JPH0666523B2 - Semiconductor optical memory - Google Patents

Description

The present invention relates to a semiconductor optical memory required for image processing, an optical computer, and the like.

(Prior art and its problems) The semiconductor optical memory, which has a function to oscillate a laser beam with a slight amount of trigger light and continue to oscillate even after the trigger light is exhausted, is designed for future optical switching and parallel optical information processing systems. It is an indispensable key device for configuration. A bistable semiconductor laser is known as a device having such a function.
Details have been reported. The problem with the bistable semiconductor laser is that it requires a relatively strong trigger light of about several to 100 μw. In order to turn on the bistable semiconductor laser with the trigger light, it is necessary to irradiate the laser end face with the light through the lens and efficiently narrow it down to the active layer in the non-excited state. The width and thickness of the active layer are approximately 1 μm and 0.
It was as narrow as 1 μm, and efficient optical coupling was difficult. Therefore, the insertion loss becomes large, and a relatively high trigger strength is required. Further, in consideration of application to optical parallel processing and the like, a structure capable of receiving trigger light in the layer thickness direction is desirable.

(Means for Solving Problems) A semiconductor optical memory provided by the present invention in order to solve the above problems comprises a pnpn thyristor, and the base n-type semiconductor is a first semiconductor layer and a second semiconductor layer. And a third semiconductor layer are sequentially stacked, and the forbidden band widths of the p-type semiconductor for anode and the n-type semiconductor for cathode are larger than the forbidden band width of either of the first and third semiconductor layers.
The band gap of the semiconductor layer is narrower than the band gaps of the first and third semiconductor layers, and electrons and holes are relaxed in the second semiconductor layer during the forward conduction state, and the electrons and holes are Laser oscillation is caused by the stimulated emission process of.

(Operation and Principle of the Invention) FIGS. 1 and 2 are band diagrams showing the principle of the present invention, and FIG. 3 is an operation diagram.

FIG. 1A is a band diagram in which no bias voltage is applied, FIG. 1B is a high impedance state, and FIG. 1C is an ON state band diagram. For simplification, the band discontinuity at the heterojunction and the like, which are not related to the essence of the present invention, are qualitatively approximated. FIG. 1 (a) shows the carrier concentration and the forbidden band energy of each layer. The forbidden band width of the p-type semiconductor for the anode and the n-type semiconductor for the cathode is E, respectively.
₄ and E ₁ (E ₄ = E _{1 in the} figure). The n-type semiconductor layer for the base has a forbidden band width E _g of E ₃ and E _a.
It is composed of two semiconductors. Of these, E _g =
The layer of E _a becomes the active layer for laser operation. The size of the forbidden band is set to E ₄ , E ₁ > E ₃ > E _a . The carrier concentration (n ₂ and n _a ) of the n-type semiconductor layer for the base is sufficiently low. When a positive voltage is applied to the anode and a negative voltage is applied to the cathode, a high impedance state in which almost no current flows is obtained at the beginning (FIG. 1 (a)). Since the n-type semiconductor layer for the base has a low concentration, the applied voltage is almost applied to the pn junction in the base region,
The depletion layer extends into the base n-type semiconductor layer. Holes in the p-type semiconductor for the anode are pn between the base and the anode.
The potential barrier occurring at the junction cannot be exceeded, which results in a high impedance state in which almost no current flows. When the applied voltage is further increased and the breakover voltage (V _BO ) shown in FIG. 3 (a) is exceeded, a current suddenly starts to flow and it is turned on (FIG. 1 (c)). The operation mechanism of this side is the same as that of a normal thyristor. ON
In this state, the voltage applied to this element is substantially one pn
It becomes the same as joining. When a semiconductor layer having a narrow bandgap (E _g = E _a ) is provided in the base n-type semiconductor, some of the electrons and holes fall into the depression of this potential. If a reflector is placed outside, laser oscillation can be obtained when the gain exceeds the loss. If the forbidden band width of the cathode n-type semiconductor and the anode p-type semiconductor is made larger than that of the base n-type semiconductor, the number of electrons flowing out to the anode and holes flowing out to the cathode in the ON state is reduced. This makes it easier to relax the carriers in the active layer.
Therefore, the luminous efficiency can be improved. A voltage is set at the point of V = V _X shown in FIG. 3 (a), an appropriate amount of light is made incident, and this is absorbed by the base n-type semiconductor. Then, holes will be injected into the p-type semiconductor for the base. The injected holes increase the number of electrons passing through this layer due to the transistor effect. These electrons moderate the slope of the potential generated in the base n-type semiconductor. Then, holes injected from the anode to the base increase. This positive feedback effect allows the device to transition from the high impedance state to the ON state. That is, as shown in FIG. 3B, this element can be oscillated by the trigger light. The trigger sensitivity can be increased as V _X approaches V _BO . E _g =
Without providing the semiconductor layer of the E _a trouble, in the active layer thickness comparable conventional semiconductor laser a n-type semiconductor layer for the base further and to from the beginning (0.1 [mu] m), considered it is sufficient to reduce the bandgap You may be able to, but it is useless. This is because the absorption of the trigger light is small at a thickness of about 0.1 μm, so that the trigger sensitivity is lowered.

