductor substrate 1 made of P, an N-type semiconductor layer 2 made of, for example, single-crystal 1nP as a cladding layer, a semiconductor layer 3 made of, for example, InGa, AsP/InP superlattice structure, etc. A P-type semiconductor layer 4 made of single-crystal 1nP and a P-type semiconductor layer 5 made of, for example, single-crystal 1NGaAs, which has high conductivity and can form an ohmic alloy layer with metal, are formed in this order. It has a semiconductor laminate 6 formed by stacking layers. In this case, the semiconductor stack 6 is
Electrode layer 7 bonded to N-type semiconductor substrate 1 for current injection
and an electrode metal layer 8 bonded to the P-type semiconductor layer 5.

The semiconductor layers 4 and 5 and the electrode metal layer 8 are divided into two or more electrically separated segments, and one segment 1
A constant voltage source 23 is applied to section 7, and a constant current source 16 is applied to the other sector 15. The semiconductor laser device according to the present invention shown in FIG. 1 differs from the conventional semiconductor device shown in FIG.
They have the same configuration except for the following. Constant voltage source 23
The superlattice portion of the saturable absorption region 21 to which a voltage is applied is partially mixed crystal by the method described below.

For example, Miyazawa et al. (Jan, J. App.
1, Phys, 28L], 039 (1989)), on the P-type semiconductor layer 5 above the superlattice structure, in order to further increase the interdiffusion of the superlattice structure, The exciton absorption peak of the superlattice can be reduced to a shorter wavelength by depositing a substance other than the one that forms the structure (for example, silicon dioxide or silicon nitride) and performing a short-time heat treatment method or a short-time repeated heat treatment method. The point is that it has shifted to the side.

FIG. 2 is a diagram showing an experimental example of partial mixed crystallization using the method described above. A part of the crystal substrate having the semiconductor stack 6 having the structure shown in FIG.
A silicon nitride film with a human thickness was deposited and the heating rate was 350°C/
The results of measuring the light absorption characteristics of the superlattice structure when heat-treated at a maximum temperature of 800° C. for 1 minute are shown. The curve d shows the light absorption characteristics before heat treatment, the curve e shows the light absorption characteristics after heat treatment in the area where the silicon nitride film is not deposited, and the curve f shows the light absorption characteristics after the heat treatment in the area where the silicon nitride film is deposited. A measurement example is shown.

Although the curves of e and f shift toward shorter wavelengths due to the heat treatment, f shifts toward shorter wavelengths due to the effect of the deposited silicon nitride, and the difference therebetween reaches 60 nm (37 meV). Furthermore, in partial mixed crystal formation using this method, the superlattice structure does not completely become mixed crystal and disappears, but phosphorus diffuses into the quantum well layer, so the band gap increases by several tens of meters.
This is because V increases, and there is a quantum confinement Stark effect characteristic of superlattice structures.

Using the above-mentioned selective partial mixing technique, the optical gain generation region 19 in FIG. 1 has an absorption characteristic as shown in curve e in FIG. Heat treatment is performed so that the characteristic becomes f in FIG. 2, and then the electrode layer 7 is
and forming segment 15.17.

Optical gain generation region 19 of active layer 3 below segment 15
The saturable absorption region 21 of the active layer 3 below the segment 17 is controllable by the principle described below. Used as a region of saturable absorption.

As already mentioned, the wavelength of laser oscillation by the optical gain generation region I9 is the peak E of the curve e in FIG. For that wavelength, the absorption in the saturable absorption region 2I is several hundred C.
IN ', and the peak F of the curve r in FIG. 5 can be shifted to a longer wavelength than the wavelength E by the electric field, and functions as a saturable absorption region that can be controlled by the electric field
A bistable laser that can be controlled over a wide range will be realized.

(Effects of the Invention) As explained above, the semiconductor laser device of the present invention has the following effects:
In a semiconductor laser device equipped with a double heterojunction,
The active layer of the above device has a superlattice structure and comprises a plurality of segment electrodes electrically separated from each other by a resistive region, and current is injected from one or more of the segment electrodes, and a segment different from the active layer has a superlattice structure. By applying a bias voltage to the electrode terminal and partially mixing the superlattice in the area where the bias voltage is applied, the quantization level can be shifted to the short wavelength side, and if the bias point is set appropriately, Optical calculations in optical information processing and optical communication, such as memory operation and on/off ratio, making multistage possible,
It is extremely useful as a functional element that performs optical exchange, optical pulse shaping, etc.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a bistable semiconductor laser device according to the present invention, and FIG. 2 is a diagram showing a region 21 of an embodiment of the present invention. Figure 3 is a diagram showing the absorption efficiency of region 19. Figure 3 is a structural diagram of a conventional electric field controlled bistable laser device. Figure 4 is a diagram showing the relationship between the wavelength characteristics of the absorption efficiency of the light absorption region and the applied voltage. , FIG. 5 is a diagram of the saturable absorption characteristics of the superlattice structure. 1... N-type semiconductor substrate made of single crystal GaAs 2.
...Clad layer, for example single crystal A1. Ga+-, As(
N-type semiconductor layer 3 consisting of 0<x<1)...active layer, for example GaAs/AlzGa+1As
(0<z<1) superlattice structure layer 4...crat layer, for example, single crystal Al, Ga+-, A
P-type semiconductor layer 5 made of s (0<x<],)...Contact layer, for example, P-type made of single crystal GaAs, has high conductivity, and can form an ohmic alloy layer with metal. Semiconductor layer 3 4 6...1. 2. 3. 4. Semiconductor laminate 7 formed by laminating 5...electrode layer 8...P bonded to the N-type semiconductor substrate 1
Electrode metal layers 15 and 17 bonded to the type semiconductor layer 5... Segment 16 electrically separating the electrode metal layer 8... Constant current source 19... Optical gain generation region 20 for laser oscillation.
... Saturable absorption region 21 that can be controlled by voltage... Exciton peaks are increased by several @-m e due to partial mixed crystallization of the superlattice
V Saturable absorption region 23 that can be controlled by a voltage shifted to the short wavelength side...constant voltage source

Claims (1)

[Claims] 1. A semiconductor laser device including a dovetail junction, wherein the active layer of the device has a superlattice structure and includes a plurality of segment electrodes electrically separated from each other by a resistance region, A semiconductor laser device characterized by having a structure in which a current is injected from one or more segment electrodes and a bias voltage is applied to a different segment electrode terminal. 2. In the semiconductor laser device according to claim 1, the active layer is made of InGaA having a smaller band gap.
s or InGaAsP quantum well layer, a superlattice structure consisting of an InP barrier layer with a larger band gap (hereinafter abbreviated as InGaAs(P)/InP superlattice structure), and InGaAs(P)/InGaAsP, I
It has an nGaAs(P)/InAlAs superlattice structure, and the part to which a bias voltage is applied is partially mixed crystal of the superlattice (
1. A semiconductor laser device characterized by having a structure in which a quantization level is shifted to a shorter wavelength side by inter-diffusion. 3. The semiconductor laser device according to claim 1, wherein the bias voltage is fixed and the injection current is adjusted so that the optical output intensity due to laser oscillation becomes binary stable. Device.