JPH0357077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an InP crystal growth method for obtaining a high-purity, high-quality InP epitaxial growth layer used in the field of semiconductor optoelectronics.

[Problems to be solved by conventional technology and invention]

InP is an intergroup compound semiconductor having similar properties to compound semiconductors such as GaAs and GaP. Crystals such as GaAs and GaP are in demand in various fields as materials for optoelectronics, and many attempts have been made to develop high-purity, high-quality crystal growth techniques. In particular, the inventors have discovered that GaAs,
Has high vapor pressure in liquid phase growth such as GaP
We have proposed various growth methods that can control the deviation from the stoichiometric composition by controlling the vapor pressure of As or P.

InP crystals are attracting attention, especially as epitaxial layers for long-wavelength lasers, but there are no reports that take into account deviations from the stoichiometric composition.

Compared to GaAs and GaP, InP has a lower melting point (approximately 1060°C) and a higher dissociation pressure of P.
Compared to materials such as GaP, it is much more difficult to obtain crystals that do not contain defects. It is not possible to obtain epitaxially grown layers of high purity and quality. Furthermore, the slow cooling temperature drop method, which is normally applied to the growth of devices, contains a large number of defects due to the fact that no vapor pressure is applied and the temperature fluctuations during slow cooling.

As a result, this has a great effect on the operating life of the obtained long wavelength laser etc., resulting in a shortened operating life and low efficiency.

[Means for solving problems]

The present invention aims to eliminate the conventional drawbacks and to obtain a high-quality, high-purity InP epitaxial growth layer that does not contain any defects.

In the InP crystal growth method of the present invention, in the InP vapor pressure controlled temperature difference method, P _ppt = 6.2×10 ⁸ exp, where the vapor pressure of P applied from above the solution during crystal growth is taken as the growth temperature Tg. (−1.21/kTgeV) Setting a constant vapor pressure within the range of Torr±30%, and
The method is characterized in that when the temperature of the substrate is raised at Tg, a P vapor pressure of P _ppt = 6.2×10 ⁸ exp (−1.21/kTgeV) Torr or higher is applied to the substrate while the temperature is raised. An example of a growth apparatus used for epitaxial growth is shown in FIG. In order to simplify the explanation, an example of single-layer growth will be described, but it goes without saying that in the case of multi-layer growth, high quality and high purity growth layers can be obtained by providing a large number of crucibles.

Growth boat 1 made of graphite etc.
consists of a slider section including a crucible section 11 and a substrate 13, and into the crucible section 11, In as a solvent, InP as a solute, and an appropriate amount of impurities as necessary are introduced. A vapor pressure applying device 2 made of quartz or the like is added separately from this growth boat. The open end of this device is inserted into the upper part of the crucible, a chamber is provided at the other closed end, and a P for vapor pressure control is placed inside the chamber, and both are connected by a quartz tube with a narrow inner diameter. . The crystal growth furnace is composed of two regions, a growth boat section 3 and a steam pressure control section 4, each having a structure in which a heater wire is wound around a furnace core tube and covered with a heat insulating material. A thermocouple for temperature control is placed near each heater. Thermocouples for temperature measurement are placed by inserting thin quartz tubes into the reaction tubes, directly below the boat section and in the steam control room, and can independently measure temperatures. Furthermore, in order to create a temperature difference between the upper and lower parts of the crucible part, a third
A heater 5 is arranged, and the temperature difference is approximately determined by the heater input, and there is a correlation with the growth layer thickness. All three heaters are controlled to be kept constant during crystal growth.

[Effect]

By setting the P pressure applied during crystal growth to a constant vapor pressure within the range determined by the above formula,
Deviations from the stoichiometric composition of the crystal are controlled, crystals with extremely good crystallinity are obtained, and because the number of defects contained is small, electrical properties such as mobility are 2 to 3 times higher, and optical properties are In the typical characteristics, only an emission peak near the forbidden band width, which does not include any deep levels, is observed.

In addition, by applying a P pressure higher than the optimum vapor pressure and increasing the temperature, the dissociation of P from the substrate crystal is suppressed, and P is transferred to the bottom of the solution without containing defects on the crystal surface, and P is removed in the growth layer. This helps prevent defects from occurring.

〔Example〕

As an example, the applied P when the crystal growth temperature is 750℃
The influence of pressure on the growth layer will be described below.

When crystal growth is performed at the same growth temperature (750°C) and growth time (1 hour) except for the applied P pressure,
The thickness of the InP growth layer obtained regardless of the applied P pressure is
It is distributed in the range of 25 to 35 μm. The substrate crystal used was a Fe-doped high-resistance crystal so that the electrical characteristics of only the grown layer could be measured. Electrodes are formed on the growth layer and the van der Pauw method is applied.
Figure 2 shows the carrier density and hole mobility measured by the Pauw method (Pauw method) plotted against the applied P pressure value. In the figure, the horizontal axis shows the applied P pressure, and the vertical axis shows the carrier density and mobility. The solid line is 77°K,
The dotted line indicates the measured value at 300°K. A crystal grown by applying a certain P pressure exhibits the lowest carrier density and the highest mobility, and each characteristic tends to deteriorate as the pressure becomes lower and higher than this. This specific P pressure (hereinafter referred to as optimal P pressure)
shows a strong correlation with the growth temperature, and shifts to the high P pressure side as the growth temperature increases. As is clear from this figure, when the growth temperature is 750°C, when a P pressure in the range of ±30% of the optimum P pressure of 600 Torr (indicated by the dashed line) is applied, the stoichiometric composition of the crystal deviates. is controlled, and a crystal with low impurity density and high mobility can be obtained. On the other hand, in crystals grown by applying P pressure values outside this range, each property does not depend on the applied P pressure and shows high impurity density and low mobility, and deviations from the stoichiometric composition. This shows that the crystal properties are deteriorated due to the inclusion of a large number of defects caused by. Therefore, by growing by applying a P pressure within the range shown by the dashed line shown in the figure, it is possible to obtain a high-purity, high-quality crystal that does not contain defects due to deviations from the stoichiometric composition of the crystal. The range of such optimal P pressure depends on the growth temperature, e.g.
300±30% Torr at 700℃, 450±30% at 720℃
The extreme value of the characteristic is shown at Torr.

Furthermore, when compared at the same growth temperature, it is more than an order of magnitude higher than the optimum vapor pressure of GaAs or GaP, and the effect of applying vapor pressure is greater than with these compounds. Furthermore, as the vapor pressure increases, the vapor pressure value fluctuates even with slight temperature changes, so it is important to strictly control the temperature of the P chamber. This optimum P pressure can be expressed as P _ppt = 6.2×10 ⁸ exp (−1.21/kTgeV) Torr (1) for each growth temperature. The relationship between Tg and P _ppt is shown in FIG. 3. The horizontal axis is the growth temperature Tg (℃) and the reciprocal of the growth temperature 1/
Tg is shown, and the vertical axis shows the optimum P pressure value in units of Torr. At each growth temperature, the P pressure range to obtain a perfect crystal with good crystallinity and no defects is as follows:
It goes without saying that the P pressure value on the solid line shown in equation (1) is the best, but the P pressure value of ±30% above and below this line (in natural phenomena, the area of 1/e is considered to be the equivalent area) The pressure region is shown by the dotted line, and when compared to the device grown using the conventional method, the luminous efficiency of the device grown by applying a constant P pressure within the range of the dotted line at each growth temperature is the same as that of the conventional method. In addition to these growth conditions, the following are also important factors in order to obtain crystals with good crystallinity.

This is due to the high vapor pressure of P, which is used to control the deviation from the stoichiometric composition of InP. Until this point is reached, the substrate crystal is covered with carbon and exposed to atmospheric gas (H ₂ or inert gas atmosphere). As a result, P having a high vapor pressure is dissociated from the substrate crystal surface before it is inserted into the lower part of the solution, resulting in a large number of defects on the crystal surface. When a substrate crystal with such a surface condition is used and grown by applying a P pressure value very close to the optimum P pressure, a crystal with relatively good surface morphology can be obtained. Most P pressure regions inherit these surface defects and cannot obtain a smooth surface morphology.
As a means to prevent this and obtain a beautiful surface morphology in any P pressure range, it is necessary to increase the P vapor pressure at each temperature above the vapor pressure shown by equation (1) during the temperature rise until the substrate crystal reaches the growth temperature. By applying this vapor onto the substrate crystal surface, P can be dissociated from the substrate crystal, and a defect-free surface can be maintained. An example of this is shown in FIGS. 4a and 4b. (a) shows a micrograph of the crystal surface when exposed to atmospheric gas under a graphite boat without applying P vapor, and (b) shows a micrograph of the crystal surface when the temperature is increased by applying the optimum P pressure. As is clear from the figure, it is clear that a large number of defects occur when no P pressure is applied.

FIG. 5 shows a growth furnace intended to prevent such dissociation of P from the substrate crystal surface. This applies to single-layer epitaxial growth, but needless to say, in the case of multi-layer growth, it is sufficient to increase the number of crucibles in the center.

The role of each crucible is that the first crucible 22 is for applying P vapor until the substrate crystal reaches the growth temperature, and the second crucible 23 is for epitaxial growth and is for supplying a solution 31 into the crucible. including, third
The crucible 24 is a crucible to which P vapor is applied until cooling to room temperature after the completion of growth. Although it is preferable that the second, first, and third P vapor pressure control chambers 25 are separate, the figure shows one using the same P vapor pressure chamber. In reality, the substrate crystal is
The crucible 22 is placed at the bottom of the growth furnace (not shown).
It is important to raise the temperature of the P chamber and the steam pressure controlled reactor (not shown) so that it is higher than the temperature that gives the vapor pressure determined by equation (1), and when the growth temperature is reached. When the P pressure is set to the optimum P pressure, the substrate is inserted into the lower part of the solution, crystal growth is performed for a certain period of time, and after the growth is completed, the substrate crystal is slid to the lower part of the third crucible and exposed for a long time in a high-temperature growth furnace. The same operation as when raising the temperature is required. However, this may not necessarily be necessary when the growth furnace is moved and rapidly cooled.

By using a growth furnace with such a configuration,
By performing crystal growth according to the above-described procedure, a grown layer having a mirror surface in which almost no defects are observed can be obtained.

〔Effect of the invention〕

The optimum P pressure line obtained in the present invention is unexpectedly high for GaAs, GaP, etc., and this is due to the deviation from the stoichiometric composition for the first time in InP due to the application of such a high vapor pressure. We were able to realize a perfect crystal with controlled defects. Therefore, since the InP crystal obtained using this crystal growth method is of high purity and high quality, it does not contain any optical defects, and almost all of the current flowing therein becomes photons. A luminous efficiency of nearly 100% can be achieved, and since deep levels caused by defects are not included, pure luminescence with a narrow half-width near the forbidden band width can be obtained.

Furthermore, since it contains no defects, it generates almost no heat during device operation, making it possible to extend its operating life to an infinitely long time.This is an extremely effective growth method that has not been seen before, and it plays a role in industry. It's huge.

[Brief explanation of drawings]

Figure 1 shows the crystal growth furnace of the present invention, Figure 2 shows the P pressure dependence of carrier density and mobility, and Figure 3 shows the optimum P pressure.
Growth temperature dependence of pressure, Figure 4a is a photograph of the crystal structure of the substrate surface when the temperature is raised without applying vapor pressure, b is a photograph of the crystal structure when the optimum P pressure is applied, and Figure 5 is a photograph of the crystal structure of the substrate surface when the temperature is increased without applying vapor pressure. FIG. 1 is a schematic diagram of a crystal growth furnace of the present invention. 1... Growth boat, 2... Steam pressure control device, 3
... Crystal growth furnace, 4 ... Steam pressure controlled furnace, 5 ... Crucible, 11 ... Solution, 12 ... Slider.

Claims (1)

[Claims] 1 In the vapor pressure controlled temperature difference method for InP, when the vapor pressure of P applied from above the solution during crystal growth is taken as the growth temperature Tg, P _ppt = 6.2 × 10 ⁸ exp (−1.21 /kTgeV) An InP crystal growth method characterized by setting a constant vapor pressure within the range of Torr±30%. 2 In the vapor pressure controlled temperature difference method for InP, a P vapor pressure of P _ppt = 6.2×10 ⁸ exp (−1.21/kTgeV) Torr or higher is applied to the substrate when the temperature of the substrate is Tg when the temperature of the furnace is raised. This is an InP crystal growth method that is characterized by increasing temperature.