DE10134181B4 - Process for producing a p-type nitride semiconductor - Google Patents

Abstract

A method of making a p-type nitride semiconductor comprising:
A process of forming a semiconductor layer for forming a p-type low resistivity nitride semiconductor layer (13) on a substrate (11) maintained at a temperature of 600 ° C or more by using a source of a p-type dopant, a nitrogen source and a group III source are supplied to the substrate (11), and a cooling process for cooling the substrate (11) supporting the p-type nitride semiconductor layer (13);
marked by
Predicting the decrease in the hole carrier density of the p-type nitride semiconductor layer (13) in a range of 0% to 95%, and controlling the cooling time and the concentration of hydrogen in the atmosphere in the cooling process to achieve the predetermined decrease in the hole carrier density.

Description

FIELD OF THE INVENTION

The The present invention relates to a process for producing a p-type nitride semiconductor based on gallium nitride (Group III-V) for use in light radiating devices, the blue light or another Light with a short wavelength radiate in particular a method which after breeding no Tempering or annealing treatment (hereinafter referred to as "temper" treatment) requires.

GENERAL PRIOR ART

One Based on gallium nitride (Group III-V), the a relatively large one Band gap is one of the future materials responsible for the light with a short wavelength radiating devices are used in optical information processing units used, which is the growing amount of information handle. In such a light emitting device, such as a diode device or a laser device, a PN junction is the essential structure, where the carriers near of the transition recombine and the light is emitted. As is well known, It is not easy to have a low specific nitride semiconductor Provide resistance because in the p-type nitride semiconductor, which is doped with magnesium, Mg, or another acceptor, the activation rate of the acceptor over the Donor is significantly lower.

Of the p-type nitride semiconductor shows a high value of specific Resistance, if he after breeding is returned to room temperature. It was normal to get a low resistivity Practice, on a p-type nitride semiconductor annealing or a other heat treatment apply to the hydrogen of a magnesium and hydrogen Separate complex formed from magnesium. There will be research activities carried out, around a p-type nitride semiconductor with low resistivity without the use of post annealing provide. If this turns out to be successful, causes this is also an advantage for improved productivity such facilities.

To the Example in the US patent publication No. 5,932,896 A (Japanese Laid-Open Patent Application No. 10-135575 A) is a method for producing a p-type nitride semiconductor without Application of post-heating disclosed.

The method disclosed in the above publication uses an organometallic vapor phase deposition (MOCVD) process to grow a p-type nitride semiconductor on a sapphire substrate. To this end, an organic magnesium compound, a Group III source such as trimethylgallium (TMG), a nitrogen source such as ammonia (NH ₃ ) and a p-type dopant are added to the substrate at 1100 ° C using a nitrogen carrier gas containing hydrogen gas at a concentration of 0.8 Contains -20 vol .-% (capacity percent), fed. In this way, the formation of a magnesium-hydrogen complex is blocked and a p-type nitride semiconductor is provided, which exhibits a low resistivity during the growth phase. It also discloses a cooling process in which the temperature is reduced to 350 ° C in an atmosphere of nitrogen gas containing about 32% by volume of ammonia and then the ammonia feed is adjusted and the temperature is lowered to room temperature.

However, the above-described conventional method for producing a p-type nitride semiconductor which eliminates the post-annealing has the following problems. As the inventor in the above-described US 5,932,896 A and another author in a work (Applied Physics Letters, Vol. 72, (1998), p. 1748) taught, the rate of activation of magnesium deteriorates markedly as the hydrogen concentration only increases from 2.4 during the crystal growth process % to 3.7%, meaning that a p-type nitride semiconductor can only be obtained when grown under a very low hydrogen concentration. What is more, when a nitride semiconductor is grown under a low hydrogen concentration, it turns out that the surface migration is insufficient and certain specific atoms are not placed at respective optimum points of the surface, making it difficult to obtain a good crystal.

From the EP 0 805 500 A1 and the US 5,891,790 A For example, methods for producing p-type nitride semiconductors are known in which no post-annealing step is needed. This is in the US 5,891,790 A1 shut off the supply of hydrogen-containing gases before the cooling process. In the EP 0 805 500 A1 For this purpose, the supply of H _{2 is} set.

BRIEF SUMMARY OF THE INVENTION

The The present invention addresses the problems described above and is seeking to offer a higher quality p-type nitride semiconductor, without needing a treatment of re-tempering and at which the low resistivity is kept in a predetermined range.

These The object is achieved by the method according to claim 1.

The A method for producing a p-type nitride semiconductor comprises a process of forming a p-type nitride semiconductor with low specific resistance stood in the growth process and a cooling, at which the cooling time and the atmosphere is controlled so that the property of the low specific Resistance is held in a practical area, which as p-type semiconductor is usable.

During the cooling process takes the hole carrier density in the p-type nitride semiconductor layer.

Thereby becomes a p-type nitride semiconductor layer on a substrate in an atmosphere formed, which contains a specific amount of hydrogen, the suppresses deactivation of the p-type dopant, and decreases the hole carrier density the p-type nitride semiconductor layer to a level where the property of the low specific Resistance can be maintained. In this way, a p-type Nitride semiconductor with a higher one crystal quality available done without any need for any post-heat treatment.

For example, assuming that the hole carrier density immediately after culturing is about 2.0 × 10 ¹⁷ cm ^-3 , a concentration of about 1.0 × 10 ¹⁶ cm ^-3 can be maintained even if the hole carrier density decreased by 95% , Thus, a p-type nitride semiconductor is provided which works practically well.

At the present method for producing a p-type nitride semiconductor it is preferred that during the cooling process there is a procedure for Reduce the substrate temperature from the breeding temperature to about 600 ° C within of 30 min.

This Make sure the hole carrier density a p-type nitride semiconductor layer for maintenance the property of low resistivity for a practical Sufficient work.

At the present method for producing a p-type nitride semiconductor it is preferred that the atmosphere for the formation of a semiconductor layer about 5-70 Vol .-% hydrogen.

If an organometallic material as a source of the element of the group III or the p-type dopant is usually used to increase the hydrogen Cutting efficiency and conveying the surface migration in the atmosphere contain. However, if the hydrogen concentration is above 70%, becomes the deactivation effect caused by the hydrogen at the acceptor significant. The deactivation of the p-type dopant can be sure repressed when the hydrogen concentration is at 5% -70% according to the present invention is controlled.

At the present method for producing a p-type nitride semiconductor It is preferable that the atmosphere during the cooling process introduced until the substrate temperature reaches about 600 ° C from the breeding temperature, about 0-50 Vol .-% hydrogen.

Thereby may be the deactivation of a p-type nitride semiconductor Reason of hydrogen suppressed become and become the property of low resistivity as a result of a relatively high hole carrier density in a p-type Nitride semiconductor layer well maintained.

In the present process for producing a p-type nitride semiconductor, it is preferable that the atmosphere introduced during the cooling process until the substrate temperature reaches about 600 ° C. from the growth temperature include ammonia, NH ₃ .

Thereby can be the removal of nitrogen from the surface of the bred p-type nitride semiconductor suppresses and as a result deterioration the surface be prevented.

Around the sooner to fulfill the task described forms the present manufacturing process in the process of training a p-type nitride semiconductor layer, a p-type nitride semiconductor with low resistivity and then set one specific plan for the cooling process ready, a specific substrate temperature range, namely a Substrate temperature range of about 950 ° C-700 ° C, covering in which the deactivation of the p-type dopant occurs in the p-type nitride Hableiterschicht.

Concrete is described in the present process for the preparation of a p-type nitride semiconductor, the p-type nitride semiconductor layer while of the specific substrate temperature range described above cooled down a certain specific condition in which the deactivation Of the p-type dopant hardly occurs, which specific condition from a combination of hydrogen concentration in the atmosphere and the cooling composed.

At the present method for producing a p-type nitride semiconductor becomes the p-type nitride layer during the above-described specific substrate temperature range below a certain specific Condition cooled, in which the deactivation of the p-doping material hardly occurs, which specific condition is a combination of the hydrogen concentration in the atmosphere and the cooling rate composed.

