CN105606588A - Raman scattering method for measuring GaN thermal expansion coefficient - Google Patents

Abstract

A kind of Raman scattering method of GaN thermal expansion coefficient measurement, comprising the following steps: 1) scribing is carried out to sample and sampled, and cleaned; 2) alternating temperature Raman test is carried out to sample; 3) linear fit is carried out to test result; Extract linear fit slope and intercept. According to extraction as a result, in conjunction with Gruneisen parameter Physical significance,Realize the test and characterization to solid material thermal expansion behavior; Present invention employs alternating temperature Raman scattering technology,The relationship obtained between the frequency displacement of Raman phonon and temperature is scattered using Raman,Can be accurately realized to GaN,AlN and InN and other group III-nitride extension layer film binary and multi-element alloy system thermal expansion behavior are carried out non-destructive testing and are characterized,It avoids in general characterizing method to the destruction of sample and the more complicated derivation of equation and mathematical computations; Since the shapes and sizes to sample do not have proper requirement,It is convenient to test the thermal expansion behavior of classes of semiconductors class material,Method is simple,It is easily achieved,Error is small.

Description

The Raman scattering method that a kind of GaN thermal coefficient of expansion is measured

Technical field

The invention belongs to the method for testing technical field of solid material thermal expansion behavior, be specifically related to a kind of GaN thermal coefficient of expansion and surveyThe Raman scattering method of amount, measures and characterizes for the thermal coefficient of expansion of GaN thin-film material, adopts the side of alternating temperature Raman scatteringMethod, analyzes the relation between the Raman frequency displacement of GaN thin-film material and temperature, in conjunction with the Expansion Regularity of solid material, and willRelation between the thermal expansion behavior of material and alternating temperature Raman scattering frequency displacement is processed, thereby it is swollen to obtain GaN thin-film material heatThe relevant information of swollen behavior.

Background technology

III group-III nitride binary and multicomponent alloy photoelectric material thereof are to realize solid luminescence (Solid-StateLighting, SSL)Ideal candidates material, be also realize semiconductor light-emitting-diode (Light-emittingDiode, LED), laser diode (LaserDiode,LD), the ideal material of high-brightness white-light illuminating engineering and energy-saving and emission-reduction. InN and relevant III group-III nitride ternary alloy three-partalloy thereof (InAlN,InGaN) there is direct, the continuously adjustable band gap properties between 0.7eV-6.2eV with it, there is the wave spectrum scope of non-constant width,Cover green glow, blue light and ultraviolet spectra, become the critical material of making solid luminescence active region, there is huge application prospect.From the angle of material, it is very difficult producing blue light and ultraviolet light, and InGaN uniquely can realize this two kinds of wave bandsLuminescent material, and mate with the spectrum (0.4eV-4.0eV) of sunshine very good, make In_xGa_1-xN is in photovoltaic industry,Have broad application prospects in fields such as array solar cells, blue green light LED and white light LEDs especially.

In the situation that pressure is constant outside, the swelling that object occurs because of temperature change is " thermal expansion ". Most of materials existWhen temperature raises, its volume increases, volume-diminished (the usually said phenomenon of expanding with heat and contract with cold) when temperature reduces. At identicalUnder part, gas expansion maximum, expansion of liquids takes second place, expansion of solids minimum. Also there is minority material in certain temperature range,When temperature raises, its volume reduces (being pyrocondensation cold expanding phenomenon) on the contrary. From the angle of molecule, in the time that object temperature raises,The mean kinetic energy of molecular motion increases, and intermolecular distance also increases, and the volume of object expands thereupon; Temperature reduces, objectWhen cooling, the mean kinetic energy of molecule diminishes, and intermolecular distance is shortened, so the volume of object will dwindle. Again due to solid,The mean kinetic energy of liquids and gases molecular motion varies in size, thereby also has significant difference from the macroscopic appearance of thermal expansion.We know, in the time that temperature changes, the volume of material there will be Swelling and contraction phenomenon, and its changing capability is with isobaric conditionUnder under (pressure p is certain), unit temperature changes the Volume Changes causing, and is the thermal coefficient of expansion of material. Coefficient of expansion tableWhen having levied object and being heated, the degree of its length, area, Volume Changes, and the physical quantity of introducing. It is linear expansion coefficient, faceThe general name of the coefficient of expansion and the coefficient of volume expansion.

III nitride epitaxial layers thin-film material, owing to lacking the cause of intrinsic backing material, often by the method for hetero-epitaxy,Be grown in such as sapphire, on the backing materials such as SiC and Si, Metalorganic Chemical Vapor Deposition (Metal-organicChemicalVaporDeposition, MOCVD) be a kind of growing method that heterogeneous epitaxial technology adopts conventionally. Due to liningBetween bottom material, there is larger lattice mismatch and the mismatch of thermal coefficient of expansion, cause in epitaxial layer thin-film material, exist higherDislocation density (comprising line dislocation density and face dislocation density), the order of magnitude is generally about 10⁹-10¹⁰/cm². In growth course,In order to reduce dislocation density and polarity effect high in the epitaxial layer film causing because of lattice mismatch, conventionally adopt several different methods and handSection, for example two-step method (substrate being carried out to nitrogenize and GaN cushion technology), low temperature AI N nucleating layer increase temperature AlN nucleating layerTechnology, AlGaN/GaN superlattice structure etc. Position in the GaN epitaxial layer film of nonetheless, growing by mocvd methodDislocation density is still up to 10⁸/cm². Fig. 1 is the typical process that adopts epitaxial growth GaN film in Sapphire Substrate.

As shown in Figure 1, temperature has been played the part of very important factor in growing GaN epitaxial layer film. Open from growing GaN cushion500 DEG C of left and right of beginning, to 1025 DEG C of growing GaN epitaxial layer, range of temperature is large therebetween, various materials variations in temperature itUnder pyrocondensation phenomenon there are differences, the thermal coefficient of expansion of therefore accurately measuring material is very important.

Thermal coefficient of expansion is defined as α=Δ V/ (V* Δ T), and in formula, Δ V is the change of object volume under given variations in temperature Δ T, and V is thingBody volume. Strict in fact, this expression formula is the difference approximation of the differential definition of range of temperature when little; Accurately definitionRequire Δ V and Δ T infinitely small, this also means, thermal coefficient of expansion is not constant conventionally in larger temperature range. Temperature becomesWhen change scope is not very large, α is a constant. Utilize it, isotropic solid and liquid volume expansion can be expressed as follows:

V(T)＝V₀(1+3αΔT)

For being similar to the object of regarding one dimension as, length is exactly to weigh the decisive factor of its volume, and thermal coefficient of expansion at this moment can letterChange is defined as: unit temperature change lower length recruitment and the ratio of raw footage, Here it is linear expansion coefficient.

For the anisotropic material of having of three-dimensional, there is dividing of linear expansion coefficient and the coefficient of volume expansion. As graphite-structure has aobviousThe anisotropy of work, thereby graphite fibre linear expansion coefficient also presents anisotropy, shows as that to be parallel to the heat of bedding angle swollenSwollen coefficient is much smaller than perpendicular to bedding angle.

To the measurement of the solid thermal coefficient of expansion, generally all adopt thermal dilatometer to carry out. Its operation principle is that sample is in to oneUnder fixed temperature program(me) (lifting/lowering/constant temperature and combination thereof) is controlled, measure the change procedure of sample length with temperature or time. In realityIn the measuring process of border, for different samples, provide different classes of removable sample holder (quartz, aluminium oxide etc.), gather aroundThere is different Range of measuring temp, be applied to the field such as ceramic material and metal material. Thermal expansion/the receipts of main test solid materialContracting phenomenon.

GaN is stabilizer pole, hard dystectic compound, and fusing point is about 1700 DEG C, and its hardness is high and property is crisp. GaN crystalGenerally hexagonal wurtzite structure, the about 850-1150 DEG C of epitaxial growth temperature. At room temperature, GaN is water insoluble, bronsted lowry acids and bases bronsted lowry,In hot aqueous slkali, dissolve with speed very slowly. NaOH, H₂SO₄And H₃PO₄Can corrode quickly second-rateGaN, GaN is at HCl or H₂Under gas, at high temperature present unstable characteristic, and at N₂The most stable under gas, be again a kind of simultaneouslyGood coating protection material.

Adopt in the thermal dilatometer test GaN epitaxial layer film thermal coefficient of expansion and have many drawbacks: 1) GaN material hardness is high,Fragility is large, is difficult to do into strips/standard specimen; 2) thermal coefficient of expansion of GaN is little, thereby in temperature-rise period, volumetric expansionIt is less that the size causing increases effect, is difficult to accurate measurement; 3) the most important thing is, GaN material adopts the growth of hetero-epitaxy moreMode, the thickness of its thin-film material generally very little (thickness is the Sapphire Substrate of 430 microns, adds cushion/nucleating layer etc.,The thickness of epitaxial growth GaN is generally 600 microns of left and right), and the structure of this stratiform, it is unfavorable to produce measurement resultImpact.

In many physical propertys of semi-conducting material, optical property is one of most important physical property wherein. Probe into electromagnetism spokePenetrate field, with semiconductor, interactional process occurs, crystal structure, band structure and electronics and the sound of semi-conducting material can be providedThe information such as the characteristics of motion of son. All the time, optical means is that characterize semiconductor material is most important, one of the most effective means.

Raman scattering provides the information of material internal lattice vibration, and it carrys out the thing of exosyndrome material in inelastically scattered modeThe number of matter composition, crystal mass, residual stress size and free carrier concentration. Crystal defect, crystal grain diminish, nothing is determinedResidual stress in shape structure and crystal all can make the peak value of Raman frequency displacement be offset, the changing of peak broadening and peak symmetric shapeBecome. The behavior at Raman phonon peak under different temperatures, the information of the optics lattice wave that has comprised material internal atomic vibration generation. FromThe angle of atomic vibration is understood, and thermal expansion belongs to the anharmonic effect of atomic vibration, and the expansion of optics lattice wave volume and optics latticeRelation between ripple meets Gruneisen (cyhalothrin is gloomy) parameter, and this is one and varies with temperature little constant. Thereby, canWith by GaN epitaxial layer films test alternating temperature Raman scattering, realize the measurement to GaN thermal coefficient of expansion.

Summary of the invention

In order to overcome above-mentioned the deficiencies in the prior art, the object of the present invention is to provide a kind of GaN thermal coefficient of expansion to measureRaman scattering method, adopts the characterization method of new alternating temperature Raman scattering, by certain temperature range (with cooling JieThe scope of matter and appropriate change), the peak frequency displacement of GaN epitaxial layer film Raman scattering phonon is with the behavior of temperature; Adopt software matchingMethod, obtain the straight slope of d ω/dT; From the slope of straight line, extract the thermal coefficient of expansion about GaN epitaxial layer film.Adopt the method for alternating temperature Raman scattering, can realize exactly GaN, AlN and InN and other III nitride epitaxial layers thinNon-Destructive Testing and sign are carried out in film binary and multicomponent alloy system thermal expansion behavior, have solved measurement GaN thermal coefficient of expansion aspect and have depositedIn technical problem, contribute to reduce experimental error, and reduce experimentation cost, there is not potential safety hazard; There is method simple, makeWith convenient, with low cost, be convenient to the feature of promoting.

For achieving the above object, the technical solution used in the present invention is: the Raman scattering side that a kind of GaN thermal coefficient of expansion is measuredMethod, comprises the steps:

The first, GaN epitaxial layer film sample is sampled, and clean;

With diamond glass cutter to growth, diameter is that the GaN film sample of 2 inches carries out scribing, make size and be aboutThe sample of 1cm × 1cm, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is putPut in vacuum 5.0 × 10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min,Remove cut and the surface attachments of film surface;

The second, GaN epitaxial layer film sample is carried out to alternating temperature Raman test;

Sample is placed on the testboard of Raman scatterometer, test surfaces is that bright and clean, matsurface is the back side; Before testThe Ar that is at room temperature 514.5nm with wavelength⁺Laser instrument is tested,Under polarization mode, measure GaN epitaxial layer thinPhonon vibration pattern E in film₂(high) frequency shift value;

