JPH01238632A - Photosemiconductor element and optical bistable element - Google Patents

Abstract

PURPOSE:To enable high-speed operation while incident power is small by laminating respective required layers on a semiconductor substrate and satisfying the prescribed conditions with the energy Ew between the 1st levels of electrons and holes and forbidden band width Eg of the quantum well layer. CONSTITUTION:The resonance tunnel barrier structure consisting of an (n)-type clad layer 1, an (n)-type light guide layer 2, a 1st spacer layer 3, a thin 1st barrier layer 4, and the quantum well layer 5 having the forbidden band width narrower than the forbidden band width of the layer 4 and the photosemiconductor element of the similar conduction type laminated with a (p)-type barrier layer 6, a 2nd spacer layer 7, a guide layer 8, a clad layer 9, etc., are laminated on a GaAs substrate 10 to form the photosemiconductor element. The energy Ew and the width Eg are so selected as to satisfy the conditions expressed by the formula. The photosemiconductor element operates with a small operating voltage and large current as a bistable element when a load resistor 14 larger than the differential load resistor of the photosemiconductor element and a power supply 15 are connected in series to (p) side and (n) side electrodes 12, 13. The resistance 14 is thereby lowered and the time constant is decreased; in addition, light is confined in the quantum well barrier by the layers 2, 8, by which the operating speed is increased while the incident power is small.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical semiconductor device used in the field of optical information processing and optical communication, and more particularly to an optical bistable device.

(Prior Art) Optical bistable devices are expected to be applied in the field of optical information processing and are actively being researched and developed. However, at present, a device that is good in all respects has not been realized. for example,
Literature Abride Physics Letters Volume 45 13-15
Although the optical bistable device called 5EED described on page 1 is expected to operate essentially at high speed, it has a drawback that its operation speed is slow (~ psec) due to its large CR time constant. Currently, there are etalons using nonlinear materials that have high operating speeds (for example, Reference Abride Physics Letters, Vol. 41, pages 221-222), but the incident power is 1 mW.
This has the disadvantage that it is relatively large.

It is an object of the present invention to provide an optical bistable device that has high speed while maintaining a relatively low incident power, and an optical semiconductor device constituting the bistable device.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides an optical semiconductor device that includes a first conductivity type or semi-insulating semiconductor substrate, and a semiconductor substrate formed on the semiconductor substrate. a lower cladding layer of one conductivity type, a light guide layer of the first conductivity type formed on the lower cladding layer, a thin barrier layer laminated in sequence on the light guide layer, and this barrier layer. A resonant tunneling barrier structure consisting of a quantum well layer with a narrower forbidden band width,
Of the barrier layers described above, a second conductivity type opposite to the first conductivity type is formed on the barrier layer provided above the quantum well layer.
It includes a light guide layer having a conductivity type and a cladding layer of a second conductivity type formed on the light guide layer, and furthermore, the energy Ew between the electrons of the quantum well layer and the first level of the regular tag and the light. It is characterized in that the forbidden band width E3 of the portion of the guide layer in contact with the barrier layer satisfies the inequality %.

Further, by connecting this optical semiconductor element, a load resistance, and a power source in series, and making the load resistance larger than the differential negative resistance of the optical semiconductor element, an optical bistable element can be obtained.

Furthermore, if a structure is created in which stripes are formed by mesa etching that reach at least the quantum wells in the optical semiconductor element, the light absorption distance can be increased.

(Function) The optical semiconductor device of the present invention has the advantage that the essential operating speed is faster than conventional devices because the essential operating speed is determined by electron resonance tunneling. In addition, when a load resistance and power supply are added to this and the device is driven as an optical bistable device, the operating voltage is small and the device operates with a relatively large current, so the load resistance can be made small and the CR time constant is small. It is capable of high-speed switching. Further, in the optical semiconductor device of the present invention, since light can be effectively confined in the quantum well barrier by providing a guide layer, coupling with incident light can be increased, and the incident sensitivity can be increased. Therefore, it is possible to construct an optical bistable element that can operate at high speed while keeping the incident power small.

(Example) Next, the present invention will be described in detail with reference to the drawings.

