JPS63158883A - Pnpn photo-thyristor - Google Patents

Abstract

PURPOSE:To increase the forbidden band width of a carrier fonfinement layer with a separation from a light-emitting layer, and to accelerate the speed of response by forming a base region by the light-emitting layer and the carrier confinement consisting of a semiconductor having forbidden band width higher than the light-emitting layer and joining with the light-emitting layer. CONSTITUTION:In a pnpn photo-thyristor in which a base region composed of a plurality of semiconductor layers having forbidden band width layer than an anode region 13 and a cathode region 15 is held by the anode region 13 made up of p-Al0.3Ga0.7As and the cathode region 15 consisting of n-Al0.3Ga0.7As, the base region has a light-emitting layer 14d composed of n-GaAs and carrier confinement layers 14c, 14e made up of n-AlZGa1-ZAs (0<=z<=0.3) having forbidden band width higher than the light-emitting layer 14d and joining with the light-emitting layer 14d. The forbidden band width of the carrier confinement layers 14c, 14e increases with a separation from the light-emitting layer 14d. Accordingly, the injection and confinement action of carriers are improved, thus allowing fast response without lowering the absorption efficiency of trigger beams.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pnpn optical thyristor used as a semiconductor optical memory required for image processing, optical logic operations, etc.

[Conventional technology]

Semiconductor optical memory, which has the ability to change its internal state in response to a minute trigger light and begin emitting light, and continue to emit light even after the trigger light has disappeared, will be essential when constructing future optical exchange and parallel information processing systems. It is a key device.

Figure 5 is from the Journal of Applied Physics.
cs) Magazine, Volume 59, Pages 596-600, 198
1 is a cross-sectional view of a conventional example of a semiconductor optical memory described in 1996.

This conventional example has a pnpn cyrisk structure. The anode region 53 and cathode region 55 are each p-AI
! GaAs and n-Al! It is made of G1As, and has a structure in which an n-type base layer 54a made of n-GaAs with a narrow forbidden band width is sandwiched therebetween. The thyristor turns on,
When the impedance state changes from the high impedance state to the low impedance state, carriers are injected into the n-type base layer 54a and are confined in this portion, thereby producing light. Since the trigger light is absorbed by the n-type base layer 54a, the layer thickness of this portion needs to be about the same as the absorption length. The absorption length of GaAs is about 1 μm for 0.8 μm light. On the other hand, from the point of view of shortening the turn-off time and increasing the response speed, the n-type base layer 5
The thinner the layer 4a, the better. The turn-off time τOFF of the thyristor can be expressed as τOFF. In equation (1), τP is the lifetime of holes, which are minority carriers, in the n-type base layer 54a, IP is the current flowing during conduction, and I) I is the current flowing during non-conduction. τop
To shorten p, it is necessary to reduce τe. τP becomes smaller as the carrier density is increased. Therefore, for a constant injection current, τP becomes smaller when the thickness of the n-type base layer 54a is made thinner, and thereby τOFF can also be shortened. Therefore, with the conventional structure shown in FIG. 5, it was not possible to simultaneously satisfy the two demands of increasing the absorption efficiency of the trigger light and increasing the response speed.

[Problem that the invention seeks to solve]

The above-mentioned conventional pnpn optical thyristor has the drawback that since the n-type base layer is composed of a single semiconductor layer, it is not possible to improve both the trigger light absorption efficiency and the response speed.

An object of the present invention is to provide a pnpn optical thyristor with improved trigger light absorption efficiency and response speed.

[Means for solving problems]

The pnpn optical thyristor of the present invention has an anode region made of an n-type semiconductor and a cathode region made of an n-type semiconductor.
p whose forbidden band width is sandwiched between a base region consisting of a plurality of semiconductor layers below the anode region and the cathode region;
In the npn optical thyristor, the base region includes a light emitting layer and a carrier confinement layer that is made of a semiconductor and whose forbidden band width is larger than that of the light emitting layer and is in contact with the light emitting layer;
The carrier confinement layer has a configuration in which the forbidden band width increases as the distance from the light emitting layer increases.

[Action of the invention]

The forbidden band width of the carrier confinement layer that is in contact with the light emitting layer is
As a result of carriers increasing in size as they move away from the light-emitting layer, carriers can be effectively injected into the light-emitting layer and confined, so the lifetime of minority carriers in the light-emitting layer can be reduced without reducing the thickness of the light-emitting layer.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor chip showing the main parts of an embodiment of the present invention.

In this example, an anode region 13 consisting of P -he □, 3Ga, ), 7As and n Aj'o, 3Gao
, and a cathode region 15 made of 7As, sandwiching a base region made of a plurality of semiconductor layers whose forbidden band width is less than that of the anode region 13 and the cathode region 15. Ga
The light-emitting layer 14d made of As has a forbidden band width greater than that of the light-emitting layer 14d, n-Aj'zGa+-z^s (0≦Z≦0
43) and are connected to the light emitting layer 14d.
carrier confinement layers 14c and 14e, and the first. Second
The forbidden band width of the carrier confinement layers 14c and 14e (7) increases as the distance from the light emitting layer 14d increases.

