JPH0476328B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor crystal and a method for manufacturing the same, and in particular to a high quality semiconductor crystal that is a quantum type infrared detection material.
The present invention relates to a semiconductor crystal suitable for a semiconductor crystal substrate useful for manufacturing HgCdTe single crystals, etc., and a method for manufacturing the same.

[Conventional technology]

HgCdTe as a material for quantum infrared detectors
The HgCdTe crystal used for this purpose is known to have excellent properties.
A composition represented by the formula: Hg _1-z Cd _z Te (where z is a number from 0.1 to 0.4) is used. High uniformity is required for the composition of the crystal, and z in the above formula
It is required that the variation in the entire crystal be 0.01 or less.

Recently, in the field of infrared detection, there has been a demand for a detection method that can detect infrared images, for example, instead of the conventional single-element spot detection method. In addition to being of high quality, the HgCdTe crystals that are used in this process are required to be large in size.

However, in HgCdTe crystals, it is extremely difficult to produce large crystals with a uniform composition because Hg has a very high vapor pressure and Hg tends to segregate violently. Therefore, a method of manufacturing a large-area HgCdTe crystal by epitaxially growing an HgCdTe crystal on another suitable bulk crystal substrate was proposed. A ZnCdTe substrate in which a portion of Zn is substituted with Zn is known.

[Problem that the invention seeks to solve]

However, although large CdTe single crystals can be obtained by, for example, the vertical Bridgeman method, there is a lattice mismatch of about 0.2 to 0.3% between the CdTe single crystal and the HgCdTe crystal that is epitaxially grown on it.
When using a CdTe single crystal substrate, CdTe crystal and
The disadvantage is that a large number of misfit dislocations occur at the interface of the HgCdTe crystal, and the quality of the grown HgCdTe crystal is low.

On the other hand, ZnCdTe crystals have been developed in an attempt to eliminate the misfit dislocations mentioned above by matching the lattice constants by adding Zn, but it has been attempted to eliminate the misfit dislocations described above by matching the lattice constants through the addition of Zn. When manufactured, the segregation coefficient of Zn with respect to CdTe is as large as 1.3 to 1.4, so the concentration of Zn changes as the crystal grows due to segregation of Zn in the crystal. As a result, the lattice constant of the resulting crystal changes and becomes non-uniform, making it difficult to obtain a crystal substrate with good lattice matching with the HgCdTe crystal.

In addition, ZnCdTe crystal substrates grown by bulk crystal growth methods such as the Bridziman method have approximately 100% dislocations.
Distributed in the crystal at a high density of 10 ⁴ to 10 ⁶ /cm ² , these dislocations form a remarkable cell structure and lineage structure, and the disadvantage is that crystal defects such as Te inclusions are likely to occur. It also has

Therefore, an object of the present invention is to provide a semiconductor crystal suitable for a semiconductor crystal substrate having almost the same lattice constant as that of these single crystals and uniform, and a method for manufacturing the same, in order to epitaxially grow high-quality HgCdTe single crystals, etc. It's about doing.

[Means for solving problems]

In order to solve the above problems, the present invention solves the above problems by formula (): Zn _l Mn _n Cd _1-(l+n) S _p Se _q Te _1-(p+q) () [where l, m , p and q are numbers greater than or equal to 0, l and p are not 0 at the same time, and m and q
is not 0 at the same time. ], and along one direction, i.e., the direction of crystal growth, the formula (): a=6.4825−0.38lk(Zn)(1−g) ^(k(Zn)−1) − 0.16mk(Mn)(1-g) ^(k(Mn)-1) −0.6505pk(S)(1-g) ^(k(S)-1) −0.433qk(Se)(1-g) ^{(k (Se)-1)} [Here, g is solidification rate, k (Zn), k (Mn), k
(S) and k(Se) represent the segregation coefficients of Zn, Mn, S and Se, respectively, and l, m, p and q are the same as above]. ≦
The present invention provides a semiconductor crystal whose composition is substantially constant within a range of 0.6.

The average composition of the semiconductor crystal of the present invention is the above l,
Although determined by m, p, and q, the actual composition changes along one direction of the crystal (which coincides with the crystal growth direction when normal solidification is established, as described later). However, the lattice constant expressed by formula () is constant, and the lattice constant of the crystal is uniform. The segregation coefficient of each element added as a dopant is larger than 1 for Zn and S (k(Zn),
k(S)>1), and smaller than 1 (k
(Mn), k(Se)<1), the contributions of these two groups of elements to the lattice constant a cancel each other out, and as a result, a becomes constant.