Before official testing, first to calibrate instrument parameter, choose after supporting grating, by standard silicon listPosition (the 520cm of brilliant main peak^-1) dead-center position of grating is calibrated, after having calibrated, just can adopt spectrometry, measure knotAfter bundle, carry software by instrument and carry out data processing, first cut baseline, then by Lorentz and Gauss's mixed function logarithmAccording to carrying out matching, draw the information of peak position and halfwidth, the alternating temperature platform model of Raman scatterometer is Linkam-Examina-THMS600, extent of alternating temperature is from 83K to 503K, and step-length is 52.5K, and precision can be controlled in 0.1K, when doing low temperature test, connectsUpper liquid nitrogen container, cooling medium adopts liquid nitrogen to lower the temperature.

The 3rd, to the processing of alternating temperature Raman data, extract thermal coefficient of expansion wherein;

Sample is taken out from Raman test macro, and the relation between the frequency displacement of phonon peak and the temperature that test is obtained is carried out linearityMatching, obtains d ω/dT straight slope, adopts following theory to analyze and process:

1) according to the definition of Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, the connotation of Gruneisen parameter, sign volumeChange and cause the change of Raman scattering phonon peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known,

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α.

The invention has the beneficial effects as follows:

Key of the present invention is the method that adopts Raman scattering, utilize in alternating temperature situation, the peak frequency displacement of Raman scattering phonon withThe characteristic of variations in temperature, the correlation between bond material thermal expansion behavior and the frequency displacement of phonon peak, oblique by analyzing d ω/dT straight lineInformation in rate, analyzes the thermal expansion behavior in GaN epitaxial layer film.

The present invention has adopted alternating temperature Raman scattering technology, utilizes Raman scattering to obtain the pass between Raman phonon frequency displacement and temperatureSystem carries out nondestructive characterisation (NDC) to the thermal expansion behavior of GaN. Can realize exactly GaN, AlN and InN and other III group-III nitridesNon-Destructive Testing and sign are carried out in epitaxial layer film binary and multicomponent alloy system thermal expansion behavior, in thermal coefficient of expansion and materialThe uniformity of portion's optics wave sound in origin mechanism, in conjunction with the physical significance of Gruneisen parameter, by skilful the relation between the twoWonderful combining, the destruction to sample and the comparatively complicated derivation of equation and mathematical computations in general characterizing method are avoided; SimultaneouslyBecause shape and the size of the present invention to sample do not have proper requirement, thereby can be easily to classes of semiconductors class materialThermal expansion behavior test, formula is simple, explicit physical meaning is easy to realize, and error is less.

Brief description of the drawings

Fig. 1 is the flow chart of available technology adopting MOCVD technology growth GaN epitaxial layer film.

The Raman phonon peak schematic diagram that under the different back scattering patterns of Fig. 2 the present invention, wurtzite structure GaN may occur.

Fig. 3 is that a pair of test data of the embodiment of the present invention is carried out linear fit coordinate diagram.

Fig. 4 is that the embodiment of the present invention two is carried out linear fit coordinate diagram to test data.

Fig. 5 is that the embodiment of the present invention three is carried out linear fit coordinate diagram to test data.

Detailed description of the invention

The present invention adopts the mode of alternating temperature Raman scattering, and the thermal expansion behavior of GaN epitaxial layer film be can't harm to table and test.In conjunction with test philosophy and test process, provide three embodiment.

Embodiment mono-

The Raman scattering method that GaN thermal coefficient of expansion is measured, includes following steps:

Step 1, samples GaN epitaxial layer film sample, and cleans.