(Example 1) Fig. 1 is an energy band diagram of an optical semiconductor device to explain an embodiment of claim (1) of the present invention, and Fig. 2 is an optical bistable device connected to the structure of the optical semiconductor device. FIG. In the figure, 1 is an n-type cladding layer (
nAlxcGal-XcAsA1 composition ratio Xo=0.3~
0.8), 2 is an n-type optical guide layer (n-AlxGGa, -
,. AsA1 composition ratio X. =Xo+X8 graded),
3 is the first spacer layer (undoped Alx8Ga1-x,
As, X8=o-0,2, typically X8~0, thickness 5
0 to 100A), 4 is the first barrier layer (undoped AlA
s, thickness 10-30 people), 5 is quantum well (undoped G
aAs, thickness 50-100 nm), 6 is the second barrier layer (undoped AlAs, thickness 10-30 nm), 7 is the second spacer layer (undoped Alx5Ga1-xsAs), 8 is the p-type optical guide layer (p -AIXGGal-XG, A1 composition ratio
Substrate (n-GaAs or semi-insulating GaAs substrate),
11 is 5102, 12 is the P side electrode, 13 is the n side electrode, 1
4 is a series resistor, 15 is a DC power supply (applied in the forward direction to the diode, voltage 1 to 5 V), 16 is signal light, and 17 is output light.

Next, a method for manufacturing the optical semiconductor device of this example will be briefly described. First, an n-type cladding layer 1 is placed on a GaAs substrate 1o,
n-type optical guide layer 2, first spacer layer 3, first barrier layer 4
, quantum well 5, second barrier layer 6, second spacer layer 7, P
A molded light guide layer 8 and a P-shaped molded rad layer 9 are sequentially laminated. At this time, when the energy between the electrons in the quantum well 5 and the first quantum level of the genuine tag is Ew, the energy between the first spacer layer and the second quantum level is Ew.
Forbidden band width E of the spacer layer. Ew-0,2eV≦Eo≦
It is necessary to determine the composition and thickness of each layer so that Ew (1). - For example, the thickness of the quantum well 5 is 5
In the case of 0 people, Ew = 1.58 eV, and the A1 composition of the spacer layer must be 0≦x8≦ to satisfy the condition of equation (1).
It is sufficient if it is 0.15. This condition is necessary for the appearance of negative resistance due to resonance tunneling. Note that in order to fabricate the bistable device of Example 2, the second
Active area stripes 18 are formed by mesa etching as shown. Using this structure, Example 2
This is effective because the light absorption distance can be increased as explained in . Finally, the 8102 film 11, the P-side electrode 12, and the N-side electrode 13 are formed.

In this example, a resonant tunnel barrier (hereinafter referred to as RT) is used at the pn junction.
B). Before explaining this structure, the current-voltage characteristics of a normal n-RTB-n structure will be explained. FIG. 3 is an energy band diagram explaining this.

In the figure, 20 is an emitter (n-GaAs, n~5X10
17cm-3), 21 is the first barrier layer (undoped Al
As, thickness ~ 20 people), 22 is a quantum well (undoped G
aAs, thickness 50-100 layers), 23 is the second barrier layer (
24 is the collector (n-GaAs, n~5X1017 cm').

In this structure, when no voltage is applied to the device, the device is in the state shown in the energy band diagram of the thermal equilibrium state shown in FIG. 3(a). At this time, the quantum level 26 of the electron in the quantum well 22 is in a state that is 40 to 140 meV higher than the lower end of the conduction band of the emitter 20 due to the quantization effect. If this value is ΔE, then approximately 2.
When a voltage of 8E is applied, as shown in FIG. 3(b), the electron level 26, the emitter 20, and the electron 25 at the lower end of the conduction band
Their energy levels match and a resonance state occurs. Therefore, the probability that electrons will pass through is increased due to the tunnel effect, and a large current flows.

However, if the voltage is further applied, the energy level of the electron level 26 and the conduction band bottom electron 25 no longer match as shown in FIG. 3(C), so that the current decreases. Therefore, the current-voltage characteristic becomes like the curve 40 in FIG. 4. In the figure, point 40 (b
), 40(c) correspond to the resonant and non-resonant states, respectively.

