JPH0329194B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal diffusion method for -group compound semiconductors, and particularly to a vapor pressure controlled diffusion method and apparatus that do not cause deviation from stoichiometric composition.

Currently, as a light emitting diode in the visible light range,
Various crystals have already been put into practical use in the wavelength range from red to green, but the realization of a light-emitting diode that emits blue light, one of the three primary colors of light, is eagerly awaited. To achieve blue light emission, at room temperature
It is necessary to have a forbidden band width of 2.6eV or more,
Such semiconductor materials include ZnS, ZnSe,
There are -, -, - group compound semiconductors such as GaN and SiC. However, each crystal has its own drawbacks, such as the fact that crystal growth takes place at high temperatures and the difficulty of obtaining crystals with both P and N-type conductivity. There were problems such as difficulty in obtaining

Among these, - group compounds are particularly likely to emit blue light, so ZnSe will be used as an example for explanation.

ZnSe crystal has a forbidden band width of 2.67 eV or more at room temperature.
It is a crystal that can be expected to emit light at short wavelengths ranging from blue to violet. However, since each of the constituent elements has a high vapor pressure, it is difficult to control lattice defects and impurities, and there are problems such as difficulty in forming a pn junction by adding impurities.

For this purpose, the present inventor has developed a - group compound with a small deviation from the stoichiometric composition by using a high vapor pressure component element as a solvent and performing crystal growth under the control of the vapor pressure of a low vapor pressure component element. A crystal growth method by which crystals can be obtained is provided in Patent No. 1313593 (Japanese Patent Publication No. 37077/1983).

In addition, the present inventor has discovered that as a p-n junction formation method,
The epitaxial growth method that is widely used for - group compound semiconductors is applied to - group compound semiconductors. Taking ZnSe as an example, we have patented an epitaxial growth method that controls the vapor pressure of Zn using Se as a solvent. No. 1328673 (Special Publication No. 60-50759), etc. Also, in JP-A No. 59-6583, the n-type
A method is provided for manufacturing high efficiency blue ZnSe light emitting diodes by epitaxially growing a p-type ZnSe layer on a ZnSe substrate.

The present invention provides a method and a diffusion device for diffusing impurities while controlling the deviation from the stoichiometric composition of the crystal when forming a p-n junction by diffusion. To do this, immerse it in a solution of a group element, which is a low vapor pressure component element among the constituent elements, to which a few mol% of a group or group impurity is added.
By thermal diffusion while controlling the vapor pressure of the group element of high vapor pressure component elements, it is possible to
form a shape diffusion layer. On the other hand, when forming a p-type diffusion layer in an n-type crystal, several group or group impurities are added.
By immersing it in a solution of a high vapor pressure component group element added in mol% and thermally diffusing the low vapor pressure component group element under vapor pressure control, it is possible to minimize deviations from the stoichiometric composition. The present invention provides a vapor pressure controlled diffusion method and a diffusion device for obtaining a group compound semiconductor device. Next, examples will be given and explained.

Example 1 A typical crystal of a − group compound semiconductor
Taking the case of ZnSe as an example, we will discuss specific examples in the first section.
As shown in the figure. Quartz tube 1 with inner diameter 5~7mmφ and wall thickness 1mm
1, a p-type ZnSe single crystal substrate (thickness 300~
500 μm) 12 is installed, and a quartz back-up spring 13 is placed on top of it to prevent the substrate crystal from floating.
Approximately 1 to 2 g of Zn14 and 3 to 10 mol % of Ga15 of the group as an n-type diffusion impurity are added relative to Zn. The upper part of the ampoule contains Se, a high vapor pressure component element.
A vapor pressure chamber 16 is provided, and a quartz spacer 17 is provided so that the passage between the two chambers becomes narrow in order to suppress the direct reaction between Se and Zn as much as possible and to isolate heat between the two chambers. It is inserted and sealed at a vacuum level of approximately 1×10 ^-6 mmHg. Various experiments were conducted regarding the diffusion temperature, but the diode characteristics were best when diffused at 700-850℃, especially 720-760℃ for about 1 hour.
In addition, light emission from deep levels is suppressed. Under these conditions, vapor pressure controlled diffusion was performed by varying the Se pressure.
An n-type layer with a thickness of several μm was formed. crystal in this state
20, the entire crystal surface is n, as shown in Figure 2.
Since it is covered with a shape diffusion layer 21, the directions of the arrows a and a' are removed by cleaving, and the bottom surface is removed by wrapping to form a 0.5 x 0.5 mm square chip as shown in FIG. This crystal is treated with an etching solution such as a Br-methanol mixture, Au22 is evaporated as the p-side electrode (Fig. 2 (3)), In is placed on the n-type layer, and the Diode chips were fabricated by sintering at ℃ for 10 minutes (second
Figure (4)), a light emitting diode was prototyped by mounting it on a stem.

FIG. 3 shows the Se pressure dependence of the ratio of the blue emission peak intensity and the deep level emission peak intensity of the injection emission spectrum at room temperature. According to this, the emission peak intensity ratio is the smallest near the Se pressure of 150 Torr, and the blue emission peak is the most dominant. In other words, when forming a diode, it is possible to form a diffusion layer with the least deviation from the stoichiometric composition.
This indicates that Se pressure was applied. This makes it possible to control the Se vacancies generated during diffusion in the Zn solution, but it is possible to control the Se vacancies generated during diffusion in the Zn solution.
The conductivity type conversion was achieved by introducing impurities rather than forming a shaped layer. By adding several mol% of Ga, a group element, as an impurity, by substituting the lattice position of Zn,
An n-type diffusion layer was reliably formed and a ZnSen type layer with good crystallinity could be obtained by reducing the deviation from the stoichiometric composition by adjusting the optimum Se pressure. The thickness of the diffusion layer is 5μm at 740℃, 1hr, and 18hr.
20 μm was obtained. Although FIG. 1 shows a specific example in which the ampoule is placed vertically, it is also possible to use an ampoule of the same shape and perform heat diffusion in the same manner in the case of a horizontally placed ampoule.

Also, conversely, using an n-type - group compound semiconductor,
When the p-layer is obtained by thermal diffusion, simply performing a thermal diffusion process will result in crystals lacking in low vapor pressure components or in excess of high vapor pressure components, resulting in defect-free crystals with controlled stoichiometric composition. cannot be obtained. To overcome this drawback, the deviation from the stoichiometric composition can be precisely controlled by compensating for the lack of low vapor pressure components during crystal growth. However, if a low vapor pressure component element is simply introduced into a high vapor pressure component element, which is a solvent, the reaction between the two will proceed and a crystal will be formed. As a result, the vapor pressure of the crystals will show different values, and the stoichiometric composition of the grown crystal will change, making it impossible to obtain a uniform crystal. In other words, it is desirable that the vapor pressure of the low vapor pressure component element be applied at a nearly constant amount during crystal growth, so that the direct reaction of both components is minimized, and the vapor pressure of the low vapor pressure component is kept at a nearly constant value during crystal growth. It is necessary to adopt a configuration in which the voltage is applied from above the solvent.

Example 2 A specific example is shown in FIG. 4, taking the case of ZnSe as an example as in Example 1. Inner diameter 12~14mm
A diameter of 8 to 10 mm is set vertically in a quartz holder 41 at the right end of a quartz tube 40 with a wall thickness of 1.5 to 2.0 mm.
Sliced into 300-500μm thick slices with mmφ
The ZnSen type substrate 42 is set, and Se
About 5 to 8 g of 43 and 8 to 20 x 10 ^-3 mol % of Li44 of the LA group as a p-type diffusion impurity, for example, are added. A Zn vapor pressure chamber 45, which is a low vapor pressure component element, is provided on the left side of the ampoule, and there is also a passageway between the two chambers in order to suppress the direct reaction between Se and Zn as much as possible and to isolate heat between the two chambers. A quartz spacer 46 is inserted so that it becomes thinner, and it is sealed with a degree of vacuum of about 1×10 ^-6 mmHg. This ampoule is placed in a vertical or diagonal furnace as shown in FIG. 4 to perform vapor pressure diffusion. After the vapor pressure diffusion is completed, immediately remove the ampoule or the entire furnace or the ampoule from the furnace and
By tilting as shown in Figure 2, Se solution and
Diffusion is terminated by separating the ZnSe substrate.

The Zn pressure and Se pressure at which the stoichiometric deviation is minimized are expressed by the following relational expressions. 1/T in Figure 5
The relationship between [〓] (T indicates the temperature of the Se solution) and the optimum Zn pressure [Torr] is shown. This relationship can be expressed as a formula: Popt=4.77×10 ⁶ exp (−0.790/K・TseeV) [Torr] …(1) Popt: Zn optimum vapor pressure [Torr] K: Boltzmann constant Tse: Thermal diffusion temperature [〓 ].

Therefore, once the thermal diffusion temperature of Se is determined, the optimal Zn pressure can be determined by substituting it into equation (1). for example,
If the Se thermal diffusion temperature is 700°C, then by substituting Tse = 973 [〓] into equation (1), it is sufficient to maintain Popt = 389 [Torr], that is, the Zn part at about 840°C. Also, in the case of thermal diffusion in a Zn solution, the thermal diffusion temperature and Se vapor pressure can be determined by using equation (1). For example, if thermal diffusion occurs in a Zn solution at 800℃, the Zn pressure at 800℃ (1223〓) (Pzn=
234.3Torr) into equation (1), Tse=923.2
[〓], that is, it is sufficient to control the Se pressure at 448 [Torr].

The vapor pressure controlled diffusion method and diffusion device according to the present invention can form a p-n junction with a small deviation from the stoichiometric composition and extremely few defects, and therefore, it is suitable for industrial use because it significantly increases luminous efficiency and lifetime. It is also of high value.

[Brief explanation of drawings]

Figures 1 and 4 show the structure and temperature distribution of the ampoule used in the present invention, and Figure 2 shows the structure and temperature distribution of the ampoule used in the present invention.
Figure 3 shows the manufacturing process of a ZnSe crystal diode using vapor pressure controlled diffusion. Figure 3 shows the Se pressure dependence of the ratio of the blue emission peak intensity of the injection emission spectrum at room temperature to the emission peak intensity of the deep level. 1/T
It is a diagram showing the relationship between [〓] and the optimum Zn pressure [Torr]. 12... p-type ZnSe substrate, 14... Zn solution, 1
5...Ga, 16...Se vapor pressure chamber, 42...n type
ZnSe substrate, 43...Se solution, 44...Li, 45
...Zn vapor pressure chamber.

Claims (1)

[Claims] A 1-group compound semiconductor crystal is heated at a constant temperature in a solution to which a predetermined amount of a group or group n-type impurity is added together with a low vapor pressure component element under the control of the vapor pressure of a high vapor pressure component element. A vapor pressure controlled diffusion method of impurities into - group compounds characterized by thermal diffusion at . Thermal diffusion of a 2-group compound semiconductor crystal at a constant temperature in a solution containing a predetermined amount of a group or group p-type impurity together with a high vapor pressure component element under vapor pressure control of a low vapor pressure component element. A vapor pressure controlled diffusion method of impurities into - group compounds, characterized by: 3. A diffusion chamber in which a solution of a group or group element containing predetermined impurities is placed and a semiconductor crystal is placed under or in the solution; a vapor pressure of the group or group element is generated and the vapor pressure is applied to the diffusion chamber. a vapor pressure chamber in which a group element or a group element is arranged, and the passage between the diffusion chamber and the vapor pressure chamber is formed to be effectively narrow.
Vapor pressure control diffusion device for group compounds.