JPS5931232B2 - GaN light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a GaN light emitting element that can change the luminance color by controlling the luminance within twice by current control.

In light emitting devices using GaN as a material, ultraviolet,
It is known that it is possible to emit light with short wavelengths such as violet and blue, and if appropriate amounts of impurities are introduced, it is also possible to emit light with long wavelengths such as yellow to red, and it is possible to obtain light emission over the entire visible light range. There is.

However, with the conventional method of introducing only one type of impurity, only a single emission color can be obtained from a single element. Therefore, if two or more different types of impurities are introduced, multiple discontinuous impurity levels can be made to exist as energy levels, so light emission from a specific level among those impurity levels can be selected. This makes it possible to control the operation of the elements. In order to enable selection control here, there must be a difference in characteristics such as carrier capture probability and lifetime of each impurity level.
When two or more types of impurity levels exist, the deeper the impurity level, the easier it is to capture carriers and the longer the lifetime, so long-wavelength light emission occurs first with respect to this impurity level.

Furthermore, when the intensity of carrier injection/excitation is increased, the initially occurring light emission becomes saturated, and light emission due to another impurity level occurs. If the concentration of the latter impurity is higher than that of the former impurity, the injection and excitation are further increased after the first emission is saturated, so that the second emission becomes the main emission. Therefore, Ga containing impurities that become two or more types of luminescent centers in this way
If a light emitting element is made using N crystal, the color of the light emitted can be changed by current control. Here, the important point is the second
Even if light emission can occur, brightness is a problem.

If the visibility of the first emission color is greater than the visibility of the second emission color, the emission color can be changed while minimizing fluctuations in brightness. As can be seen from the discussion of the red, green, and blue visibility factors (not described in the examples below), the total visibility factor (same as the green factor) that determines the brightness at the peak wavelength (456 nm) of the blue visibility factor ) to the peak value is ~3 x 10-2, so for example, after the yellow-green emission is saturated, the blue emission increases and reaches 10% of the saturation value of the yellow-green emission.
Even when the intensity is doubled, the hue changes from yellow-green to almost blue, but the brightness increases by only 30% at most. Therefore, by making the visibility at the first emission wavelength greater than that at the second wavelength, it is possible to suppress the variation in luminance to within twice and change the hue. From a practical sense of brightness, a change within twice the brightness is hardly recognized as a change, so in practical terms, the brightness can be considered to be almost constant. Next, when introducing two or more types of impurities, the following points must be considered.

First, two or more types of impurities must be introduced at the same location, which is a region where the junction current of the light emitting element effectively contributes to light emission. Second, in order to make the hue variable within a doubling of the luminance change, the relative ratio of these impurity concentrations must be strictly controlled. Therefore, from these points of view, it is difficult to introduce two or more types of impurities using only the conventional method of introduction during growth. Introducing two or more types of impurities during crystal growth has some practical technical problems, such as complicating the reaction tube, but from the second point mentioned above, the impurity concentration must be strictly controlled. Not valid. From this point of view, ion implantation is the most effective method. It is. Although the introduction of two or more types of impurities may be performed entirely by ion implantation, the device of the present invention can be fabricated by using a method for introducing one impurity during crystal growth, in combination with the ion implantation method. It is also effective. This is because, as mentioned above, in order to realize the characteristics of the device according to the present invention, the relative values of the ferocity of each impurity are particularly important, but if the second impurity conductor is ion-implanted, This is because the impurity concentration can be strictly set and introduced in accordance with the impurity concentration introduced during growth. This will be specifically explained in Examples below.

A light emitting device based on the present invention was created using a GaN crystal obtained by vapor phase epitaxial growth on a sapphire substrate.

During vapor phase growth, at the same time Zn is added as the first impurity which becomes a luminescent center. It was introduced at a low concentration of -3. Next, a second impurity, Mg, which will become a luminescent center, is added to a concentration of 1019 cm-3 by ion implantation.
It was introduced to a certain extent. Here, the introduction of Mg effectively changes the luminescent color and at the same time increases the resistance of the high resistance layer (1 layer).
High concentrations were used for both reasons and to encourage bond formation. Specifically, the light emitting device was produced by the steps shown in FIG. Since it is difficult to introduce two or more different types of impurities using only the conventional simultaneous introduction method during vapor phase growth, a simpler and more effective ion implantation method was used. First, as shown in FIG. 1a, the Z
Ion implantation is performed by irradiating an n-doped GaN crystal 2 with an Mg ion beam 3 to form an implantation layer 4 on the surface of the crystal, as shown in b.

Ion implantation was performed using an energy multiplexing method so that the impurity distribution was flat, and the total dose was 1.9×1015.
cTrL-2. Next, as shown in c, a protective film of about 2,000 layers was coated on the crystal surface using the CVD method.
After depositing the iO2 film 5, heat treatment is performed at a temperature of 1050° C. for 1 to 20 hours in a nitrogen atmosphere. Then Si
After removing the O2 film, as shown in d, a groove 6 deep enough to exceed the thickness of the i-layer 4 formed by ion implantation is cut, and as shown in e, both the crystal surface and the groove 6 are cut. , In metal is deposited by dots or vapor deposition to form an electrode.
FIG. 2 shows changes in the electroluminescence spectrum of the light emitting device produced as described above, depending on the current.

Samples A and b were heat treated for 3 hours and 20 hours, respectively. (The current value is a, A is 4mA, and mouth is 10mAb.
The spectral lines are ~380nm, 430nm,
Three lines of ~510 nm can be seen. These are each M
The light emission is related to the g acceptor level, the Zn acceptor level, and the deep level due to the Mg complex. Corresponding to each vector shown in Fig. 2, the relative value of luminance Y
The chromaticity (X, y) was calculated using the following equation. However, P is the intensity at each wavelength of the spectrum, λ is the wavelength, and X, V, and V2 are visibility factors for red, green, and blue, respectively.

Figure 3 is a chromaticity diagram (X
, y).

The solid arrow indicates the hue change within a constant luminance Y range when the amount of current is increased. In this example, the luminance is kept strictly constant because the light emission on the longer wavelength side reaches saturation due to the increase in current and then decreases slightly. The dotted line indicates the hue change including the case where there is a change in luminance Y. As is clear from this, by current control, b
) shows the change from blue-green to blue, and a) shows the change from blue to bluish-purple.

In the above, two types of impurities, Zn and Mg, were used to change the emission color by current control, but other impurities such as Cd (blue), Hg (green), and Be (yellow at high concentration) could also be combined. Therefore, it is also effective to carry out the present invention.As described above, the present invention provides a GaN light-emitting element in which the color of emitted light can be controlled by controlling the current using two types of impurities with different emission wavelengths. It has features such as being able to easily change the color of the emitted light under conditions of constant brightness.

[Brief explanation of the drawing]

Figures 1 a-e are cross-sectional views showing the manufacturing process of the GaN light emitting device of the present invention, Figures 2 A and b are diagrams showing the electroluminescence spectrum of the GaN light emitting device of the present invention, and Figure 3 is a color diagram. It is a degree diagram. 1...Saphire substrate, 2...GaN
Crystal, 4...i layer.

Claims (1)

[Claims] 1. A GaN crystal formed on an insulating substrate has a region containing two or more types of impurities that can serve as emission centers of different wavelengths, and the luminous efficiency at the emission wavelength of each of the impurities is increased by a long wavelength. 1. A GaN light-emitting device characterized in that the concentration of an impurity serving as a luminescence center is gradually lowered as the emission of light becomes longer. 2. The GaN light emitting device according to claim 1, wherein at least two of the impurities are Zn and Mg.