This make it possible, that a p-type nitride semiconductor has the property of low specific resistance in a certain area in which he can work as a practical p-type semiconductor.

Further relates to a p-type nitride semiconductor of the present invention a p-type nitride semiconductor attached to a substrate a breeding temperature of 600 ° C or higher is formed, in which the hole carrier density immediately after the cooling process about 5% -100% that at the breeding temperature is.

In a case where the hole carrier density immediately after culturing is about 2.0 × 10 ¹⁷ cm ^-3 , a concentration of about 1.0 × 10 ¹⁶ cm ^{-3 can be} provided even if the hole carrier density is set to 5% of that directly decreased after breeding. Thus, a p-type nitride semiconductor is provided which operates in practical use.

One another p-type nitride semiconductor of the present invention relates to a p-type nitride semiconductor mounted on a substrate one after the other at the breeding temperature of 600 ° C or higher is formed, wherein the hydrogen concentration in the vicinity of the surface is the same about 1 to 10 times that inside the p-type nitride semiconductor is.

at the conventional one p-type nitride semiconductor, produced by the processes being accompanied by a treatment of the remixing the hydrogen concentration near the surface exposed to it is more than 10 times larger than the one inside the p-type nitride semiconductor. At a p-type nitride semiconductor however, the hydrogen concentration remains in the present invention near the surface of the p-type nitride semiconductor at the same level, or within about 10 times that one inside the p-type nitride semiconductor. Therefore, according to the present Invention with the p-type dopant a p-type nitride semiconductor provided with an improved activation rate.

BRIEF DESCRIPTION OF THE DRAWINGS

1 FIG. 12 is a cross-sectional view showing the structure of a p-type nitride semiconductor in Embodiment 1 of the present invention. FIG.

2 Fig. 12 is a graph showing the dependence of the hole carrier density on the cooling time during the cooling process in a method of manufacturing a p-type nitride semiconductor in Embodiment 1 of the present invention.

3 FIG. 12 is a cross-sectional view showing the structure of a p-type nitride semiconductor in Embodiment 2 of the present invention. FIG.

4 is a graph showing the distribution of hydrogen concentration in depth In light emitting devices with the nitride semiconductor in Embodiment 2, including a first modification and a comparative sample, the present invention shows.

5 Fig. 12 is a graph showing the dependence of the hole carrier density on the holding temperature for the substrate during the cooling process in a method of manufacturing a p-type nitride semiconductor in an embodiment of the present invention.

6 Fig. 4 is a graph showing the dependence of the hole carrier density on the time for cooling the substrate from about 950 ° C to about 700 ° C during the cooling process in a method of preparing a p-type nitride semiconductor in an embodiment of the present invention.

7 FIG. 15 is a graph showing the relationship between the concentration of hydrogen in the atmosphere and the time for cooling the substrate from about 950 ° C. to about 700 ° C. during the cooling process in a method of manufacturing a p-type nitride semiconductor in an embodiment of FIG present invention.

8th Fig. 12 is a graph showing the relationship between the concentration of hydrogen in the atmosphere and the cooling rate of the substrate at about 800 ° C during the cooling process in a method of manufacturing a p-type nitride semiconductor in an embodiment of the present invention.

9 Fig. 12 is a cross-sectional view showing the structure of a p-type nitride semiconductor in another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It become embodiments of the present invention with reference to the drawings.

(embodiment 1)

It will be a first exemplary embodiment of the present Invention described with reference to the accompanying drawings.

1 FIG. 12 is a cross-sectional view showing the structure of a p-type nitride semiconductor fabricated according to a first exemplary embodiment of the present invention. FIG. On a substrate made of sapphire 11 are a buffer layer formed of gallium nitride (GaN) to reduce the lattice mismatch between the semiconductor deposited on the substrate 11 and the sapphire and a GaN p-type nitride semiconductor layer 13 arranged one above the other in this order.

Hereinafter, the method for producing the above p-type nitride semiconductor layer will be described. First, the substrate 11 having a mirror-finished main surface disposed in a reaction chamber (not shown) and held by a substrate holder, and then the temperature of the substrate is raised to about 1000 ° C and hydrogen gas is applied to the substrate 11 while heating for about 10 minutes. Thus, organic matter stains and moisture adhering to the main surface are removed.

The substrate temperature is reduced to about 550 ° C and then nitrogen gas as the carrier gas at a rate of about 16 liters / min and ammonia gas, NH ₃ , as a nitrogen source at a rate of about 4 l / min, trimethylgallium (TMG) as a source of the group III with a throughput of about 40 .mu.mol / min to the substrate 11 guided. Thus, the buffer layer becomes 12 GaN on the main surface of the substrate 11 grown to a thickness of 25 nm.

The TMG supply to the reaction chamber is adjusted once and the substrate temperature is raised to about 1050 ° C; and on the buffer layer 12 becomes a 2 μm thick p-type nitride semiconductor layer 13 grown from Mg doped GaN, by nitrogen gas at a rate of about 13 l / min, hydrogen gas at a rate of about 3 l / min as a carrier gas and ammonia gas, NH ₃ , at a rate of about 4 l / min, TMG with a Throughput of about 80 .mu.mol / min and containing as p-type dopant Bicyclopentadienylmagnesium (Cp ₂ Mg) at a rate of about 0.2 .mu.mol / min for about 60 minutes on the substrate 11 to be led. The above throughput of hydrogen gas includes the hydrogen gas needed to vaporize the TMG and the Cp ₂ Mg.

The feeds of TMG and Cp ₂ Mg to the reaction chamber are set and then the substrate becomes 11 cooled from the breeding temperature to room temperature; nitrogen gas at a rate of about 13 l / min, hydrogen gas at a rate of about 3 l / min, and ammonia gas, NH ₃ , at a rate of about 4 l / min as ambient gas to the substrate 11 be guided. After the cooling is completed, it becomes the p-type nitride semiconductor layer 13 carrying substrate 11 taken from the reaction chamber.

Now, the cooling process of the present invention, that of the p-type nitride semiconductor layer, will be described below 13 carrying substrate is described.

2 FIG. 12 is a graph showing the dependence of the hole carrier density on the cooling time during the cooling process in a method of manufacturing a p-type nitride semiconductor in the first exemplary embodiment of the present invention. FIG. The hole carrier densities of the p-type nitride semiconductor layers 13 which measured five different cooling times from 5 minutes to 40 minutes to reduce the substrate temperature from 1050 ° C, or the growth temperature, to 600 ° C was measured. The hole carrier density measurement was performed by measuring the Hall effect with a 5 mm square sample chip prepared by cutting specifically for the measurement of the substrates provided in the five different cases 11 was produced.

As in 2 As can be seen, all five sample chips show the p-type conduction and the hole carrier density decreases with time to cool down from the culture temperature to 600 ° C. By extrapolating the straight line of 2 to the y-axis for the cooling time zero can be found that the p-type nitride semiconductor layer 13 In the present embodiment, a p-type conductivity of about 2 × 10 ¹⁷ cm ^-3 hole carrier density immediately after its growth.

2 also shows that the hole carrier density is 1.2 × 10 ¹⁷ cm ^-3 at 5 min cooling time, 3.0 × 10 ¹⁶ cm ^-3 at 20 min cooling time, which corresponds to about 7% of the pre-cooling concentration, and 30 min cooling time is 1.0 × 10 ¹⁶ cm ^-3 , which corresponds to about 5% of the concentration before cooling. The case with the cooling time of 30 minutes is almost at the lower limit that can be used for a p-type layer in a device. In the case with a cooling time of 40 minutes, the concentration is 2.2 × 10 ¹⁵ cm ^-3 , indicating that the carrier density is insufficient for use in a device.

(First modification of the embodiment 1)

Below discloses a method for producing a p-type nitride semiconductor layer according to one First Modification Example of Embodiment 1 described.

The first buffer layer 12 and the p-type nitride semiconductor layer 13 with a hole carrier density of about 2 × 10 ¹⁷ cm ^-3 are prepared in the order on the substrate by the same method as Embodiment 1 11 trained as in 1 shown.

