JP2804093B2 - Optical semiconductor device - Google Patents

Description

The present invention relates to an optical semiconductor device having a II-VI compound semiconductor layer used for a light emitting diode, a semiconductor laser, a photodetector, and the like. .

(Prior Art) Various II-VI compound semiconductors having a bandgap energy corresponding to a wavelength from infrared to ultraviolet including a visible region and mixed crystal semiconductors thereof include light emitting diodes, semiconductor lasers, photodetectors and the like. It is suitable as a material for an optical semiconductor device such as a composite element.

By the way, since high-quality crystals are required to manufacture a high-performance optical semiconductor device, an epitaxial crystal is generally grown on a desired crystal substrate, and an active layer such as a pn junction is formed during the crystal growth. The method has been adopted. It is desirable for the crystal substrate to be a crystal of the same kind as the epitaxial crystal growth layer in order to grow a high-quality crystal layer. However, in the case of II-VI group compound semiconductors, since a technology for producing a large-diameter crystal having a quality sufficient for industrial needs has not been established, II-VI group compound semiconductors are used as materials. Conventionally, optical semiconductor devices are mainly manufactured by using a group III-V compound semiconductor crystal or an elemental semiconductor crystal such as Si or Ge as a substrate and performing epitaxial growth on the substrate.

As the epitaxial growth of II-VI compound semiconductor crystals, various crystal growth methods including a metal organic chemical vapor deposition method (MOCVD method) and a molecular beam epitaxial method (MBE method) are known. However, the II-VI group compound semiconductor layer epitaxially grown on the III-V group compound semiconductor crystal has insufficient crystal quality for manufacturing an optical semiconductor device, and the manufactured optical semiconductor device is characteristically practical. It was not enduring.

A light emitting diode manufactured by growing a ZnSSe mixed crystal layer on a GaAs crystal substrate by MOCVD will be described as an example. In the case where the III-V compound semiconductor layer is also epitaxially grown on the III-V compound semiconductor crystal substrate by MOCVD, a crystal growth apparatus with excellent confidentiality and lattice matching with the crystal substrate using a high-purity source gas are used. If a crystal having a composition is grown, it is easy to obtain an epitaxial crystal layer having p-type and n-type conductivity with few crystal defects and high carrier concentration. However, when a ZnSSe layer is epitaxially grown on a GaAs substrate, even if a crystal that is lattice-matched to the substrate is grown using a similar crystal growth apparatus and high-purity source gas, various problems such as dislocations, stacking faults, and twins can occur. Cannot be avoided during the epitaxial growth. Further, even if p-type and n-type impurity elements are converted, they are not sufficiently activated, so that a sufficiently low resistance cannot be expected. Further, Ga as a constituent element of the substrate is taken into the ZnSSe epitaxial growth layer, which causes various problems such as an effect of compensating for p-type carriers and formation of an abnormal junction at an interface between the substrate and the epitaxial layer. In order to manufacture a light-emitting element with high luminance and a light-receiving element with high quantum efficiency, it is essential to increase the carrier concentration and reduce the resistance. In fact, the ZnSSe layer grown so far on the GaAs substrate has a p-type carrier concentration of 10 ¹⁶ cm ⁻³ and an n-type carrier concentration of 10 ¹⁷
Only about cm ^-3 is obtained, and it is thought that the emission from deep impurities is remarkably found, which is thought to be related to the fact that the added impurities are not activated. Various problems such as low luminous efficiency have been found, and at present it is not possible to obtain a light emitting diode with practical luminous efficiency by growing a ZnSSe layer with a pn junction on a GaAs crystal substrate. is there.

When a ZnSSe layer is epitaxially grown on a GaAs substrate by the MOCVD method, a high carrier concentration p
The problem that the n-type and n-type conductive layers cannot be obtained is that various II-VI compound semiconductors are mounted on another III-V compound semiconductor substrate.
This also occurs when epitaxial growth is performed by a crystal growth method such as the D method, which has been a major obstacle in manufacturing an optical semiconductor device having a pn junction in a II-VI compound semiconductor.

