JP2002289918A - Method for manufacturing p-type semiconductor crystal and light emitting device - Google Patents

Abstract

(57) Abstract: Provided is a method for manufacturing a p-type semiconductor crystal having a high activation rate in a wide gap semiconductor. SOLUTION: In a method of manufacturing a p-type semiconductor crystal by simultaneously doping a donor and an acceptor into a semiconductor crystal, a donor impurity (eg, Ga) is added to the semiconductor crystal (eg, ZnO) in a process of manufacturing the p-type semiconductor crystal. ) Is supplied intermittently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a p-type semiconductor device having a high activation rate capable of realizing a light-emitting device with high efficiency and low power consumption.
The present invention relates to a type semiconductor crystal, particularly a zinc oxide (ZnO) -based p-type semiconductor crystal, and more particularly to a method for manufacturing such a p-type semiconductor crystal.

[0002]

2. Description of the Related Art Direct transition type semiconductors having a band gap of about 3 eV or more are expected as materials capable of realizing blue to ultraviolet light emitting devices. Such materials include gallium nitride (GaN), a III-V compound semiconductor.
And II-VI compound semiconductor zinc selenide (ZnS
e), zinc oxide (ZnO) and the like. Above all, ZnO
Has an extremely high exciton binding energy of 60 meV, and exciton emission is observed even at room temperature. Therefore, if this is used, it has higher efficiency and lower power consumption than the light emitting devices based on GaN or ZnSe which are currently in practical use. There is a possibility that a light emitting device can be realized.

[0003] With these wide-gap semiconductors, it has been difficult to obtain a p-type semiconductor crystal which is indispensable for a carrier injection type light emitting device. In particular, in II-VI group compound semiconductor materials, the defect generation energy is large and the self-compensation effect is strongly generated by acceptor doping, so that it is extremely difficult to control p-type conduction and its conductivity.

To solve this problem, a "co-doping method" for realizing low-resistance p-type conduction has been invented, and ZnS
10 ¹⁹ to 10 ²¹ cm ^-3 in e-crystal and GaN crystal
(See JP-A-10-53497 and JP-A-10-101496). According to the publication, when a donor impurity and an acceptor impurity are introduced at a ratio of 1: 2, first, II
Group (or group III) lattice-substituted donor atom and VI
Acceptor atoms substituted at the group (or group V) position form a pair, and stabilization by electrostatic energy occurs. It was shown that coordination of another acceptor atom in this state results in stable replacement without lattice defects, enabling high-concentration doping and realizing low-resistance p-type conduction. I have.

[0005]

However, in order to obtain the above-mentioned effect in co-doping, it is necessary that the donor-acceptor complex forms a special bonding state.
FIG. 7 shows a crystal structure model when co-doping is applied to the II-VI group compound semiconductor. In FIG. 7, a hollow circle in a thick line represents a group II element regardless of size, and a hollow circle in a thin line represents a group VI element regardless of size. Black circles represent Group III elements as donors, and shaded circles represent Group V elements as acceptors. In addition, the surplus donor or acceptor that does not adopt the coordination as shown in the figure generates lattice defects and compensates for p-type conduction by causing n-type conduction. Must be 2.

The coordination state described above is difficult to realize only by simultaneously doping donor and acceptor impurities. Therefore, the solubility limit is increased as compared with the single doping of the acceptor, but the activation rate is not sufficient, and it has been difficult to obtain conductivity and mobility applicable to a light emitting device.

In particular, ZnO has a high electronegativity of oxygen, so that it is difficult to stably perform substitution with an acceptor impurity as compared with other wide gap semiconductors.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and it has been proposed to manufacture a p-type semiconductor crystal having a high activation rate in a wide gap semiconductor which has been conventionally difficult, and to provide such a p-type semiconductor crystal. The purpose of the present invention is to manufacture a light-emitting device with high efficiency and low power consumption by using a light emitting device.

[0009]

Means for Solving the Problems The present inventors have proposed a donor
As a result of intensive studies on the method of supplying the acceptor impurity, the present inventors have found that the above-mentioned coordination state can be adopted with a high probability by intermittently supplying the donor impurity during crystal growth.