Below, the dependence of the hole carrier density on the concentration of hydrogen gas contained in the ambient gas during the cooling process in the first modification example will be described. The hole carrier density was measured using four different atmospheres with four different hydrogen gas concentrations, 0%, 30%, 50% and 70%. The concentration of ammonia gas, NH ₃ , in each of the atmospheres was about 20%, the remainder being nitrogen gas. The substrate was cooled to about 600 ° C in about 5 minutes from about 1050 ° C, or the growth temperature.

The results of the measurement are: 1) 0% hydrogen concentration about 2 × 10 ¹⁷ cm ^-3 , right after the breeding 2) 30% hydrogen concentration about 4.2 × 10 ¹⁶ cm ^-3 3) 50% hydrogen concentration about 1 × 10 ¹⁶ cm ^-3 , about 5% of those directly after breeding 4) 70% hydrogen concentration about 2.5 × 10 ¹⁵ cm ^-3 , equal to about 1% of those directly after breeding

As The p-type layer will be seen above for use in one Establishment inadequate if in an environment with a hydrogen concentration of 70% chilled even when cooled to 600 ° C in a period of 5 minutes.

(Second Modification of the Embodiment 1)

Below discloses a method for producing a p-type nitride semiconductor layer according to one second modification example of the embodiment 1 described.

The first buffer layer 12 and the p-type nitride semiconductor layer 13 with a hole carrier density of about 2 × 10 ¹⁷ cm ^-3 are prepared in the order on the substrate by the same method as Embodiment 1 11 trained as in 1 shown.

The dependence of the hole carrier density on the concentration of ammonia gas contained in the atmosphere, NH ₃ , during the cooling process in the second Modifikationsbei game will be described. The concentration of hydrogen gas in the atmosphere was about 15%, the rest was nitrogen gas. The substrate was cooled to about 600 ° C in about 5 minutes from about 1050 ° C, or the growth temperature.

As a result of the measurement, it was confirmed that there is little difference in the rate of decrease of the hole carrier density during the cooling process, even when the concentration of the ammonia gas, NH ₃ , was varied; it remains at a level corresponding to a concentration of ammonia gas, NH ₃ , of 20%. When the concentration of ammonia gas, NH ₃ , is in a range of 0% -0.5%, the crystal property due to separation of nitrogen from the surface of the p-type nitride semiconductor layer deteriorates 13 ,

(Third Modification of the Embodiment 1)

A method of manufacturing a p-type nitride semiconductor layer according to a third modification example of the embodiment 1 will be described below. In the present modification example, the dependence of the hole carrier density during the formation of in 1 shown p-type nitride semiconductor layer 13 described by the hydrogen gas concentration in the carrier gas. In Embodiment 1, the hydrogen gas concentration in the carrier gas was about 15%; while in the present modification example, the concentration of the hydrogen gas in the carrier gas varies in five steps with an interval of 5% from 0% to 20% and in six steps with an interval of 10% from 20% to 80%, a total of eleven steps. In the case of a hydrogen gas concentration of 0%, TMG and Cp ₂ Mg were evaporated using nitrogen gas, respectively.

The result of measurements on each of the p-type nitride semiconductor layers 13 grown in an atmosphere in which the hydrogen gas concentration falls within a range of 5% -70% indicated that the hole carrier density immediately after culturing was 1 × 10 ¹⁶ cm ^-3 or more, which means that they have a p-type conductivity; the value became similar to what was in 2 was shown by extrapolating the cooling time to zero. More concretely, the hole carrier density was about 5 × 10 ¹⁶ cm ^-3 or more at a hydrogen gas concentration of about 5% -50%, about 1 × 10 ¹⁷ cm ^-3 or more at a hydrogen gas concentration of about 10% -20%. When, in other cases, a hydrogen concentration of 15% is grown, the hole carrier density immediately after culturing has its peak at a height of 2 × 10 ¹⁷ cm ^-3 .

The Half-width of the rocking curve, which is a criterion for the rating represents the crystal property becomes with increasing hydrogen gas concentration lower; the half width is less than 300 "when the concentration of hydrogen gas 10% or more. If, however, in an atmosphere is grown with zero hydrogen gas concentration, becomes the half width of the rocking curve in X-ray diffraction 500 '', which is a significant indicating deteriorated crystal property. Furthermore, it does that high specific resistance impossible the hole carrier density to eat.

If in an atmosphere is grown with a hydrogen gas concentration of about 80% it is impossible for the same reason the high resistivity that Hole carrier density to eat. The reason for this is probably an elevated one Amount of during the growth process into the hydrogen atoms taken up in the GaN, which reduces the activation rate of magnesium.

Although ammonia, NH ₃ , was used as the nitrogen source in the present embodiment, may also include other nitrogen materials such as hydrazine, N ₂ H _4, ethylamine, C ₂ H ₅ NH ₂ are used for the purpose.

(embodiment 2)

It will be a second exemplary embodiment of the present Invention described with reference to the accompanying drawings.

3 FIG. 10 is a cross-sectional view showing the structure of a nitride semiconductor light emitting device according to a second exemplary embodiment of the present invention. FIG. The epitaxial layer of a nitride semiconductor light emitting device in the second embodiment comprises a buffer layer 22 of undoped GaN deposited on a sapphire substrate 21 is arranged, an n-type contact layer 23 made of Si-doped GaN, a light-emitting layer 24 of undoped InGaN, a first cladding layer 25 of undoped GaN, a p-type second cladding layer 26 of Mg-doped AlGaN and a p-type contact layer 27 of Mg-doped GaN stacked in this order. On the p-type contact layer 27 there is a translucent positive electrode 28 consisting of Ni and Au layers stacked on top of each other in order. A negative electrode 29 Al is on the exposed region of the n-type contact layer 23 educated. Thus, the present light emitting device is a light emitting diode with a pn junction of the n-type contact layer 23 and the second plating layer 26 wherein the undoped, light emitting layer 24 and the first cladding layer 25 are arranged between them.

in the Below is a method for producing the light emitting diode with the above structure.

First, a substrate 21 having a mirror-finished main surface disposed in a reaction chamber (not shown) and held by a substrate holder, and then the temperature of the substrate is raised to about 1000 ° C and hydrogen gas is applied to the substrate 21 while heating for about 10 minutes. Thus, organic matter stains and moisture adhering to the main surface are removed and a clean surface is provided.

The substrate temperature is reduced to about 550 ° C and then nitrogen gas as a carrier gas at a rate of about 16 l / min and ammonia gas, NH ₃ , as a nitrogen source at a rate of about 4 l / min and trimethylgallium (TMG) as a source of the group III with a throughput of about 40 .mu.mol / min to the substrate 21 guided; thus, the buffer layer becomes 22 with GaN on the main surface of the substrate 21 formed with a thickness of 25 nm. The flow rate of the hydrogen gas in the carrier gas includes the hydrogen gas needed to vaporize the TMG or the Cp ₂ Mg.

The TMG feed to the reaction chamber is adjusted once and the substrate temperature is increased to about 1050 ° C, and on the buffer layer 22 becomes a 2 μm thick n-type contact layer 23 grown from Si doped GaN, by nitrogen gas at a rate of about 13 l / min, hydrogen gas at a rate of about 3 l / min as a carrier gas and ammonia gas, NH ₃ , at a rate of about 4 l / min, TMG with a Throughput of about 80 .mu.mol / min and monosilane, SiH ₄ , the silicon containing an n-type dopant material, with a throughput of about 10 cm ³ / min for about 60 minutes on the substrate 21 to be led.

The feeds of TMG and SiH ₄ gas are adjusted and then the substrate temperature is lowered to about 750 ° C. At this growth temperature, on the n-type contact layer 23 an SQW light emitting layer (SQW light emitting layer) 24 grown from 3 nm thick InGaN by passing nitrogen gas as a carrier gas at a rate of about 14 l / min, ammonia gas, NH ₃ , at a rate of about 6 l / min, TMG at a rate of about 4 μmol / min and trimethylindium (TMI ), another group III source, at a rate of about 5 μmol / min to the substrate 21 to be led. The In portion of Group III elements in the light-emitting layer 24 of the present case is about 0.2.