On the other hand, an RTB like the optical semiconductor device of the first embodiment and a p-n
In the p-RTB-n structure in which junctions are combined, in addition to the flow of electrons, it is also necessary to take into account the positive charge, but basically negative resistance appears due to the resonance phenomenon described above. However, p-
Since the voltage at which negative resistance appears increases by the diffusion voltage of the n-junction, a current-voltage characteristic as shown by curve 41 in FIG. 4 is obtained.

(Embodiment 2) Next, an optical bistable element will be described as a second embodiment of the present invention. As described above, since the optical semiconductor device of this example has an RTB, it has the current-voltage characteristic 41 shown in FIG. 4 in a state where no light is irradiated. When an optical bistable element is manufactured by connecting the load resistor 14 and the DC power supply 15 as shown in FIG. 2, a load resistance straight line 43 as shown in FIG. 5 is obtained. The operating point is the intersection A of the load resistance straight line 43 and the dark current-voltage characteristic 41.

During light irradiation, the current-voltage characteristic moves in the negative current direction as shown in the current-voltage characteristic 42, so the operating point moves to point B. At the operating point A, the quantum well 5 is in a resonant state, and the electric field strength at the quantum well 5 is relatively small, but at the operating point B, the quantum well 5 is in a non-resonant state, and the quantum well 5 has a large electric field (~10
0 kv/cm) is applied. Due to the difference in the electric field applied to the quantum well 5, the absorption spectrum of the quantum well 5 changes from an absorption spectrum 60 (operating point A) to an absorption spectrum 61 (operating point B) in FIG. 6.

Therefore, at a wavelength λ1 shorter than the absorption edge, absorption decreases during the transition from operating point A to B, and at a wavelength λ2 longer than the -force absorption edge, absorption increases. The light input/output characteristics shown in FIG. 7 are obtained by the above changes in the absorption spectrum. In other words, as shown in Figure 2, when the signal light 16 is input and the output light 17 is observed, the wavelength of the signal light is λ1 (shorter wavelength side than the absorption edge).
As shown in the optical input/output characteristic 70 in FIG. 7, the output light 17 increases at the time of transition from operating point A to B. On the other hand, the wavelength λ2
(on the longer wavelength side than the absorption edge), as shown in the optical input/output characteristic 71, the output light 17 decreases when transitioning from the operating point A to B.

Since the essential operating speed of the optical semiconductor device of the present invention is determined by the resonant tunneling speed of electrons, it has the advantage of faster operating speed than conventional devices.

Furthermore, since the operating voltage is about an order of magnitude lower than that of the conventional 5EED, high-speed repetitive operation is possible by using a high-speed pulse power source instead of the DC power source 150. Furthermore, in this embodiment, the signal light 16 is incident from the end face of the stripe 18 parallel to the layer, so the distance over which the light is absorbed is long. Further, it has a waveguide structure including a spacer layer and a guide layer to effectively concentrate light on the quantum well 5. Therefore, it is possible to absorb most of the signal light and operate with low optical power.

(Example 3) Next, another example of the optical bistable element will be described. 8th
The figure shows connections. In the figure, 80 is the p-RTB-n structure optical semiconductor element explained in the first embodiment, 81 is a photodiode that functions as a load resistor, 82 is a DC power supply, and 83 is a bias light for causing current to flow through the photodiode. be. 90 in FIG. 9 is a load resistance curve due to the photodiode 81 and the DC power supply 82 when the DC bias light 83 is incident on the photodiode 81. Therefore, when the signal light 16 is not incident on the optical semiconductor element 80, the operating point is the dark current-voltage characteristic 41 and the fulcrum A of the load resistance curve 90 in FIG. Next, when the signal light 16 is incident on the optical semiconductor element 80, the current-voltage characteristics change to become the curve shown in FIG. 9, and the intersection B between this and the load resistance curve 90 becomes the operating point. Therefore, as in the first embodiment, the electric field applied to the quantum well changes and the light transmission characteristics of the quantum well change, so the intensity of the output light 17 changes. The second embodiment has the advantage that the operating point can be adjusted by changing the light intensity of the bias light 83 incident on the photodiode 81.