That is, a method for producing a p-type semiconductor crystal according to the present invention is a method for producing a p-type semiconductor crystal by simultaneously doping a semiconductor crystal with a donor and an acceptor. It is characterized in that a donor impurity is intermittently supplied to a semiconductor crystal.

According to the method of manufacturing a p-type semiconductor crystal of the present invention, it is easier to form a (acceptor)-(donor)-(acceptor) complex than to continuously supply donor impurities to a semiconductor crystal. . Further, each atom of the complex is appropriately substituted at a lattice position of the constituent element of the base semiconductor. As a result, one acceptor of the complex is activated without generating lattice defects, and a high-concentration and low-resistance p-type semiconductor crystal is obtained.

If the acceptor impurity is intermittently supplied in synchronization with the supply cycle of the donor impurity, isolated extra acceptor atoms can be hardly generated. As a result, lattice defects that are likely to occur during acceptor doping can be suppressed, and a p-type semiconductor crystal having a high activation rate can be obtained.

Here, "synchronization with the supply cycle of the donor impurity" does not mean that the supply timing and the supply time are completely coincident with each other, but rather that the donor impurity and the acceptor impurity exist at the same time. This means that the acceptor impurity is supplied in synchronization with the supply timing of the donor impurity so that the supply times of the donor impurities at least partially overlap. Of course, the supply timing and the supply time of both may completely match.

Further, if the supply period of the donor impurity is set shorter than the growth time of the unit molecular layer of the semiconductor crystal, the donor-acceptor complex causing p-type conduction is incorporated into the unit molecular layer. This achieves uniform doping in the thin film crystal.

In one embodiment, the semiconductor crystal is II
A compound semiconductor crystal comprising a Group III and Group VI element is produced.

A group II-VI element compound semiconductor crystal has a large defect generation energy and cannot obtain a sufficient acceptor activation rate by the conventional simultaneous doping method. By applying the present invention, a p-type semiconductor crystal having a high concentration and a low resistance can be obtained.

II suitably produced by the method of the present invention
-VI group compound semiconductor crystal is typically ZnO, ZnMg
The semiconductor crystal is a zinc oxide-based semiconductor crystal such as O or ZnCdO, that is, a zinc oxide-based semiconductor crystal. in this case,
When nitrogen is used as the acceptor impurity and gallium is used as the donor impurity, the effect of forming a donor-acceptor complex or reducing the acceptor level to lower the p-type resistance can be obtained most remarkably.

In the simultaneous doping of the zinc oxide-based semiconductor crystal, it is desirable to irradiate the crystal growth surface with active atoms converted into plasma by electromagnetic waves as a method of doping an acceptor impurity. This is because a crystal defect hardly occurs in such a case. As a result, the acceptor activation effect due to the intermittent supply of donor impurities becomes more remarkable, and a high-concentration, low-resistance p-type zinc oxide-based semiconductor crystal can be obtained.

In the method of manufacturing a p-type semiconductor crystal according to the present invention, if a molecular beam epitaxy method using an ultra-high vacuum growth chamber is used as a crystal growth method, a gas valve or a cell shutter is opened and closed to allow the crystal growth during the crystal growth. It is possible to sharply control the intermittent supply of impurities. Therefore, the formation of the donor-acceptor complex can be performed more reliably than in other crystal growth methods. In particular, in the case of the laser molecular beam epitaxy method, the intermittent supply of impurities can be controlled extremely steeply by the pulse laser irradiation sequence.

Among the group II-VI compound semiconductor crystals, especially p
For a ZnO-based semiconductor for which type doping has been difficult, it is extremely effective to apply the manufacturing method according to the present invention in order to obtain a high-concentration, low-resistance p-type semiconductor crystal. This facilitates the fabrication of a room-temperature exciton device that can only be realized using the same material, and achieves high efficiency by stacking a zinc oxide-based p-type semiconductor crystal layer and a zinc oxide-based n-type semiconductor crystal layer. -A light emitting device with low power consumption can be provided.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. As an embodiment, the donor
An example in which the present invention is applied to the production of a p-type ZnO thin film using an acceptor simultaneous doping method will be described.

(Embodiment 1) FIG. 1 is a schematic view of a laser molecular beam epitaxy apparatus used in this embodiment. A substrate holder 2 is arranged above a growth chamber 1 which can be evacuated to an ultra-high vacuum, and a substrate 3 is fixed to the substrate holder 2.
The back surface of the substrate holder 2 is heated by the heater 4 arranged above the substrate holder 2, and the heat conduction thereof causes the substrate 3 to be heated.
Is heated.

A target table 5 is disposed directly below the substrate holder 2 at an appropriate distance, and a plurality of thin film material targets 6 are disposed on the target table 5. The surface of the target 6 is ablated (ground) by a pulsed laser beam 8 radiated through a view port 7 provided above the side surface of the growth chamber 1, and a plume 6 a of the raw material of the target 6 that has evaporated instantaneously is placed on the substrate 3. The deposition grows a thin film.

The target table 5 has a rotating mechanism,
By controlling the rotation in synchronization with the irradiation sequence of the pulsed laser beam 8, thin films can be stacked using target materials having different components.

The growth chamber 1 is provided with a plurality of gas introduction pipes 10 and 11 so that a plurality of types of gases can be introduced. The gas introduction pipe 10 is connected to the radical source 9,
As a result, the nitrogen gas (N ₂ ) introduced from the gas introduction tube 10 is turned into plasma by the electromagnetic wave, so that the substrate 3 can be irradiated with the activated atomic beam.

In growing a ZnO thin film, Z
Although nO single crystal and sapphire can be used,
In the present embodiment, the (0001) plane of a ScMgAlO ₄ single crystal substrate having extremely small (0.09%) lattice mismatch with the ZnO in the a-axis direction was used.

As the heater 4 for heating the substrate, Nd: YA
Using a G laser (wavelength: 1064 nm), the spot diameter on the back surface of the substrate holder and the irradiation position were controlled to uniformly heat the entire substrate 3.

During the growth of the thin film, oxygen gas is supplied at a partial pressure of 1 × 10 ^−5.
The gas was introduced from the gas introduction pipe 11 so that the pressure became Torr. Also,
As nitrogen (N) which is an acceptor impurity, a gas introduction pipe 1
The nitrogen (N ₂ ) gas introduced from 0 was turned into plasma by the radical source 9 to generate active nitrogen, which was irradiated onto the substrate 3. The partial pressure was 3 × 10 ⁻⁵ Torr.

As target materials, a ZnO single crystal with no impurity added and Ga as a donor impurity were replaced with Ga ₂ O ₃
Was used. A plurality of the Ga ₂ O ₃ added ZnO sintered bodies were prepared by changing the amount of Ga ₂ O ₃ added. A KrF excimer laser (wavelength: 248 nm, pulse number: 10 Hz, output: 0.9 mJ / cm ² ) was used as a pulse laser for ablation. At this time, the drive sequence of the target table 5 by the rotation mechanism and the pulse irradiation sequence of the KrF excimer laser were synchronized by an external control device (not shown), and the targets 6 were alternately ablated in an arbitrary sequence. FIG. 2 shows a raw material supply sequence according to the present embodiment. FIG. 2 shows that the irradiation of the Ga ₂ O ₃ -added ZnO sintered body and the irradiation of the impurity-free ZnO single crystal are performed alternately although the number of pulse irradiations is different from each other, and that a constant amount of irradiation is continuously performed during the irradiation. Indicates that active nitrogen is supplied.

FIG. 3 shows ablation ratios and secondary ion mass spectroscopy (SIMS: Secondary Ion Mass Spectroscopies) of ZnO sintered compacts with different amounts of Ga ₂ O ₃ added.
The relationship with the Ga doping concentration identified by py) is shown. Here, the “ablation ratio” is defined as Ga ₂ O ₃ added Z
It is defined as the number of ablation pulses of an impurity-free ZnO single crystal based on the number of ablation pulses of an nO sintered body target. FIG. 3 shows that the Ga doping concentration is inversely proportional to the ablation ratio.

The doping concentration of N, which is an acceptor impurity, was controlled by the substrate temperature (that is, the crystal growth temperature). FIG. 4 shows the substrate temperature (growth temperature) dependency of the N doping concentration identified by SIMS.