On the other hand, by epitaxially growing a II-VI compound semiconductor layer on a III-V compound semiconductor crystal substrate having an Al composition ratio of 0 to 0.13, rectification of electric conduction caused by band discontinuity generated at their junction interface. A technique for suppressing the occurrence of the property is disclosed in JP-A-61-46031.

(Problems to be Solved by the Invention) The present invention has been made to solve the above conventional problems, and has a high-quality crystal structure with few crystal defects on a III-V compound semiconductor, and a pn junction. It is intended to provide an optical semiconductor device having a group II-VI compound semiconductor layer having the following.

[Structure of the Invention] (Means for Solving the Problems) An optical semiconductor device according to the present invention comprises Al as a group III element.
Is formed on an n-type III-V compound semiconductor containing at least 0.15 in a composition ratio, and the II-VI compound semiconductor layer is formed.
A pn junction is formed in the group III compound semiconductor layer.

As the III-V group compound semiconductor containing Al, for example, Al _x In _y Ga _{1 -xy} As (0.15 ≦ x <1, 0 ≦ 1-xy ≦
1, y includes 0), Al _x In _y Ga _1-xy P (0.15 ≦ x <1,
0 ≦ 1-xy ≦ 1, y includes 0) or Al _x In _y Ga
_1-xy As _z P _w Sb _1-zw (0.15 ≦ x <1, 0 ≦ 1-xy ≦
1 and y include 0, and a mixed crystal compound semiconductor expressed in the form of 0 ≦ z ≦ 1, 0 ≦ w ≦ 1) can be given. Such a group III-V compound semiconductor may be used in the form of a substrate itself, or may be used in the form of a layer formed on a group III-V compound semiconductor substrate containing no Al. Examples of the group III-V compound semiconductor not containing Al include GaAs
Examples include s, GaP, GaSb, InP, InAs, InSb, and mixed crystal compound semiconductors thereof. In addition, II containing Al
When an IV group compound semiconductor layer is grown on a III-V group compound semiconductor substrate not containing Al, for example, a GaAs substrate and an Al
It is desirable that the lattice constant consistency is satisfied as in the combination with _x Ga _1-x As.

The reason for limiting the composition ratio of Al in the III-V group compound semiconductor containing Al is that if the composition ratio is less than 0.15, II-
This is because, when a group VI compound semiconductor is grown on the above-mentioned Al-containing group III-V compound semiconductor, a group II-VI compound semiconductor having good crystallinity cannot be formed.

As the II-VI group compound semiconductor, for example, ZnSe, Zn
Examples thereof include S, ZnTe, CdSe, CdS, and a mixed crystal compound semiconductor thereof.

Next, a method for manufacturing an optical semiconductor device according to the present invention will be described.

First, a II-VI group compound semiconductor layer containing an n-type (or p-type) impurity is epitaxially grown on a III-V group compound semiconductor having an Al composition ratio of 0.15 or more by MOCVD or the like at a temperature of, for example, 620 ° C. or more. . Subsequently, the n-type (or p-type)
II-VI containing p-type (or n-type) impurities by diffusing or ion-implanting p-type (or n-type) impurities on a II-VI group compound semiconductor layer containing the The group III-V compound semiconductor is epitaxially grown, or
An II-VI compound semiconductor layer having an n-junction is formed to manufacture an optical semiconductor device.

In the epitaxial growth of the II-VI compound semiconductor layer on the Al-containing III-V compound semiconductor,
When the surface of the group V compound semiconductor is exposed to air, an oxide film is generated due to the property of being easily oxidized due to containing Al,
Epitaxial growth of the II-VI compound semiconductor layer becomes difficult. To avoid this, it is desirable to employ the following method.

. After growing a group III-V compound semiconductor layer containing Al on a group III-V compound semiconductor substrate containing no Al in the reaction vessel, without subsequently exposing it to the air,
A II-VI compound semiconductor layer is immediately grown on the IV compound semiconductor layer.

A thin layer of a III-V compound semiconductor not containing Al is grown as an antioxidant on a III-V compound semiconductor substrate containing Al, and when the II-VI compound semiconductor layer is epitaxially grown, the Al Is evaporated by a high-temperature treatment or removed by etching with hydrochloric acid gas or the like, and then a II-VI compound semiconductor layer is grown.

