JPH0358015A - Photosemiconductor device - Google Patents

Abstract

PURPOSE:To reduce the loss of a Fabri-Perot resonator and to realize an optical gate with a high extinction rate by providing a multiple quantum well structure in the Fabri-Perot resonator, and applying a voltage thereto and controlling the passage or reflection characteristics of the resonator. CONSTITUTION:A buffer layer 12, an etching stop layer 13, and a clad layer 14 are formed on a substrate 11, an active layer 15 in multiple quantum structure is laminated by 40 laminating well layers 151 and 40 barrier layers 12 alternately, and then an insulating layer 16 is formed. Then electrodes 17 and 18 are formed and reflecting mirrors 19 and 20 are formed. Consequently, by reducing the absorption by free carriers, the loss in the Fabri-Perot resonator can be reduced. When an electric field of 120 KV/cm is applied to the multiple quantum well structure, a 20 extinction ratio is obtained for 0.72 mum thickness.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical modulation element used for optical information processing and the like.

(Prior Art) In recent years, ultrahigh-speed parallel information processing using light has been attracting attention. For this purpose, it is necessary to develop a so-called planar modulation element that controls light two-dimensionally. One of these is an optical gate that electrically turns on and off optical signals. Conventionally, the structure shown in Fig. 2 as a planar optical gate was developed by Applied Physics Letters.
44, p. 16, (1983) by Wood, T. H. et al. This optical gate consists of GaAs and Ga
It has a pin structure in which a quantum well layer 21 in which thin films of AIAs are alternately laminated is sandwiched between cladding layers 22 and 23 made of GaAIAs of p-type and n-type conductivity, respectively. From the surface. The incident light passes through the quantum well layer 51 and exits from the back side of the substrate. Application of an electric field reduces the effective band gap, so switching is performed by utilizing the fact that the absorption coefficient of excitons in the quantum well for light on the low energy side increases. In this structure, since the length of the region where light is absorbed is short, the extinction ratio is as small as about 2:1. Increasing the extinction ratio Namenirira (Lee, Y.H.
et al. ) is Abride Physics Letters (
Applied Physics Letters)5
3, p. 1684 (1988) and Sines, R. J. et al.
ics Letters) Volume 53, Page 637, (198
8), it was considered to form the Fabry-Perot etalon structure by providing reflectors 19 and 20 shown in Fig. 3, and it was possible to obtain an extinction ratio of 5:E to 8:1, respectively. There is.

(Problems to be Solved by the Invention) As described above, the extinction ratio of the planar optical gate has been improved by using the Fab 1 Rubero etalon structure, but this level is still not sufficient. In order to further improve the extinction ratio, it is necessary to reduce the loss within the Fabry-Bello resonator and increase the Q value of the etalon.

An object of the present invention is to provide a planar optical gate that reduces loss within a Fabry-Perot resonator and has a high extinction ratio.

(Means for Solving the Problems) The optical semiconductor device of the present invention has a multi-quantum well structure as an active layer inside a Fabry-Perot resonator consisting of two parallel reflecting mirrors, and has a multi-quantum well structure. metal. The present invention is characterized in that transmission or reflection characteristics of the Fab 1 Rubero resonator are controlled by applying an electric field through an insulating film.

(Function) In a planar optical gate with a Fab 1 rubero etalon structure, when a voltage is applied to the multiple quantum well structure serving as the active layer, the energy of excitons in the multiple quantum well structure shifts to the lower energy side. Therefore, the absorption coefficient for light having slightly lower energy than the exciton increases, and the refractive index changes accordingly. When no voltage is applied, the energy of light is generated in Fab 1.
When it resonates with the Luperot resonator and turns on,
When a voltage is applied, the refractive index changes, which deviates from resonance and reduces transmittance, resulting in an off state. The extinction ratio at this time can be written as ION IOFF. Here, r is the ratio of the intensity when light reaches the other reflecting mirror of the etalon, and when there is no resonator or loss, r = t, and as the loss increases, r becomes smaller. From the above equation, absorption acts to reduce the effective reflectance in the form of Rr. Naturally, the closer r is to 1, the better. In an optical modulation element using a semiconductor, a reverse bias is applied to the pn junction in order to apply an electric field to the semiconductor layer, which is an active layer. Therefore, free carriers exist in the p-type semiconductor layer and the n-type semiconductor layer, causing loss. Absorption by free carriers reduces the carrier density to n=p
= IX10 cm, and the thickness of the n-doped layer is df1
=1.3\lm, thickness of p-doped layer is d, =1.5p
If m, then rrc=0.94. If losses other than free carrier absorption are included, r becomes 0.9 or less, and the extinction ratio decreases. In the present invention, a MIS structure is used for applying an electric field. In this structure, since the number of layers in which free carriers exist is smaller than that in the case where a pn junction is used, absorption by free carriers is small. Therefore, the loss inside the Fabry-Perot resonator can be reduced, and a planar optical gate with a high extinction ratio can be realized.

(Example) FIG. 1 is a structural diagram showing an embodiment of the present invention.

Thickness on the Sn-doped InP substrate 11! OOnm 5
X 1017-3 cm Si-doped even buffer layer 12, ? X1
0 cm Si-doped n-type InO. 53GaO. Etch stop layer 13 made of 47 As, 2 pm thick 5X10 am Si doped InP cladding layer 14, 7 nm thick non-doped 0.53 Gao.4 As well layer 151, 10 nm thick non-doped InP. An active layer 15 having a multi-quantum well structure in which 40 barrier layers 152 are alternately laminated is sequentially laminated, and SiN is further deposited to a thickness of 100 nm to form an insulating film 16.The substrate 11 is formed to a thickness of 100 nm.
After polishing to a mirror surface, an electrode 17 made of AuGeNi/AuNi and an electrode 18 made of Ti/Au are formed on the surface. Electrode 17 and substrate 1 where light enters and exits
1 and the electrode 18 are removed by etching, and a reflecting mirror 19. of a dielectric multilayer film made of SiO2 and amorphous Si is formed. 2
Precept 0. The reflectance of the reflecting mirrors 19 and 20 is 98%.

In this example, the influence of free carrier absorption is small < r =
o. It will take about 9 seconds. Therefore, even if other loss factors are considered, the overall r is about 0.95. When an electric field of 120 kV/cm is applied to the multiple quantum well structure of this example, the change in absorption coefficient obtained is Δα = 5300 cm, and the change in refractive index is approximately Δn = -0.028. When the thickness of the active layer is 0.72 pm, the extinction ratio is 2.
0 is obtained. There is free carrier absorption, and r is 0.
When it is 9, the extinction ratio is 8.6, so it is improved by more than twice.

In this embodiment, SiN was used as the insulating film 16, but AIG
A film such as aAs may also be used. The manufacturing process is the same up to the layering of the active layer 15, and on top of that, for example, AIGaAs is layered.
are laminated to a thickness of 100 nm. By using the MOVPE method for crystal lengthening, LnP and InGa can be produced using the same lengthening device.
As and AIGaAs can be stacked. The subsequent steps are the same as in the previous example. By using AIGaAs as the insulating layer, a good interface could be obtained, and a high electric field required for optical modulation could be stably applied. In this example, the values of r and extinction ratio were comparable to those of the previous example.

(Effects of the Invention) According to the present invention, a planar optical gate with reduced loss in a Fabry-Perot resonator and a high extinction ratio can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention. In the figure, 11 is a substrate, 12 is a buffer layer, 13 is an etch stop layer, 1
4 is a cladding layer, 15 is an active layer, 16 is an insulating film, 17.
18 is an electrode; 19. 20 is a reflecting mirror. Also, 1
51 is a well layer, and 152 is a barrier layer 152. FIG. 2 is a composition diagram showing an example of a conventional technique. In the figure, 21 is a quantum well layer, and 22 and 23 are cladding layers. FIG. 3 is a diagram showing another example of the conventional technique. 31 in the figure is n. The cladding layer 32 is a p-cladding layer.

Claims (1)

[Claims] Inside the Fabry-Perot resonator, which consists of two reflecting mirrors,
It has a multiple quantum well structure as an active layer, an insulating film is provided on the multiple quantum well structure, an electrode is formed on it, and a voltage is applied to this electrode to control the transmission or reflection characteristics of the Fabry-Perot resonator. An optical semiconductor device characterized by: