JPH0219823A - Superlattice optical semiconductor device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] An object of the present invention is to provide a superlattice optical semiconductor device using a superlattice structure, using a mixed crystal material as a well layer of the superlattice structure, and having high response. and has a superlattice structure including a well layer formed of a ternary or more mixed crystal material containing a plurality of semiconductor substances in an integral ratio, and each layer of the well layer is a stack of monoatomic layers consisting of atoms of a single species. 6 [Industrial Application Field] The present invention relates to an optical semiconductor device, and particularly to a superlattice optical semiconductor device using a superlattice.

[Prior Art] An optical modulation device as shown in FIG. 7 has been proposed as an optical semiconductor device using a superlattice structure forming multi-quantum wells.

A superlattice structure 53 is sandwiched between the P-type head region 51 and the n-type region 52. Above the p-type head area 51 and the n-type mark area 52,
Electrodes 57 , 58 are formed and connected via a modulator 59 to a reverse bias power supply 60 . The incident light has a superlattice structure 5
3 and receives light absorption modulation by the superlattice structure 53 whose reverse bias is modulated by the modulator 59.

Inside the superlattice structure 53, two types of semiconductors having different forbidden band widths are alternately stacked, forming a well-shaped potential as shown in FIG. 8(A).

Here, the semiconductor layer with the wider forbidden band width is called the barrier layer B, the semiconductor layer with the narrower forbidden band width is called the well layer W, and the width of the well layer is called Lw. Although it slightly penetrates into the interior, it is mostly confined in the well layer W. When the well layer W is sufficiently wide, the behavior of carriers is almost the same as that in the bulk state, but the width Lw of the well layer W
As the size of the superlattice structure becomes smaller, it begins to exhibit characteristics unique to the superlattice structure. That is, when the width Lw of the well layer W is reduced to about 100, the lateral movement of electrons or holes in the well layer W is restricted, and the energy level Ei, EJ is quantized.

The quantization energy unit changes depending on the width Lw of the well layer W.

The wave function of the electron and the wave number of the hole overlap,
When attracted by Coulomb force, excitons can be formed. When electrons and holes exist in the well layer of the superlattice, their movement in the thickness direction of the layer is restricted, and the wave function is compressed in the thickness direction. For this reason, a strong Coulomb attraction acts, increasing the binding energy and allowing excitons to exist stably even at room temperature.

The solid line in FIG. 10 shows a clear exciton absorption peak, which indicates the light absorption spectrum due to the superlattice structure.

When a reverse bias is applied to the structure shown in Figure 7, the well-shaped potential of the superlattice becomes as shown in Figure 8 (B) due to the electric field.At this time, the energy is quantized by the triangular potential formed at the bottom of the well. The units decrease from one end of the well to the other.

In the figure, for electrons, the right side of the well has low energy;
For Hall, the left side of the well has low energy. Therefore, the electric field acts in a direction to separate the electron-hole pairs, but since both electrons and holes are confined within the well layer W by the potential barrier of the barrier layer B, excitons exist even under a high electric field. The optical absorption spectrum when an electric field is applied is as shown by the broken line in FIG. The height of the exciton absorption peak is lowered, and its energy position is shifted several + leV toward the lower energy side (longer wavelength side). It is considered that the reduction in peak height represents the relative separation of electron-hole pairs within the well layer W due to the electric field, and the reduction in the peak energy position represents the electric field energy within the well layer W.

As shown in FIG. 10, by using a superlattice structure, it is possible to greatly change the absorption coefficient at a certain wavelength depending on the electric field. Further, although it is known that the real part and imaginary part of the dielectric constant have a Kramers-Kronig relationship, the refractive index in the wavelength region around the absorption peak also changes sensitively to the electric field. In the case of a bulk, the change in refractive index due to an electric field is often about 0.01%, but in the case of a superlattice, a change in refractive index of about 1% is possible.

By utilizing the above effects, it is possible to produce devices such as high-performance optical intensity modulators, optical phase modulators, and optical switches, and research is currently underway.

In the configuration shown in Fig. 7, I
A superlattice structure is used in which nP is used as a barrier layer and mixed crystal layers of InO, 53GaO, and 47As are used as well layers.

In Figure 9, which schematically shows the structure of the mixed crystal layer of Ino, s3Gao, and 47A S, the triangular marks indicate As.
The circles represent Ga atoms, and the squares represent In
The second and fourth columns from the top, which represent atoms, are As atomic layers in which only As atoms are arranged. The first, third, and fifth columns are mixed layers in which Ga atoms and In atoms are randomly distributed at a ratio of 0.47 to 0.53.

The shape of the exciton absorption peak is shown in FIG. 11, and the shape of the absorption peak can be expressed by a Gaussian distribution. If the oscillator strength related to absorption is constant, (peak height)×(half width) is constant for one absorption peak. Therefore, the narrower the half width, the sharper the absorption peak. When a change in absorption coefficient due to the application of an electric field is used in optical communication, the narrower the half-value width and the sharper the absorption peak, the larger the amount of change can be obtained, and the higher the performance of the device.

Figure 12 is I no, 53G ao, 47A
The half width of the exciton emission peak at 4.2°K of the S superlattice structure is plotted against the width Lw of the well layer of the superlattice. If the width Lw of the well layer is about 2000 people,
The conditions within the well layer are considered to be almost the same as those in the bulk. When the width Lw of the well layer becomes smaller than about 100 nm, the half-width increases.This increase is caused by the manufacturing process.The unevenness of the surface of each layer of the superlattice structure, that is, the presence or absence of local atomic layers, increases the well width. This is thought to be because the effect becomes relatively more significant as the layer thickness decreases.

[Problems to be Solved by the Invention] The minimum value of the half-value width shown in FIG. 12 of the emission peak of a superlattice structure having an Ino, 53Gao, 47A S mixed crystal layer as a well layer is about 3 meV. In the case of a superlattice with GaAs as a well layer, the half-width of the exciton emission peak is approximately 1
This is very large compared to meV.

A large half-value width leads to a low response of the optical semiconductor device.

An object of the present invention is to provide an optical semiconductor device that uses a ternary or more mixed crystal material as a well layer and has a high response.

[Consideration of the prior art] When the thickness of the well layer of a superlattice structure is several molecular layers, the unevenness of the well layer-barrier layer interface (disturbance due to not being a perfect monomolecular layer, or the thickness of the well layer) (disturbance) causes a large change in the quantum unit. The width of the change becomes larger as the width Lw of the well layer becomes narrower. When the width Lw of the well layer increases to about 80 people, the change becomes gradual, and at about 200 people it becomes almost constant.

Even for a sample of Lw = 2000 people, in which the quantum well effect is almost negligible, the half width of the emission peak from the well layer is about 31 eV. This spread is considered to be due to the uncertainty in the composition on the sublattice points occupied by group II atoms in the crystal lattice. Overall, In atoms and Ga atoms are 0.
Although it is distributed at a ratio of 53 to 0.47, it is not determined whether In or Ga is present on each group II sublattice point, and when viewed locally on a microscopic scale, the composition varies spatially. I'm here. Such local compositional uncertainties or changes due to fluctuations are called mixed crystal effects.

One way to reduce the mixed crystal effect is to reduce local compositional fluctuations.

[Means for Solving the Problems] Referring to FIGS. 1A and 1B, the well layer W of the superlattice structure 3 is made of a ternary or more elemental material containing a plurality of semiconductor materials M, , M, in an integer ratio. Each well layer W is formed with a laminated structure of monoatomic layers a L + a 2 + a3 made of atoms of a single species.

[Effect] In order to reduce the mixed crystal effect while using a substance with a mixed crystal composition,
Atoms or molecules may be arranged regularly.

Since each layer of the superlattice structure is composed of a stack of monoatomic layers made of atoms of a single type, mixed crystal effects can be prevented and the response of the optical semiconductor device can be increased.

[Example] FIGS. 1A and 1B show a superlattice optical semiconductor device according to an example of the present invention. In FIG. 1B, as in the prior art, a p-type region 1 and an n-type region 2 A superlattice structure 3 is sandwiched between. An electrode 7 is provided on the p-type region 1 and the n-type region 2.
．． 8 is formed, and a reverse bias power source 1o is connected via a modulator 9.
It is connected to the. The incident light enters one end of the superlattice structure 3 and is modulated by the superlattice structure 3 whose reverse bias is modulated by the modulator 9 . In the superlattice structure 3, two types of semiconductors with different forbidden band widths are stacked alternately, forming a well-shaped potential as shown in FIG. 8 (A>.The one with the wider forbidden band width The semiconductor layer having the narrower forbidden band width is called the barrier layer B, the semiconductor layer with the narrower forbidden band width is called the well layer W, and the width of the well layer is called Lw.

The atoms in the well layer are arranged as shown in FIG. 1(A). That is, from above, a monoatomic layer a1 consisting only of first atoms, a monoatomic layer a2 consisting only of second atoms are stacked to form a first monolayer M1, and then a monoatomic layer a1 consisting only of third atoms is laminated. The second monolayer M2 is formed by stacking the monoatomic layer a3 consisting of the monoatomic layer a3 and the monoatomic layer 71faz consisting only of the second atoms. The two monomolecular layers M1 and M2 form a repeating unit and are laminated to a desired thickness.