In the first embodiment, there is only one quantum well layer, but the quantum well is not limited to this, and may have multiple layers of two or more layers. In the case of a multilayer structure, since the LV characteristic has two or more peaks of negative resistance, tristable or fourstable operation is possible instead of bistable. Further, in the first embodiment, the light guide layer is a graded layer, but it is not limited to this, and may be a layer with a uniform composition11). However, a graded layer has the effect of making it easier to inject carriers into the quantum well. Further, in the first embodiment, a spacer layer was provided to prevent the dopant from entering the quantum well, but this spacer layer can be omitted by devising low-temperature growth or the like. Further, although a DC power source was used in the third embodiment, the DC power source can be omitted by selecting a photodiode with a large optical output voltage.

(Effects of the Invention) Finally, to summarize the effects of the present invention, it is possible to obtain an optical bistable element capable of high speed and low optical power operation and an optical semiconductor element constituting the same.

[Brief explanation of the drawing]

Fig. 1 is an energy band diagram of the optical semiconductor device used in the first embodiment, Fig. 2 is a diagram showing the structure and connections of the second embodiment, and Fig. 3 is the energy band of the n-RTB-n structure. Diagram, Figure 4 is n-RTB-n
Structure and current-voltage characteristics of the optical semiconductor device of the first example,
Figure 5 shows the current-voltage characteristics of the optical bistable device (input 2) 1' of the second embodiment, Figure 6 shows the absorption spectrum of the quantum well,
Fig. 7 shows the optical input/output characteristics of the second embodiment, Fig. 8 shows the connection diagram of the third embodiment, and Fig. 9 shows the current-voltage characteristics of the optical bistable device fabricated in the third embodiment. . In the figure, 1 is an n-type cladding layer, 2 is an n-type optical guide layer, 3 is a first spacer layer, 4 is a first barrier layer, 5 is a quantum well, and 6
7 is a second barrier layer, 7 is a second spacer layer, 8 is a P-type optical guide layer, 9 is a P-type cladding layer, 10 is a GaAs substrate, 11
is a SiO2 film, 12 is a P-side electrode, 13 is an n-side electrode, 14
is a load resistance, 15 is a DC power supply, 16 is a signal light, 17 is an output light, 18 is a stripe, 20 is an emitter, 21 is a first
barrier layer, 22 is a quantum well, 23 is a second barrier layer, 24
is the collector, 25 is the electron at the lower end of the conduction band, 26 is the quantum level of the electron, 40 is the current-voltage characteristic of the n-RTB-n structure, 4
1 is the current-voltage characteristic of the optical semiconductor device of the first example, 42
is the current-voltage characteristic of the optical bistable element of the second embodiment when irradiated with light, 43 is the load resistance line of the second embodiment, 60 is the absorption spectrum at operating point A, 61 is the absorption spectrum at operating point B, 70 is the optical input/output characteristic at wavelength λ, 71 is the optical input/output characteristic at wavelength λ2, 80 is the optical semiconductor element of the first embodiment,
81 is a photodiode, 82 is a DC power supply, 83 is a bias light, 84 is a signal light, and 90 is a load resistance curve of the optical bistable element manufactured in the third embodiment.

Claims (3)

[Claims] (1) A first conductivity type or semi-insulating semiconductor substrate, a first conductivity type lower cladding layer formed on this semiconductor substrate, and a first conductivity type formed on this lower cladding layer. a resonant tunneling barrier structure comprising a type light guide layer, a thin barrier layer sequentially stacked on the light guide layer, and a quantum well layer having a narrower band gap than the barrier layer;
Of the barrier layers described above, a second conductivity type opposite to the first conductivity type is formed on the barrier layer provided above the quantum well layer.
It includes a light guide layer having a conductivity type and a cladding layer of a second conductivity type formed on the light guide layer, and furthermore, the energy Ew between the electrons of the quantum well layer and the first level of the regular tag and the light. An optical semiconductor device characterized in that a forbidden band width Eg of a portion of a guide layer in contact with a barrier layer satisfies the inequality Ew-0.2eV≦Eg≦Ew. (2) An optical semiconductor characterized in that the optical semiconductor according to claim 1, a load resistance, and a power source are connected in series, and the load resistance is larger than the differential negative resistance of the optical semiconductor element. Bistable element. (3) An optical semiconductor device according to claim 1, characterized in that it has stripes formed by mesa etching that reach at least up to the quantum wells.