With diamond glass cutter to growth, diameter is that the GaN film sample of 2 inches carries out scribing, make size and be aboutThe sample of 1cm × 1cm, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is putPut in vacuum 5.0 × 10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min,Remove cut and the surface attachments of film surface;

Step 2, carries out alternating temperature Raman test to GaN sample;

1) the GaN epitaxial layer film sample after clean is placed on Raman scattering testboard, adjusts Raman scatterometer, connectAlternating temperature platform and liquid nitrogen container, set Range of measuring temp and step-length; Excitation source adopts Ar⁺, optical maser wavelength is 514nm;

2) setting polarization mode isSlowly open alternating temperature cooling device, whole test macro is cooled to 77K (liquid nitrogenBoiling point), in the time of temperature stabilization, start to test;

Step 3, processes measuring alternating temperature Raman data, extracts thermal coefficient of expansion wherein;

1) sample is taken out from Raman test macro to the frequency displacement of phonon peak and the temperature that adopt Origin8.0 software to obtain testBetween relation carry out linear fit, the result obtaining as shown in Figure 3, is obtained d ω/dT straight slope, adopts following theory to enterRow is analyzed and is processed:

Definition according to Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, and the variation that characterizes volume causes Raman diffuse soundThe change of sub-peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known,

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α;

Computational process is as follows: known in the same figure, d ω/dT is straight slope-0.0110 in Fig. 3, and intercept is ω₀＝573.46；To Raman phonon modes E₂(high), its Gruneisen parameter γ value is about 1.47, sets up relation of equal quantity:

-3ω₀αγ＝-0.0110

Known as calculated, thermalexpansioncoefficientα=4.35 × 10^-6/ K, in this value and following table, GaN thermal coefficient of expansion is at a direction and cThe mean value 4.38 × 10 of direction^-6It is less that/K differs.

It should be noted that, although to GaN thermal coefficient of expansion, often there be dividing of a direction and c direction in educational circles,, forGruneisen parameter γ and ω₀, but there is no the differentiation of a direction and c direction, therefore, adopt these two constants to calculateThe thermal expansion behavior of material entirety that the thermal coefficient of expansion of GaN is comprehensive characterization itself is relevant;

The Main physical character (300K) of III hi-nitride semiconductor material

Embodiment bis-

The Raman scattering method that GaN thermal coefficient of expansion is measured, includes following steps:

Step 1, samples GaN epitaxial layer film sample, and cleans;

With diamond glass cutter to growth, diameter is that the GaN film sample of 2 inches carries out scribing, make size and be aboutThe sample of 1cm × 1cm, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is putPut in vacuum 5.0 × 10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min,Remove cut and the surface attachments of film surface;

Step 2, carries out alternating temperature Raman test to GaN sample;

1) the GaN epitaxial layer film sample after clean is placed on Raman scattering testboard, adjusts Raman scatterometer, connectAlternating temperature platform and liquid nitrogen container, set Range of measuring temp and step-length; Excitation source adopts Ar⁺, optical maser wavelength is 514nm;

2) setting polarization mode isSlowly open alternating temperature cooling device, whole test macro is cooled to 77K (liquid nitrogenBoiling point), in the time of temperature stabilization, start to test;

Step 3, processes the alternating temperature Raman data of measuring, and extracts thermal coefficient of expansion wherein;

1) sample is taken out from Raman test macro to the frequency displacement of phonon peak and the temperature that adopt Origin8.0 software to obtain testBetween relation carry out linear fit, the result obtaining as shown in Figure 4, is obtained d ω/dT straight slope, adopts following theory to enterRow is analyzed and is processed:

Definition according to Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, and the variation that characterizes volume causes Raman diffuse soundThe change of sub-peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known,

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α:

Computational process is as follows: with known in Fig. 4, d ω/dT is straight slope-0.0111 in Fig. 4, and intercept is ω₀＝574.40；To Raman phonon modes E₂(high), its Gruneisen parameter γ value is about 1.47, sets up relation of equal quantity:

-3ω₀αγ＝-0.0111

Known as calculated, thermalexpansioncoefficientα=4.34 × 10^-6/ K, in this value and following table, GaN thermal coefficient of expansion is at a direction and cThe mean value 4.38 × 10 of direction^-6/ K relatively approaches;

It should be noted that, although to GaN thermal coefficient of expansion, often there be dividing of a direction and c direction in educational circles,, forGruneisen parameter γ and ω₀, but there is no the differentiation of a direction and c direction, therefore, adopt these two constants to calculateThe thermal expansion behavior of material entirety that the thermal coefficient of expansion of GaN is comprehensive characterization itself is relevant.

The Main physical character (300K) of III hi-nitride semiconductor material

Embodiment tri-

The Raman scattering method that GaN thermal coefficient of expansion is measured, includes following steps:

Step 1, samples GaN epitaxial layer film sample, and cleans;

With diamond glass cutter to growth, diameter is that the GaN film sample of 2 inches carries out scribing, make size and be aboutThe sample of 1cm × 1cm, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is putPut in vacuum 5.0 × 10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min,Remove cut and the surface attachments of film surface;

Step 2, carries out alternating temperature Raman test to GaN epitaxial layer film sample;

1) the GaN epitaxial layer film sample after clean is placed on Raman scattering testboard, adjusts Raman scatterometer, connectAlternating temperature platform and liquid nitrogen container, set Range of measuring temp and step-length; Excitation source adopts Ar⁺, optical maser wavelength is 514nm;

2) setting polarization mode isSlowly open alternating temperature cooling device, whole test macro is cooled to 77K (liquid nitrogenBoiling point), in the time of temperature stabilization, start to test;

Step 3, processes measurement data, extracts thermal coefficient of expansion wherein;

1) sample is taken out from Raman test macro to the frequency displacement of phonon peak and the temperature that adopt Origin8.0 software to obtain testBetween relation carry out linear fit, the result obtaining as shown in Figure 5, is obtained d ω/dT straight slope, then adopts following reasonOpinion is analyzed and is processed:

Definition according to Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, and the variation that characterizes volume causes Raman diffuse soundThe change of sub-peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known,

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α:

Computational process is as follows: with known in Fig. 5, d ω/dT is straight slope-0.0111 in Fig. 5, and intercept is ω₀＝570.20；To Raman phonon modes E₂(high), its Gruneisen parameter γ value is about 1.47 left and right, sets up relation of equal quantity:

-3ω₀αγ＝-0.0111

Known as calculated, thermalexpansioncoefficientα=4.41 × 10^-6/ K, in this value and following table, GaN thermal coefficient of expansion is in a direction and c sideTo mean value 4.38 × 10^-6/ K relatively approaches;

It should be noted that, although to GaN thermal coefficient of expansion, often there be dividing of a direction and c direction in educational circles,, forGruneisen parameter γ and ω₀, but there is no the differentiation of a direction and c direction, therefore, adopt these two constants to calculateThe thermal expansion behavior of material entirety that the thermal coefficient of expansion of GaN is comprehensive characterization itself is relevant.

The Main physical character (300K) of III hi-nitride semiconductor material

Claims (4)

1. the Raman scattering method that GaN thermal coefficient of expansion is measured, is characterized in that, comprises the steps:

The first, GaN epitaxial layer film sample is sampled, and clean;

With diamond glass cutter to growth, diameter is that the GaN film sample of 2 inches carries out scribing, makes size and be aboutThe sample of 1cm × 1cm, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is putPut in vacuum 5.0 × 10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min,Remove cut and the surface attachments of film surface;

The second, GaN epitaxial layer film sample is carried out to alternating temperature Raman test;

Sample is placed on the testboard of Raman scatterometer, test surfaces is that bright and clean, matsurface is the back side; Before testThe Ar that is at room temperature 514.5nm with wavelength⁺Laser instrument is tested, at x (yy)Under polarization mode, measure GaN epitaxial layer thinPhonon vibration pattern E in film₂(high) frequency shift value;

First, instrument parameter is calibrated, choose supporting grating, by the position of standard silicon monocrystalline main peak is come lightThe dead-center position of grid is calibrated, and after having calibrated, adopts spectrometry, and after measurement finishes, carry software by instrument and carry out data processing,First cut baseline, then, by Lorentz and Gauss's mixed function, data are carried out to matching, draw the letter of peak position and halfwidthBreath, the alternating temperature platform model of Raman scatterometer is Linkam-Examina-THMS600, extent of alternating temperature from 83K to 503K, step-lengthFor 52.5K, precision can be controlled in 0.1K, connects liquid nitrogen container while doing low temperature test, and cooling medium adopts liquid nitrogen to lower the temperature;

The 3rd, to the processing of the alternating temperature Raman data of measuring, extract thermal coefficient of expansion wherein;

1) sample is taken out from Raman test macro, the relation between the frequency displacement of phonon peak and the temperature that test is obtained is carried out lineProperty matching, obtains d ω/dT straight slope, adopts following theory to analyze and process:

Definition according to Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, and the variation that characterizes volume causes Raman diffuse soundThe change of sub-peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known,

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about 10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α.

2. the Raman scattering method that a kind of GaN thermal coefficient of expansion according to claim 1 is measured, is characterized in that, bagDraw together following steps:

Step 1, samples GaN epitaxial layer film sample, and cleans;

With diamond glass cutter to growth, diameter is that the GaN film sample of 2 inches carries out scribing, make size and be aboutThe sample of 1cm × 1cm, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is putPut in vacuum 5.0 × 10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min,Remove cut and the surface attachments of film surface;

Step 2, carries out alternating temperature Raman test to GaN sample;

1) the GaN epitaxial layer film sample after clean is placed on Raman scattering testboard, adjusts Raman scatterometer, connectAlternating temperature platform and liquid nitrogen container, set Range of measuring temp and step-length; Excitation source adopts Ar⁺, optical maser wavelength is 514nm;

2) setting polarization mode isSlowly open alternating temperature cooling device, whole test macro is cooled to 77K, treat temperatureWhen degree is stablized, start to test;

Step 3, processes the alternating temperature Raman data of measuring, and extracts thermal coefficient of expansion wherein;

1) sample is taken out from Raman test macro to the frequency displacement of phonon peak and the temperature that adopt Origin8.0 software to obtain testBetween relation carry out linear fit, obtain d ω/dT straight slope, then adopt following theory to analyze and process:

Definition according to Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, and the variation that characterizes volume causes Raman diffuse soundThe change of sub-peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known, $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}={\mathrm{\ω}}_0{(1+3\mathrm{\α}T)}^{-\mathrm{\γ}}$

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α:

Computational process is as follows: d ω/dT is straight slope-0.0110 that matching obtains, and intercept is ω₀=573.46; To RamanPhonon modes E2 (high), its Gruneisen parameter γ value is about 1.47, sets up relation of equal quantity:

-3ω₀αγ＝-0.0110

Known as calculated, thermalexpansioncoefficientα=4.35 × 10-6/K, in this value and following table GaN thermal coefficient of expansion in a direction andThe mean value 4.38 × 10 of c direction^-6It is less that/K differs.

3. the Raman scattering method that a kind of GaN thermal coefficient of expansion according to claim 1 is measured, is characterized in that, bagDraw together following steps:

Step 1, samples GaN epitaxial layer film sample, and cleans;

With diamond glass cutter to growth, diameter is that the GaN film sample of 2 inches carries out scribing, make size and be aboutThe sample of 1cm × 1cm, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is putPut in vacuum 5.0 × 10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min,Remove cut and the surface attachments of film surface;

Step 2, carries out alternating temperature Raman test to GaN sample;

1) the GaN epitaxial layer film sample after clean is placed on Raman scattering testboard, adjusts Raman scatterometer, connectAlternating temperature platform and liquid nitrogen container, set Range of measuring temp and step-length; Excitation source adopts Ar⁺, optical maser wavelength is 514nm;

2) setting polarization mode isSlowly open alternating temperature cooling device, whole test macro is cooled to 77K, treat temperatureWhen degree is stablized, start to test;

Step 3, processes the alternating temperature Raman data of measuring, and extracts thermal coefficient of expansion wherein;

1) sample is taken out from Raman test macro to the frequency displacement of phonon peak and the temperature that adopt Origin8.0 software to obtain testBetween relation carry out linear fit, obtain d ω/dT straight slope, adopt following theory to analyze and process:

Definition according to Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, and the variation that characterizes volume causes Raman diffuse soundThe change of sub-peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known, $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}={\mathrm{\ω}}_0{(1+3\mathrm{\α}T)}^{-\mathrm{\γ}}$

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α:

Computational process is as follows: straight slope-0.0111 of d ω/dT, intercept is ω₀=574.40; To Raman phonon modes E2 (high), its Gruneisen parameter γ value is about 1.47, sets up relation of equal quantity:

-3ω₀αγ＝-0.0111

Known as calculated, thermalexpansioncoefficientα=4.34 × 10^-6/ K, in this value and following table, GaN thermal coefficient of expansion is at a direction and cThe mean value 4.38 × 10 of direction^-6/ K relatively approaches.

4. the Raman scattering method that a kind of GaN thermal coefficient of expansion according to claim 1 is measured, is characterized in that, bagDraw together following steps:

Step 1, samples GaN epitaxial layer film sample, and cleans;

With diamond glass cutter to growth form, 2 inches of GaN film samples carry out scribing, make size and be about 1cm × 1cm'sSample, described GaN epitaxial layer film carries out surface cleaning processing, is a face GaN epitaxial layer film is placed on to vacuum5.0×10^-3In the CVD furnace chamber of mbar, pass at ambient temperature flow and be the nitrogen of 60～100 liters/min, remove filmCut and the surface attachments on surface;

Step 2, carries out alternating temperature Raman test to GaN epitaxial layer film sample;

1) the GaN epitaxial layer film sample after clean is placed on Raman scattering testboard, adjusts Raman scatterometer, connectAlternating temperature platform and liquid nitrogen container, set Range of measuring temp and step-length; Excitation source adopts Ar⁺, optical maser wavelength is 514nm;

2) setting polarization mode isSlowly open alternating temperature cooling device, whole test macro is cooled to 77K, treat temperatureWhen degree is stablized, start to test;

Step 3, processes the alternating temperature Raman data of measuring, and extracts thermal coefficient of expansion wherein;

1) sample is taken out from Raman test macro to the frequency displacement of phonon peak and the temperature that adopt Origin8.0 software to obtain testBetween relation carry out linear fit, obtain d ω/dT straight slope, then adopt following theory to analyze and process:

Definition according to Gruneisen parameter: $\frac{dln\mathrm{\ω}}{d\ln V}=\frac{V}{\mathrm{\ω}}\·\frac{d\mathrm{\ω}}{dV}=-\mathrm{\γ},$ Known: $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}$

In above formula, V is volume, V₀Volume during for absolute 0K, ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; Known according to definition, γ is phonon peak Gruneisen parameter, and the variation that characterizes volume causes Raman diffuse soundThe change of sub-peak frequency displacement, and in the variation of volume, comprised the behavior relevant to thermal expansion and information;

2) basis formula V (T)=V above₀(1+3 α Δ T) is known, $\mathrm{\ω}={\mathrm{\ω}}_0{\left(\frac{V}{V_0}\right)}^{-\mathrm{\γ}}={\mathrm{\ω}}_0{(1+3\mathrm{\α}T)}^{-\mathrm{\γ}}$

In above formula, T is KShi temperature; Δ T is the variation of temperature; ω₀For the frequency displacement of phonon intrinsic, i.e. definitely frequency displacement when 0K; ωFor phonon frequency displacement; γ is phonon peak Gruneisen parameter; α is thermal coefficient of expansion, and its value is less, and the order of magnitude of representative value is about10^-5～10^-6/ K, therefore:

ω＝ω₀(1+3αT)^-γ≈ω₀(1-3αγT)

Can see by above formula, by measuring the relation of Raman phonon frequency displacement to temperature in certain temperature range, carry out linearityMatching, straight slope-3 α γ ω₀Numerical value in, can extract the value about material thermal expansion coefficient α:

Computational process is as follows: straight slope-0.0111 of d ω/dT, intercept is ω₀=570.20; To Raman phonon modes E2 (high), its Gruneisen parameter γ value is about 1.47 left and right, sets up relation of equal quantity:

-3ω₀αγ＝-0.0111

Known as calculated, thermalexpansioncoefficientα=4.41 × 10^-6/ K, in this value and following table, GaN thermal coefficient of expansion is at a direction and cThe mean value 4.38 × 10 of direction^-6/ K relatively approaches.