Since monoatomic layers consisting of a single type of atoms or monomolecular layers, which are stacked layers thereof, are stacked regularly, properties as a mixed crystal can be realized without uncertainty or fluctuation.

To realize such a mixed crystal, it is appropriate to include a plurality of pure substances in a simple integer ratio (for example, 1:1 to 2:1).

In a superlattice, the quantum level can be controlled not only by the composition of the constituent materials of the well layer, but also by the thickness of the well layer, the material of the barrier layer, the thickness, etc., so various quantum units can be obtained even with a limited composition ratio. , has a wide range of uses.

In addition, in the case of a superlattice structure, even if there is some mismatch in lattice constants, strain can be absorbed without producing lattice defects. If the thickness of the well layer is too large, electrons and holes will not necessarily combine and will separate when an electric field is applied, and if the thickness of the well layer is too small, the half width of the absorption peak will become too large. In the case of a modulator using absorption, the thickness of the well layer is 80
~2°C crying would be appropriate.

The well layer W is made of InGaAs, and the barrier layer is made of InP.
5 0.5 When forming the wall layer B, the well layer W is formed by sequentially and repeatedly growing a monoatomic layer of In, a monoatomic layer of As, a monoatomic layer of Ga, and a monoatomic layer of As. This is In
This is equivalent to sequentially and repeatedly growing an As monomolecular layer and a GaAs monomolecular layer. I n configured in this way
The well layer W of o, s G a o, s A s is ■
The group atoms are also arranged periodically and regularly, and there is no mixed crystal effect due to local fluctuations in the composition.

Due to its regularity, spatial fluctuations of quantum levels do not occur, and the half-width of the exciton peak can be reduced to 1 leV or less, making it possible to obtain a very sharp peak.

Monoatomic or monolayer growth as described above can be suitably carried out by atomic layer epitaxy.

Figure 2 shows a molecular beam epitaxy apparatus. The interior of the vacuum chamber 2 is kept at an ultra-high vacuum of 10" Torr or more. Molecular beams (atomic beams) are generated from the evaporation source 13.14.15. It is directed onto the substrate 19 through shutters 16, 17, and 18. For example, In, Ga, and As vapors are generated from evaporation sources 13.14, -15. One of the vapor sources
Select one and open the corresponding shutter to grow a single molecule (atom) N.

The monomolecular layer is controlled using, for example, in-situ observation using RHEED (high energy electron diffraction).

A high-energy (high-speed) electron beam is emitted from the electron gun 21,
Just four monoatomic layers strike the substrate 19, are reflected and hit the fluorescent screen 23, on the back side of the fluorescent screen the emission from the fluorescent screen 23 is collected by a lens 24 and detected by a receiver 26 through an optical fiber 25. When completed, the reflection is strongest, and as the nucleus or islands grow on top of it, the surface becomes uneven, and the intensity of the reflected electron beam decreases.

As the growth of the next layer further progresses, the intensity of the reflected electron beam increases from the minimum value and reaches the maximum value, and when the monoatomic layer is completed, the intensity of the reflected electron beam reaches the maximum value again. This change is monitored on the spot, and the shutters 16, 17, 18 are controlled via the process control computer 28 to grow a desired number of monoatomic layers in a desired order.

FIG. 3(A) shows a monomolecular (atomic) layer growth apparatus by MOCVD (metal organic CVD).

Raw material gas is supplied from two raw material gas supply ducts 31 and 32. For example, arsine A s H3 diluted with hydrogen
and trimethyl gallium (TMG) diluted with hydrogen. In order to prevent the two types of gases from mixing, another gas supply port 33 is provided in the middle, and hydrogen gas is passed therethrough and applied to the wedge 35 to separate both raw material gases.

The support carrying the substrate 36 is rotatable and housed in a case 3 having an opening below the source gas supply ducts 31, 32. This rotating Ti structure is shown in an enlarged view in Fig. 3 (B). When the substrate rotates and comes to the position where it receives arsine gas, one As layer grows. 6 Next, when it comes to the position where it receives TMG gas, , one Ga layer grows. In this way, the As layer and the Ga layer can be grown IM by IM. ■
Since it is difficult to grow a group (1) atomic layer on a group atomic layer and a group V atomic layer on a group V atomic layer, a monoatomic layer can be grown by appropriately setting conditions.

Other embodiments will be described below.