The segregation coefficient of each additive element for CdTe is k(Zn) = 1.35, k(Se) = 0.9,
k(S)=1.4, and k(Mn)=about 0.93. 2
If more than one species is added, it may vary slightly, so the segregation coefficient value needs to be adjusted depending on the amount added.

The fact that the lattice constant a is substantially constant means that variation is allowed within a range that does not cause problems in terms of lattice matching, and usually means that the variation is within a range of ±0.01%.

In the crystal of the present invention, the lattice constant a is 6.4000~
It can be adjusted in the range of 6.4825A, and when a substrate is created from this and used for epitaxial growth of HgCdTe crystal, a = 6.462 ~
6.476A range, especially 6.464A or
6.465A is preferred.

The crystal of the present invention has the formula (): Zn _l ′Mn _n ′Cd _1-(l ′ _+n ′ ₎ S _p ′Se _q ′Te _1-(p ′ _+q ′ ₎ () [where l , m', p' and q' are numbers greater than or equal to 0, l' and p' are not 0 at the same time, and m' and
q′ is not 0 at the same time, and furthermore, the formula: a′=6.4825−0.38l′k(Zn)(1−g′) ^(k(Zn)−1) −0.16m′k(Mn)(1−g ′) ^(k(Mn)-1) −0.6505p′k(S)(1−g′) ^(k(S)-1) −0.433q′k(Se)(1−g′) ^{(k(Se )-1)} () (In the formula, g' is a variable that changes within the range of 0≦g'≦1, and k (Zn), k (Mn), k (S) and k (Se) are
The number a', which represents the segregation coefficient of Zn, Mn, S, and Se with respect to CdTe, respectively, is selected such that the numerical value a' is substantially constant at least in the range of 0≦g′≦0.6. ].

It can be produced by normally solidifying a melt having a uniform composition expressed by:

When Zn, Mn, S, or Se is added to a CdTe crystal, Zn and Mn replace Cd, and S and Se replace Te, each having the effect of decreasing the lattice constant of the CdTe crystal depending on the substitution rate. show.

Now, if the amount of decrease in the lattice constant per unit substitution rate of element M is d _M and the substitution rate is C _M , then the lattice constant a of the CdTe crystal is expressed by the formula () a=6.4825−d _M C _M () It will be done. On the other hand, when a crystal is grown using a crystal growth method that follows normal solidification, segregation of the added element M occurs, so the concentration of M (substitution rate) in the resulting crystal
C _M is calculated by the following formula C _M = C _MO k(1-g) ^k-1 () [Here, C _MO is the average substitution rate of the additive element M, k
is the segregation coefficient of the additive element M with respect to CdTe, and g is the solidification rate, that is, the proportion of the crystallized portion of the total melt to be crystallized]. Therefore, the element M is CdTe
When solidified normally, the lattice constant a of the crystal at the solidification rate g is calculated from equations () and () by the following equation () a=6.4825-d _M C _MO k(1-g) ^{k -1} () indicates the value.

As can be seen from equation (), elements with a segregation coefficient k greater than 1 gradually increase their lattice constant a as g increases, that is, with crystal growth, and conversely, elements with a segregation coefficient k smaller than 1 gradually decrease a. to work. Based on this fact, the crystal of the present invention uses at least one of Zn and S, which has a segregation coefficient of greater than 1, and at least one of Mn and Se, which has a segregation coefficient of less than 1, as additive elements for CdTe. Therefore, the two effects on a cancel each other out, and the lattice constant a increases along the crystal growth direction.
is kept constant.

The above formula () shows the initial composition of the melt when producing the crystal of the present invention by normal solidification, and the formula () in the formula
l', m', p' and q' are respectively the substitution rates of Zn, Mn, S and Se in the initial composition, and the average substitution rates l, m, p in equation () after crystal growth.
and the value corresponding to q. Also, Zn, Mn,
The amount of lattice constant reduction brought about per unit substitution rate of S and Se is 0.38A for Zn and 0.38A for Mn, respectively.
0.16A, 0.433A for Se, and 0.6505A for S, so it can be predicted from the above that the lattice constant in the case of normal coagulation will follow the formula (). Therefore, l', m', p' and q' are prepared in advance so that a' expressed by formula () is substantially constant at least within the range of the desired g' (a numerical value corresponding to the solidification rate g). The crystal of the present invention can be automatically obtained by selecting , determining the initial composition of the melt, and later growing the crystal by a method that follows normal solidification.

