JPS6042199B2 - ZnSe crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the crystal growth of group 1-2 compound semiconductors, and particularly to a method for growing ZnSe crystals using a solution.

Since ZnSe is a direct transition type and has a wide forbidden band (2.67 eV at room temperature), it emits light at an even shorter wavelength than green (
It is a crystal that can be expected to have a color (ranging from blue to purple).

However, in crystals obtained by the conventional melt growth method, many Be vacancies with high vapor pressure occur, and because these act as doors, only n-type high-resistance crystals are usually obtained. However, a practical p-type crystal has not been obtained, and therefore a pn junction has not been formed. In other words, when the vacancy of this Group Ⅰ element combines with the impurity, it acts as a non-emissive center or forms a deep level, so even if a p-n junction is formed, the generation efficiency is extremely low or it is a deep level. This means that only those where the light emission from the position is dominant can be produced. Therefore, there is a strong desire for the emergence of p-n junctions formed from highly perfect crystals that do not contain deep levels.For this purpose, liquid phase formation methods using various solvents have been attempted in various places. However, none of them have been able to obtain high quality ZnSe crystals. The inventor of the present application used Be as a solvent, and Z
A separate patent has provided a crystal growth method that can obtain ZnSe crystals with little deviation from the stoichiometric composition by performing crystal growth under n-pressure control.

In addition, the inventor of the present application applied the epitaxial growth method, which is widely and generally used for ■-V intergroup compound semiconductors, as a p-n junction formation method to ■-■ intergroup compound semiconductors, and
Taking Se as an example, an epitaxial growth method using Be as a solvent and controlling the vapor pressure of Zn was proposed in Japanese Patent Application No. 78620/1986.
No. 55-149093. Further, Japanese Patent Application No. 57-115894 provides a highly efficient blue ZnSe light emitting diode by epitaxially growing a p-type ZnSe layer on an n-type ZnSe substrate. In the present invention, by adding the optimal vapor pressure of Zn to the growth temperature when Be is used as a solvent, there is no small deviation from an extremely good stoichiometric composition, and deep impurity levels are minimized. The present invention provides a growth method for obtaining crystals with a reduced density.

A specific example for growing a ZnSe Berg crystal under the vapor pressure of Zn using Be as a solvent is shown in FIGS. 1 and 2.

In general, when a quartz tube with an inner diameter of about 10 wgnφ is processed and a quartz crucible 4 as shown in Fig. 1 is manufactured, the wall thickness is 2 wrm.
It can withstand explosions up to about 8 to 1000 atmospheric pressures. However, if the pressure exceeds m atm, there is an extremely high risk of explosion if the crucible is distorted or has thin sections. , air/Ar-N2
It is necessary to reduce the effective pressure applied to the quartz crucible 4 by applying pressure with a gas such as quartz crucible 4. When pressure is applied to the outside of the quartz crucible, the thermal conductivity of the gas increases in proportion to the pressure, so setting the temperature difference between the crystal precipitation area and the source crystal area is important. Generally, the temperature difference between the two is suitably about 10 to 50°C. Although there is no particular limitation on the amount of source crystals, it is preferable that the amount of source crystals be about 2 to 20 volts per 10 y of solvent. There are various methods for setting the source crystal, but it is preferable to set it based on the relationship between the specific gravity of the solvent and the crystal to be grown.If the specific gravity of the solvent is large, it is preferable to set the source crystal by floating it on the solution. It is relatively easy to set up.

However, in the case of the opposite relationship, the source crystal dissolves in the solvent. Therefore, the purpose can be achieved by making the relationship between the two chambers into a horizontal structure as shown in FIG. 1. In addition, if only high vapor pressure components of the constituent elements are used as a solvent, it is possible to compensate for the high vapor pressure components of the grown crystal, but conversely, the lack of low vapor pressure components or the high vapor pressure components This results in the growth of excessive crystals, making it impossible to obtain defect-free crystals with controlled stoichiometric composition in the strict sense.

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, it is simply a high vapor pressure composition with a low vapor pressure component element as a solvent. When added to a component element, the reaction between the two proceeds and crystals are formed, so the vapor pressure of the low vapor pressure component element will show different values at the start and end of growth. The stoichiometric composition of the crystals changes, making it impossible to obtain uniform crystals. That is, during growth, it is desirable that the vapor pressure of the low vapor pressure component element be applied at a nearly constant value, so that the diameter reaction of both components is minimized, and the vapor pressure of the low vapor pressure component is kept constant during crystal growth. It is necessary to have a configuration in which a substantially constant value is applied from above the solvent. The growth method and growth apparatus according to the present invention will be explained. Zn
In order to keep the vapor pressure of
It is necessary to use a growth ampoule 4 as shown in FIGS.