Note that 11 is a semiconductor substrate made of p-GaAs, and 12 is a semiconductor substrate made of p-GaAs.
is a 0.5 μm thick buffer layer made of p-GaAs. The anode region 13 has a thickness of 0.5 μm.

pAN O of s4 substance concentration I x 1018cri3,
The first layer consists of 3GaO-7As layers. The second carrier confinement layers 14c and 14e have a thickness of 0.5 μm and an impurity concentration of 1×106c11-3 n −Aj? zGal,-
It is made of a zAs layer, and Z is 0.2 on the side of the light-emitting layer 14d, and increases monotonically to 0.3 as the distance from the light-emitting layer 14d increases. The light emitting layer 14d is made of an n-GaAs layer with a thickness of 0.1.4 zn and an impurity concentration of I x 10 l6 cm-3. 14c, i4d.

14e constitutes the n-type base region 14a. 14b has a thickness of 0.05 μm and an impurity concentration of 5×1
A p-type base region 15 made of a p-GaAs layer with a thickness of 0"cta-', a thickness of Oj .mu.m, and an impurity concentration of 1.times.10.sup.18
C11'-3 n-Aj'o, Ga1), a cathode region made of a 7As layer, 16 a cap layer made of n-GaAs with a thickness of 0.1 μm and an impurity concentration of 5×10"Cal, 17 a AuGe- Cathode electrode made of Ni,
18 is an anode electrode made of AuZn. Note that the mesa portion does not have a cylindrical shape with a diameter of 60 μm.

FIG. 2 is an energy band diagram of the example, but for the sake of simplicity, portions that are not related to the present invention, such as band discontinuity at a heterojunction, are qualitatively approximated. Figure 2 (a) is an energy band diagram when no external bias voltage is applied, Figure 2 (b) is an energy band diagram in a high impedance state, and Figure 2 (c) is an energy band diagram in a low impedance and on state. It is an energy band diagram.

After the thyristor is turned on, each pn junction becomes forward biased (FIG. 2(c)).

When the n-type base region is formed of a single semiconductor layer as in the conventional example, the injected carriers spread into the region by diffusion, but on the other hand, a band structure as shown in Fig. 2(c) When n-Ga is formed, carriers drift along the potential gradient built inside, and the thin n-Ga
It efficiently and quickly falls during As (14d) (,
The thickness of the n-type base region is effectively n for carriers.
- It can be considered that the thickness is approximately equal to the thickness of GaAs (14d). Also, the wavelength of the trigger light is A in terms of forbidden band width.
/yGal-wAs (w) 0.2), the absorption efficiency will not be lowered.

FIG. 3 qualitatively shows the current (I)-voltage (V) characteristics, and the vertical axis on the right side shows the optical output (Pa). If the bias voltage is set to V=Vo and a trigger light of appropriate intensity is applied thereto, the thyristor is turned on.

After turning on, the optical output increases as the forward current increases.

FIG. 4 is a characteristic design diagram for determining parameters such as carrier concentration and layer thickness in the base region.

The transition of the thyristor from a high impedance state to a low impedance state is determined by the punch-through voltage 72 of the n-type base region and the avalanche breakdown voltage VBH. If the n-type base region is made of a single semiconductor layer, the on-voltage is: For the punch-through limit, using the step junction approximation, and for the avalanche breakdown limit, ■Bθ=Va (1−αl−α) 1 /a...
・(3) Va “60 (Eg/l, 1)” (ND
/10 ”) −”'...(4) It can be written as: In equations (2) to (4), ND is the carrier concentration of the base layer, d is the base layer thickness, and ′εS is the dielectric constant α
IIα2 is the current gain of the transistor (npn, pnp, respectively), n is a constant, and E5 is the forbidden band energy. (
4) In the formula, the units of E, and No are e V and C, respectively.
11-'. FIG. 4 shows the relationship between on-voltage and carrier concentration for the case where the base is GaAs. In the present invention, the on-voltage is slightly higher than the value shown in FIG.
Shift to high voltage side.

In the embodiment described above, the on-voltage was approximately determined by the punch-through of the n-type base region 14a, and was approximately 6V. As for the response speed, it can be operated at a speed of 100 MIIz.

In the above embodiments, output light was obtained in the layer thickness direction, but if cleavage planes are formed in a direction perpendicular to the layer thickness, it is also possible to obtain light emission in the longitudinal direction, which is advantageous in terms of application.

〔Effect of the invention〕

As explained above, in the present invention, by providing a heterojunction in the light-emitting layer, carrier injection and confinement effects are improved, and as a result, a pnpn optical thyristor that can respond quickly without reducing trigger light absorption efficiency can be obtained. effective.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a semiconductor chip showing the main parts of an embodiment of the present invention, FIG. 2(a) is an energy band diagram of the embodiment with no bias voltage applied, and FIG. 2(b)
is also the energy band diagram in the high impedance state,
Figure 2 (C) is an energy band diagram in the same low impedance state, Figure 3 is a characteristic diagram showing the relationship between voltage-current characteristics and optical output of one embodiment, Figure 4 is a characteristic design diagram, and Figure 5 is FIG. 2 is a cross-sectional view of a semiconductor chip showing a conventional example.

Claims (1)

[Claims] In the pnpn optical thyristor, an anode region made of a p-type semiconductor and a cathode region made of an n-type semiconductor sandwich a base region made of a plurality of semiconductor layers whose forbidden band width is less than that of the anode region and the cathode region. The base region includes a light emitting layer and a carrier confinement layer which is made of a semiconductor and whose forbidden band width is larger than that of the light emitting layer and is in contact with the light emitting layer, and the forbidden band width of the carrier confinement layer is greater than that of the light emitting layer. A pnpn optical thyristor, characterized in that the size of the pnpn optical thyristor increases as the distance from the pnpn optical thyristor increases.