JPS6328511B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a blue light emitting device, and particularly to an MIS type blue light emitting device using a novel ZnSe (zinc selenide). Currently, blue light-emitting devices made of materials such as GaN (gallium nitride) and SiC (silicon carbide) have been developed and are on the verge of commercialization. However, because ZnSe has a wide bandgap of 2.7 eV at room temperature, it has not been put into practical use despite being seen as a promising material for blue light-emitting devices.
The reason for this is that ZnSe crystals grown using conventional liquid phase and vapor phase growth methods have many twin crystals, and it is extremely difficult to control the impurity concentration, making it impossible to obtain the desired emission color. Can be mentioned. In addition, in the conventional method, undesirable impurities such as Cu or Na are mixed in during growth, and these undesirable impurities form a luminescent center with a fringe color or a red color, making it impossible to obtain pure blue luminescence. . Recently, it has been discovered that high-quality ZnSe single crystals with stoichiometric composition can be obtained at low temperatures by molecular beam epitaxy (hereinafter referred to as MBE). Since this method performs crystal growth in an ultra-high vacuum atmosphere of 10 ^-10 Torr or less, it is possible to prevent as much as possible the unintended contamination of impurities that would occur in conventional methods. Furthermore, since the growth temperature is as low as 300 to 400°C, crystals without twins and having a stoichiometric composition can be grown. It also has the excellent feature of being able to mix impurities while completely controlling the type and concentration of impurities during crystal growth. According to experiments by the present inventors, the growth temperature is 300℃~
Ga (gallium) as impurity 3× at 400℃
When n-type ZnSe containing about 10 ¹⁶ /cm ³ was grown by MBE, it was found by photoluminescence measurement that pure blue light emission was obtained. Conventionally, it has been considered impossible to obtain ZnSe with p-type conductivity, and it is extremely difficult even using MBE. type ZnSe layer 2,
An MIS (metal-insulating film-semiconductor) structure in which an insulating layer 3 and a metal layer 4 are sequentially laminated is considered. In order to obtain blue light emission in the light emitting device shown in FIG. 1, as mentioned above, the n-type ZnSe layer 2 is
It is sufficient to grow it by MBE at a growth temperature of 300°C to 400°C and a carrier concentration of Ga as an impurity of 3 × 10 ¹⁶ /cm ³ , and when a forward bias is applied to a device configured in this way, it becomes insulated. n-type near layer 3
Blue light emission can be obtained from the ZnSe layer 2. However, in such a light emitting device, the n-type ZnSe layer 2
Since the specific resistance of the capacitor is extremely high at approximately 5 Ω-cm, a forward rising voltage of 40 V or more is required. Furthermore, if a forward current of several milliamps is passed, at which point light emission occurs, dielectric breakdown occurs and the element is frequently damaged, making it unstable as a light emitting element. A possible solution to this problem is to increase the carrier concentration of the n-type ZnSe layer 2 to lower the resistivity (0.05Ω-cm at a carrier concentration of 5×10 ¹⁷ /cm ³ ), but the color of the emitted light depends on the carrier concentration. Therefore, if the carrier concentration is increased, blue light cannot be obtained. It is also possible to reduce the resistance value by reducing the thickness of the n-type ZnSe layer 2 as much as possible, but normally the substrate on which such ZnSe is grown has a smaller band gap than ZnSe from the viewpoint of lattice constant etc.
Since GaAs is used, the above ZnSe layer is
If the thickness is less than 10 μm, the light emitted from the ZnSe layer 2 will be absorbed by the substrate 1. The present invention has been made in view of these points, and aims to provide an MIS type blue light emitting element made of ZnSe that can emit light with high efficiency at low voltage. The invention will be explained below with reference to Examples. FIG. 2 shows an embodiment of the present invention, in which numeral 11 is an n-type GaAs substrate whose one main surface is a (100) plane, and numeral 12 is an n-type GaAs substrate with a carrier concentration of 5×10 ¹⁷ /cm ³ laminated on the substrate.
The first ZnSe layer 13 of the type is laminated on the first ZnSe layer and has a carrier concentration of 5×10 ¹⁶ /cm ³ .
Layer 14 is an insulating layer laminated on the second ZnSe layer, and the insulating layer is made of, for example, SiO ₂ (silicon dioxide).
Consisting of 15 is a metal layer formed on the insulating layer. For both the first and second ZnSe layers 12 and 13, high quality single crystal films can be obtained by MBE. FIG. 3 shows the principle of an MBE apparatus for obtaining the first and second ZnSe layers 12 and 13. The substrate section 21 and the first to third cells 2 are placed in a vacuum chamber evacuated to a background vacuum level of 5×10 ^-11 Torr or less.
2a to 22c are arranged facing each other, and a main shutter 23 and individual shutters 24a to 24c are interposed between them. The substrate part 21 is a substrate holder 2 equipped with a heater mechanism.
5 and a GaAs substrate 11 adhered thereon with an In (indium) metal 26. The first to third cells 22a to 22c are crucibles 28a to 28, respectively.
Zn, Se, and Ga are individually housed in 8c, and a heater 29 for heating the crucible is provided around the crucible, and a thermocouple 30 for detecting the temperature of each crucible is provided. The MBE device itself is well known and controls the temperature of the substrate 11 and each cell, as well as controlling the temperature of each shutter 24.
By appropriately opening and closing ports a to 24c, the first and second ZnSe layers 1 are formed on the GaAs substrate 11 as shown in FIG.
2,13 grows. Note that the above Ga is an impurity. Next, the growth conditions for the first and second ZnSe layers 12 and 13 are shown in the table below. The temperature of the substrate 11 at this time is
The temperature was 360° to 370°C.

[Table] Also, as mentioned above, the first and second ZnSe layers 12 and 13
The thickness of the ZnSe layer consisting of is required to be 10 μm or more so that the emitted light is not absorbed by the substrate 11, and furthermore, since the emission wavelength of the first ZnSe layer 12 is located on the longer wavelength side than the blue color, the emission recombination occurs in such a layer. It is necessary to prevent this from occurring. Considering this point, in this example, the layer thickness of the first ZnSe layer 12 is set to 10 μm, and the
The layer thickness of the 2ZnSe layer 13 was set to 5000 Å. Further, when forming the insulating layer 14, it is preferable to use a sputtering method or a plasma CVD method that allows low-temperature growth, since the ZnSe layer will undergo thermal decomposition if formed at a high temperature. Further, the thickness of the insulating layer 14 is preferably about 60 Å, although it is preferable that it be thinner, but if it is too thin, pinholes etc. will occur. In the device of this example configured in this way, the second ZnSe layer 13 that emits blue light and has high resistance is made extremely thin to 5000 Å, and the same band gap as that of the second ZnSe layer 13 is formed between the second ZnSe layer 13 and the substrate 11. Since the first ZnSe layer 12 with a layer thickness of 10 μm was arranged,
The light emitted by the 2ZnSe layer 13 is not absorbed by the substrate 11. Moreover, the resistance value of the first ZnSe layer 12 is
Since it is very small compared to the first ZnSe layer 13, the first
The resistance value of the entire element is smaller than that of the figure element. Therefore, in the device of this example, highly efficient pure blue light was obtained with a rising voltage of about 8 V, and no dielectric breakdown occurred even when a current of about 10 mA was continuously applied. As is clear from the above description, according to the present invention, an MIS-type ZnSe blue light-emitting device that can emit light with high efficiency at low voltage can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional ZnSe blue light emitting device, FIG. 2 is a sectional view showing a ZnSe blue light emitting device of the present invention, and FIG. 3 is a principle diagram showing a typical MBE device. 11... Substrate, 12... First ZnSe layer, 13...
2nd ZnSe layer, 14...insulating layer, 15...metal layer.

Claims (1)

[Claims] 1 substrate, n-type first ZnSe layered on the substrate
a second n-type ZnSe layer laminated on the first ZnSe layer and having a lower carrier concentration than the first ZnSe layer;
A blue light emitting device consisting of an insulating layer laminated on a 2ZnSe layer and a metal layer laminated on the insulating layer.