JP2829311B2 - Light emitting device manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a single crystal Al _x Ga ₁ -xN (X
= 0) (including 0) as an active layer, in particular, to achieve monochromatic emission and high luminance.

[Prior art]

2. Description of the Related Art Conventionally, a diode configured of a GaN semiconductor has been known as a blue light emitting diode. The light-emitting diode is made of single-crystal GaN on a sapphire substrate by metalorganic chemical vapor deposition (MOCVD).
After growing an N-type N layer of N-type, an intrinsic (INTRINSIC) GaN I-layer is formed by vapor-phase growth on the N-layer while adding zinc as an impurity. This is a configuration in which electrodes are formed on the layer and the I layer. The light emitting diode having such a structure emits light by causing the I layer to have a positive potential with respect to the N layer, thereby recombining carriers injected into the I layer as an active layer.

[Problems to be solved by the invention]

As described above, the optical property and the electrical property of the I layer, which is the active layer, depend on the emission color, emission luminance,
Light emission characteristics such as light emission efficiency are determined. By the way, one of the physical properties of the I layer that determines the light emission
This is the impurity concentration of zinc to be doped. In the case the impurity concentration of zinc is low (less than 1 × 10 ²⁰ cm ^-3), larger by blue light relatively luminous intensity is observed. Therefore, if the I layer has such a low impurity concentration, a light emitting diode of monochromatic emission of blue light can be obtained. However, if the impurity concentration of the I layer is low, the I layer becomes electrically unstable, With the operation described above, the barrier necessary for light emission is removed, and the element often becomes a resistor. On the other hand, when the impurity concentration of zinc is high (1 × 10 ²⁰
(cm ^-3 or more), the emission intensity of blue light is small, and emission of visible light other than blue is strongly observed. Therefore, when the I layer is made to have a high impurity concentration, the layer is electrically stable, but visible light other than blue is strongly observed due to the influence of visibility, and the monochromatic emission of blue is inhibited. As described above, it is difficult to control the optical properties and the electrical properties at the same time, and it is difficult to produce a high-luminance blue light emitting diode. The present invention has been made to solve the above problems, and an object of the present invention is to achieve high luminance and monochromatic blue light emitting elements.

[Means for Solving the Problems]

The present inventors have intensively studied a growth method and physical properties of an Al _x Ga ₁ -xN (including X = 0) semiconductor in order to achieve high luminance and monochromatic blue light emitting elements. In the course of the process, the present inventors have found that the doped Al _x G
a _1-x N (including X = 0) semiconductor scanning electron microscope (SEM)
It was found that there was a remarkable difference in the photoluminescence intensity characteristics before and after the image photographing by. That is, Al _x Ga _1-x N (X =
In the photoluminescence intensity characteristics of the semiconductor (including 0), it was found that the emission intensity of the spectrum other than blue decreased and the emission intensity of blue increased. The present invention has been made based on such a finding, and therefore, the configuration of the present invention which has solved the above-mentioned problems includes at least an n-type gallium nitride-based compound semiconductor and a p-type impurity-doped gallium nitride-based compound semiconductor. In a gallium nitride-based compound semiconductor light emitting device having a gallium nitride-based compound semiconductor doped with a p-type impurity, the current density is 0.
It is characterized by being irradiated with an electron beam of 02 to 4.07 mA / mm ² . If the acceleration voltage of the electron beam is 9 kV or more, the irradiation intensity of the electron beam becomes too large, and the sample temperature locally rises in the irradiated portion, which is not desirable. On the other hand, if the acceleration voltage of the electron beam is 0.1 kV or less, there is no effect on improving the optical properties of the active layer. Similarly, the sample current is desirably in the range of 0.2 μA to 1 mA. Further, the irradiation area of the electron beam is desirably 0.01 mmφ to 1 mmφ. When the irradiation area of the electron beam is 1 mmφ or more, the energy of the irradiated electron beam is excessively dispersed, and the strength is undesirably reduced. In contrast, the irradiation area of the electron beam is 0.
When the diameter is less than 01 mmφ, the irradiation intensity of the electron beam becomes too large, which is not preferable. The active layer is made of zinc (Zn) having an impurity concentration of 1 × 10 ²⁰ cm ^−3.
The above doping is desirable for stabilizing the electronic characteristics of the device, and has a great effect of improving the optical properties.

【The invention's effect】

By irradiating a gallium nitride-based compound semiconductor doped with a p-type impurity with an electron beam having a current density of 0.02 to 4.07 mA / mm ² , the optical properties of the layer were able to be improved. That is, in the light emission characteristics, it was possible to improve the emission luminance of blue and to decrease the emission luminance of the spectrum other than blue. In addition, the emission luminance, which makes the sensitivity in the visible light band, also improved by the irradiation of the electron beam. The optical properties were stable for a long time even after irradiation with an electron beam. In addition, the present invention can use a conventional scanning electron microscope, electron beam diffractometer, or cathode ray luminescence measuring device, and is excellent in productivity because processing is performed in a short time.

【Example】

Hereinafter, the present invention will be described based on specific examples. The light-emitting device is a metal-organic compound vapor deposition method (hereinafter referred to as “MOVP”).
E ") to produce the structure shown in FIG. The gases used were NH ₃ , carrier gas H ₂ , N ₂ , triethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), and diethyl zinc (Zn (C ₂ H ₅ )) as a dopant gas. ₂ )
(Hereinafter referred to as “DEZ”). First, a single-crystal sapphire substrate 1 whose main surface is a c-plane cleaned by organic cleaning and heat treatment is mounted on a susceptor placed in a reaction chamber of a MOVPE apparatus. Then, the pressure in the reaction chamber was reduced to 5 Torr, flow rate 0.3 of H ₂
The sapphire substrate 1 was subjected to vapor phase etching at a temperature of 1100 ° C. while flowing into the reaction chamber at a rate of 1 minute. Then, maintaining the temperature of the sapphire substrate 1 to 600 ° C., H ₂
2.5 / min, NH ₃ 1.5 / min, TMG 1.7 × 10 ⁻⁵ mol /
N layer 2 made of GaN having a thickness of about 3 μm
Was formed. Next, the sapphire substrate 1 on the surface of which the N layer 2 is formed as described above is taken out of the reaction chamber,
Through an etching process or the like, a semiconductor doped with impurities on the N layer 2 was formed as a mask in a portion where the vapor phase growth was not performed. Thereafter, the sapphire substrate 1 on which the mask was formed was washed and then mounted again on the susceptor, and the pressure in the reaction chamber was set to the same state as before. Then, after the gas phase etching as before, keeping the temperature of the sapphire substrate 1 to 700 ° C., H ₂
2.5 / min, the NH ₃ 1.5 / min, 1.7 × 10 ^-5 mol / min TMG, by supplying 5 minutes DEZ at 5 × 10 ^-6 mol / min, I layer 3 made of I-type GaN Was formed to a thickness of 1.0 μm. Thereafter, the N layer 2 and I
The sapphire substrate 1 on which the layer 3 was grown was taken out, the mask was removed and the substrate was washed, and then the I layer 3 as an active layer was irradiated with an electron beam using an improved reflection electron beam diffractometer. The improved reflection electron beam diffractometer reduces the acceleration voltage to 50KV or less,
The sample current can be varied continuously over the entire range of 1 mA or less. After irradiating the I layer 3 as an active layer with an electron beam under the conditions of an acceleration voltage of 0.1 kV to 9 kV and a sample current of 0.2 μA to 1 mA, aluminum electrodes 4 and 5 are formed on the N layer 2 and the I layer 3. Each was deposited. Then, the sapphire substrate 1 was cut into a predetermined size, and lead wires 6 and 7 were connected to the electrodes 4 and 5, respectively, to produce light emitting diodes. The light emitting diode emits light from the I layer 3 which is an active layer by setting the I layer 3 at a positive potential with respect to the N layer 2 and recombining electrons injected from the N layer 2 into the I layer 3. As described above, the light emitting diode in which the electron beam was irradiated to the active layer I layer had improved luminance in the visible light band as compared to before the electron beam was irradiated. In the speckle, the luminance of blue was improved, and the luminance of spectra other than blue was reduced.
In addition, stable light emission characteristics were obtained over a long period of time. The inventor further manufactured GaN layers having different impurity concentrations as various samples in order to investigate in detail the relationship between the impurity concentration in the I layer 3 as the active layer and the effect of electron beam irradiation. The GaN layers having different impurity concentrations are vapor-phase grown to a thickness of 5 μm by MOPVE while doping zinc on a sapphire substrate. Experiment 1 An electron beam was perpendicularly incident on the surface of a GaN layer doped with 1.4 × 10 ²⁰ cm ^{−3 of} zinc. The irradiation area is about 0.1 mmφ, the sample current is 32 μA, the acceleration voltage is 6 kV, the irradiation time of the spot is 2 minutes, and the scanning area is 16 mm ² . FIG. 2 shows the measurement results of the photoluminescence intensity characteristics of the sample before and after the irradiation with the electron beam. In FIG. 2, curve B shows the characteristics before irradiation, and curve A shows the characteristics after irradiation. The photoluminescence intensity at a wavelength of 424 nm was increased 20 times by electron beam irradiation. On the other hand, the photoluminescence intensity at a wavelength of 660 nm was reduced to 1/5 by electron beam irradiation. From this, it can be seen that the emission color changes to blue and the emission luminance increases by the irradiation of the electron beam. Experiment 2 An electron beam was perpendicularly incident on the surface of a GaN layer doped with 1.7 × 10 ¹⁹ cm ^{−3 of} zinc. The irradiation area is about 0.1 mmφ, the sample current is 20 μA, the acceleration voltage is 6 kV, the irradiation time of the spot is 2 minutes, and the scanning area is 9 mm ² . FIG. 3 shows the measurement results of the photoluminescence intensity characteristics of the sample before and after the irradiation with the electron beam. In FIG. 3, curve B shows the characteristics before irradiation, and curve A shows the characteristics after irradiation. The photoluminescence intensity at a wavelength of 436 nm is four times higher than that at a wavelength of 420 nm before irradiation by irradiation with an electron beam. It is considered that the spectrum other than blue was not observed because the impurity concentration was low. Experiment 3 An electron beam was perpendicularly incident on the surface of a GaN layer doped with 1.6 × 10 ¹⁹ cm ^{−3 of} zinc. The irradiation area is about 0.1 mmφ, the sample current is 30 μA, the acceleration voltage is 6 kV, the irradiation time of the spot is 2 minutes, and the scanning area is 9 mm ² . FIG. 4 shows the measurement results of the photoluminescence intensity characteristics of the sample before and after the irradiation with the electron beam. In FIG. 4, curve B shows the characteristics before irradiation, and curve A shows the characteristics after irradiation. The photoluminescence intensity at a wavelength of 428 nm has been improved by a factor of 10 by electron beam irradiation. Experiment 3 has almost the same impurity concentration, the same acceleration voltage, and a large sample current as those of Experiment 2,
It is understood that, when the sample current at the time of electron beam irradiation is increased, the emission luminance of blue is further improved. Experiment 4 An electron beam was perpendicularly incident on the surface of a GaN layer doped with 1.1 × 10 ¹⁹ cm ^{−3 of} zinc. The irradiation area is about 0.1 mmφ, the sample current is 30 μA, the acceleration voltage is 6 kV, the irradiation time of the spot is 2 minutes, and the scanning area is 16 mm ² . FIG. 5 shows the measurement results of the photoluminescence intensity characteristics of the sample before and after the irradiation with the electron beam. In FIG. 5, curve B shows the characteristics before irradiation, and curve A shows the characteristics after irradiation. The photoluminescence intensity at a wavelength of 420 nm has been improved by a factor of 2.5 by electron beam irradiation. On the other hand, the photoluminescence intensity at a wavelength of 656 nm was reduced to half by irradiation with an electron beam. From this,
It can be seen that the emission of the electron beam has made the emission color monochromatic to blue. Experiment 5 An electron beam was perpendicularly incident on the surface of a GaN layer doped with 1.9 × 10 ²⁰ cm ^{−3 of} zinc. The irradiation area is about 0.1 mmφ, the sample current is 20 μA, the acceleration voltage is 6 kV, the irradiation time is 2 minutes, and the scanning area is 9 mm ² . FIG. 6 shows the measurement results of the photoluminescence intensity characteristics of the sample before and after the irradiation with the electron beam. In FIG. 6, curve B shows the characteristics before irradiation, and curve A shows the characteristics after irradiation. The photoluminescence intensity at a wavelength of 420 nm has been increased by a factor of 10 by irradiation with an electron beam. On the other hand, the photoluminescence intensity at a wavelength of 656 nm was reduced to half by irradiation with an electron beam. From this, it can be understood that the emission of the electron beam causes the emission color to become monochromatic to blue. Experiment 6 An electron beam was incident on a GaN layer doped with 1.2 × 10 ²⁰ cm ^{−3 of} zinc perpendicularly to the surface. The irradiation area is about 0.1 mmφ, the sample current is 30 μA, the acceleration voltage is 6 kV, the irradiation time is 2 minutes, and the scanning area is 16 mm ² . FIG. 7 shows the measurement results of the photoluminescence intensity characteristics of the sample before and after the irradiation with the electron beam. In FIG. 7, curve B shows the characteristics before irradiation, and curve A shows the characteristics after irradiation. The photoluminescence intensity at a wavelength of 420 nm is improved by a factor of four by irradiation with an electron beam. On the other hand, the photoluminescence intensity at a wavelength of 656 nm was reduced to half by irradiation with an electron beam. From this, it can be understood that the emission of the electron beam causes the emission color to become monochromatic to blue. Conclusion The above experiment has revealed the following. (1) The emission luminance of blue light having a wavelength of about 420 nm is improved by irradiation with an electron beam. (2) The emission luminance of red light having a wavelength of about 656 nm is reduced by electron beam irradiation. (3) In the case of the same impurity concentration, the effects (1) and (2) are more remarkable as the sample current at the time of electron beam irradiation is larger. Since an increase in the temperature of the sample causes an adverse effect, it is necessary to reduce the irradiation area of the electron beam and perform the processing in a short time. Therefore, the irradiation area is preferably 1 mmφ or less. The acceleration voltage is preferably 9 kV or less.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of a light emitting diode manufactured by a specific embodiment of the present invention. FIG. 2 to FIG. 7
The figure is a measurement diagram of photoluminescence intensity characteristics of a GaN layer doped with a Zn impurity before and after electron beam irradiation. 1 ... Sapphire substrate, 2 ... N layer, 3 ... I layer 4,5 ... Electrode, 6,7 ... Lead wire

────────────────────────────────────────────────── ─── Continuing on the front page (72) Kuki Kato, Inventor Nagahata 1 Ochiai, Kasuga-mura, Nishikasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. Nagoya University (72) Inventor Hiroshi Amano Furo-cho, Chikusa-ku, Nagoya-shi, Aichi (Nanbanashi) Nagoya University (56) References IEICE Technical Report, February 17, 1988, Vol. 87, No. 373, p. 7-12 (CPM 87-104) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 33/00 JOIS

Claims (1)

(57) [Claims] 1. A gallium nitride-based compound semiconductor light emitting device having at least an n-type gallium nitride-based compound semiconductor and a p-type impurity-doped gallium nitride-based compound semiconductor, wherein the p-type impurity-doped gallium nitride-based compound semiconductor is A gallium nitride-based compound semiconductor light emitting device, which is irradiated with an electron beam having a current density of 0.02 to 4.07 mA / mm ² .