The feed of the TMI is adjusted while the nitrogen carrier gas, the ammonia gas, NH ₃ , as the nitrogen source, and the TMG as the Group III source continue to flow through the substrate 21 be flown. In this way, during the temperature elevation of the substrate to about 1050 ° C, a first plating layer 25 GaN on the light emitting layer 24 grown to a thickness of 10 nm.

After the substrate temperature arrives at 1050 ° C, nitrogen gas at a rate of about 13 l / min, hydrogen gas at a rate of about 3 l / min as a carrier gas and ammonia gas, NH ₃ , at a rate of about 4 l / min, TMG at a rate of about 40 μmol / min, trimethylaluminum (TMA) as another Group III source at a rate of about 6 μmol / min, and Cp ₂ Mg at a throughput of about 0.1 μmol / min onto the substrate 21 led to a second cladding layer 26 of Mg-doped AlGaN on the first cladding layer 25 to grow to a thickness of 0.2 microns.

After adjusting the TMA supply and maintaining the substrate temperature at about 1050 ° C, nitrogen gas at a rate of about 13 L / min, hydrogen gas at a rate of about 3 L / min as a carrier gas and ammonia gas, NH ₃ , at a throughput about 4 l / min, TMG at a rate of about 80 μmol / min, and Cp ₂ Mg at a rate of about 0.2 μmol / min were applied to the substrate to form a p-type contact layer of Mg-doped, p- conductive GaN on the second cladding layer 26 to grow to a thickness of 0.3 microns.

After the p-type contact layer 27 is formed, the temperature is lowered from the growing temperature to room temperature, while nitrogen gas at a rate of about 13 l / min, hydrogen gas at a rate of about 3 l / min and ammonia gas, NH ₃ , with a throughput of about 4 l / min be introduced as ambient gas in the reaction chamber. The substrate 21 supporting an epitaxial layer formed of a plurality of nitride semiconductor layers is taken out of the reaction chamber. In the ambient gas, the hydrogen gas concentration is about 15%, the concentration of ammonia gas, NH ₃ , is about 20%. The substrate 21 was cooled in 5 minutes from the breeding temperature, about 1050 ° C, to 600 ° C.

The thus provided nitride semiconductor layers, including the p-type second cladding layer 26 and the p-type contact layer 27 were formed by the same growth process and the cooling process as in Embodiment 1. Therefore, better low resistivity p-type semiconductor layers have been provided without undergoing the post-anneal treatment needed to activate the Mg with which the second cladding layer 26 and the p-type contact layer is doped.

Next, for example, by using a CVD process, on the p-type contact layer 27 formed by depositing a silicon oxide layer, a special pattern is provided by photolithography to form an etching mask, and then the epitaxial layer is etched by a reactive ion etching using the mask until the n-type contact layer 23 is exposed.

An n-electrode 29 becomes on the exposed surface of the n-type contact layer 23 for example, selectively formed using an evaporation process; in the same way becomes a p-electrode 28 on the p-type contact layer 27 selectively formed.

The underside or the side of the substrate opposite the epitaxial layer 21 is ground to the thickness of the substrate 21 to about 100 microns, and the substrate is separated by dicing into chips. Each of the separate chips is attached to a foot having electrodes thereon with the device bearing surface facing up. The p-electrode 28 and the n-electrode 29 of the chip are connected to respective electrodes of the foot and then the entire chip is reshaped with a resin to become a finished light emitting diode.

It was confirmed, that provided by the procedure described above light emitting diode emitting blue light with a peak wavelength of 470 nm, when operated with 20 mA forward current. The Light output was 2.0 mW, the operating voltage in the forward direction was 4.0 V.

(First modification of the embodiment 2)

It was a light-emitting diode with the structure of 3 by modifying the cooling time of Embodiment 2 to 25 minutes, in which the temperature of the substrate carrying the epitaxial layer is modified 21 is lowered from the breeding temperature, about 1050 ° C, to 600 ° C. The above LED emit blue light having a peak wavelength of 470 nm when it was forward-biased with a current of 20 mA. The light power was 0.5 mW, the operating voltage in the forward direction was 5.0 V.

(Comparative Example)

It was a light-emitting diode with the structure of 3 by modifying the cooling time of Embodiment 2 to 40 minutes, in which the temperature of the substrate carrying the epitaxial layer 21 is lowered from the breeding temperature, about 1050 ° C, to 600 ° C. Because of the high resistance, the electric current did not flow in the above LED, thus no light was emitted.

4 FIG. 12 is a graph showing hydrogen distribution in the direction of depth from the surface in the nitride semiconductor light emitting devices in Embodiment 2, the first modification of Embodiment 2, and Comparative Example measured by SIMS (Secondary Ion Mass Spectroscopy). The hydrogen concentration is shown in terms of the three different time periods provided above for cooling. In 4 are the areas that the semiconductor layers of 3 identified by providing the same reference numerals. Curve 1A FIG. 12 illustrates the case of Embodiment 2, in which the cooling time from the growth temperature of about 1050 ° C to 600 ° C is 5 minutes, curve 1B represents the case of modification in which it is 25 minutes, and curve 1C represents the case of the comparative example in which it is 40 minutes.

Curve 1A in 4 , which represents the cooling time of 5 minutes, indicates that the hydrogen concentration at a point near the surface is about 3.0 × 10 ¹⁹ cm ^-3 , which concentration as it proceeds to the substrate (the direction to the n-type contact layer) 23 towards) and in the second cladding layer 26 For example, the hydrogen concentration becomes almost constant at about 1.0 × 10 ¹⁹ cm ^-3 . In the first cladding layer 25 , the light emitting layer 24 and the n-type contact layer 23 it is less than 2.0 × 10 ¹⁸ cm ^-3 , which is the lower detection limit.

Curve 1B The first modification representing the cooling time of 25 minutes indicates that the hydrogen concentration at a point near the surface is about 1.0 × 10 ²⁰ cm ^-3 , which concentration decreases with the progress toward the substrate, and in the second clad layer 26 the hydrogen concentration is almost constant at about 1 × 10 ¹⁹ cm ^-3 .

Curve 1C of the comparative example, which represents the cooling time of 40 minutes, indicates that the hydrogen concentration at a point near the surface is about 3.0 × 10 ²⁰ cm ^-3 , which concentration decreases with the progress toward the substrate, and in the second clad layer 26 the hydrogen concentration is almost constant at about 1 × 10 ¹⁹ cm ^-3 .

4 also indicates that in the case where the cooling time is shorter than 25 minutes, the hydrogen concentration at the top of the p-type contact layer 27 below 10 times that in the second cladding layer 26 lies.

As the above Embodiment 2 and its first modification indicate, a better p-type layer provided with a low resistivity immediately after growth is made available by growing it during growth of the p-type second cladding layer 26 and the p-type contact layer 27 used carrier gas can contain about 5 to 70 vol .-% hydrogen, preferably about 15 vol .-% hydrogen.

Further, the decreasing rate of the hole carrier density of the p-type semiconductor layer can be suppressed to about 0% to 95% by cooling the cooling time to about 600 ° C in the cooling process in which it is cooled from the growth temperature higher than 600 ° C is set to be shorter than about 30 minutes, preferably about 5 minutes, and by the atmosphere gas with hydrogen gas having about 50% by volume or less and ammonia gas, NH ₃ , having about 0.5% by volume or more is formed. As a result, a low-voltage forward-conducting, high-power nitride semiconductor light-emitting device is realized.

(embodiment 3)

1 FIG. 10 is a cross-sectional view showing the structure of a p-type nitride semiconductor according to a third exemplary embodiment of the present invention. FIG. On a substrate made of sapphire 11 become a buffer layer formed of GaN 12 and a p-type nitride semiconductor layer formed of GaN 13 arranged one above the other in order.