From the results of FIGS. 3 and 4, the ablation ratio corresponding to an arbitrary Ga doping concentration and the substrate temperature at which the N doping concentration becomes twice the Ga doping concentration are determined.

FIG. 5 shows the relationship between the N doping concentration by SIMS and the hole carrier concentration obtained by hole measurement. The curve shown by the solid line in FIG. 5 is the result of simultaneous doping with intermittent supply of Ga donor by alternating ablation, and the curve shown by the dashed line is Ga
This is the result of co-doping with a continuous supply of donors (ie, no ablation of the undoped ZnO single crystal and therefore an ablation ratio of 0).

As can be seen from FIG. 5, the N doping concentration
Is 5 × 10¹⁸cm^-3The hole carrier concentration at the time of
About 4 × 10 in case of continuous donor supply¹⁷cm^-3Is
On the other hand, in the case of intermittent supply of Ga donor, about 1.2 × 1
0¹⁷cm^-3To almost three times that of Ga donor continuous supply
And the N doping concentration is 7 × 10¹⁹cm
^-3The hole carrier concentration at the time of
About 1.5 × 10 in case¹⁸cm^-3, While G
a About 1 × 10 in case of intermittent supply of donor¹⁹cm ^-3And G
(a) It is about 7 times that of the case of continuous donor supply. Toes
Therefore, intermittent supply of Ga donor is more effective than continuous supply.
In all cases, the hole carrier concentration can be increased, and the activity of N acceptor
Conversion rate can be increased about 3 to 7 times. For this reason,
It is considered as follows.

Active nitrogen irradiated on the growth surface through the radical source 9 is not immediately taken into the film, but floats on the surface while repeating adsorption and desorption. When the Ga donor is irradiated when the surface occupation density of the active nitrogen reaches a certain value or more, the Ga reaching the surface is bonded with two nearby active nitrogens immediately after being diffused, and the coordination state shown in FIG. 7 is high. Promoted by probability. On the other hand, in the case of continuous supply, the irradiated Ga diffuses on the growth surface in the same manner as active nitrogen, and in such a state, there is a probability that the Ga: N is stabilized at the point of 1: 1 coupling. It is considered high.

As for the intermittent supply of the donor impurity, the Ga is supplied within the time for growing ZnO of the unit molecular layer (see FIG. 2).
Preferably, the sequence is such that the donor is irradiated at least once. That is, since each unit molecular layer contains one or more donor-acceptor complexes, uniform acceptor doping is realized, and a low-resistance p-type crystal is produced. Such intermittent supply of impurities can be realized by opening and closing valves and shutters. However, in vapor phase growth such as CVD, there is a limit to the steepness of supply control depending on the time and route for gas to reach the substrate. On the other hand, in the molecular beam epitaxy method, since crystal growth is realized by a molecular beam traveling straight from a material to a substrate in an ultra-high vacuum, the intermittent supply of impurities can be sharply controlled by opening and closing a cell shutter. In particular, in the case of the laser molecular beam epitaxy method used in the present embodiment, it is possible to control the intermittent supply of impurities extremely steeply by the pulse laser irradiation sequence. Therefore, higher efficiency of simultaneous doping can be achieved more reliably than in other crystal growth methods.

(Embodiment 2) Embodiment 2 differs from Embodiment 1 in that active nitrogen, which is an acceptor impurity, is intermittently supplied in synchronization with the ablation period of a Ga ₂ O ₃ -added ZnO sintered body target. Similarly, p-type Z
An nO thin film was produced. Therefore, in the following description, the reference numerals used in FIG. 1 will be used as appropriate.

The intermittent supply of active nitrogen was carried out by controlling the opening and closing of a cell shutter (not shown) mounted on the head of the radical source 9. FIG. 6 shows a raw material supply sequence according to the present embodiment. As can be seen from FIG. 6, in the present embodiment, the supply time of the active nitrogen (open time of the cell shutter) is G
a ₂ O ₃ doped ZnO sintered target ablation time (laser pulse width) are fully matched. However, the raw material supply sequence may be controlled such that the two do not completely coincide with each other, but partially overlap.

The p-type ZnO manufactured according to this embodiment
When the relationship between the N doping concentration by SIMS and the hole carrier concentration obtained by hole measurement was determined for the thin film, a result substantially similar to that in FIG. 5 was obtained, and the activation of the N acceptor was smaller than the continuous supply of acceptor impurities. The rate was found to be higher.

In this embodiment, the number of the donor-acceptor complexes coordinated in the state shown in FIG. 7 is smaller than that of the first embodiment, and the ratio of the complex in which Ga: N is bonded by 1: 1 is occupied. Seems to be increasing. Nevertheless, the reason why the acceptor activation rate is high is that the acceptor impurity (N), which becomes an interstitial atom and generates a crystal defect, because the surface occupation density of active nitrogen is smaller than that of the first embodiment. It is considered that the amount can be suppressed.

The self-compensation effect (acceptance of electron-hole recombination energy is larger than the defect generation energy required for acceptor compensation, so that doping causes a donor vacancy defect to cancel the acceptor) due to the acceptor impurity is as follows. A p-type crystal having a high activation rate can be manufactured by applying the present invention, which is remarkable in a wide gap semiconductor, particularly a II-VI group compound semiconductor crystal. Particularly for ZnO to which the present invention is applied in Embodiments 1 and 2, in order to fabricate a room-temperature exciton device expected for the same material, Coulomb interaction between electron and hole is screened by high-density current injection. It is necessary to realize high carrier activation efficiency so as not to be performed. Therefore, it is extremely effective to apply the manufacturing method according to the present invention to obtain a low-resistance p-type semiconductor crystal.

Although there are a plurality of combinations of impurities in the simultaneous doping of ZnO, the present invention has the same effect on the formation of a complex by any combination of impurities. However, the combination of the Ga donor and N acceptor used in the first and second embodiments is most preferable in that the effect is highest and the intermittent supply method of the impurity is easily applied. Furthermore, the method of irradiating the acceptor impurity as an active atomic beam with a radical source is preferable because the rate of defect generation due to doping is small and the acceptor activation according to the present invention is not compensated.

In the first and second embodiments, the N ₂ gas is used as the N acceptor source. However, the N ₂ O gas or the NO ₂ gas may be used in addition to the high efficiency effect of the present invention.

Further, the method of manufacturing a semiconductor crystal described in the first and second embodiments can be applied to a mixed crystal such as ZnMgO or ZnCdO to which band gap engineering is applied.
It can be applied similarly to nO, and has the same effect as in the case of manufacturing ZnO crystal.

The method for manufacturing a semiconductor crystal described in the first and second embodiments can be similarly used for manufacturing a III-V group compound semiconductor crystal in addition to the above-described II-VI group compound semiconductor crystal. In this case, as a donor impurity, a group VI element (for example, Se, Te) or a group IV element (for example, Si)
And a group II element (eg, Be,
Mg, Zn, Cd) may be used.

The ZnO-based p-type semiconductor manufactured by the method according to the first or second embodiment has a high acceptor concentration and thus low resistance. Therefore, when combined with a ZnO-based n-type semiconductor, the luminous efficiency is high and the consumption is high. A light-emitting device with low power can be provided. FIG. 8 schematically shows an example of such a light emitting device. In FIG. 8, reference numeral 21 denotes an n-type ZnO layer;
22 is a p-type ZnO layer. The ratio between the N doping concentration and the Ga doping concentration in the p-type ZnO layer 22 is 2:
It is 1. As a semiconductor constituting the layers 21 and 22, as is clear from the above description, in addition to ZnO, Zn
MgO or ZnCdO can be used.

[0047]

As described above, according to the present invention,
According to the method for manufacturing a p-type semiconductor crystal, the activation rate of acceptor impurities in the donor / acceptor simultaneous doping method is improved, so that a high-resistance, uniformly doped, low-resistance p-type semiconductor crystal can be obtained. Further, by using the molecular beam epitaxy method, particularly the laser molecular beam epitaxy method, in the manufacturing method of the present invention, it becomes possible to control the intermittent supply of impurities extremely steeply, and it is possible to increase the activity compared to other crystal growth methods. A p-type semiconductor crystal having a high conversion ratio can be obtained.