That is, another chamber 21 is created in addition to the crystal precipitation section 12 and the source crystal 13, and the Zn 22 is placed in this chamber, thereby making it possible to control the vapor pressure to a certain extent. However, if the connecting pipe 23 between the crystal growth section and the Zn chamber is thick, high vapor pressure vapor phase Se. Due to the gas phase reaction with 5Zn, ZnSe is formed in the Zn chamber 21, making it impossible to control the vapor pressure of Zn. In order to avoid this, the surface area of See24 in the crystal growth section should be made as small as possible, and the surface area of See24 on the source crystal setting section and connecting pipe should be
It is effective to provide a roof 25 on the top of the area e, and it is preferable to have a structure in which Zn vapor is applied only from above the crystal precipitation area. Moreover, between the crystal precipitation part and the Zn chamber,
- It is effective to make the passage narrow for the purpose of thermal separation between the two chambers. The method for making it thinner is to insert a quartz vibrator 26 with a narrow inner diameter after inputting the raw materials, and insert the vibrator with a narrow inner diameter and an outer diameter approximately equal to the inner diameter of the ampoule into the tube that connects both areas inside the ampoule. In addition, a heat sink 9 is placed at the tip of the quartz ampoule to allow heat to escape from a single point in the crystal growth area.The specific shape of the ampoule, temperature distribution and vapor pressure in each part An example of the relationship with the distribution is shown in Figures 1 and 2.The temperature of the crystal precipitation part 12 is kept constant at 1050 °C, and a temperature difference of 5 to 50 °C is provided between it and the temperature T2 of the source crystal part 13. It is necessary to keep the temperature of each part constant during growth, and this temperature difference is one of the factors strongly related to crystallinity.Next, the temperature of the vapor pressure control chamber 21 is controlled so that it can be controlled independently. In order to find the deviation from the stoichiometric composition, growth was carried out under various temperature conditions using the temperature of the vapor pressure control chamber as a parameter.9000'
In the high temperature range above C, the relationship between Zn vapor pressure and temperature is as follows:
PCAReview969Jurlepp. 285~
Pp. It can be determined from a relational expression obtained by extrapolating the data of HOnig et al. for 3O5.

Further, in the temperature range of 6000C to 800C, the relational expression between the vapor pressure of Zn and the temperature can be more clearly determined.

These relational expressions are as shown in Table 1, for example.

A specific example will be described.

Se:20y. ．． ZnSe: 5y. ．． Zn:4y material was made into an ampoule of the shape shown in Figure 1 (height: 3cm, length: 8α).
, a total capacity of 10 cc), in a shape such that Se is connected between the crystal precipitation part and the source crystal part, and put it into an ampoule, and seal the ampoule with a vacuum degree of about 1 x 10-6 gourd Hg. Crystal growth was carried out at a temperature of 1050°C in the crystal precipitation part, a temperature of 1060°C in the source crystal part, and a temperature of 1087°C in the Zn. We were able to obtain bulk crystals of .

A crystal grown at a constant temperature with the addition of a group 1a element such as Ll under the same conditions other than the Zn pressure applied during growth exhibits p-type conduction at any Zn pressure.

A piece of the ZnSe single crystal grown in this way is used as a substrate, and by diffusing Zn in the Zn melt, n
It has been successful to form layers and thereby form p-n junctions.

A specific example is shown in FIG.

As shown in the figure, an ampoule 31 in which a ZnSe crystal 34 was immersed in a Zn solution 32 was sealed in a vacuum and heat-treated at 1000° C. to form an n-type layer of about several μm. One side of this crystal was lapped, polished, and treated with an etching solution such as a Br-methanol mixture, and Au was evaporated as the p-side electrode.
1-powder sintering was carried out at 100°C, then In was placed on the n-side electrode, and 1-powder sintering was performed at 320 to 340°C in the same Ar atmosphere to produce a diode chip, which was then mounted on a stem and used as a light-emitting diode. We made a prototype. FIG. 5 shows the emission/spectrum of the 77th test K, in which a peak near the forbidden band (IEdge) and a peak involving a deep level (IDeep) are usually observed.

The intensities of these two peaks depend on the applied Zn pressure, and Figure 6 shows the intensity ratio of IDeep/IEdge when Zn
Plotted against pressure. As is clear from this figure, the graph showing the intensity ratio of both peaks is 7. It has a minimum value near the leakage pressure, and the strength ratio is large even below that pressure. That is, 7. This shows that the deep level density in the grown crystal is minimized when a pressure close to steam pressure is applied. However, in the case of diffusion in a Zn solution, Zn atoms are thought to enter the interstitials of the ZnSe crystal, and conversely, a large number of Se vacancies are also generated, resulting in a large deviation from the stoichiometric composition. Crystallinity also deteriorates.

This drawback can be solved by controlling the Se vapor pressure, but there is a risk that the diffusion layer will react with Zn during diffusion and become highly resistive. is substituted at the lattice position of Zn in group ■,
A ZnSen type layer with good crystallinity could be obtained by maintaining the diffusion layer reliably in the n-type and further reducing the deviation from the stoichiometric composition by Se pressure. j A concrete example is shown in FIG.

A quartz tube 41 with an inner diameter of 5 wftφ and a wall thickness of 1 wm is made of Zn32.
about 1y, . Ga42 3-51T10I%, and Zn
Insert the Se substrate 33. A Se vapor pressure chamber 43 is provided in the upper part of the ampoule. In order to suppress the reaction of 5Zn as much as possible, a quartz gate spacer 44 was inserted, and the
It is sealed with a vacuum level of about 7LHg. Various experiments were conducted regarding the diffusion temperature, but the diode characteristics were best when diffusion was performed at 740°C for about 1 hour. Under these conditions, vapor pressure controlled diffusion was performed by varying the Se pressure. formed a layer. This crystal was processed under the same diode manufacturing conditions as described above to fabricate a diode. FIG. 7 shows the Se pressure dependence of the blue emission peak intensity of electroluminescence when emitting light at room temperature.

According to this, the Se pressure is approximately 150T0rr (575℃
) The emission intensity is the strongest near ), indicating that the Se pressure most effectively acted on the diode. From these values, 1/TCKO] and Zn pressure [TOrr]
FIG. 8 shows the relationship.

This relationship can be expressed as POpt. :Zn optimum vapor pressure [
TOrO k: Boltzmann constant T. e: Growth temperature [0K],
There is a relationship in which the optimum Zn pressure also increases in proportion to the increase in growth temperature.

The optimal Zn pressure range can be wide, but according to the general interpretation of natural phenomena, the range of 1/e,
That is, it can be said that about ±30% is the most preferable range of Zn pressure.

For example, if the ZnSe bulk growth temperature Tse=800°C, P from equation (1).

pt. (Optimal Zn pressure) is in the range of 936±281 [TOrr]. The crystal obtained by applying this Zn pressure is Se
It has no inclusions and has extremely few defects, and has a high degree of integrity. Furthermore, the reduction of Zn vacancies not only reduces the light emission at deep levels where they are involved, but also reduces the concentration of oxygen and excitons near the absorption edge. It is an industrially valuable growth method because it strengthens the generation between bands, greatly increases the generation intensity at room temperature, and significantly increases the luminous efficiency.

[Brief explanation of drawings]

l Figures 1 and 2 show the structure and temperature distribution of the quartz ampoule used in the present invention, Figure 3 shows the structure and temperature distribution of the Zn diffusion ampoule, and Figure 4 shows the structure of the Se vapor pressure controlled Zn diffusion ampoule. and temperature distribution, Figure 5 shows a typical 77pK
Figure 6 shows the emission spectrum of IDeep/IEd.
Figure 7 shows the Se pressure dependence of the blue emission peak intensity of electroluminescence at room temperature, and Figure 8 shows the relationship between 1/T [0K] and Zn pressure. It is. 12... Crystal precipitation part, 13... Source crystal part, 21... Vapor pressure control part, 9......
heat sink.

Claims (1)

[Claims] 1. In the liquid phase growth of ZnSe using Se as a solvent, where k is Boltzmann's constant and T is the growth temperature expressed in absolute temperature, the pressure of Zn, which is a low vapor pressure component element, is P_z_n=4.77×10^6 for each growth temperature
exp{(-0.790/k・T_s_e)eV}±3
A ZnSe crystal growth method characterized by growing at a constant temperature under a constant vapor pressure in the range of 0% [Torr].