FIG. 2 is a band diagram of the improved element performed to enhance the trigger sensitivity. The difference from FIG. 1 is that the layer thickness of the base p-type semiconductor is thin. Make this layer thinner,
For example, it is made thin enough to be depleted when the voltage applied from the outside is zero. Then, the photocurrent gain of the n (cathode) -p (base) -n (base) transistor is further increased,
It is convenient to increase the trigger sensitivity.

Journal of Applied Physics (J.App
59 (2), pp. 596-600, 1986), an optical thyristor in which the layer thickness of the p-type base semiconductor is thin as shown in FIG. 2 is reported. According to this paper, it is possible to turn on and pass a current of 100 mA or more with a trigger light of ˜several μw, and if such a current efficiently flows into the active layer, sufficient laser oscillation is possible.

(Embodiment) FIG. 4 is a perspective view showing an embodiment of the present invention. It is an optical memory for 1 μm band using InP semiconductor. n-InP
N-InP on the substrate 41 on the cathode side (thickness d = 2 μm, n =
2 × 10 ¹⁸ cm ^-3 ) 42, p-In used as p-type semiconductor for base
GaAsP (λg = 1.3μm, d = 30Å, n = 2 × 10 ¹⁸ cm ^-3 ) 4
3. Undoped n-InGaAsP that will be the n-type semiconductor for the base
(Λg = 1.3 μm, d = 1 μm, n = 5 × 10 ¹⁵ cm ⁻³ ) 44, undoped n-In _0.53 Ga _0.47 As (d = 0.1 μm, n = 5 × 10 5
¹⁵ cm ⁻³ ) 45, undoped n-InGaAsP (λg = 1.3 μ
m, d = 0.3 μm, n = 5 × 10 ¹⁵ cm ⁻³ ) 46 is grown, and p-InP (d = 0.5 μm, n = 2 × 10 ¹⁸ cm) serving as an anode is further grown.
^-3 ) 47 and p-InGaAsP for the cap layer (λg = 1.15μ
m, d = 0.5 μm, n = 2 × 10 ¹⁹ cm ⁻³ ) 48.
Layers 44, 45 and 46 correspond to n ₂ , n _a and n ₂ of FIG. 1 (a), respectively. The n-InGaAs45 serves as an active layer. The band diagram is almost the same as in FIG. Width 1.5 as shown in Figure 4
Etching is performed with a thickness of μm to form a striped upper part. Both sides thereof are covered with polyimide 51, and the transverse mode is controlled by reducing the difference in refractive index between the active layer and both sides thereof. The polyimide coat also serves as passivation. A cleavage plane forms a resonance surface. Resonator length is 100
μm. By adjusting the bias voltage, the number 10
The laser oscillation was generated by the trigger light of μw, and the output of several mw could be obtained.

FIG. 5 is an application example of the present invention. If a 45 ° mirror 53 is formed on the outside of the semiconductor optical memory 52 according to the present invention by etching and is arranged near the resonance surface, light can be extracted in the layer thickness direction. It is useful for application to parallel optical information processing.

(Effect of the Invention) As described above, according to the present invention, since the structure is such that light is incident and absorbed in the layer thickness direction, an optical memory with high trigger light sensitivity can be realized.

[Brief description of drawings]

1 and 2 are band diagrams showing the principle of the present invention, FIG. 3 (a) is a characteristic diagram of a semiconductor memory according to the present invention, and FIG.
FIG. 4B is a timing diagram of input / output signals of the semiconductor memory, FIG. 4 is a perspective view showing an embodiment of the present invention, and FIG. 5 is a perspective view showing an application example of the present invention. In the figure, 41 is an n-InP substrate, 42 is an n-InP, 43 and
48 is p-InGaAsP, 44 and 46 are n-InGaAsP, 45 is n-In
GaAs, 47 are p-InP, 49 and 50 are electrodes, 51 is polyimide, 52 is a semiconductor optical memory, and 53 is a 45 ° mirror.

Claims (2)

[Claims] 1. In a pnpn thyristor, an n-type semiconductor for a base is formed by laminating a first semiconductor layer, a second semiconductor layer and a third semiconductor layer in this order, and a p-type semiconductor for an anode and an n-type for a cathode. The forbidden band width of the type semiconductor is the above-mentioned first and third
Larger than any of the forbidden band widths of the semiconductor layers, the forbidden band width of the second semiconductor layer is narrower than the forbidden band widths of the first and third semiconductor layers, and the electrons and holes are absorbed in the forward conduction state. A semiconductor optical memory characterized by being relaxed in a second semiconductor layer and causing laser oscillation in the stimulated emission process of electrons and holes. 2. The semiconductor optical memory according to claim 1, wherein a forward conduction state is caused by absorbing light in the base n-type semiconductor.