A group II-VI element compound semiconductor crystal in which a sufficient acceptor activation rate has not been obtained, especially Z
As for nO, it is extremely effective to apply the manufacturing method according to the present invention to obtain a high-concentration and low-resistance p-type semiconductor crystal. This facilitates fabrication of a room-temperature exciton device that can only be realized using the same material.

[Brief description of the drawings]

FIG. 1 is a schematic view of a laser molecular beam epitaxy apparatus used in an embodiment of the present invention.

FIG. 2 is a raw material supply sequence during crystal growth according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between ablation ratio and Ga doping concentration for a Ga ₂ O ₃ added ZnO sintered body target.

FIG. 4 is a graph showing a substrate temperature dependence of an N doping concentration in an embodiment of the present invention.

FIG. 5 shows an embodiment of the present invention and a comparative example.
4 is a graph showing a relationship between a doping concentration and a hole carrier concentration.

FIG. 6 is a raw material supply sequence during crystal growth in Embodiment 2 of the present invention.

FIG. 7 is a crystal structure model when co-doping is applied to a II-VI group compound semiconductor.

FIG. 8 is a schematic cross-sectional view of a light-emitting device including an n-type semiconductor crystal and a p-type semiconductor crystal manufactured using the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Growth chamber 2 Substrate holder 3 Substrate 4 Heater (Nd: YAG laser) 5 Target table 6 Raw material target 7 Viewport 8 Pulsed laser beam 9 Radical source 10 Gas introduction tube 11 Gas introduction tube 21 p-type ZnO layer 22 n-type ZnO layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masashi Kawasaki 6-11-7-303 Hino, Konan-ku, Yokohama-shi, Kanagawa F-term (reference) 4G077 AA03 BB07 DA03 DA05 EB01 EB02 ED06 HA02 5F041 AA03 AA24 CA41 CA43 CA66 CA67 5F045 AA05 AB22 AC19 AF09 BB04 BB05 BB12 CA10 DA58 5F103 AA04 BB08 BB23 BB42 DD30 GG01 HH03 HH04 HH08 JJ01 JJ03 KK10 LL02 RR05 RR10

Claims (10)

[Claims] 1. A method of manufacturing a p-type semiconductor crystal by simultaneously doping a donor and an acceptor into a semiconductor crystal, comprising: intermittently supplying a donor impurity to the semiconductor crystal in the process of manufacturing the p-type semiconductor crystal. Feature
A method for manufacturing a p-type semiconductor crystal. 2. The p-type semiconductor crystal manufacturing method according to claim 1, wherein said acceptor impurity is intermittently supplied to said semiconductor crystal in synchronization with a supply cycle of said donor impurity. A method for manufacturing a semiconductor crystal. 3. The method of manufacturing a p-type semiconductor crystal according to claim 1, wherein a supply cycle of the donor impurity is shorter than a unit molecular layer growth time of the semiconductor crystal. A method for manufacturing a semiconductor crystal. 4. The p according to claim 1, wherein
In the method for producing a type semiconductor crystal, the semiconductor crystal may be II
A method for producing a p-type semiconductor crystal, characterized by being a compound semiconductor comprising Group III and Group VI elements. 5. The p according to claim 1, wherein
A method for producing a p-type semiconductor crystal, comprising: performing crystal growth using a molecular beam epitaxy method. 6. The method for producing a p-type semiconductor crystal according to claim 5, wherein said molecular beam epitaxy method is a laser molecular beam epitaxy method. 7. The p according to any one of claims 1 to 6,
A method of manufacturing a p-type semiconductor crystal, wherein the semiconductor crystal is a zinc oxide-based semiconductor crystal. 8. The method for manufacturing a p-type semiconductor crystal according to claim 7, wherein the acceptor impurity is nitrogen and the donor impurity is gallium. 9. The method of manufacturing a p-type semiconductor crystal according to claim 7, wherein the doping of the acceptor impurity includes irradiating the crystal growth surface with active atoms converted into plasma by an electromagnetic wave. Method for producing crystals. 10. A light-emitting device comprising a zinc oxide-based p-type semiconductor crystal layer and a zinc oxide-based n-type semiconductor crystal layer.