In practice, the substrate becomes 11 in a reaction chamber (not shown) and arranged by a Substrate holder held and then the temperature of the substrate 11 increased to about 1000 ° C and the surface of the substrate 11 purified by introducing a nitrogen gas and hydrogen gas stream.

The substrate temperature is lowered to about 550 ° C and then nitrogen gas is introduced as a carrier gas and ammonia, NH ₃ , and trimethylgallium (TMG) are fed to the surface of the substrate 11 a buffer layer 12 to build.

The TMG supply to the reaction chamber is once set, and the substrate temperature is raised to about 1050 ° C, and it becomes a p-type nitride semiconductor layer 13 of GaN doped with Mg, which is a p-type dopant, on the buffer layer 12 grown by supplying ammonia, NH ₃ , TMG and bicyclopentadienylmagnesium (Cp ₂ Mg) while introducing nitrogen gas and hydrogen gas as a carrier gas.

The feeds of TMG and Cp ₂ Mg to the reaction chamber are set and then the substrate becomes 11 cooled from 1050 ° C to 700 ° C, wherein the ambient flow of nitrogen gas, hydrogen gas and ammonia gas, NH ₃ , is maintained. Thereafter, the supply of hydrogen gas and ammonia, NH ₃ , is adjusted and the substrate 11 is cooled below 100 ° C, wherein the nitrogen gas stream is maintained as ambient gas.

The Method for producing a p-type nitride semiconductor in embodiment 3 is characterized in that the p-type nitride semiconductor layer in the cooling process while about 950 ° C-about 700 ° C substrate temperature under a combination of hydrogen concentration in the atmosphere and the cooling chilled in which deactivation hardly occurs in the p-type dopant. A further description in this regard follows.

Regarding the cooling process, to be applied to a p-type nitride semiconductor after it was formed at a substrate temperature of about 950 ° C or higher found the inventors of the present invention, the fact that the hole carrier density in the p-type nitride semiconductor especially during a temperature range from about 950 ° C to about 700 ° C substrate temperature is reduced by existing hydrogen in the environment.

5 FIG. 10 is a graph showing the dependence of the hole carrier density in Embodiment 3 on the holding temperature for the substrate during the cooling process. FIG. Namely, the respective temperatures shown in the graph represent a temperature at which a substrate carrying a Mg-doped GaN layer formed at a substrate temperature of 1050 ° C is held for 10 minutes during the cooling process before it rises Room temperature is cooled; the horizontal axis represents the substrate temperature at which it is held for 10 minutes while the hole carrier density is plotted on the vertical axis. The atmosphere for the cooling process was prepared with a concentration of ammonia, NH ₃ , of 20% in nitrogen in two versions with different hydrogen concentrations, 30% and 0%. As in 5 shown decreases in the case of a hydrogen concentration of 30%, the hole carrier density at temperatures between 950 ° C-700 ° C significantly, with the lowest is about 800 ° C. The case of a hydrogen concentration of 0% also shows similar tendencies at the same temperatures, but the amount of decrease was smaller. Namely, it has been clarified that the hole carrier density in a p-type nitride semiconductor decreases in accordance with the concentration of hydrogen present in the atmosphere in the temperature range 950 ° C-700 ° C. It is believed that the sinking of the hole carrier density was caused by a p-doping material contained in the p-type nitride semiconductor, which p-type dopant is deactivated as a result of coupling with hydrogen. The slight decrease, which occurred even in the case of a hydrogen concentration of 0%, appears to have been caused by hydrogen generated from decomposed ammonia, NH ₃ .

Further the relationship between the hole carrier density and the cooling time was also investigated in the cooling process to lower the substrate temperature from about 950 ° C to about 700 ° C has been.

6 Fig. 4 is a graph showing the dependence of the hole carrier density in Embodiment 3 on the cooling time for the substrate taken in the cooling process for lowering from about 950 ° C to about 700 ° C. Namely, Mg-doped GaN layers formed at substrate temperatures of 1050 ° C were cooled at different cooling rates to 700 ° C and then to room temperature; the horizontal axis represents that taken for lowering the substrate temperature from about 950 ° C to about 700 ° C

Cooling time, while the hole carrier density is plotted on the vertical axis. The cooling rate was controlled to be substantially constant at least during the substrate temperature range of about 950 ° C to about 700 ° C. The atmosphere for the cooling process was prepared with a concentration of ammonia, NH ₃ , of 20% in nitrogen in four versions with different hydrogen concentrations, 50%, 30%, 10% and 0%. As in 6 In all cases, with different hydrogen concentrations, the hole carrier density decreased with the lengthening of the cooling time. It was off 6 calculated the cooling time required for the hole carrier density to become about 1 × 10 ¹⁶ cm ^-3 at room temperature; the results were 1.0 min, 1.8 min, 4.1 min and 15 min for the hydrogen concentrations 50%, 30%, 10% and 0%, respectively. Namely, to ensure the value of about 1 × 10 ¹⁶ cm ^-3 or higher, which is the requirement for being a practical p-type semiconductor, it has been found that the cooling time for lowering the substrate temperature is about 950 ° C at about 700 ° C for the cases of hydrogen concentrations of 50%, 30%, 10% and 0% within 1.0 min, 1.8 min, 4.1 min and 15 min, respectively.

7 FIG. 12 is a graph showing the relationship between the concentration of hydrogen in the atmosphere of the cooling time for the substrate, which is taken to decrease from about 950 ° C. to about 700 ° C. during the cooling process, in a process for producing a p-type nitride Semiconductor according to an embodiment of the present invention.

On the basis of the above results, it can be found that the combinations of the concentration of hydrogen in the atmosphere and the cooling time during the cooling process for the substrate from about 950 ° C to about 700 ° C, which comes after a p-type semiconductor out forms is in one in 7 range should fall. In the coordination system (X, Y), where the X-axis represents the hydrogen concentration (%) in the atmosphere, while the Y-axis represents the cooling time (min) used to cool a substrate from about 950 ° C to about 700 ° C, the area is shown by an area surrounded by the points A-B-C-D-E-F, where the point A (50, 1.0), point B (30, 1, 8), point C (10, 4, 1), point D (0, 15), point E (0, 0.5) and point F (50, 0.5). The reason why the lowest limit of the cooling time is specified by a straight line EF of 0.5 min regardless of the hydrogen concentration is that when it is cooled in a shorter cooling time than this, the p-type nitride semiconductor is in danger to be damaged by cracks caused by thermal shock.

(embodiment 4)

Similar to Embodiment 3, a p-type nitride semiconductor having the structure of FIG 1 produced by a method according to a fourth exemplary embodiment of the present invention.

First, in the same manner as Embodiment 3, a buffer layer is formed 12 and a p-type nitride semiconductor layer 13 in order on a substrate 11 , as in 1 shown, trained.

at the method for producing a p-type nitride semiconductor in embodiment 4 becomes the p-type nitride semiconductor layer when the substrate temperature near from about 800 ° C lies under a combination of hydrogen concentration in the the atmosphere and the cooling rate cooled, in which the deactivation hardly occurs at the p-type dopant.

As in 5 to see the deactivation of the p-type dopant most clearly when the substrate temperature in a range between about 950 ° C and about 700 ° C is about 800 ° C. Therefore, in order to maintain the low resistivity property of a p-type nitride semiconductor, it is effective to make the residence time of the substrate in the vicinity of 800 ° C as short as possible.

Out 6 It can be seen that, to ensure a hole concentration of about 1 × 10 ¹⁶ cm ^-3 or higher, which is a requirement for being a practical p-type semiconductor, the cooling speed is close to a substrate temperature of about 800 ° C for the cases of a hydrogen concentration of 50%, 30%, 10% and 0% must be 250 ° C / min, 140 ° C / min, 61 ° C / min and 17 ° C / min or more.