(Operation) Generally, in order to arrange the atoms to be epitaxially grown correctly according to the atomic arrangement of the crystal substrate and achieve the most thermodynamically stable atomic arrangement, it is necessary to grow the crystal at least at a certain temperature or higher. If the growth is performed at an insufficient temperature, that is, at a low temperature, an atomic arrangement in which each atom is most stable even if an epitaxial growth layer having a crystal surface which seems to be flat and good in appearance is obtained. Is not realized, and the crystal becomes a state in which point defects and various impurities depending on the crystal growth process are incorporated. II−
In the case of a crystal in which two types of atoms are required to be arranged alternately and regularly in a crystal, such as in the case of a group VI compound semiconductor crystal, the crystal is far more than a crystal composed of a single element. The regular arrangement of atoms causes crystal defects and increases the incorporation of impurities. In fact, a ZnSSe layer
500 ℃ when grown epitaxially by OCVD method
At such a low temperature, it was found that various impurities such as carbon contained as constituent atoms of organic metal and organic chalcogenide as growth source gases contained more than 10 ¹⁸ cm ^-3 .

In the crystal growth process, in order to suppress the generation of crystal defects and the incorporation of impurities due to the unstable arrangement of atoms, it is desirable to perform epitaxial growth at a high temperature. However, II on the III-V compound semiconductor crystal substrate
In the case of epitaxial growth of a -VI compound semiconductor crystal layer, raising the crystal growth temperature causes the following problem. That is, when attempting to epitaxially grow a crystal having a composition different from that of the substrate, the surface of the crystal substrate is temporarily exposed to a gas phase having a vapor unsaturated with respect to the constituent elements.
In the case of a group III-V compound semiconductor, the saturated vapor pressure of group V atoms generally takes a much higher value than the saturated vapor pressure of group III atoms. Therefore, when the group III-V compound semiconductor crystal substrate is exposed to a high temperature state, group V atoms are selectively evaporated from the surface of the crystal substrate, and group III atoms are left on the crystal surface. When such evaporation of group V atoms proceeds to some extent,
Group III atoms aggregate on the crystal surface to form droplets, dissolution of the crystal constituting the substrate in the formed droplets, evaporation of Group V atoms progresses rapidly, and the crystal substrate surface exhibits remarkable unevenness, etc. Extreme phenomena also occur. When such modification on the surface of the III-V compound semiconductor crystal substrate occurs, a diffusion phenomenon in which the group III atom is taken in during the epitaxial growth of the II-VI compound semiconductor crystal, or a crystal composed of the group III atom and the epitaxially grown atom. Crystals having a composition and structure different from those of the substrate and the epitaxially grown crystal are generated on the substrate surface, and hinder subsequent epitaxial growth. From such a problem, it has conventionally been substantially difficult to epitaxially grow a II-VI compound semiconductor crystal on a III-V compound semiconductor crystal substrate at a sufficiently high temperature.

The present inventors, based on the experimental facts described above, at least the surface of the substrate as the III-V compound semiconductor crystal used as the substrate, the Al composition ratio in the group III element is set to 0.15 or more, on this substrate By epitaxially growing a group II-VI compound semiconductor crystal, even if the growth is set at a high temperature, the surface of the substrate is made uneven due to denaturation on the surface of the substrate, and the epitaxially grown crystal layer of group III atoms of the substrate is formed. It has been found that high-quality II-VI compound semiconductor crystals having extremely good crystallinity can be grown by suppressing the phenomenon of diffusion, dislocations in the epitaxially grown crystal layer, stacking faults, and the occurrence of twin boundaries. Further, since the modification of the substrate surface during the epitaxial growth under the high temperature can be suppressed, the activation rate of the p-type and n-type impurities can be improved, and both the p-type and the n-type have a high carrier concentration, that is, a pn junction with a low resistance. A group II-VI compound semiconductor crystal layer having the following formula can be formed.

