CN102732951A - Method for solidifying gallium-rich gallium arsenide melt used for liquid phase epitaxy - Google Patents

Abstract

The invention discloses a method for solidifying gallium-rich gallium arsenide melt used for liquid phase epitaxy. The method is characterized in that after the epitaxial layer growth is finished, a gallium-rich gallium arsenide melt is subjected to rapid cooling, so that the melting source is in a melt state under the room temperature, for secondary epitaxial growth of the melting source, the solidification of the melt is required for sampling or loading in the liquid phase epitaxial growth, a microscale gallium solvent is added, and is rotated and stirred along clockwise or anticlockwise direction, the gallium-rich gallium arsenide melt can be solidified by following the motion of a crystal growth czochralski method. The invention has the advantages that a technology that microscale gallium crystal grains drive the melt to move for solidification is used, no pollution is generated during the operation process, the operation time is short, the exposure duration of melting source, graphite boat and a quartz tube cavity in air can be reduced, the loading time for experiments can be substantially shortened, the unintentionally adsorption in the material loading process can be reduced, the material growth purity can be enhanced, and the possiblility for realizing the growth of the unsolidified gallium-rich melt material by a liquid phase epitaxial technology can be provided.

Description

A kind ofly be used for the method that rheotaxy is solidified with the GaAs melt of rich gallium

Technical field

The present invention relates to the method for the rheotaxy of the rich gallium sosoloid of a kind of III of growing-V epitaxial material with melt solidifying; Be meant that especially the growth of low dimensional structures materials such as ultra-thin individual layer, SQW, MQW and quantum dot uses Ga rich melt; It is low excessively because of fusing point to solve Ga rich melt with this method; The noncondensing difficulty of room temperature under quick supercooled condition can promote the research of liquid phase epitaxial technique aspect rich gallium sosoloid epitaxial film.

Background technology

The fusing point of metal Ga is 29.76 ℃, and the theoretical temperature of solidification of the GaAs sosoloid of rich Ga is 29.5 ℃.Adopt liquid phase epitaxial technique growing film or low only structured material; All be after outer layer growth finishes; Push process furnace open, sharply cool off at room temperature molten source, because too fast rate of temperature fall (10 ~ 20 ℃) causes the very low GaAs sosoloid of zero pour cold and noncondensing phenomenon to occur.Liquid molten source is prone to flow and is polluted in the process of rheotaxy sampling or dress appearance, more is inconvenient to adjust its position.For solving the freezing problem of rich gallium gallium arsenide sosoloid; Domestic method is to improve arsenic content or increase condensate depression, increases with As content, and temperature of solidification increases not obvious; After too much As combines Ga to separate out GaAs in the solution, do not promote the As solution solidifies of the rich Ga of remainder; The GaAs solution of rich Ga can not solidify keeping under the frozen water mixing temperature more than 48 hours in addition, promptly has too high condensate depression and whole solidification phenomenons do not occur.Conventional means can not realize well that all it is a solid phase by liquid-phase conversion, and this molten source of GaAs that rich Ga is described meets obstructions when liquid sosoloid solidifies.

Metal solidify the diffusion that depends on constituent element, reach equilibrium freezing, need each process in phase transition process must have time enough to carry out the abundant diffusion of atoms metal.But because of quick cooling causes under each temperature the diffusion of Ga atoms metal insufficient, make process of setting depart from equilibrium conditions, want big 3-4 one magnitude because of its thermal conductivity ratio spread coefficient again.So when solidifying, each nucleus forms a crystal grain, intragranular composition is uneven, non-equilibrium non-homogeneous solidifying occur for this reason.The GaAs sosoloid of rich gallium is under the not high condition of temperature, and the solubleness of As is very little, can be considered to contain impure impurity (As) among the metal Ga, and so the GaAs sosoloid of liquid rich gallium solidifies the non-homogeneous SOLIDIFICATION MODEL that just can be reduced to the impure metal.Constituent element is just more single like this, just only needs during forming core to consider that structure rises and falls, fluctuation of energy, rises and falls and ignore composition.The heterogeneous nucleation model of metal comprises four processes basically: embryos, nucleus, crystal grain and solid crystals metal.

The liquid gallium metal freezing needs structural condition, thermodynamic condition and energy condition.The fluctuating of fluctuating or structure is the crystalline structural condition mutually, and having condensate depression is thermodynamic condition, and the fluctuation of Gibbs free energy is an energy condition.

Because of the atomic arrangement of liquid-gallium has short range order, long-range is unordered.The continuous appearing and subsiding of short range order group is among the variation.And the orderly group that these moments occur, disappear is called structure and rises and falls or rise and fall mutually.Only the fluctuating mutually in supercooled liquid could form embryos, and these embryos just possibly form the nucleus crystallization.

The actual Tc Tn of GALLIUM metal pure and the difference of theoretical Tc Tm are called condensate depression (Δ T), about 6.2 ℃.

ΔT＝T _m-T _n

According to thermodynamic argument, liquid-solid two-phase Gibbs free energy difference Δ Gv is:

ΔG _v＝-ΔH _f-TΔS＝-ΔH _f+TΔH _f/T _m＝-ΔH _fΔT/T _m

Δ H _fBe latent heat of phase change, S is the entropy of system.Gibbs free energy descended when liquid changed solid into, just had the crystalline motivating force, and crystallisation process could take place, and therefore actual Tc must be lower than theoretical Tc, and condensate depression is promptly arranged, and could satisfy the crystalline thermodynamic condition.

Under certain condensate depression, if solid-state nucleus occurs, this regional energy variation comprises two aspects in the liquid, the one, and the decline of volume free energy when liquid crystalization is solid, the 2nd, the interfacial free energy of newly-increased nucleus.

ΔG＝VΔG _v+σS

V: nucleus volume; σ: interfacial energy; S: the surface-area of nucleus

Δ Gv: the solid-liquid Gibbs free energy is poor in the unit volume, r _cBe called critical nucleus radius.

As embryos Ban Jingr>r _c, Gibbs free energy descended when embryos was grown up, and embryos can be grown and is nucleus.So under the environment of melt undercooling, embryos is forming core and growing up slowly, finally is frozen into crystal, be a result who rises and falls mutually with fluctuation of energy.Impure Ga metal can be followed the crystalline rule from settable liquid, and promptly crystallisation process is forming core and the process of growing up.The formation of nucleus needs energy to cross to do work, and the surface energy that nucleus forms cannot be fully compensated by the decline of volume free energy, and insufficient part needs to supply with in addition, promptly need be to the forming core work done, so the title insufficient section is the forming core merit.

$\mathrm{\Δ}{G}_c=\frac{4}{3}\mathrm{\π}{r_c}^3\·\mathrm{\Δ}{G}_v+4\mathrm{\π}{r_c}^2\·\mathrm{\σ}=\frac{1}{3}\left[4\mathrm{\π}{\left(\frac{2\mathrm{\σ}}{\mathrm{\Δ}{G}_v}\right)}^2\mathrm{\σ}\right]$

$=\frac{1}{3}\left[4\mathrm{\π}{r_c}^2\mathrm{\σ}\right]=\frac{16\mathrm{\π}{\mathrm{\σ}}^3{T}_m^2}{3\mathrm{\Δ}{H}_f^2}\frac{1}{\mathrm{\Δ}{T}^2}>0$

It is thus clear that the reduction of volume free energy has only compensated 2/3 surface energy increase when forming critical nucleus, remaining 1/3 part is Δ G _cNeed to supply with in addition, promptly need be to the forming core work done.So Δ G _cBe called maximum forming core merit or critical forming core merit.Condensate depression increases, and critical forming core merit significantly reduces, and forming core is easy to carry out.

After embryos formed stable nucleus in liquid, nucleus will be grown up, and the essence of growing up is exactly the transfer of atom in solid in the liquid, and the energy that this process will consume comprises diffusion, the lattice defect of atom, adhesion and four aspects of crystallization latent heat of atom.Condensate depression in the dependence liquid realizes the power of energy expenditure; Promptly with condensate depression drive atom diffusion, balance the power that high free energy that lattice defect has, loss provide crystallization latent heat to derive in the adhesion process neutralization of atom; The consumption control crystalline growth of these four energy, it mainly is the release that crystallization latent heat is derived that pure metal is solidified.Crossing cold gallium liquid is the unsteady state on a kind of thermodynamics, under through effects such as external world's frictions, can solidify rapidly, and makes temperature recovery, shows on the cold curve it is a V font, and liquid is pure more, and surfusion is obvious more.

Not only existing structure to rise and fall in the liquid metal, and have fluctuation of energy, also be that the free energy in the liquid metal different zones is also also inequality, so the forming core merit can provide through the fluctuation of energy of system.When the energetic atom in a certain zone in the system attached to critical nucleus on, will discharge part energy, a stable nucleus can form.

Liquid gallium metal noncondensing reason under supercooled state has: one of which, embryos form and receive resistance.For gallium metal, excessive condensate depression increases the big or small r of rising and falling mutually, but the probability that occurs when increasing is very little, so embryos is grown up to critical size r _c, the probability that becomes nucleus is just little; Its two, under the supercooled environment, lack the forming core merit, forming core is obstructed, this is the incoagulable major cause of melt gallium.The reduction of Gibbs free energy at first will be crossed critical nucleus, and growing up of embryos needs extra acting before the critical nucleus, have only the so-called forming core merit of absorption after, the embryos formation nucleus of growing up, nuclei growth forms crystal grain and crystallization.Liquid melts has very big condensate depression, and the crystallization latent heat that in process of setting, discharges is crossed the sloppy heat bulk absorption, can suppress the forming core of sloppy heat body.Its three, lack nucleus.Because of the formation of nucleus is suppressed, just there are not a large amount of formation of crystal grain, liquid metal just can not solidify.Its four, the speed of liquid gallium metal freezing is very slow, time length can obtain the possibility that more nucleus forms, promptly structure rises and falls the formation of embryos is provided for a long time, fluctuation of energy provides the forming core merit.

The present invention makes the explanation of liquid rich gallium gallium arsenide sosoloid clotting method through the technology of adding micro-Ga solvent and stirring: one of which; Through adding trace solvent and in melt, stirring along a certain direction; Purpose provides the forming core merit that embryos is grown up; The increase free energy rises and falls and improves the probability that nucleus forms, and promotes the release of crystallization latent heat, promotes the formation of nucleus also to grow up into crystal grain.Its two, drive crystal grain and stir and follow crystal to lift technology in a certain direction.Purpose is to adopt churned mechanically mechanics method, impels that xln fractures, fragmentation, and crystal grain quantity is increased, and size reduces, and then grain refining occurs and solidify.Its three, add micro-Ga solvent, purpose is the crystal grain induced crystallization.

Summary of the invention

The objective of the invention is to design and a kind ofly be used for rheotaxy, be convenient to the operability in the experimentation, promote liquid phase epitaxial technique to use rich gallium sosoloid epitaxial film to make up the research of new device with the method that the GaAs melt of rich gallium solidifies.

Method of the present invention comprises quality and shape, the speed of agitation movement and the direction of agitation movement of trace gallium.There is condensate depression in the liquid gallium metal under condition of fast cooling, about 6.2 ℃ and uncrystallizable be the laboratory common phenomenon, this explanation liquid metal solidification process is obstructed.The Ga thin slice the other end of trace is injected in the liquid rich gallium GaAs melt; Stir clockwise or counterclockwise; Along with the melt liquid state is slowly solidified, the zone radius of rotation slowly diminishes, the technology of lifting that when stirring, adopts single crystal growing along kinematic axis to outwards pulling out and inserting; All solidify until molten source, rich gallium sosoloid such as rich gallium GaSb can be realized the noncondensing difficult problem in molten source under the room temperature with this technology.The quality of said trace gallium accounts for molten source quality ratio and is about 0.1%, and sosoloid is added 0.1% solvent, can ignore the influence of solute solubility.This method can realize solidifying of liquid metal very soon, and convenient experiment continues operation, and the minimizing growth reduces the air plankton that the high purity graphite boat is infected with the duration of contact of equipment and air, and baking is easy to desorption under high-temperature hydrogen.The taking-up and the load substrates of the inconvenient laboratory sample in the molten source of liquid metal more are prone to bring into involuntary contaminating impurity in addition.Solid-state trace gallium needs very thin thin slice, is convenient to stir melt inside like this, more can ignore because of the little components influence to the melt system of quality.Said clockwise or stirring counterclockwise, speed approximately are that per second 0.5 ~ 1 changes, and the purpose of stirring provides the forming core merit, provides Gibbs free energy bigger fluctuating, promotes the formation of melt embryos, and stirring also is to derive crystallization latent heat, promotion melt crystallization in addition.

The advantage of this reality invention is to design the method that a kind of Ga rich melt solidifies, and realizes the grow epitaxial film of rich gallium sosoloid of LPE technology near-equilibrium state, expands rich gallium and dissolves the application of source on liquid phase epitaxial technique.

Embodiment

Following specific embodiments of the invention is done further detailed description:

1, join the source.The molten source of rich gallium GaAs of joining 580 ℃ according to the Ga--As phasor; The mol ratio of 580 ℃ of following As approximately is 0.0012mol; Take by weighing 5.76mg gallium arsenide (semi-insulated substrate slice) As is provided the source, high-purity metal Ga (5N) 2.2818g, GaAs source and GaAs substrate are after corrosive fluid corrosion surface zone of oxidation; Nitrogen dries up and GALLIUM metal pure is loaded in the graphite boat of rheotaxy equipment together.

2, obtain rich gallium GaAs melt.After the heating high growth temperature epitaxial film, the molten source of the rich gallium GaAs that zero pour is low the molten source of supercooled liquid occurs because of cooling off fast in room temperature.Taking out in growth is good on the substrate epitaxial film materials and before loading the GaAs substrate that another sheet corroded cleaning, need let liquid molten source solidify.

3, take by weighing the trace gallium thin slice.Take by weighing 1.5 ~ 2mg metal Ga thin slice, with clean antimagnetic type tweezer gripping one of which end.The Ga thin slice the other end of trace is injected in the liquid GaAs sosoloid.

4, folk prescription is to rotation.The Ga thin slice of trace is along stir clockwise or counterclockwise, and speed approximately is that per second 0.5 ~ 1 changes.

5, pulling technique.When stirring, adopt the technology that lifts of single crystal growing outwards to pull out vertically and insert.The zone liquid along with sosoloid slowly diminishes, clockwise or the radius that rotates counterclockwise diminish, with reference to pulling technique, pulling out and inserting and drive molten source and all solidify with crystallising part.

Claims (2)

1. one kind is used for rheotaxy with the method that the GaAs melt of rich gallium solidifies, and it is characterized in that:

Micro-Ga thin slice one end is injected in the liquid rich gallium GaAs melt; Speed so that per second 0.5 ~ 1 changes is stirred clockwise or counterclockwise; Along with the melt liquid state is slowly solidified; The zone radius that rotates slowly diminishes, and the technology of lifting of employing single crystal growing, is all solidified until molten source to outwards pulling out and inserting along kinematic axis when stirring.

2. according to claim 1ly a kind ofly be used for rheotaxy with the method that the GaAs melt of rich gallium solidifies, it is characterized in that: the quality of said micro-Ga thin slice accounts for molten source total mass ratio and is about 0.1%.