JPH06268332A - Semiconductor light emitting device - Google Patents

Abstract

(57) [Summary] [Objective] The object of the present invention is a semiconductor light-emitting device having a simple structure, good reliability, long life, and display color changing target temperature and applied current level can be easily adjusted. It is to provide a device. A semiconductor light emitting device according to the present invention comprises two active layers 11 and 13 having different band gap energies separated by a barrier layer 12 along an electron flow direction,
It is characterized in that the emission intensity from each active layer 11 and 13 changes in response to a change in at least one of the temperature and the applied current, and the emission spectrum changes in the visible region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of visually recognizing changes in external temperature and applied current by changing the emission spectrum in the visible region in response to changes in external temperature and / or applied current. The present invention relates to a semiconductor light emitting device that makes it possible.

[0002]

2. Description of the Related Art Conventionally, an indicator for displaying a change in temperature or current is an analog or digital display device for a sensor for detecting a change in temperature or current in order to visualize a detected value of the temperature or current. It is common to connect with, and it is possible to easily recognize that the detected temperature or current has reached a certain value. Further, as another indicator, a temperature-sensitive substance whose color changes in accordance with a change in temperature, for example, one using a liquid crystal device,
There is a color change temperature indicator or the like in which the display color changes when a predetermined temperature is reached. However, such a conventional indicator has the following problems. First
The problem of (1) is that the device configuration becomes complicated because a display device is required in addition to the sensor. The second problem is that the liquid crystal device has a problem of non-reciprocity, has a short life, and requires an external illumination, which complicates the device configuration.

The third problem is that in the conventional color change temperature indicator, the temperature at which the display color changes (hereinafter referred to as "target temperature") is unique to the material used.
In order to arbitrarily adjust the target temperature, it is necessary to search for another material, and it is difficult to set an arbitrary temperature. In addition, there may be no material whose display color changes at the desired target temperature.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor light emitting device having a simple structure, good reliability, long life, and a display color that changes the target temperature and applied current level easily. It is to provide a device.

[0005]

A semiconductor light emitting device according to the present invention comprises a plurality of active layers having different bandgap energies separated by a barrier layer along an electron flow direction and having at least temperature and applied current. It is characterized in that the emission intensity from each of the above active layers changes in accordance with the change in one of them, and the emission spectrum changes in the visible region. Further, the active layer is formed of, for example, In _Y (Ga _{1 -x} A
l _x ) _1-Y P, and X and Y are set within the range of 0 to 1.0.

[0006]

According to the semiconductor light emitting device of the present invention, since a plurality of active layers having different bandgap energies separated by the barrier layer are provided along the electron flow direction, at least one of temperature and applied current has a constant value. Then, the electron overflow phenomenon occurs in one active layer, the light emitting operation is started in the other active layer, the emission intensity of each active layer changes, and as a result, the emission spectrum changes in the visible region. Therefore, it is possible to display that the temperature or the applied current has reached a certain value by the change of the emission color.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the semiconductor light emitting device according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a semiconductor light emitting device according to this embodiment.

In FIG. 1, 1 is a GaAs substrate,
On this GaAs substrate 1, about 1 μm thick n-type In
_0.5 (Ga _1-x Al _x ) _0.5 P cladding layer 2, active layer 3, p-type In _0.5 (Ga _1-x Al _x ) _{0.5 with a} thickness of about 1 μm
A light emitting layer having a double hetero structure in which the P clad layer 4 is sequentially stacked is formed. The light emitting layer may have another structure such as a multiple quantum well structure. The active layer 3 is deposited with a composition change so that the band gap energies separated by the barrier layer 2 are different.
It is formed to have two active layers, which will be described in detail later.

On the cladding layer 4, n-type In _0.5 (Ga
_1-x Al _{x) 0.5} P current blocking layer 5 are etched with a substantially circular opening current density is adjusted diameter in the range of 5~100μm so as to obtain desired. Since the overflow current can be controlled by adjusting the current density by adjusting the diameter of the opening, it is possible to adjust (enlarge) the temperature range in which the device operates and the applied current range to desired ranges.

On the current blocking layer 5, a p-type AlGaAs current diffusion layer 6 whose band gap energy is adjusted so that light emitted from the active layer 3 is not absorbed is grown and formed. A p-type GaAs contact layer 7 and a p-side Au / Zn electrode 8 are deposited on the current diffusion layer 6. The contact layer 7 and the electrode 8 face the opening of the current blocking layer 5 by lift-off, and have circular emission with a diameter slightly larger than the opening (usually about 10 μm or more) so that the emission is radially diffused. A window is formed. The n-side Au is on the back surface of the substrate 1.
/ Ge electrode 9 is formed.

The active layer 3 is made of In _0.5 (Ga _1-x Al).
_x ) _0.5 P, and by changing the composition ratio x, the layers are deposited in order from the cladding layer 2 side to a three-layer structure of a first active layer, a p-type barrier layer, and a second active layer.

The thickness of each of the first active layer, the p-type barrier layer, and the second active layer is determined by the change timing of the composition ratio x in the deposition process. In addition, these first active layers,
The energy gap of each layer of the p-type barrier layer and the second active layer is adjusted as shown in FIG. 2 by adjusting the composition ratio x. FIG. 2 is a diagram showing changes in the bandgap energy along the electron flow direction, with the horizontal axis representing the electron flow direction from the cladding layer 2 to the cladding layer 4 and the vertical axis representing the bandgap energy.

The band gap energies of the first active layer 11 and the second active layer 13 are such that the emission colors from the respective layers are colors that can be clearly discriminated in the visible light region, for example, red and green. The second active layer 13 is adjusted to have a bandgap energy larger than that of the first active layer 11 so that the light emitted from the active layer 11 is not absorbed by the second active layer 13 and is output to the outside. In this embodiment, the first
The composition X of the active layer 11 was 0.15 (wavelength 630 nm), and the composition X of the second active layer 13 was 0.45 (wavelength 570 nm).

The bandgap energy of the barrier layer 12 is set so that electrons will overflow from the first active layer 11 with respect to a desired temperature or an applied current.
Relative to the bandgap energy of In addition, the thickness of the barrier layer needs to be thicker than 15 nm so that electrons do not pass through the tunnel process, and the diffusion length of electrons (usually on the order of μm) so that overflowed electrons can reach the second active layer 13. Need to be thinner. The difference in bandgap energy between the first active layer 11 and the barrier layer 12 is hereinafter referred to as "barrier height". Further, the thickness of the first active layer 11 is adjusted so that electrons may overflow from the first active layer 11 with respect to a desired temperature and applied current. That is, the temperature and applied current (hereinafter referred to as “target temperature or target applied current”) when electrons cause overflow can be adjusted by two parameters, the barrier height and the thickness of the first active layer 11. . In this embodiment, the composition X of the barrier layer 12 is 0.7 and the barrier height is about 200 meV. The thickness of the barrier layer 12 was 200 nm, the thickness of the first active layer 11 was 30 nm, and the thickness of the second active layer 13 was 200 nm. When the external temperature or applied current applied to the device reaches the target temperature or target applied current,
Electrons in the first active layer 11 cross the barrier layer 12 to cause an overflow phenomenon, and the overflowed electrons are recombined in the second active layer 13 to start a light emission phenomenon in the second active layer 13. Second in the emission spectrum from the emission window
The wavelength component of the active layer 13, for example, the green wavelength component increases, and the operator can recognize that the detected temperature or the detected applied current has reached the target temperature or the target applied current by the change of the display color. Will be able to. By adjusting the above two parameters, it is possible to arbitrarily adjust the target temperature or the target applied current when the emission color from the device changes.

The barrier layer 12 is doped with p-type impurities at a sufficiently high concentration so as not to serve as a barrier against holes. It should be noted that the barrier layer 12 increases as the composition ratio x increases.
It becomes difficult to dope with high concentration with p-type impurities. In addition, the crystal quality of the layer grown with a high composition ratio x is deteriorated. In order to solve these problems, a multiple quantum barrier (MQB) structure is used for the barrier layer 12 in this embodiment.
When this structure is used, the desired barrier height is set to the barrier layer 1
It is possible to adjust without increasing the composition ratio of 2. Therefore, by using the MQB structure, it is possible to expand the temperature range and applied current width at which the device operates. Next, the operation of the apparatus of this embodiment configured as described above will be described. Here, a case where the applied current is changed under a constant temperature environment will be described.

When a current equal to or lower than the target applied current is applied to the device, the electron overflow phenomenon does not occur in the first active layer 11, so that only the first active layer 11 emits light.
The second active layer 13 does not emit light. At this time, as shown in FIG. 3, the emission spectrum of the output light output from the light emitting window of the present device has a wavelength component specific to the first active layer 11 as shown in FIG. The intensity is relatively high with respect to other wavelength components. Therefore, the operator can confirm that the current applied current is less than or equal to the target applied current by confirming the red color of the light emitted from the device.

Then, when the applied current is increased and exceeds the target applied current, electrons in the first active layer 11 cross the barrier layer 12 and an overflow phenomenon occurs. The overflowed electrons are recombined in the second active layer 13, whereby the light emission phenomenon is started in the second active layer 13. At this time, the emission spectrum of the output light output from the emission window is shown in FIG.
As shown in (b), the wavelength component specific to the second active layer 13, here the green wavelength component, increases. Therefore,
The operator can confirm that the color of light emitted from this device has changed from red to orange, and can recognize that the current applied current has reached the target applied current.

When the applied current is further increased, the emission from the second active layer 13 becomes dominant, and the emission spectrum of the emission color from this device shows the emission spectrum of the second active layer as shown in FIG. 4 (c). The green component unique to 13 is projected. Therefore, the operator can confirm that the green density of the emission color from the present device has become dark and recognize that the current applied current greatly exceeds the target applied current. Of course, if the applied current increases significantly, an electron overflow phenomenon of the second active layer 13 may occur. However, since such a significantly increased applied current can be sufficiently separated from the target applied current, no problem occurs. In addition,
The above operation is the same when the applied current is maintained at a constant value and the external temperature changes.

As described above, according to the semiconductor light emitting device of this embodiment, the emission color changes when the temperature or the applied current reaches a constant value (the target temperature or the target applied current).
It is possible to visually recognize that the temperature or the applied current has reached a certain value. Further, according to the semiconductor light emitting device of the present embodiment, the target temperature and the target applied current when the emission color changes can be easily adjusted by adjusting the barrier height and the thickness of the first active layer. . Further, unlike the conventional case, a display device such as a liquid crystal device is not required, so that the device configuration is simplified and the life performance is not affected by the life of the display device, which can be improved. The present invention is not limited to the above-described embodiments, but can be implemented with various modifications.

[0020]

The semiconductor light emitting device according to the present invention comprises a plurality of active layers having different band gap energies separated by a barrier layer along the electron flow direction, and at least one of temperature and applied current is changed. It is characterized in that the emission intensity from each active layer changes according to the above, and the emission spectrum changes in the visible region, so that when at least one of temperature and applied current reaches a constant value, one active layer An electron overflow phenomenon occurs, a light emitting operation is started in another active layer, and the emission intensity of each active layer changes, and as a result, the emission spectrum changes in the visible region. Therefore, it is possible to display that the temperature or the applied current has reached a certain value by the change of the emission color.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor light emitting device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a three-layer structure due to a difference in bandgap energy of the active layer shown in FIG.

FIG. 3 is a diagram showing how light is output from an active layer.

FIG. 4 is a diagram showing changes in emission spectrum with respect to changes in external temperature and applied current.

[Explanation of symbols]

1 ... GaAs substrate, 2 ... n-type In _0.5 (Ga _1-x A
1 _x ) _0.5 P clad layer, 3 ... Active layer, 4 ... P-type In
_0.5 (Ga _1-x Al _x ) _0.5 P clad layer, 5 ... n-type I
n _0.5 (Ga _1-x Al _x ) _0.5 P current blocking layer, 6 ... p-type AlGaAs current diffusion layer, 7 ... p-type GaAs contact layer, 8 ... p-side Au / Zn electrode, 9 ... n-side Au / Ge electrode , 11 ... First active layer, 12 ... Barrier layer, 13 ... Second active layer.

Claims (1)

[Claims] 1. A plurality of active layers having different bandgap energies separated by a barrier layer along a direction in which electrons flow, each of the active layers being responsive to a change in at least one of temperature and applied current. The semiconductor light emitting device is characterized in that the emission intensity from the light changes and the emission spectrum changes in the visible region.