8th FIG. 10 is a graph showing the relationship between the concentration of hydrogen in the atmosphere and the cooling rate of the substrate in the vicinity of 800 ° C during the cooling process in a method of manufacturing a p-type nitride semiconductor according to a fourth exemplary embodiment of the present invention ,

On the basis of the above results, it can be found that the combinations of the concentration of hydrogen in the atmosphere and the cooling rate, during the cooling process, which comes after a p-type semiconductor is formed into an in 8th should be shown; in the coordination system (X, Y), in which the X-axis represents the hydrogen concentration (%) in the atmosphere, while the Y-axis represents the cooling rate (° C / min) in the vicinity of a substrate temperature of 800 ° C the area is shown by an area surrounded by the points O-P-Q-R-S-T, where the point O (50, 250), point P (30, 140), point Q (10, 61) , Point R (0, 17), point S (0, 500) and point T (50, 500). The reason why the upper limit of the cooling rate for hydrogen concentration is irrelevant by a straight line ST at 500 ° C / min is that when cooled at a cooling rate higher than that, a p-type nitride semiconductor is in danger is to be damaged by cracks due to thermal shock.

The substrate 11 Besides sapphire, it can consist of various other materials such as SiC, spinel, Si, GaAs, etc. It may also consist of GaN or other nitride semiconductor materials. In a case where the substrate 11 is not a nitride semiconductor, becomes a buffer layer 12 of GaN, etc., at a low substrate temperature of about 400 ° C-about 600 ° C between the substrate 11 and the p-type nitride semiconductor layer to be formed thereon 13 formed in order to reduce the lattice offset between the nitride semiconductor and the substrate 11 to reduce. In a case where the substrate 11 is made of a nitride semiconductor, a p-type nitride semiconductor layer can be provided without providing a buffer layer 12 directly on the substrate 11 be formed.

The p-type nitride semiconductor layer 13 can on a substrate 11 on which an n-type nitride semiconductor layer and an active layer of a nitride semiconductor are formed in advance. Thus, the layer structure of a device with pn junction can be formed.

The p-type nitride semiconductor layer 13 can be formed by introducing the sources of a p-type dopant, nitrogen and sources of group III while the substrate temperature 11 is kept at about 950 ° C or higher. A preferred temperature range for the substrate is about 950 ° C-about 1200 ° C. When the substrate temperature is below 950 ° C, it couples during formation of the p-type nitride semiconductor layer 13 the p-type dopant easily with hydrogen, which makes it inactive. This makes it difficult to form a p-type nitride semiconductor layer having a low resistivity. When the substrate temperature is higher than 1200 ° C, it becomes difficult to form a p-type nitride semiconductor layer having good crystal property.

The p-type nitride semiconductor layer 13 may be provided in the form of a single layer of GaN, AlGaN, InGaN, InAlGaN, etc., or by superimposing some of these layers. Of these, Al _x Ga _1-x N (0 ≤ x <1), which provides a better crystal property at a substrate temperature of about 950 ° C or higher and may be doped with a very small amount of In, is preferable.

For the p-type dopant for the p-type nitride semiconductor layer 13 Mg, Zn, Cd, C can be used. Of these, Mg is preferable with which the p-type conduction is relatively easily made available. The concentration of the p-type dopant should preferably be not less than 1 × 10 ¹⁹ cm ^-3 and not more than 5 × 10 ²⁰ cm ^-3 . When the concentration of p-type dopant is less than 1 × 10 ¹⁹ cm ^-3 , the hole carrier density of the p-type nitride semiconductor layer becomes 13 low and the ohmic contact resistance becomes high when on the p-type nitride semiconductor layer 13 an electrode is formed. If it is higher than 5 × 10 ²⁰ cm ^-3 , the crystal property of the p-type nitride semiconductor layer deteriorates 13 ; which makes it difficult to obtain the p-type.

What the atmosphere in a reaction chamber for forming the p-type nitride semiconductor layer 13 is concerned, it is preferred that it contains hydrogen in a concentration of 5% -70%, more preferably in a concentration of 10% -30%. When the concentration is less than 5%, the crystal property of the p-type nitride semiconductor layer deteriorates 13 due to a reduced atomic migration at the surface for formation and the rate at which the p-type dopant enters the p-type nitride semiconductor layer 13 recorded, decreases. When the concentration exceeds 70%, the p-type dopant becomes p-type during formation of the nitride semiconductor layer 13 deactivated by hydrogen.

In the cooling process, the concentration of ammonia, NH ₃ , in the atmosphere should preferably be kept at 5% or more, at least at the time when the substrate temperature becomes lower than 950 ° C. When the concentration is less than 5%, nitrogen easily separates from the surface of the p-type nitride semiconductor, which easily results in deteriorated crystal property at the surface.

Also, in the cooling process, the concentration of ammonia, NH ₃ , in the atmosphere during the time when the substrate temperature is about 950 ° C-about 700 ° C should preferably be 30% or less. If it is higher than 30%, the hole carrier density in the p-type nitride semiconductor slightly decreases because of the increased hydrogen generated as a result of thermal decomposition of ammonia, NH ₃ .

CONCRETE EXAMPLE

Now In the following, the process for producing a p-type nitride semiconductor will be described of the present invention by concrete examples with reference described on the drawings.

(Concrete example 1)

A p-type nitride semiconductor was produced whose cross-sectional structure is as in 1 is shown.

First, it became a substrate 11 having a mirror-finished main surface disposed in a reaction chamber (not shown) and held by a substrate holder, and then the temperature of the substrate was raised to about 1000 ° C and nitrogen gas was introduced at 5 L / min, hydrogen gas at 5 L / min while the substrate was heated for about 10 minutes. Thus, stains were formed of organic matter and on the main surface of the substrate 11 sticking moisture away.

The substrate temperature was reduced to about 550 ° C and then nitrogen gas as a carrier gas at a rate of about 16 l / min and ammonia, NH ₃ , at a rate of about 4 l / min, TMG at a rate of about 40 .mu.mol / min introduced to on the surface of the substrate 11 a buffer layer 12 GaN to form to a thickness of about 0.03 microns.

The TMG feed to the reaction chamber was once set and the substrate temperature was increased to about 1050 ° C and to the buffer layer 12 became a 2 μm thick p-type nitride semiconductor layer 13 of GaN doped with Mg, a p-type dopant, by nitrogen gas at a rate of about 12 l / min, hydrogen gas at a rate of about 4 l / min as a carrier gas, and ammonia, NH ₃ , at a rate at about 4 l / min, TMG at a rate of about 80 μmol / min and Cp ₂ Mg at a rate of about 0.2 μmol / min. The Mg concentration in the p-type nitride semiconductor was about 2 × 10 ¹⁹ cm ^-3 . The throughput of hydrogen gas includes the hydrogen gas needed to vaporize the TMG and Cp ₂ Mg.

The supply of TMG and Cp ₂ Mg to the reaction chamber was stopped and then the substrate became 11 cooled from 1050 ° C to 950 ° C in about 0.5 minutes, while nitrogen gas at a rate of about 12 l / min, hydrogen gas at a rate of about 4 l / min and ammonia, NH ₃ , with a throughput of about 4 l / min were introduced as ambient gas.

And then, the hydrogen gas was adjusted and nitrogen gas was supplied at a rate of about 16 l / min, ammonia, NH ₃ , at a rate of about 4 l / min as the ambient gas, while the temperature of the substrate 11 was lowered from 950 ° C to 700 ° C in about 1.2 minutes. The cooling rate for the substrate 11 near 800 ° C was about 210 ° C / min. Thereafter, the supply of ammonia, NH ₃ , was stopped and nitrogen gas was allowed to flow as the ambient gas at a rate of about 20 l / min until the substrate temperature became lower than 100 ° C.

After the cooling was completed, it became the p-type nitride semiconductor layer 13 provided substrate 11 taken from the reaction chamber. The substrate 11 was separated into individual chips of 5 mm square without undergoing post-annealing. The Hall effect of the chip was measured by the Van der Pauw method; the result showed that the hole carrier density was 1.6 × 10 ¹⁷ cm ^-3 and there was a good p-type semiconductor layer with low resistivity. The hole carrier density of the p-type nitride semiconductor layer 13 before cooling, at about 2.0 × 10 ¹⁷ cm ^-3 as a result of extrapolation of the cooling time to zero in 6 estimated. Consequently, the decrease in the hole carrier density during the cooling process was suppressed within about 20%.

(Concrete example 2)

A p-type nitride semiconductor of the present example 2 was prepared in the same procedure as in Example 1 Herge except that the conditions of the atmosphere were modified during the cooling process.

After the p-type semiconductor layer 13 was formed, the supply of TMG and Cp ₂ Mg was adjusted to the reaction chamber and then the substrate became 11 cooled from 1050 ° C to 700 ° C in about 1.7 minutes, while nitrogen gas at a rate of about 12 l / min, hydrogen gas at a rate of about 4 l / min and ammonia, NH ₃ , with a throughput of about 4 l / min were supplied as ambient gas. It took about 0.5 min to reach the temperature of the substrate 11 from 1050 ° C to 950 ° C, for about 1.2 minutes from 950 ° C to 700 ° C. The cooling rate for the substrate 11 near 800 ° C was about 210 ° C / min.

After the temperature of the substrate 11 was lower than 700 ° C, the supply of hydrogen gas and ammonia, NH ₃ , was adjusted and nitrogen gas was allowed to flow as ambient gas at a rate of about 20 l / min until the substrate temperature became lower than 100 ° C.

After the cooling was completed, it became the p-type nitride semiconductor layer 13 provided substrate 11 taken from the reaction chamber. The substrate 11 was separated into individual chips of 5 mm square. The Hall effect of the chip was measured. The result of the measurement showed that the hole carrier density was about 4.6 × 10 ¹⁶ cm ^-3 . The hole carrier density of the p-type nitride semiconductor layer 13 before cooling, it was assumed to be about 2.0 × 10 ¹⁷ cm ^-3 . Consequently, the decrease in the positive punch carrier density during the cooling process was suppressed within about 77%.

Comparative Example 1

One p-type nitride semiconductor of the present comparative example 1 was prepared in the same procedure as in Example 2, except that the cooling time (o the speed) during the cooling process were modified.

After the p-type semiconductor layer 13 was formed, the supply of TMG and Cp ₂ Mg was adjusted to the reaction chamber and then the substrate became 11 cooled from 1050 ° C to 700 ° C in about 5.6 min, while nitrogen gas at a rate of about 12 l / min, hydrogen gas at a rate of about 4 l / min and ammonia, NH ₃ , with a throughput of about 4 l / min were supplied as ambient gas. It took about 1.6 min, until the temperature of the substrate 11 from 1050 ° C to 950 ° C, about 4.0 minutes from 950 ° C to 700 °. The cooling rate for the substrate 11 near 800 ° C was about 63 ° C / min.

After the temperature of the substrate 11 was lower than 700 ° C, the supply of hydrogen gas and ammonia, NH ₃ , was adjusted and nitrogen gas was allowed to flow as ambient gas at a rate of about 20 l / min until the substrate temperature became lower than 100 ° C.

After the cooling was completed, it became the p-type nitride semiconductor layer 13 provided substrate 11 taken from the reaction chamber. The substrate 11 was separated into individual chips of 5 mm square. The Hall effect of the chip was measured. The result of the measurement showed that the hole carrier density was about 2 × 10 ¹⁵ cm ^-3 .

The hole carrier density of the p-type nitride semiconductor layer 13 before cooling, it was assumed to be about 2.0 × 10 ¹⁷ cm ^-3 . Consequently, the hole carrier density decreased by about 99% during the cooling process.

(Concrete example 3)

9 FIG. 12 is a cross-sectional view showing the structure of a p-type nitride semiconductor fabricated according to another exemplary embodiment of the present invention. FIG.

in the The present concrete example has been a light emitting device made with nitride semiconductors, at the top of a p-type nitride semiconductor layer was arranged.

The nitride semiconductor light emitting device comprises a first n-type cladding layer 22 of undoped GaN, a second n-type cladding layer 23 of undoped AlGaN, a light emitting layer 24 of undoped InGaN and an intermediate layer 25 of undoped GaN and a p-type cladding layer 26 from Mg-doped AlGaN, in order on a substrate 21 of Si doped n-type GaN are arranged one above the other. On the p-type cladding layer 26 there is a p-electrode consisting of Pt and Au 27 which is arranged in order while an n-electrode 28 Ti and Au, which are in the exposed area of the substrate 21 is arranged. Thus, the present light emitting device is a light emitting diode having a pn junction with the light emitting layer 24 forms between.

in the Below is a method for producing the light emitting diode with of the above configuration.

First, it became a substrate 21 GaN composed of GaN doped with Si to provide an n-type property and having a mirror-finished surface, disposed in a reaction chamber (not shown) and held by a substrate holder. The temperature of the substrate 21 was increased to about 1100 ° C and the substrate 21 It was heated for about 1 minute while nitrogen gas at a flow rate of 4 l / min, hydrogen gas at a flow rate of 4 l / min and ammonia, NH ₃ , at a rate of 2 l / min to the substrate 21 were fed. Thus, organic matter stains and surface moisture were removed.

The substrate temperature was maintained at about 1100 ° C and there were nitrogen gas at a rate of about 13 l / min, hydrogen gas at a rate of about 3 l / min as a carrier gas and ammonia, NH ₃ , at a rate of about 4 l / min , TMG introduced at a rate of about 80 μmol / min to the first n-type cladding layer 22 of undoped GaN to a thickness of 0.5 μm.

After the first n-type cladding layer 22 was formed, the temperature of the substrate was 21 held at about 1050 ° C and were nitrogen gas at a rate of about 15 l / min, hydrogen gas at a rate of about 3 l / min as a carrier gas and ammonia, NH ₃ , with a throughput of about 2 l / min, TMG with a Throughput of about 40 .mu.mol / min and trimethylaluminum (TMA) with a throughput of about 3 .mu.mol / min introduced to a 0.05 micron thick second n-type cladding layer 23 of undoped Al _0.05 Ga _0.95 N.

After the second n-type plating layer 23 was formed, the supply of TMG and TMA was adjusted, the temperature of the substrate was 21 lowered to about 700 ° C and held at this altitude. Nitrogen gas as a carrier gas at a rate of about 14 l / min, ammonia, NH ₃ , at a rate of about 6 l / min, TMG at a rate of about 4 μmol / min and trimethylindium (TMI) at a rate of about 1 μmol / min introduced to a SQW light emitting layer 24 of _undoped In _0.15 Ga _0.85 N to form a thickness of about 0.002 microns.

After the light-emitting layer 24 The supply of TMI was stopped, and nitrogen gas as a carrier gas at a rate of about 14 l / min and ammonia, NH ₃ , at a rate of 6 l / min, TMG at a rate of 2 μmol / min substratum 21 allowed to flow, wherein the substrate temperature was increased to 1050 ° C out. In this way, the intermediate layer became 25 formed of non-doped GaN to a thickness of 0.004 microns.

After the temperature of the substrate 21 Reached 1050 ° C were nitrogen gas at a rate of about 14 l / min, hydrogen gas at a rate of about 4 l / min as the carrier gas and ammonia, NH ₃ , at a rate of 2 l / min, TMG at a rate of 40 μmol / min, TMA at a rate of 3 μmol / min and Cp ₂ Mg at a rate of 0.4 μmol / min introduced to form a p-type cladding layer 26 from Mg-doped Al _0.05 Ga _0.95 N to form a thickness of 0.2 microns. The Mg concentration in the p-type cladding layer was about 8 × 10 ¹⁹ cm ^-3 .

After the p-type cladding layer 26 was bred, the supply of TMG, TMA and Cp ₂ Mg was stopped and became the temperature of the substrate 21 from 1050 ° C to 950 ° C in about 0.5 minutes, while nitrogen gas at a rate of about 14 l / min, hydrogen gas at a rate of about 4 l / min and ammonia, NH ₃ , at a rate of about 2 l / min were introduced as ambient gas.

The supply of the hydrogen gas was stopped and then the temperature of the substrate became 21 from 950 ° C to 700 ° C in about 1.2 minutes, while feeding nitrogen gas at a rate of about 18 l / min, ammonia, NH ₃ , at a rate of about 2 l / min as the ambient gas. The cooling rate for the substrate 21 near 800 ° C was about 210 ° C / min.

After the temperature of the substrate 21 was less than 700 ° C, the supply of Ammo ammonia, NH ₃ , while nitrogen gas was allowed to flow as ambient gas at a rate of about 20 l / min until the temperature of the substrate 21 less than 100 ° C was. Then the substrate became 21 taken from the reaction chamber.

The thus provided p-nitride semiconductor layers, including the p-type cladding layer 26 , themselves proved to be good p-type low resistivity semiconductor layers without undergoing the post-annealing process to activate the doped Mg.

Next, an SiO ₂ layer was deposited over the surface of the nitride semiconductor with a stacked layer structure thus formed by a CVD process, without applying any night-time tempering. Then, a rectangular pattern was provided by photolithography and a wet etching, and an etching mask of SiO _{2 was} formed. Using a reactive ion etching process, the p-type cladding layer became 26 , the intermediate layer 25 , the light emitting layer 24 , the second n-type cladding layer 23 , the first n-type cladding layer 22 and removing a portion of the substrate in a direction reverse to the stacking direction until the substrate 21 was etched away to a depth of about 1 micron. Thus, the surface of the substrate became 21 partially uncovered. On a part of the exposed surface of the substrate 21 became an n-electrode 28 formed by superimposing 0.1 μm thick Ti and 0.5 μm thick Au by photolithography and an evaporation process. After removing the etching mask of SiO ₂ by wet etching, a p-electrode consisting of 0.3 μm thick Pt and 0.5 μm thick Au was formed 27 covering most of the surface of the p-type cladding layer 26 provided using photolithography and an evaporation process. The thickness of the substrate 21 was set by grinding the backside to a thickness of 100 μm and then separated by dicing into individual chips.

Thus, in the construction as in 9 1, a light-emitting device with nitride semiconductor is provided.

The light emitting device was attached with the electrodes of the chip down to a Si diode on which a pair of positive and negative electrodes are provided. They are connected by an Au cusp. The light emitting device was mounted so that the p-electrode 27 or the n-electrode 28 be connected to the negative electrode and the positive electrode of the Si diode. Then, the Si-diode supporting the light-emitting device was attached to a foot using Ag paste, the positive electrode of the Si-diode was connected to an electrode on the foot with a wire, and then molded with a resin to form a finished light-emitting diode provide. The LED was operated with a forward current of 20mA and emitted blue light with a peak wavelength of 470nm from the back side of the substrate 21 showed a uniform light emission. The light power was 4 mW, the operating voltage in the forward direction was 3.4 V.

As described above, in the present concrete example, a p-type semiconductor layer having low resistivity and good quality has been used as the p-type cladding layer 26 educated. In the cooling process, the low resistivity property of the p-type cladding layer becomes 26 maintained. As a result, a nitride semiconductor light emitting device operating at a low voltage and high in performance is provided without requiring any post-annealing or other such specific processing.

at a method for producing a p-type nitride semiconductor The present invention is a p-type on a substrate Nitride semiconductor layer with low resistivity in an atmosphere formed, the hydrogen up to a specific specific Contains grade, in which the deactivation of a p-type dopant are well suppressed can; and becomes the p-type nitride semiconductor layer thus formed cooled in a specific specific cooling time or atmosphere, so that the hole carrier density the p-type nitride semiconductor layer decreases in a manner in that the property of low resistivity quite is maintained. As a result, a p-type nitride semiconductor made available with a good crystal property without any Night tempering needed becomes.

In a method for producing a p-type nitride semiconductor of the present invention, a p-type nitride semiconductor layer is formed on a substrate, and the p-type nitride semiconductor layer is cooled during a certain specific substrate temperature range under a certain specific combination of hydrogen concentration in the atmosphere and cooling time or hydrogen concentration in the atmosphere and cooling rate cooled, under which combination the p-type dopant is hardly deactivated. As a result, a p-type nitride semiconductor having a low resistivity and a good crystal quality is provided without requiring any post-annealing or other such specific processing.

Further In the method of the present invention, the manufacturing process for the p-type nitride semiconductor be simplified, so that the cost of producing a nitride semiconductor device, the a p-type nitride semiconductor can be reduced.

Claims (10)

A method of fabricating a p-type nitride semiconductor, comprising: a semiconductor layer-forming process of forming a p-type nitride semiconductor layer ( 13 ) with low resistivity on a substrate ( 11 ) maintained at a temperature of 600 ° C or more by exposing a source of a p-type dopant, a nitrogen source and a group III source to the substrate ( 11 ) and a cooling process for cooling the p-type nitride semiconductor layer ( 13 ) supporting substrate ( 11 ); characterized by predetermining the decrease in the hole carrier density of the p-type nitride semiconductor layer ( 13 ) in a range of 0% to 95%, and controlling the cooling time and the hydrogen concentration in the atmosphere in the cooling process to achieve the predetermined decrease in the hole carrier density. A method of fabricating a p-type nitride semiconductor according to claim 1, wherein the cooling process includes a procedure during which the substrate ( 11 ) is cooled to 600 ° C within 30 minutes from the substrate temperature in the process of forming a semiconductor layer. Process for producing a p-type nitride semiconductor according to claim 1 or 2, wherein the atmosphere in a semiconductor layer forming process 5-70 Vol .-% hydrogen contains. A method of fabricating a p-type nitride semiconductor according to claim 1 or 2, wherein the atmosphere introduced during a procedure in the cooling process for cooling the substrate ( 11 ) from a substrate temperature in the semiconductor layer forming process to 600 ° C 5-50 vol .-% hydrogen. A method of fabricating a p-type nitride semiconductor according to claim 1 or 2, wherein the atmosphere introduced during a procedure in the cooling process for cooling the substrate ( 11 ) from the substrate temperature in the process forming a semiconductor layer to 600 ° C ammonia, NH ₃ . A method of making a p-type nitride semiconductor according to any of claims 1-5, wherein the substrate ( 11 ) is maintained at a temperature of 950 ° C or more, and wherein the substrate ( 11 ) in the cooling process during a procedure for cooling the substrate ( 11 ) is cooled from 950 ° C to 700 ° C under certain specific combinations of the concentration of hydrogen in the atmosphere and the cooling time during which the p-type nitride semiconductor layer ( 13 ) can maintain the property of low resistivity. Process for producing a p-type nitride semiconductor according to claim 6, wherein the combination of the hydrogen concentration in the atmosphere and the cooling time falling into an area that by points A-B-C-D-E-F in a X-Y coordinate specified where the x-axis is the hydrogen concentration (%) in the atmosphere represents and the Y-axis represents the cooling time (min), in the point A (50, 1.5), point B (30, 1.8), point C (10, 4.1), Point D (0, 15), point E (0, 0.5) and point F (50, 0.5). A process for producing a p-type nitride semiconductor according to any one of claims 1-7, wherein the substrate ( 11 ) is maintained at a temperature of 950 ° C or more, and wherein the substrate ( 11 ) is cooled in the vicinity of 800 ° C under certain specific combinations of the concentration of hydrogen in the atmosphere and the cooling rate at which the p-type nitride semiconductor layer ( 13 ) can maintain the property of low resistivity. A method of making a p-type nitride semiconductor according to claim 8, wherein the combination of the hydrogen concentration in the atmosphere and the cooling time falls within a range represented by points O - P - Q - R - S - T in an XY Coordinate can be specified, where the X-axis represents the hydrogen concentration (%) in the atmosphere and the Y-axis represents the cooling rate (° C / min), in the point O (50, 250). Point P (30, 140), point Q (10, 61), point R (0, 17), point S (0, 500) and point T (50, 500). A method for producing a p-type nitride semiconductor according to any one of claims 1-9, wherein the surface of the p-type nitride semiconductor ( 13 ) and in which the concentration of hydrogen in the vicinity of the surface of the p-type nitride semiconductor ( 13 ) equal to 1 to 10 times that inside the p-type nitride semiconductor ( 13 ).