CA1271393A - Method of manufacturing a semi-insulating single crystal of gallium indium arsenide - Google Patents

Method of manufacturing a semi-insulating single crystal of gallium indium arsenide

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Publication number
CA1271393A
CA1271393A CA000492218A CA492218A CA1271393A CA 1271393 A CA1271393 A CA 1271393A CA 000492218 A CA000492218 A CA 000492218A CA 492218 A CA492218 A CA 492218A CA 1271393 A CA1271393 A CA 1271393A
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Prior art keywords
single crystal
indium
semi
gallium
mass
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CA000492218A
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French (fr)
Inventor
Marc P. Duseaux
Sylvie A. Martin
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Koninklijke Philips NV
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Philips Gloeilampenfabrieken NV
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Abstract

ABSTRACT:

A method of obtaining a single crystal of gallium arsenide (GaAs) of semi-insulating type including indium (In) for reducing dislocations, characterized in that this single crystal is formed from a molten bath in which the mass of arsenic (As) with respect to the total mass of arsenic plus gallium (Ga + As) is higher than 45% and lower than 51%, in that indium (In) is introduced in the form of indium arsenide (InAs), the mass of indium arsenide (InAs) with respect to the mass of arsenic plus gallium (Ga + As) is higher than 5%
and lower than 10% in such a manner that the single crystal obtained from this molten bath is of p-conductivity type and the concentration of the element indium in the single crystal, which has the formula Ga1-xInAs, is x?0,01, and in that this single crystal is then subjected to a sinter-ing treatment for increasing the level of the deep donors EL2 up to such a value that the single crystal has the properties of a semi-insulator. In this way semi-insulating substrates without dislocations can be made.

Description

~.271393 .
P~ 84.574 1 21-08-1985 Metho~ of manufact ~ing a semi-insulating single crystal of gallium indium arsenide.

The invention relates to a method of manufacturing a single crystal of gallium arsenide (Ga~s) of semi-insulating type including indium (In) for reducing dislocations.
The invention can ke used in the manufacture of semi-insula-ting substrates for semiconductor devices in those cases in which a high integration density and high performances are required.
A method of manufacturing such a single crystal is knownfrom British Patent GB~PS 1242410 in which method mono-crystalline lay-ers of galium arsenide are grown from a solution, into which indium is incorporated in a cluantity less than 5% so that, due to the lcw segre-gation coefficient of indium, the quantity of indium in the finished single crystal is negligible (less than 0.5%). As a result of the addi-tion of indium to the solution the crystalline qualities of the gallium arsenide layers are materially impro~ed.
The known method, how~ver, which is the method of epitaxy from the liquid phase~ is not suitable for obtaining very bulky single crys-tals. Besides, impurities, such as ehromium, which have to ke included in the bath in order to obtain a crystal having, for example, semi-in-sulating properties, have very low se~regation c oefficients. Consecluent-ly, they are not uniformly incorporated into the cry~tal and have a tendency to diffuse unduly in the epitaxial layers which can be formed afterwards on this crystal when used as a substrate.
Object of the invention is obtaining a bulky single crystal without dislocations ~nd of the semi-insulating type without addition of disturbing impurities. Therefore, according to the invention, the method mentioned before is characterized in that the single erystal is formed from a m~lten bath, in which the mass of arsenic (As) withrespect to the total mass of arsenic plus gallium (Ga + A~s) is higher than 45 and lower than 51~, in that indium (In) is introducecl in the form of indium arsenidP (InAs), the mass of indium arsenide (In~s) with re~spect to the mass of arsenic plus gallium (Ga ~ As) is higher than 5% and lower than 10~ and in that this single crystal is then subjected to a sinter mg treatment.

39;3 P~ 84.574 2 21-08~1985 The crystal obtained Erom the b~ath contains a~out 1~ indium and has a p-type conc~lctivity. D~le to the sintering treatment the level of deep donors ~L2 is increased and the crystal becomes semi-insulating.
The advantage of the method in accordance wlth the invention is therefore that it provides a single crystal which is semi-insulating and free frc~m disturbing dopants.
In order that the invention may be readily carried out, it will now be described more fully with reference to the accompanying drawing, in which:
Fig. 1 is a sectional view of the distribution of the defect EL2 in a crysta] of gallium arsenide doped with indium (Ga1_xInx As), where Fig. 1a shows this distribution before sintering in a sectional view perpendicular to the pulling axis, Fig. 1b shows this distribution before sintering in a sectional view parallel to the pulling axis, Fig.
1S 1c shows this distribution after sintering in a sectional view perpen-dicular to the pulling axis and Fig. 1d shows this distribution after sintering in a sectional view parallel to the pulling axis.
According to the invention, a bulk~7 single crystal devoid of dislocations is obtained ~y pulling, by means of the Czochralski method, of a single crystal of gallium arsenide doped by means of an iso-elec-tronic element, such as indium, in quantities of 1019 to 2.102 atoms/cm3. Such a single crystal corresponds to the general formula:
Ga1 xIn As, in which the concentration x is of the order of 1%.
Pulliny by means of the Czochralski method certainly permits of obtaining single erystals of large cross-section, but gives rise to difficulties, such as, for example, tensi~ns in the crystal. These difficulties can be solved only ky defining in a specific manner the different parameters of the pulling process.
By a suitab]e pulling method and by a suitable doping with indium, crystals having a high crystalline quality required for suk-strates of integrated circuits can ke obtained. However, a further problem has still to be solved, which consists in forming such a crys-tal having the properties of a semi-insulator.
The electrical properties of gallium arsenide are given by the combination of the active centres present in the material and more particularly by their respective concentrations and their energy level in the forbidden band. This combination permits of determining the 39~3 P~E` 84.574 3 21-08-1985 ~ermi level. If this level is in the proximity of the conduction band, the crystal is of the n-conductivity type, ancl, if this level is in the proximity of the valency bandl the crystal is of the E~conductivity type. If the level is blocked in the midclle of the forbidden band, the crystal is semi insulating and has a high resistivity. The active centres can be of two types:
- impurities (residual or introduced at will) - natural defects, among which EL2, which have energy levels lying approximately in the middle of the forbidden band for gallium arsenide.
The electrical type of the undoped crystals of gallium arseni-de consequently first depends upon the stoichiometry of the pulling bath during their processing. If the bath is rich of gallium, the crys-tal has a E~conductivity ty~e and has an excess of acceptors. If on the contrary the bath is rich of arsenic, the crystal has an n-conductivity type and has an excess of donors.
In these conditions, in order to obtain a semi-insulating crystal according to the invention, the starting material is a crystal of ~-conductivity type, in which a suitable quantity of deep donors is caused to appear.
Ps shown in Figs. 1a and 1b, it can e ascertained that a crystal of gallium indium arsenide obtained according to the invention has a level of concentration of the defects EL2 which is simultaneously:
- very hcm~geneous and ~ very lcwl of the order of 3 to 5 . 1015 cm 3.
The Table gives the concentration of defects EL2 f the different zones of this erystal for a ~etter understanding of the figures.
TABLE

__ . . .................... _ _ _ _ Reference numerals of the zones Concentration of defects EL2 , , _ _ 1 3 to 4.9 . 1015 cm 3 35 2 5 to 6.9 . 1015 . cm 3 3 7 to 9.9 . 1015 c~-3 4 10 to12.4 . 1015 . cm 3 _ ~11.;~'7~3~
, PHF 84.574 4 21-08-1985 The ~ehaviour of the defect EL2 in gallium arsenide is known Erom the publication of D~ RUMSBY et al, in GaAs I.C. Symposium 1983, I.E.E,E., entitled "Improved uniformity of L.E.C. undoped Gallium Arsenide produced by high temperatllre annealing". This publication in-dicates that there is a solution for rendering the electrical propertiesof an undoped gallium arsenide crystal homogeneous. This solution con-sists in sintering this crystal at a temperature of 950 for at least 5 hours. Due to this treatment, the values of the concentrations of the defects EL2 are levelled. Although the publication indicates the means for obtaining homDgeneous electrical properties and more particularly a constant concentration level of the defects in an undoped crystal of gallium arsenide, it does not state anything about the behaviour of the level of defects EL2 in a crystal of gallium indium arsenide and about a method of obtaining a semi-insulating crystal without disturbing lS dopants.
According to the invention, the last-mentioned problem is solved by first forming a single crystal of gallium indium arsenide by means of the method described above from a bath rich in gallium so that the single crystal obtained is of p-conductivity type, and by then sub-jecting this single crystal to a single sintering treatment.
In fact is has been found that due to this operation, thelevel of defects EL2 of the crystal of indium-doped gallium arsenide, which had a low level of these defects, as shown in Figures 1a and 1b, rises in a surprising manner, as shown in Figures 1c and 1d, whilst remaining uniform.
Thi~ result is the more surprising as if the prior art indi-cated that uniformuty of the level of the defects EL2 was obtained in a crystal of substantially similar ccmposition, it did not indicate that the value thereof was considerab]y changed. Due to the fact that in a crystal according to the invention the uniformity of the defects EL2 was obtained from the origin, it was not obvious to carry out a sintering treatment for finding a solution for the problem.
However, after the sintering treatment, the concentration of deep donors in the single crystal of gallium indium arsenide has be-35 come sufficient for this single crystal to be semi-insulating. The addition of disturbing impurities, such as chromium, is thus avoided.
It can be readily imagined that the level of defects EL2 is connected with an intrinsic defect of the crystal which could be the ~;~73L3~ 33 PHF 84.574 5 21-08-198S

positioning of arsenic atoms at the gallium sites (anti-sites). The results obtained by the use of the invention suggest that, in contrast with what was assumed hitherto, the homogenization of the defects EI,2 duriny a sintering treatment of undoped gallium arsenide is not due to the diffusion of defects existing in the material, but on the contrary to the evolution towards a thermodynamic equilibrium. The increase of the level of defects EL2 in indium-doped gallium arsenide during the sintering treatment would then be due to the evolution towards such an equilibrium.
Thus a eriori unexFected result conseq~lently pe~mits of obtai-ning, from indiumrdoped gallium arsenide crystals formed in accordance with the invention, semi-insulating substrates which have great advan-tages due to the fact that they are devoid of dislocations. This per-mits of for~ing at their surfaces epitaxial layers which are as perfect as possible and miniaturized circuit elements whose properties are repetitive.
Such a method may be carried out in the ollowing manner. The indium-doped gallium arsenide crystal is formed by the pulling method of Czochralski with liquid encapsulation in a crucible of quartz or of 20 boropolynitride (BPN). The bath is rich in gàllium, which ~ecomes mani fest by the fact that the concentration of the mass of gallium with respect to the mass of arsenic plus gallium in the molten bath is higher than 49% or by the fact that the concentration of the mass of arsenic with respect to the mass of arsenic plus gallium in the molten bath lies 25 between 45 and 51%. The doping with indium can be effected by introducing into the bath a quantity of indium arsenide defined by the ratio between the mass ~ nAs f indium arsenide and the mass mGaAS of gallium arsenide ' ~ InAs/ Ga~s ~ 0,1 which is obtained, for example, by masses of 550 g of arsenic (As) associated with 510 g of gallium ~Ga) and with 70 g of indium arsenide (In~s) in the molten bath.
The pulling speed is low, for example, lower than 15 mm per 35 hour. The general formula of the crystal obtained is:
Ga1 xInxAs, in which the concentration ~ ~0,01.
A suitable sintering temperature lies between 800C and 1000C, .

~71~Y3;.~

PHF 84.574 6 21-08-1985 for example, is of the order of 900C. This sintering treatment has to be effected Eor at least 1 hcur~
Before the sintering treatment, the level of deects EL2 lies b~tween 3 and 5.1015 cm 3 (Figs. 1a and 1b). Afte~ the sintering treatm~nt, this level is > 12.1015 cm 3, as is illustrated in Figs. 1b and 1c.
It is clear that certain variations are possible in the comr position of the starting III-V compound and in the kind of sintering treatment to whlch it is subjected without departing from the scope of the invention as defined by the appended claims.

Claims (3)

PHF 84.574 7 21-08-1985 THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of obtaining a single crystal of gallium arsenide (GaAs) of semi-insulating type including indium (In) for reducing dis-locations, characterized in that the single crystal is formed from a molten bath in which the mass of arsenic (As) with respect to the total mass of arsenic plus gallium (Ga + As) is higher than 45% and lower than 51%, in that indium (In) is introduced in the form of indium arsenide (InAs), the mass of indium arsenide (InAs) with respect to the mass of arsenic plus gallium (Ga + As) is higher than 5% and lower than 10% and in that this single crystal is then subjected to a sintering treatment.
2. A method as claimed in Claim 1, characterized in that the single crystal of gallium indium arsenide is obtained from the molten bath by means of the method Czochralski of pulling with liquid encapsu-lation at a pulling speed lower that or equal to 15 mm per hour.
3. A method as claimed in Claim 2, characterized in that the sintering treatment to which the single crystal is subjected to render it semi-insulating is effected at a temperature lying between 800°C
and 1000°C for at least 1 hour.
CA000492218A 1985-10-03 1985-10-03 Method of manufacturing a semi-insulating single crystal of gallium indium arsenide Expired CA1271393A (en)

Priority Applications (1)

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CA000492218A CA1271393A (en) 1985-10-03 1985-10-03 Method of manufacturing a semi-insulating single crystal of gallium indium arsenide

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Application Number Priority Date Filing Date Title
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Publications (1)

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CA1271393A true CA1271393A (en) 1990-07-10

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