II-VI to III-V compound semiconductor containing Al as described above
Considering the behavior of the group III-V compound semiconductor during epitaxial growth of the group III compound semiconductor crystal, A
The bond between the l atom and the group V atom is stronger than the bond between the group III atom and the group V atom such as Ga or In, and the group V atom bonded to the Al atom is desorbed from the crystal surface and evaporates into the gas phase. It is presumed to be difficult. In fact, according to the experiments of the present inventors, when a III-V compound semiconductor crystal having a relatively small Al composition ratio is used, the modification of the semiconductor crystal, that is, the effect of suppressing evaporation of group V atoms is not sufficient. , The Al composition ratio in group III atoms is
When it exceeds 0.15 or more, it has been found that the effect of preventing denaturation of the semiconductor crystal surface is remarkably produced. Thus, the Al composition ratio
The effect of suppressing the evaporation of group V atoms such as As at a value of 0.15 is due to the fact that each of the group V atoms in the group III-V compound semiconductor crystal has a crystal coordination structure bonded to four group III atoms. Therefore, it is estimated that when the Al composition ratio becomes about 0.15, most of the group V atoms are bonded to Al atoms in the crystal.

As described above, according to the present invention, Al is contained as a group III element,
By using a group III-V compound semiconductor having a composition ratio of 0.15 or more, dislocation, stacking fault, generation of twin interface at least on a substrate provided with the semiconductor is excellent in crystallinity II- A group VI compound semiconductor layer can be formed and
Since a pn junction with a high carrier concentration can be formed in the II-VI compound semiconductor layer, various deep levels including self-activated luminescence and various luminescence lines based on crystal defects have been reduced to achieve high luminous efficiency. An optical semiconductor device having excellent characteristics can be obtained.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Example 1 First, an n-type GaAs substrate having a plane orientation of (100) was etched with a sulfuric acid / hydrogen peroxide solution to clean the surface.
It was set in the reaction vessel of the MOCVD crystal growth apparatus. Subsequently, the GaAs substrate was heated to 750 ° C. and left for 10 minutes while supplying arsine (AsH ₃ ) gas as a group V element source gas in a hydrogen gas atmosphere at normal pressure in the reaction vessel, and allowed to stand for 10 minutes.
Trimethylgallium (TMG) and trimethylaluminum (TMA) are supplied as group-group element source gases so that the supply ratio (V / III ratio) with the group-V element gas becomes 20 and n
Hydrogen selenide (H ₂ Se) gas is supplied as a source material gas of Al type to form Al _x Ga _1-x having an Al composition ratio x (x> 0.15) on a GaAs substrate.
As layer was grown.

Next, the supply of each of the raw material gases was stopped, and the temperature in the reactor was lowered while exhausting the gas. Subsequently, a mixed gas of diethyl selenium (DESe) and diethyl sulfur (DES) was supplied as a Group VI raw material gas at a predetermined ratio. When the temperature rises and reaches 650 ° C, diethylzinc (DEZ) is used as a Group II element raw material.
While supplying t-butyllithium gas as a p-type impurity (Li raw material) while supplying so that the ratio (VI / II ratio) with respect to the group VI raw material gas becomes 2, the Al composition ratio x is different.
_A p-type ZnS _0.06 Se _0.94 layer was grown on the _x Ga _1-x As layer.

The etch pit density of the p-type ZnS _0.06 Se _0.94 layer formed on the Al _x Ga _{1 -x} As layers having different Al composition ratios on the obtained GaAs substrate was measured. The etch pit density was evaluated by measuring the dislocation density corresponding to the etch pit density using a diluted bromo-methanol mixed solution. The results are shown in FIG. As is clear from FIG. 2, when a p-type ZnS _0.06 Se _0.94 layer is grown on an Al _x Ga _{1 -x} As layer having an Al composition ratio of 0.15 or more, even if the growth is performed at a high temperature of 650 ° C. It can be seen that dislocation generation during growth of the II-VI compound semiconductor crystal based on the modification of the III-V compound semiconductor crystal surface can be effectively suppressed.

In addition, diethyl selenium (DESe) and diethyl sulfur (DES) were used as group VI source gases on the Al _0.4 Ga _0.6 As layer on the GaAs substrate.
Is supplied at a predetermined ratio and the temperature is raised. When the temperature reaches a predetermined temperature (450 to 800 ° C.), diethylzinc (DEZ) as a Group II element raw material is added to the Group VI raw material gas at a ratio (VI / II The ZnS _0.06 Se _0.94 layer was grown by supplying so as to have a ratio of 2 and the impurity carbon atom concentration in the layer was measured by secondary ion mass spectrometry. FIG. 3 shows the results.
As apparent from FIG. 3, the growth temperature was set to about 620.
C. or higher, the impurity carbon atom concentration is reduced to the detection limit concentration of carbon atoms, that is, p necessary for good pn junction formation.
It can be seen that the concentration can be suppressed to 10 ¹⁶ cm ⁻³ or less, which is the carrier concentration of the type and n-type conductive layers.

Example 2 First, an n-type GaAs substrate 1 having a plane orientation of (100) was etched with a sulfuric acid / hydrogen peroxide solution to clean the surface, and then placed in a reaction vessel of a MOCVD crystal growth apparatus. Subsequently, the GaAs substrate was heated to 750 ° C. while being supplied with arsine (AsH ₃ ) gas as a group V element source gas under a normal pressure and a hydrogen gas atmosphere in the reaction vessel, and allowed to stand for 10 minutes. Trimethylgallium (TM
G), trimethylaluminum (TMA) was supplied so that the supply ratio (V / III ratio) to the group V element gas became 20, and hydrogen selenide (H ₂ Se) gas was supplied as an n-type impurity. 1 μm thick n-type GaAs buffer layer 2 on GaAs substrate 1
Then, an Al _0.3 Ga _0.7 As layer 3 having a thickness of 2 μm was grown (FIG. 1A).

Next, the supply of the group III source gas and the hydrogen selenide gas was stopped, the temperature of the GaAs substrate was immediately started, and after the temperature was lowered to 500 ° C., the supply of the arsine gas was stopped. After the supply of arsine gas is stopped, the arsine gas in the reaction vessel is replaced and evacuated by leaving for 20 seconds, and diethyl selenium (DESe) and diethyl sulfur (DES) are directly used as group VI source gases.
The mixed gas is supplied at a predetermined ratio and the temperature is increased,
When the temperature reaches 650 ° C., bromine gas as an n-type impurity raw material is introduced while supplying diethyl zinc (DEZ) as a group II element raw material so that the ratio (VI / II ratio) to the group VI raw material gas becomes 2. Then, an n-type ZnS _0.06 Se _0.94 layer 4 having a thickness of 4 μm was grown on the Al _0.3 Ga _0.7 As layer 3. Subsequently, the supply of bromine gas was stopped, and a 4 μm thick undoped ZnS _0.06 S
e A _0.94 layer 5a was grown (FIG. 1 (b)).

Next, the supply of the group II source gas (DEZ) was stopped, and the temperature was immediately started. When the temperature of the GaAs substrate 1 dropped to 350 ° C., the supply of the group VI source gas (DES, DESe) was stopped. Subsequently, the undoped ZnS _0.06 Se _0.94 layer 5a
Is grown in a quartz ampoule together with ZnS, ZnSe powder and Li ₂ Se powder, and heat-treated at 500 ° C. for 1 hour to diffuse Li into the ZnS _0.06 Se _0.94 layer 5a to form p.
A type ZnS _0.06 Se _0.94 layer 5 was formed (FIG. 1 (c)). The concentration of Li in the ZnS _0.06 Se _0.94 layer 5 is 1 × 10 ¹⁸ c
m ^-3 and the carrier concentration were about 1 × 10 ¹⁷ cm ^-3 .

Next, the back surface of the n-type GaAs substrate 1 is polished and removed, and an n-type electrode 6 made of AuGe is deposited on the back surface of the n-type GaAs substrate 1.
Heat treatment for a short period of time, and further apply A on ZnS _0.06 Se _0.94 layer 5.
A p-type electrode 7 made of u was deposited (shown in FIG. 1 (d)). The substrate after the electrodes were formed was cleaved into chips to produce blue light emitting diodes (not shown).

The light emitting diode obtained according to Example 2 has a good
It has a current-voltage characteristic indicating that a pn junction has been formed, a current of 10 mA flows when a forward voltage of 4 V is applied, and a high efficiency blue light emission with a center wavelength of 400 nm and a luminance of 10 mCandela, which could not be obtained conventionally. The characteristics were shown.