Added elements are those with a segregation coefficient greater than 1.
One or two types of Zn and S, and one or two types of Mn and Se can be used as smaller than 1 type, but usually only one type of each is sufficient. Practical combinations are Zn and Se and Zn and Mn.

When Zn and Se are added, the Zn/Se atomic ratio (l/p) is preferably 1 to 6, particularly 3.7. Further, when adding Zn and Mn, the Zn/Mn atomic ratio (l/m) is preferably 4 to 20, particularly 12.
At this preferred atomic ratio, the lattice constant becomes constant over a wider range of solidification rates.

A method for preparing a melt having a desired initial composition is to add a predetermined amount of the above 4 to a Cd and Te melt.
By melting the elements selected from the added elements of the seeds,
A method for producing a melt having the above composition, or
Examples include a method in which Cd, Te, and an element selected from the above four elements are mixed to form a powder mixture having a predetermined composition, and this is melted to form a melt. Conditions such as melting temperature and pressure are appropriately determined depending on the type and amount of the added element.

Examples of methods for growing crystals by normally solidifying the melt obtained in this way include bulk crystal growth methods such as the vertical Bridgeman method and the pulling method including LEC. can be manufactured.

On a substrate obtained from the semiconductor crystal of the present invention
Examples of methods for epitaxially growing HgCdTe crystals include metal organic vapor phase epitaxy, molecular beam epitaxial growth, vacuum evaporation, and hot wall growth.

〔Example〕

The present invention will now be described in detail with reference to Examples.

Example 1 An attempt was made to produce a crystal with a lattice constant of 6.4636A. Zn and Se were used as additive elements. The segregation coefficients of Zn and Se relative to CdTe were experimentally determined to be 1.35 and 0.9, respectively. Using formula (), we calculated the conditions under which the above lattice constant could be achieved over as wide a range as possible, and found that if Zn was added in place of Cd at 0.96 mol% and Se in place of Te at 3.6 mol%, ± within the range of crystal solidification rate of 0 to 0.6
It was found that a crystal with a lattice constant of 6.4636A could be obtained within an error of 0.00004A (±0.0006%), and within an error of ±0.0005A (±0.0077%) in the solidification rate range of 0 to 0.9. Based on this calculation result, an attempt was made to manufacture the product as follows.

A quartz ampoule with an inner diameter of 50 mm and a purity of 99.9999%.
Cd, Te, Zn and Se, molar composition Mr. Cd:
Te:Zn:Se=99.04:96.4:0.96:3.60 and a total amount of 800 g was added and vacuum sealed (pressure: 10 ^-6 torr or less). Next, this ampoule was heated to 1140°C in a vertical Bridgmann furnace to melt each element. Thereafter, the temperature of the furnace was cooled at a cooling rate of 0.1°C/h under a temperature gradient of 2 to 3°C/cm to crystallize, thereby obtaining an ingot. The obtained crystals contained some rotational twins in the (111) plane, but were composed of large crystal grains. A sample of 5 x 5 x 1 mm was cut out from each part along the growth direction of this crystal ingot using a crystal cutting device, and the Zn concentration was measured using atomic absorption spectrometry.
The Se concentration was measured by the Plasma method, and the lattice constants were also measured. As a result, the changes in the Zn concentration and Se concentration in the obtained crystal are shown in Figure 1. Regarding the lattice constant, the horizontal axis represents the solidification rate corresponding to the crystal growth direction, and the vertical axis represents the lattice constant. The change in the lattice constant is shown by the solid line in FIG. 2, and a crystal as predicted by the previous calculation was obtained. Furthermore, the dislocation density in the crystal was less than 7×10 ⁴ /cm ² , and no cell structure was observed at all.

In addition, as a result of measuring the Vickers hardness of the crystal,
It was 60.

Comparative Example 1 Cd, Te and Zn with a molar composition ratio of Cd:Te:
Crystals were grown in the same manner as in Example 1, except that Zn=96.3:100:3.7.

The change in the lattice constant of the obtained crystal is shown in FIG. 2 by a chain line.

Further, the dislocation density in the crystal was less than 1×10 ⁵ /cm ² , a cell structure was observed in some parts, and the Vickers hardness was about 50.

Comparative Example 2 Cd, Te and Se with a molar composition ratio of Cd:Te:
A crystal was grown in the same manner as in Example 1 except that Se=100:95.1:4.9.

The change in the lattice constant of the obtained crystal is shown in FIG. 2 by a dashed-dotted line.

Further, the dislocation density in the crystal was less than 1×10 ⁵ /cm ² , a cell structure was observed in some parts, and the Vickers hardness was about 53.

Example 2 An attempt was made to produce a crystal with a lattice constant of 6.4783A. The same method as in Example 1 was conducted except that crystals were grown from a melt having a molar composition ratio of Cd:Te:Zn:Mn=89.2:100:0.8:10.

Comparative Examples 3 and 4 Crystals were obtained from a melt with a molar composition ratio of Cd:Te:Zn=96.3:100:3.7 (Comparative Example 3) or Cd:Te:Se=87:100:13 (Comparative Example 4). Other than being raised,
An attempt was made to produce crystals in the same manner as in Example 1.

The relationship between the lattice constant and solidification rate of the crystals obtained in Example 2 and Comparative Examples 3 and 4 was as shown in FIG.

〔Effect of the invention〕

The substrate obtained from the semiconductor crystal of the present invention is suitable for epitaxial growth of HgCdTe crystal in terms of lattice matching, and is also excellent in terms of dislocation density, mechanical strength, etc., so it is a high-quality substrate.
HgCdTe crystals can be grown. This crystal can have a lattice constant adjusted within a certain range, and is useful as a substrate for producing HgCdTe crystals as well as other crystals. In addition, a constant lattice constant can be obtained over a wide range of crystals regardless of the solidification rate of the crystals, making it possible to manufacture large substrates and improving the yield of substrates.

[Brief explanation of the drawing]

Figure 1 shows changes in Zn concentration and Se concentration in semiconductor crystals produced in Examples, and Figures 2 and 3 are diagrams showing changes in lattice constant with respect to solidification rate of semiconductor crystals produced in Examples and Comparative Examples. be.

Claims (1)

[Claims] 1 Formula (): Zn _l Mn _n Cd _1-(l+n) S _p Se _q Te _1-(p+q) () [Here, l, m, p and q are 0 or more, l and p are not 0 at the same time, m and q
is simultaneously non-zero], and along one direction,
Formula () a=6.4825−0.38lk(Zn)・(1−g) ^(k(Zn)−1) −0.16mk(Mn)(1−g) ^(k(Mn)−1) −0.6505pk(S )(1-g) ^(k(S)-1) -0.433qk(Se)(1-g) ^(k(Se)-1) [Here, g is solidification rate, k(Zn), k(Mn ),k
(S) and k(Se) respectively indicate the segregation coefficients of Zn, Mn, S and Se with respect to CdTe, and l, m,
p and q are the same as above] The lattice constant a expressed by is at least 0≦g≦
A semiconductor crystal whose composition varies in such a way that it remains essentially constant over a range of 0.6. 2 Equation (): Zn _l ′Mn _n Cd _1-(l ′ _+n ′ ₎ S _p ′Se _q ′Te _1-(p ′ _+q ′ ₎ () [Here, l′, m′, p′ and q' are numbers greater than or equal to 0, l' and p' are not 0 at the same time, m' and
q′ is not 0 at the same time, and furthermore, the formula: a′=6.4825 −0.38l′k(Zn)(1−g′) ^(k(Zn)−1) −0.16m′k(Mn)(1−g ′) ^(k(Mn)-1) −0.6505p′k(S)(1−g′) ^(k(S)-1) −0.433q′k(Se)(1−g′) ^{(k(Se )-1)} () (In the formula, g' is a variable that changes within the range of 0≦g'≦1, and k (Zn), k (Mn), k (S) and k (Se) are
The number a', which represents the segregation coefficient of Zn, Mn, S, and Se with respect to CdTe, respectively, is selected such that the numerical value a' is substantially constant at least in the range of 0≦g′≦0.6. ]. A method for manufacturing a semiconductor crystal, comprising a step of normally solidifying a melt having a uniform composition represented by: