JPH0480877B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to N-type diffusion of ZnSe, and in particular to Zn-type diffusion.
Concerning a diffusion method using Tl.

Prior art ZnSe N-type crystals are usually produced by enclosing ZnSe crystals and Zn or Zn-Ga (or In) in a quartz ampoule and heat-treating them at 1000°C for several hours to several tens of hours, as shown in Figure 1. can get.

By this treatment, a ZnSe crystal with a high resistance of about 10 ¹² Ω·cm can be made into a low resistance crystal of about 1.3 to 2 Ωcm. Using this N-type crystal, a blue light emitting diode with an MIS structure has been prototyped. For example, JZ Merz, H. Kukimoto, K. Nassau; JW Shiever, Phys.
Please refer to Rev.B3, 410 (1971) or Hideto Ozaki, Mitsuo Furukoshi; Ibaraki University Faculty of Engineering Research Bulletin, Vol. 30 (1982).

In such conventional methods, Zn or Zn-Ga
Even if a low-resistance N-type crystal is obtained by heat treatment in (or In), effective luminescent centers are difficult to form and the blue luminescent intensity is weak.

Furthermore, Ga and In are relatively active and easily form complex defects with Zn vacancies in the crystal, resulting in strong orange light emission with a peak at around 600 nm (see Figure 2).

Purpose In view of the above circumstances, the present invention provides a method for obtaining a ZnSe N-type crystal with a strong blue emission intensity.

Summary According to the method of the present invention, the above purpose is to produce ZnSe crystals.
This is achieved by heat treatment in a Zn-Tl solution.

Example The present invention will be specifically explained below.

When ZnSe is obtained by crystal growth, it contains a large amount of impurities due to the high growth temperature. These impurities form deep impurity levels,
It forms complex defects with Zn vacancies, significantly impairing crystallinity. Therefore, as-grown ZnSe is pretreated in Zn at 950℃ to 1000℃ for several hours to 1 hour.
Heat treatment is performed for about a day to reduce impurities.

The pretreated ZnSe is placed in a quartz ampoule together with Tl and Zn, the inside is evacuated (eg, 2×10 ^-7 Torr or less), and the mouth is sealed.

The ampoule is fixed in a horizontal furnace as shown in FIG. At this time, ZnSe and Tl/Zn are separated. This is because the solubility of ZnSe in Tl is high, and Tl
This is because if the ratio is too high, there is a risk that it will dissolve during temperature rise. However, when Zn and Tl enter a solid solution state, the solubility decreases, so
In order to suppress the increase in vacancies in ZnSe, completely immerse the ZnSe in the Zn-Tl solution by placing it vertically in the furnace as shown in FIG. The temperature at which this vertical type is switched is Zn−Tl
Please refer to the phase diagram as it varies depending on the mol% of Tl in the solution. For example, in the case of 50 mol%, the temperature is 780°C.
When the temperature reaches a predetermined temperature of, for example, 1000° C. in the state shown in FIG. 4, that state is maintained and liquid phase diffusion is performed. The holding time will depend on the temperature chosen and the desired performance, but for example 24 hours of diffusion at 1000° C. is sufficient. The measurement results in that case are as follows.

Figure 5 shows impurity density and Tl according to Schottky.
This shows the relationship between the ratio of The impurity concentration decreases with increasing mol% of Tl. The reason is not clear, but it may be because Tl ³⁺ replaces the Se lattice position or Tl ⁺ replaces the Zn lattice position and becomes an acceptor and compensates for the N type, forming a complex defect with the Zn vacancy. It is thought that this is because of this.

FIG. 6 is a diagram showing the relationship between the intensity of blue light emitted by cathodoluminescence and the proportion of Tl.
It can be seen that the blue emission intensity increases rapidly from around 50 mol% Tl. Using the relationship shown in FIG. 5, this corresponds to an N-type impurity density of about 3×10 ¹⁶ cm ⁻³ . Although it is not clear what kind of transition process this light emission is based on, it is largely dependent on the N-type impurity density.

In this way, in the liquid phase diffusion in Zn-Tl, a luminescent center with high luminous efficiency is formed in ZnSe with an impurity density of 3×10 ¹⁶ cm ^-3 or less.

FIG. 7 shows the emission spectrum obtained by forming a diode with an MIS structure. A peak of blue light emission is seen around 460 nm, and almost no peak is seen in the long wavelength region.

Figure 8 shows the measurement results for liquid phase diffusion in Zn-Ga similar to Zn-Tl.
Although a peak can be seen on the shorter wavelength side than in the case of Zn-Tl, the problem is the orange emission that has a peak at 600 nm on the long wavelength side, and in reality, blue emission can hardly be observed. From this, Zn-
It is shown that liquid phase diffusion of Tl is effective.

The above results are exemplified for the case of diffusion at 1000℃, but above 1000℃, there is no substantial
A similar effect can be obtained since it is considered as an increase in mol% of Tl.

Although the diffusion time was 24 hours, as shown in Figure 9, the impurity density did not change over time, but the blue intensity due to cathodoluminescence was 10
It cannot be obtained unless it is diffused for more than time.

Therefore, to improve crystallinity by diffusion, at 1000℃
It is necessary to diffuse for more than 10 hours.

Effects of the Invention Next, the effects of the present invention are listed below.

() ZnSe crystal can be made into a low-resistance N-type crystal.

() Impurity density can be controlled by the molar ratio of Tl.

() Pure blue light emission is obtained. The reason for this is that the heat treatment effect of Zn on Zn-Tl is large;
In addition, Tl replaces the Zn vacancy, when the molar ratio of Tl is increased, some of it replaces the Se lattice position of ZnSe and becomes an acceptor, and Tl is stable due to the inactive electron pair effect. Since it is difficult to form complex defects with Zn vacancies, it is conceivable that other light emission levels are reduced, but the present invention is not bound by any particular theory.

[Brief explanation of the drawing]

Figure 1 shows the usual method for obtaining N-type crystals of ZnSe, and Figure 2 shows ZnSe obtained using Ga or In.
Figure 3 is a schematic diagram of one of the apparatuses used to carry out the method of the present invention, and Figure 4 is a diagram showing the relationship between the relative intensity and wavelength of light emitted from an N-type crystal of the present invention. Another schematic diagram of the apparatus used in carrying out the process, FIG. 5, shows the ZnSe N-type according to the present invention obtained by treating ZnSe in a Zn-Tl solution at a diffusion temperature of 1000°C and a diffusion time of 24 hours. Figure 6 shows the relationship between impurity density and Tl ratio according to Schottky of the crystal, and Figure 6 shows the blue luminescence intensity due to cathodoluminescence of the crystal according to the present invention used in Figure 5.
Figure 7 shows the emission spectrum of the MIS structure diode formed using the crystal according to the present invention used in Figure 5, and Figure 8 shows the relationship with the ratio of Tl. ZnSeN obtained by phase diffusion
Figure 9 is a diagram showing the emission spectrum of a diode with the same structure as that used in Figure 7 for the crystal type crystal, and Figure 9 is a diagram showing the relationship between diffusion time, impurity density, and relative blue intensity due to cathodoluminescence according to the method of the present invention. be. 1...Quartz ampoule, 2...Zn or Zn-Ga
(In), 3, 4...ZnSe crystal, 5...Tl, 6...
Zn, 7...Quartz ampoule, 8...Support rod, 9...
...Thermocouple, 10... Furnace tube, 11... Heater,
12...Zn-Tl solution.

Claims (1)

[Claims] 1. An N-type diffusion method characterized by heat-treating ZnSe crystals in a Zn-Tl solution containing 50 mol% or more of Tl at 1000°C or more for 10 hours or more.