Example 3 First, a 2 μm thick n-type GaAs substrate with (100) plane orientation was formed.
The n-type Al _0.3 Ga _0.7 As layer was further epitaxially grown on the n-type Al _0.3 Ga _0.7 As layer. Subsequently, the GaAs substrate was placed in a reaction vessel of a MOCVD crystal growth apparatus, and was placed under a hydrogen gas atmosphere containing a small amount of arsine for 800 hours.
° C and left for 10 minutes.
Only the undoped GaAs thin layer was selectively evaporated. In this step, the evaporation of the Al-free GaAs thin layer is caused by the underlying Al
_{Since the 0.3} Ga _0.7 As layer is stable, it progresses uniformly over the whole without locally proceeding. Subsequently, the temperature was started and the supply of arsine gas was stopped. When the temperature was lowered to 650 ° C., a mixed gas of diethylsenlen (DESe) and diethylsulfur (DES) was supplied at a predetermined ratio, and diethylzinc (DEZ) was supplied. The ratio to the group VI source gas (VI / II
Ratio) of 2, while introducing bromine gas, which is an n-type impurity raw material, to form a 4 μm-thick n-type ZnS _0.06 Se _0.94
The layer was epitaxially grown, the introduction of bromine gas was stopped, and an undoped ZnS _0.06 Se _0.94 layer having a thickness of 4 μm was epitaxially grown. The undoped ZnS _0.06 Se _0.94 layer is made of the Al
_Since the surface of the _0.3 Ga _0.7 As layer was smooth and no Ga or the like remained, the crystallinity and the like were extremely good. Thereafter, the second embodiment
In the same manner as described above, the undoped ZnS _0.06 Se _0.94 layer
i is diffused to form a p-type ZnS _0.06 Se _0.94 layer,
A p-type electrode was formed and cleaved into chips to produce a blue light emitting diode.

The light emitting diode of the third embodiment exhibited high-efficiency blue light emission characteristics as in the second embodiment.

In the third embodiment, the removal of the Al-free GaAs thin layer is performed by heat treatment. However, the removal may be performed by flowing an etching gas such as a hydrogen chloride gas.

[Effects of the Invention] As described in detail above, according to the present invention, A
l, the composition ratio of Al is 0.15 or more, by using a group III-V compound semiconductor, the dislocation, stacking faults on at least the substrate provided on the surface of the semiconductor, the crystallinity in which the occurrence of twin boundaries is suppressed II-VI compound semiconductor layer having a good carrier density and a high carrier concentration in the II-VI compound semiconductor layer.
Since a pn junction can be formed, light emitting diodes, semiconductor lasers, and light with excellent characteristics such as high luminous efficiency with reduced various emission lines based on various deep levels and crystal defects including self-activated light emission An optical semiconductor device useful for a detector or the like can be provided.

[Brief description of the drawings]

1 (a) to 1 (d) are cross-sectional views showing manufacturing steps of a light-emitting diode according to Example 2 of the present invention, and FIG. 2 shows Al _x Ga _1-x As having different Al composition ratios and formed on these layers. ZnS _0.06 S
e is a characteristic diagram showing the relationship between the etch pit density of the _0.94 layer and FIG. 3 shows the temperature and the amount of impurity carbon in the ZnS _0.06 Se _0.94 layer when the ZnS _0.06 Se _0.94 layer is epitaxially grown on the Al _0.3 Ga _0.7 As layer. FIG. 4 is a characteristic diagram showing a relationship between 1 n-type GaAs substrate 3 n-type Al _0.3 Ga _0.7 As layer 4 n-type ZnS _0.06 Se _0.94 layer 5 a undoped ZnS _0.06 Se _0.94 layer 5 p-type ZnS _0.06 Se _0.94 Layers 6, 7, ... electrodes.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 33/00 H01L 31/10

Claims (1)

(57) [Claims] An II-VI compound semiconductor layer is formed on an n-type III-V compound semiconductor containing 0.15 or more Al as a group III element, and pn is formed on the II-VI compound semiconductor layer.
An optical semiconductor device, wherein a junction is formed.