JPS5911688A - Blue light-emitting element - Google Patents

Abstract

PURPOSE:To obtain a blue color of high luminance brightness by low currents even when ZnSe is used as a material for the blue light-emitting element by laminating an N type first ZnSe layer on a P type ZnTe layer and laminating an N type second ZnSe layer, carrier concentration thereof is larger than the first ZnSe layer, on the first ZnSe layer. CONSTITUTION:The blue light-emitting element consists of a P type GaAs substrate 11, one main surface thereof is a 100 face and carrier concentration thereof is 10<18>/cm<3>, the P type ZnTe layer 12, which is laminated on the substrate 11 and carrier concentration thereof is approximately 2X10<17>/cm<3>, the N type first ZnSe layer 13, which is laminated on the ZnTe layer 12 and carrier concentration thereof is approximately 5X10<16>/cm<3>, the N type second ZnSe layer 14, which is laminated on the first ZnSe layer 13 and carrier concentration thereof is approximately 5X10<17>/cm<3>, and a P-N junction 15 existing in a boundary between the P type ZnTe layer 12 and the first ZnSe layer 13, and each growth layer 12-14 can be formed by an MBE. With the blue light-emitting diode, holes are easily injected to the first ZnSe layer 13 side because the relation, Np>>Nn is formed in the carrier concentration Np of the P type ZnTe layer 12 and the carrier concentration Nn of the first ZnSe layer 13 when a forward bias is applied to the P-N junction 15. A pure blue light is obtained because there is the first ZnSe layer 13 only in said blue light-emitting sensor.

Description

[Detailed description of the invention] The present invention relates to a blue light emitting device.

Light-emitting devices were first used as solid-state lamps to replace conventional pilot lamps, and the range of applications has expanded year by year, including numeric display devices and character display devices, and demand has increased accordingly.
Today, the company has grown to the point where it has become one of the most marketable fields in compound semiconductors.

Recently, as the industry in the office automation field has grown, applications in the field of image display devices are expanding, not just in the conventional television field. Currently, the image display devices mainly used in this field are CRTs;
, TLTs have disadvantages such as requiring high voltage, space limitations, short lifespan, and being susceptible to vibration and other shocks.However, TLTs can be driven with ICs at low voltages, require a small space, and are reliable. There is a desire to develop a flat image display device with high performance, and development of flat image display devices using LCDs, ELs, FDPs, LEDs, etc. is gaining momentum.

In particular, the development of flat image display devices using LEDs capable of color display is seen as a promising future replacement for CRTs. However, at present, red to green LEDs have already been developed and commercialized, but the development of blue LEDs, which is one of the primary colors, is lagging behind.

Materials used for blue LEDs include GaN (gallium nitride), 5ic (silicon carbide), and Zn5e.
(zinc selenium), Zn5 (zinc sulfide), etc. GaN
The development of SiO has progressed to the point of commercialization, but the development of Zn5e has been delayed compared to the above two materials, although it has many excellent features as a material. . The reason is that medium to high quality single crystals cannot be obtained.

(1) Since only n-type conductivity type can be obtained in one direction, P-n
A junction cannot be formed and luminous efficiency cannot be achieved.

■It is difficult to control impurities using conventional liquid phase and vapor phase growth methods.

There are three points to mention.

Recently, molecular beam epitaxial growth (hereinafter referred to as MBE) has been attracting attention as a technique for obtaining single crystal thin films of a quality comparable to or higher than that of conventional crystal growth methods. In other words, when grown using MBE, it is possible to obtain a single crystalline thin film of high quality and having a desired impurity concentration. Therefore, the above problem (1)(i) can be solved by growing the Zn8e single crystal by MBE.

Among I-l compounds, ZnTe (zinc tellurium) is a material that can obtain P-type, but this has a band gap of 2.26 eV, which is smaller than Zn5e, and has a long wavelength of green color or longer. All you can get is luminescence. However, if electrons and holes are recombined on the n-type Zn5e side in a hetero-type Pn junction in which P-type ZnTe and n-type Zn8e are combined, it is possible to obtain blue light with high φ efficiency. be. Therefore, the above problem (c)('I) is also solved.

FIG. 1 shows a conventional P-type ZnTe-n-Zn5e heterojunction light-emitting device based on such knowledge, (11 is a P-type GaAs (gallium arsenide) substrate, (2)
(3) is the P-type ZnTe layer laminated on the substrate, and (3) is the ZnTe layer laminated on the substrate.
The n-type Zn 8e layer is laminated on the nTe layer, and the Z
There is a Pn junction (4) at the boundary between n8el and ZnTe layer (2).
) exists.

In such a structure, the ZnTe layer (2) and Zn
By forming the 5e layer (3) by MBE, a high quality single crystal thin film with few crystal defects such as vacancies 7Qi4 can be obtained, and the carrier concentration Np and 2 of the ZnTe layer (2) can be
The carrier concentration Nn of the nSe layer (3) is Np >> N
By controlling the concentration of each impurity so that 5Zn
Recombination light emission is obtained on the 8e layer (3) side.

In addition, when trying to generate blue light emission in the n-type Zn8e layer (3), the growth temperature (substrate temperature in MBE) is set to about 4
It has been confirmed that the above-mentioned Zn5e layer (3) can be grown by MBE at a temperature of 00° C. or lower and a carrier concentration of 5×1[], 7 or lower. In addition, the growth temperature is 400
It has also been found that when the temperature is above .degree. C., even if the carrier concentration is controlled, long-wavelength light such as green light is emitted.

Therefore, the n-type Zn5e layer (3) is grown by MBE at a substrate temperature of 400°C or less so that its carrier concentration is 5X10/d or more, and the carrier concentration of the P-type ZnTe layer (2) is about 2X10/d or more. By doing so, blue light emission can be obtained in the above Zn5e layer (3).

However, Zn8e has a low carrier concentration of 5x10/d.
Layer (3) has a very high specific resistance of about 5Ω-scratch, and has very poor ohmic characteristics, so the forward rising stain voltage is high and it is difficult to obtain a high current, and the efficiency is low even though it is a Pn junction. is low.

The present invention has been made in view of these points, and the present invention will be described below with reference to one embodiment.

FIG. 2 shows a blue light emitting device according to an embodiment of the present invention, 01)
is a P-type G whose principal plane is the (b) plane and whose carrier concentration is 10/i.
The aAs substrate, Coffin, is a P-type ZnTe layer (I3
) has a carrier concentration of about 5X layered on the ZnTe layer.
The n-type first Znse layer (14) of 10/cIA is laminated on the first Zn5e layer and has a carrier concentration of about 5X1.
0/d n-type second ZnSe layer, 05) is P-type ZnTe
Pn existing at the boundary between 1Q3 and the first Zn5e layer a3
It is a joining.

The above growth layers (121 to (141) can be formed by MBE.

FIG. 6 shows the principle of a molecular beam epitaxial device. In a vacuum container evacuated to a background vacuum level of 5 x 10 Torr, the substrate section (21) and the first to fifth cells ■ to ■ are arranged facing each other. -(28e) are interposed.

The board part (21) is a board holder (support) equipped with a heater mechanism.
and a GaA+s substrate (111) on which an In (I) metal can is attached. 1st to 5th cells ■
〜(branch) contains 8b, Te, Zn, Be, Ga individually in (31 &) 〜(31e) 9,
Around it, each bolt has a heater for heating, and each bolt is equipped with a thermocouple for detecting temperature.

The MBE device itself is well known and controls the temperature of the substrate αυ and each cell, as well as controlling the temperature of each shutter (28a) to (286).
) by appropriately opening and closing the GaA
A p-type ZnTe layer is formed on the s substrate 01), and a first n-type ZnSe
MQ3) and a second ZnSe layer 04) are grown.

Next, the growth conditions for each of the above growth layers are shown in the table below.

Growth conditions for the growth layer: The substrate 01) is maintained at a temperature of 36°C to 370°C.

Furthermore, in the above table, sb (antimony) and Ga (gallium) are impurities in the ZnTe layer and Zn5e layer, respectively.

In the blue light emitting diode of this embodiment, when a forward bias is applied to the Pnn junction 9, the carrier concentration Np of the P-type ZnTe layer 07 and the carrier concentration Nn of the first Znse layer 03) are Np>>Nn. Injection of holes to the side easily occurs. Further, as described above, the first ZnSe layer αQ only has blue light emitting centers. Therefore, pure blue light can be obtained.

In addition, since the carrier concentration of the second ZnSe layer 04) is very high, its ohmic characteristics are excellent. Therefore, if a metal electrode is formed in such a layer, it will be more difficult to form a metal electrode than if it is directly formed in the first Zn5e layer α. The rising stain pressure can be reduced.

In addition, even if an electrode with good ohmic characteristics is obtained at this time, the first Znse layer 03) has a high resistance, so if the layer thickness is large, the internal resistance will become large and there is a risk of internal damage. The first ZnSem (13) is best if it is as thin as possible. However, if the first ZnSe layer (13) has a hole diffusion length or less, a problem arises in that the holes spread to the second ZnSe layer, causing light emission other than blue light emission in the layer.

According to the inventor's experiments, the diffusion distance of the holes is approximately 1 μm.
It turned out to be. Therefore, in this example, the first Zn
SeN03) was set to 1 μm. Note that such layer thickness control can be easily performed by MBE.

In the above example element, the rise voltage υ was as low as 2■, and high-intensity blue light emission was obtained. In addition, the first ZnSe layer (13), which has a high resistance even when holding a current of 10 mA or more, has a thickness of 1 μm.
Because it was so thin, no internal damage or deterioration occurred.

As is clear from the above explanation, the blue light emitting device of the present invention can produce high brightness blue light with a low current even though it is made of Zn8e.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional ZnTe-Zn8e heterojunction type light emitting device, FIG. 2 is a sectional view showing an embodiment of the present invention, and FIG. 6 is a principle diagram showing a molecular beam epitaxial growth apparatus. (1'lr-...-P-type ZnTe layer, 03)...
- First ZnSe layer, circle...second ZnSe layer.

Claims (1)

[Claims] (1) P mZnTe layer, an n-type first Zn5e layer stacked on the ZnTe layer, and an n-type second Zn5e layer stacked on the first Zn5e layer and having a higher carrier concentration than the first Znse layer. A blue light emitting device consisting of layers. (2. In claim 1, the first Zns
A blue light-emitting device characterized in that the e-layer has a carrier concentration of 5x10/d or less, and the second ZnBe layer has a carrier concentration of 5x10/d or more.