FIG. 4 shows a cross-sectional view of an optical modulator in which a multi-quantum well (MQW) is formed using an InGaAs/InP superlattice, which is manufactured by the gas source MBE method.

Approximately 0.1. czm thick n-type In
After growing the P buffer layer 39, 50 cycles of nGaA
An s/InP superlattice 40 is formed. Each layer will be about 100 people thick. After that, about 3000 n-type In
A P layer 41 and a p-type InP layer 42 of approximately 1 μm are grown over one surface. By applying a reverse bias to the pn junction, which is shaped into a desired pattern and covered with a dielectric film, an electric field is applied to the superlattice structure, causing a large change in the absorption coefficient.

FIG. 5 shows an example in which a DFB (distributed feedback) laser and a superlattice optical modulator are monolithically formed on an InP substrate 43.
After selectively etching the left side of the 0th order fabricated using the active layer 71, guide layer 72, cladding layer 73, and cap layer 74 grown by LPE, InGaAs/ I nA
A superlattice structure 45 of 40 layers of IAs is formed, and a cladding 7176 and a cap layer 77 are formed thereon. The light emitted from the DFB laser 44 on the right side is modulated by the superlattice structure 45 on the left side. The n-side electrode is made of, for example, AuGe.
Ni, pHJ! The It pole is made of AuZnNt, for example.

FIG. 6 shows an optical switch, where the X-shaped part is G a
A superlattice structure 47 of As/AIAs is formed by selectively etching. When no electric field is applied, light propagates along the waveguide a4.

By applying a voltage to the electrode 48, an electric field is applied to the underlying superlattice structure 47, causing a large refractive index change. That is, the refractive index decreases under the electrode 48 at the intersection, total reflection occurs, and the light propagates along the direction b. In this way, it can operate as an optical switch.

[Effects of the Invention] A high-response optical semiconductor device is provided that has a mixed crystal composition and prevents a decrease in response due to the mixed crystal effect.

[Brief explanation of the drawing]

1(A) and (B) show a superlattice optical semiconductor device according to an embodiment of the present invention, (A) is a schematic diagram showing the atomic arrangement in the well layer, and (B) is a schematic diagram of the superlattice optical semiconductor device. Schematic diagram, Figure 2 is a schematic diagram of the molecular beam epitaxy apparatus, Figure 3 (Ah
(B) is a schematic diagram of the MOCVD device, (A> is an overall view, (B) is a partially enlarged view, FIG. 4 is a cross-sectional view of an optical modulation device according to another embodiment of the present invention, and FIG. 5 is a schematic diagram of an MOCVD device. 6(A) and 6(B) are perspective views and sectional views of an optical switch according to an embodiment of the present invention; FIG. 7 is a prior art The schematic diagram of the superlattice optical semiconductor device, FIGS. 8(A) and (B) are the band diagrams in the superlattice, (A) is when no electric field is applied, (B) is when an electric field is applied, and FIG. 9 is A schematic diagram showing a mixed crystal according to the prior art, Fig. 10 is a graph showing an example of the absorption spectrum of a superlattice, Fig. 11 is a graph showing the shape of the absorption peak, and Fig. 12 is a well of the half width of the emission peak of the superlattice. It is a graph showing layer width dependence. In the figure, al, a2, monoatomic layers M1 and M consisting of atoms of a single species. Monolayer superlattice structure ゛2" Illustrated by Tsuki, 6th June, 6th month, 111th child, 19th change!
Figure 4 (A) /! in the well layer. +Sequence Diagram Molecular Linear Figure 2176M day Abandoned 1st country, fake light switch No. 6r Fig. 7 A photo of the binding technology Fig. 9 Absorption spectrum of liquid long superlattice Fig. 10 Shape of energy absorption peak Fig. 11 Masuto layer/1 angle; Direct radiation malification No. 12
figure

Claims (2)

[Claims] (1) It has a superlattice structure including a well layer (W) formed of a ternary or more mixed crystal material containing a plurality of semiconductor substances in an integral ratio, and each layer of the well layer (W) is formed of a single species. A superlattice optical semiconductor device characterized in that it is formed in a stacked structure of monoatomic layers (a_1, a_2, a_3) consisting of atoms. (2) Superlattice light including a superlattice structure (3) consisting of a semiconductor barrier layer (B) with a wide forbidden band width and a well layer (W) of a ternary or higher mixed crystal semiconductor with a narrow bandgap width A semiconductor device, wherein each layer of the well layer (W) is formed by alternately stacking monomolecular layers (M_1, M_2) of two types of semiconductor materials, and means (9) for selectively applying an electric field to the superlattice structure. , 10)
A superlattice optical semiconductor device comprising: