CN105606588B - A kind of Raman scattering methods of GaN thermal coefficient of expansions measurement - Google Patents
A kind of Raman scattering methods of GaN thermal coefficient of expansions measurement Download PDFInfo
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Abstract
A kind of Raman scattering methods of GaN thermal coefficient of expansions measurement, comprise the following steps：1）Scribing is carried out to sample and is sampled, and is cleaned；2）Alternating temperature Raman tests are carried out to sample；3）Linear fit is carried out to test result；Extract linear fit slope and intercept.According to the result of extraction, with reference to Gruneisen parametersPhysical significance, realize the test to solid material thermal expansion behavior and sign；Present invention employs alternating temperature Raman scattering technologies, the relation obtained between the frequency displacement of Raman phonons and temperature is scattered using Raman, it can exactly realize and Non-Destructive Testing and sign are carried out to GaN, AlN and InN and other group III-nitride extension layer film binary and multi-element alloy system thermal expansion behavior, avoid the destruction in general characterizing method to sample and the complex derivation of equation and mathematical computations；Due to there is no proper requirement to the shapes and sizes of sample, it is convenient to the thermal expansion behavior of classes of semiconductors class material is tested, method is simple, it is easy to accomplish, error is small.
Description
Technical field
The invention belongs to the method for testing technical field of solid material thermal expansion behavior, and in particular to a kind of GaN thermal expansions
The Raman scattering methods of coefficient measurement, thermal coefficient of expansion measurement and sign for GaN film material, are dissipated using alternating temperature Raman
The method penetrated, the relation between GaN film material Raman frequency displacements and temperature is analyzed, advised with reference to the expansion of solid material
Rule, the relation between the thermal expansion behavior of material and alternating temperature Raman scattering frequency displacements is handled, so as to obtain GaN film material
Expect the relevant information of thermal expansion behavior.
Background technology
Group III-nitride binary and its multicomponent alloy photoelectric material are to realize solid luminescence (Solid-State
Lighting, SSL) ideal candidates material, and realize semiconductor light-emitting-diode (Light-emitting Diode,
LED), laser diode (Laser Diode, LD), high-brightness white-light illuminating engineering and the ideal material of energy-saving and emission-reduction.InN and
Its related group III-nitride ternary alloy three-partalloy (InAlN, InGaN) has direct, continuous between 0.7eV-6.2eV with it
Adjustable band gap properties, there is the spectral range of non-constant width, cover green glow, blue light and ultraviolet spectra, turn into and make solid hair
The critical material of photoactive region, there is huge application prospect.From the perspective of material, it is very tired to produce blue light and ultraviolet light
It is difficult, and InGaN is the luminescent material that can uniquely realize both wave bands, and with the spectrum (0.4eV- of sunshine
4.0eV) matching is very good so that InxGa1-xN is in photovoltaic industry, especially in array solar cells, blue green light LED and white
The fields such as light LED have broad application prospects.
In the case where outer pressure is constant, object is because the swelling that temperature changes and occurs is " thermal expansion ".It is most of
Material is when temperature raises, the increase of its volume, volume-diminished (usually said phenomenon of expanding with heat and contract with cold) when temperature reduces.In phase
With under the conditions of, gas expansion is maximum, and liquid expansion is taken second place, and expansion of solids is minimum.Also there are a small number of materials in certain temperature range
Interior, when temperature raises, its volume reduces (i.e. pyrocondensation cold expanding phenomenon) on the contrary.From the perspective of molecule, when object temperature raises
When, the mean kinetic energy increase of molecular motion, intermolecular distance also increases, and the volume of object expands therewith；Temperature reduces, thing
The mean kinetic energy of molecule diminishes when body cools down, and shortens intermolecular distance, then the volume of object will reduce.Again due to solid
Body, the mean kinetic energy of liquids and gases molecular motion are of different sizes, thus also have significantly from the point of view of the macroscopic appearance of thermal expansion
Difference.It is known that when temperature changes, the volume of material occurs expansion and shrinkage phenomenon, its changing capability with etc.
Under the conditions of pressure under (pressure p is certain), the thermal coefficient of expansion of Volume Changes, as material caused by unit temperature change.Expansion
Coefficient characterize object it is heated when, its length, area, the degree of Volume Changes, and the physical quantity introduced.It is line expansion system
The general name of number, superficial expansivity and the coefficient of volume expansion.
Group III-nitride extension layer membrane materials, due to lacking the reason of intrinsic backing material, often through hetero-epitaxy
Method, be grown in such as sapphire, on the backing material such as SiC and Si, Metalorganic Chemical Vapor Deposition (Metal-
Organic Chemical Vapor Deposition, MOCVD) be heterogeneous epitaxial technology generally use a kind of growing method.
Due to the mismatch of larger lattice mismatch and thermal coefficient of expansion between backing material be present, cause to deposit in extension layer membrane materials
In higher dislocation density (including threading dislocation density and face dislocation density), the order of magnitude is typically about 109-1010/cm2.In life
In growth process, in order to reduce because of dislocation density and polarity effect high in extension layer film caused by lattice mismatch, generally use
A variety of ways and meanses, such as two-step method (nitrogenized to substrate and GaN buffer layer techniques), low temperature AI N nucleating layers are increased
Warm AlN nucleating layers technology, AlGaN/GaN superlattice structures etc..Nonetheless, the GaN epitaxial layer film grown by mocvd method
In dislocation density still be up to 108/cm2.Fig. 1 is the typical process using Sapphire Substrate Epitaxial growth GaN film.
As shown in Figure 1, temperature plays very important factor in GaN epitaxial layer film is grown.From growth GaN bufferings
500 DEG C or so of layer beginning, to 1025 DEG C of growth GaN epitaxial layer, range of temperature is big therebetween, and various materials become in temperature
Pyrocondensation phenomenon under change has differences, therefore the thermal coefficient of expansion of accurate measurement material is very important.
Thermal coefficient of expansion is defined as α=Δ V/ (V* Δ T), in formula Δ V for change to object volume under change in temperature Δ T
Become, V is object volume.Narrowly, the expression formula is the difference approximation of differential definition when range of temperature is little；
Accurate definition requires that Δ V and Δ T is infinitely small, this also means that, thermal coefficient of expansion is not usually in larger temperature range
Constant.When range of temperature is not very big, α is a constant., can be isotropic solid and liquid volume using it
Expansion represents as follows：
V (T)=V0(1+3αΔT)
For that approximate can regard one-dimensional object as, length is exactly to weigh the determinant of its volume, thermal expansion system at this moment
Number, which can simplify, to be defined as：Unit temperature change lower length incrementss and raw footage ratio, here it is linear expansion coefficient.
There is anisotropic material for three-dimensional, point for having linear expansion coefficient and the coefficient of volume expansion.Such as graphite-structure
With significant anisotropy, thus graphite fibre linear expansion coefficient also shows anisotropy, shows as parallel to aspect side
To thermal coefficient of expansion be much smaller than perpendicular to bedding angle.
Measurement to solid thermal expansion coefficient, generally carried out using thermal dilatometer.Its operation principle is, at sample
Under certain temperature program(me) (lifting/lowering/constant temperature and combinations thereof) control, change of the sample length with temperature or time is measured
Journey.In actual measurement process, for different samples, there is provided different classes of replaceable sample holder (quartz, aluminum oxide
Deng), possess different Range of measuring temp, applied to fields such as ceramic material and metal materials.Main test solid material
Thermal expansion/contraction 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 is brilliant
Body is usually hexagonal wurtzite structure, about 850-1150 DEG C of epitaxial growth temperature.At room temperature, GaN is not soluble in water, bronsted lowry acids and bases bronsted lowry,
Dissolved in the aqueous slkali of heat with slowly speed.NaOH、H2SO4And H3PO4Second-rate GaN can be corroded quickly,
GaN is in HCl or H2Under gas, unstable characteristic is presented at high temperature, and in N2It is the most stable under gas, while be a kind of good again
Coating protection materials.
Tested using thermal dilatometer in GaN epitaxial layer film thermal coefficient of expansion and the drawbacks of many be present：1) GaN material hardness
Height, fragility are big, it is difficult to make into strips/standard specimen；2) GaN thermal coefficient of expansion is small, thus in temperature-rise period, volumetric expansion
Caused size increase effect is smaller, it is difficult to accurate measurement；3) most of all, GaN material uses the growth of hetero-epitaxy more
Mode, its thin-film material the general very little of thickness (thickness is 430 microns of Sapphire Substrate, plus cushion/nucleating layer etc.,
Epitaxial growth GaN thickness is generally 600 microns), and the structure of this stratiform, it will it is unfavorable that measurement result is produced
Influence.
In many physical properties of semi-conducting material, optical property is one of most important of which physical property.Probe into
The process that electromagnetic radiation field and semiconductor interact, can provide the crystal structure of semi-conducting material, band structure and
The information such as the characteristics of motion of electronics and phonon.All the time, optical means is to characterize that semi-conducting material is most important, maximally effective hand
One of section.
Raman scatters the information for providing material internal lattice vibration, and it characterizes material in a manner of inelastically scattered
The material composition of material, crystal mass, the number of residual stress size and free carrier concentration.Crystal defect, crystal grain diminishes,
Residual stress in impalpable structure and crystal can all make the peak value of Raman frequency displacements shift, peak broadening and peak symmetric figure
The change of shape.The behavior at Raman phonons peak under different temperatures, contain the letter of optics lattice wave caused by material internal atomic vibration
Breath.Understand from the angle of atomic vibration, thermal expansion belongs to the anhar-monic effect of atomic vibration, and the expansion of optics lattice wave volume with
Relation between optics lattice wave meets Gruneisen (cyhalothrin is gloomy) parameter, and this is one and varies with temperature little constant.Cause
And can be by being scattered to GaN epitaxial layer films test alternating temperature Raman, to realize the measurement to GaN thermal coefficient of expansions.
The content of the invention
In order to overcome the above-mentioned deficiencies of the prior art, it is an object of the invention to provide a kind of measurement of GaN thermal coefficient of expansions
Raman scattering methods, the characterization method scattered using new alternating temperature Raman, by (being situated between in certain temperature range with cooling
The scope of matter and suitably change), GaN epitaxial layer film Raman scatter phonon peak frequency displacement with temperature behavior；It is fitted using software
Method, obtain d ω/dT straight slope；Thermal coefficient of expansion of the extraction on GaN epitaxial layer film from the slope of straight line.
The method scattered using alternating temperature Raman, can be realized thin to GaN, AlN and InN and other group III-nitride epitaxial layers exactly
Film binary and multi-element alloy system thermal expansion behavior carry out Non-Destructive Testing and sign, in terms of solving measurement GaN thermal coefficient of expansions
Technical problem be present, help to reduce experimental error, and reduce experimentation cost, in the absence of potential safety hazard；It is simple with method, make
With conveniently, cost is cheap, the characteristics of being easy to promote.
To achieve the above object, the technical solution adopted by the present invention is：A kind of Raman of GaN thermal coefficient of expansions measurement dissipates
Shooting method, comprise the following steps：
First, GaN epitaxial layer film sample is sampled, and cleans；
Scribing is carried out with GaN film sample of the diamond glass cutter to growth, a diameter of 2 inches, making size is about
1cm × 1cm sample, described GaN epitaxial layer film carry out surface cleaning processing, are to be placed on a faces GaN epitaxial layer film
Vacuum 5.0 × 10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, is removed
The cut and surface attachments of film surface；
Second, alternating temperature Raman tests are carried out to GaN epitaxial layer film sample；
Sample is placed on the testboard of Raman scatterometers, test surfaces are bright and clean, mat surface is the back side；Testing
The Ar for being at room temperature before 514.5nm with wavelength+Laser is tested,Under polarization mode, GaN epitaxy is measured
Phonon vibration pattern E in layer film2(high) frequency shift value；
Before official testing, first have to calibrate instrument parameter, after choosing supporting grating, by standard
Position (the 520cm of silicon single crystal main peak-1) dead-center position of grating is calibrated, it can adopt spectrometry after the completion of calibration, survey
Amount carries software by instrument after terminating and carries out data processing, first cuts baseline, then passes through Lorentz and the mixing letter of Gauss
It is several that data are fitted, draw peak position and the information of halfwidth, the alternating temperature platform model Linkam- of Raman scatterometers
Examina-THMS600, from 83K to 503K, step-length 52.5K, precision is can be controlled within 0.1K extent of alternating temperature, does low temperature reality
Liquid nitrogen container is connected when testing, cooling medium is cooled using liquid nitrogen.
3rd, the processing to alternating temperature Raman data, extract thermal coefficient of expansion therein；
Sample is taken out from Raman test systems, the relation tested between obtained phonon peak frequency displacement and temperature is entered
Row linear fit, d ω/dT straight slopes are obtained, is analyzed and is handled using following theory：
1) according to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；Understood according to definition, γ is phonon peak Gruneisen parameters, the connotation of Gruneisen parameters, characterizes body
Long-pending change causes the change of Raman scattering phonon peak frequency displacements, and the behavior related to thermal expansion is contained in the change of volume
And information；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is about
For 10-5~10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out by measuring Raman phonons frequency displacement in certain temperature range by above formula
Linear fit, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α.
The beneficial effects of the invention are as follows：
The key of the present invention is using the method for Raman scatterings, and using in the case of alternating temperature, Raman scattering phonons peak is frequently
Move the characteristic varied with temperature, the correlation between bond material thermal expansion behavior and the frequency displacement of phonon peak, by analyzing d ω/dT
Information in straight slope, to analyze the thermal expansion behavior in GaN epitaxial layer film.
Present invention employs alternating temperature Raman scattering technologies, scattered using Raman obtain the frequency displacement of Raman phonons and temperature it
Between relation pair GaN thermal expansion behavior carry out nondestructive characterisation (NDC).It can realize exactly to GaN, AlN and InN and other IIIs
Nitride epitaxial layer film binary and multi-element alloy system thermal expansion behavior carry out Non-Destructive Testing and sign, pass through thermal coefficient of expansion
, will the two it with reference to the physical significance of Gruneisen parameters with uniformity of material internal optics wave sound in the mechanism of origin
Between relation it is ingenious combine, avoid in general characterizing method to the destruction of sample and complex derivation of equation sum
Learn and calculate；Simultaneously because the present invention does not have proper requirement to the shapes and sizes of sample, thus can be easily to each
The thermal expansion behavior of based semiconductor class material is tested, and formula is simple, explicit physical meaning, it is easy to accomplish, and error compared with
It is small.
Brief description of the drawings
Fig. 1 is the flow chart for using MOCVD technology growth GaN epitaxial layer films in the prior art.
The Raman phonons peak schematic diagram that wurtzite structure GaN is likely to occur under the different backscatter modes of Fig. 2 present invention.
Fig. 3 is that a pair of test datas of the embodiment of the present invention carry out linear fit coordinate diagram.
Fig. 4 is that the embodiment of the present invention two carries out linear fit coordinate diagram to test data.
Fig. 5 is that the embodiment of the present invention three carries out linear fit coordinate diagram to test data.
Embodiment
By the way of the present invention is using alternating temperature Raman scatterings, to the lossless table of the thermal expansion behavior of GaN epitaxial layer film progress and
Test.Binding test principle and test process, provide three embodiments.
Embodiment one
A kind of Raman scattering methods of GaN thermal coefficient of expansions measurement, including have the following steps：
Step 1, GaN epitaxial layer film sample is sampled, and cleaned.
Scribing is carried out with GaN film sample of the diamond glass cutter to growth, a diameter of 2 inches, making size is about
1cm × 1cm sample, described GaN epitaxial layer film carry out surface cleaning processing, are to be placed on a faces GaN epitaxial layer film
Vacuum 5.0 × 10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, is removed
The cut and surface attachments of film surface；
Step 2, alternating temperature Raman tests are carried out to GaN samples；
1) the GaN epitaxial layer film sample after cleaning is placed on Raman scattering testboards, adjusts Raman scatterometers, even
Alternating temperature platform and liquid nitrogen container are connect, sets Range of measuring temp and step-length；Excitation source uses Ar+, optical maser wavelength 514nm；
2) set polarization mode asAlternating temperature cooling device is slowly opened, 77K is cooled to whole test system
(boiling point of liquid nitrogen), when temperature stabilization, proceed by test；
Step 3, measurement alternating temperature Raman data are handled, extract thermal coefficient of expansion therein；
1) sample is taken out from Raman test systems, the phonon peak frequency displacement obtained using Origin8.0 softwares to test
Relation between temperature carries out linear fit, and for obtained result as shown in figure 3, obtaining d ω/dT straight slopes, use is following
Theory is analyzed and handled：
According to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；Understand that γ is phonon peak Gruneisen parameters, and the change for characterizing volume causes Raman to scatter according to definition
The change of phonon peak frequency displacement, and the behavior related to thermal expansion and information are contained in the change of volume；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is about
For 10-5~10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out by measuring Raman phonons frequency displacement in certain temperature range by above formula
Linear fit, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α；
Calculating process is as follows：Ibid understood in figure, d ω/dT are straight slope -0.0110 in Fig. 3, intercept ω0
=573.46；To Raman phonon modes E2(high) for, its Gruneisen parameter γ value is about 1.47, establishes equivalent pass
System：
-3ω0α γ=- 0.0110
It is computed understanding, thermalexpansioncoefficientα=4.35 × 10-6/ K, this value is with GaN thermal coefficient of expansions in following table in a side
To the average value 4.38 × 10 with c directions-6/ K differences are smaller.
It should be noted that, although to GaN thermal coefficient of expansions, often there be point in a directions and c directions in educational circles, still, for
Gruneisen parameters γ and ω0, but without the differentiation in a directions and c directions, therefore, calculated using the two constants
Overall thermal expansion behavior is relevant in itself for GaN thermal coefficient of expansion has been comprehensive characterization material；
The Main physical property (300K) of III hi-nitride semiconductor material
Embodiment two
A kind of Raman scattering methods of GaN thermal coefficient of expansions measurement, including have the following steps：
Step 1, GaN epitaxial layer film sample is sampled, and cleaned；
Scribing is carried out with GaN film sample of the diamond glass cutter to growth, a diameter of 2 inches, making size is about
1cm × 1cm sample, described GaN epitaxial layer film carry out surface cleaning processing, are to be placed on a faces GaN epitaxial layer film
Vacuum 5.0 × 10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, is removed
The cut and surface attachments of film surface；
Step 2, alternating temperature Raman tests are carried out to GaN samples；
1) the GaN epitaxial layer film sample after cleaning is placed on Raman scattering testboards, adjusts Raman scatterometers, even
Alternating temperature platform and liquid nitrogen container are connect, sets Range of measuring temp and step-length；Excitation source uses Ar+, optical maser wavelength 514nm；
2) set polarization mode asAlternating temperature cooling device is slowly opened, 77K is cooled to whole test system
(boiling point of liquid nitrogen), when temperature stabilization, proceed by test；
Step 3, the alternating temperature Raman data of measurement are handled, extract thermal coefficient of expansion therein；
1) sample is taken out from Raman test systems, the phonon peak frequency displacement obtained using Origin8.0 softwares to test
Relation between temperature carries out linear fit, and for obtained result as shown in figure 4, obtaining d ω/dT straight slopes, use is following
Theory is analyzed and handled：
According to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；Understand that γ is phonon peak Gruneisen parameters, and the change for characterizing volume causes Raman to scatter according to definition
The change of phonon peak frequency displacement, and the behavior related to thermal expansion and information are contained in the change of volume；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is about
For 10-5~10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out by measuring Raman phonons frequency displacement in certain temperature range by above formula
Linear fit, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α：
Calculating process is as follows：Understood with Fig. 4, d ω/dT are straight slope -0.0111 in Fig. 4, intercept ω0=
574.40；To Raman phonon modes E2(high) for, its Gruneisen parameter γ value is about 1.47, establishes relation of equal quantity：
-3ω0α γ=- 0.0111
It is computed understanding, thermalexpansioncoefficientα=4.34 × 10-6/ K, this value is with GaN thermal coefficient of expansions in following table in a side
To the average value 4.38 × 10 with c directions-6/ K is relatively；
It should be noted that, although to GaN thermal coefficient of expansions, often there be point in a directions and c directions in educational circles, still, for
Gruneisen parameters γ and ω0, but without the differentiation in a directions and c directions, therefore, calculated using the two constants
Overall thermal expansion behavior is relevant in itself for GaN thermal coefficient of expansion has been comprehensive characterization material.
The Main physical property (300K) of III hi-nitride semiconductor material
Embodiment three
A kind of Raman scattering methods of GaN thermal coefficient of expansions measurement, including have the following steps：
Step 1, GaN epitaxial layer film sample is sampled, and cleaned；
Scribing is carried out with GaN film sample of the diamond glass cutter to growth, a diameter of 2 inches, making size is about
1cm × 1cm sample, described GaN epitaxial layer film carry out surface cleaning processing, are to be placed on a faces GaN epitaxial layer film
Vacuum 5.0 × 10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, is removed
The cut and surface attachments of film surface；
Step 2, alternating temperature Raman tests are carried out to GaN epitaxial layer film sample；
1) the GaN epitaxial layer film sample after cleaning is placed on Raman scattering testboards, adjusts Raman scatterometers, even
Alternating temperature platform and liquid nitrogen container are connect, sets Range of measuring temp and step-length；Excitation source uses Ar+, optical maser wavelength 514nm；
2) set polarization mode asAlternating temperature cooling device is slowly opened, 77K is cooled to whole test system
(boiling point of liquid nitrogen), when temperature stabilization, proceed by test；
Step 3, measurement data is handled, extract thermal coefficient of expansion therein；
1) sample is taken out from Raman test systems, the phonon peak frequency displacement obtained using Origin8.0 softwares to test
Relation between temperature carries out linear fit, then obtained result uses as shown in figure 5, acquisition d ω/dT straight slopes
Following theory is analyzed and handled：
According to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；Understand that γ is phonon peak Gruneisen parameters, and the change for characterizing volume causes Raman to scatter according to definition
The change of phonon peak frequency displacement, and the behavior related to thermal expansion and information are contained in the change of volume；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；
ω is phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is about
For 10-5~10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out by measuring Raman phonons frequency displacement in certain temperature range by above formula
Linear fit, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α：
Calculating process is as follows：Understood with Fig. 5, d ω/dT are straight slope -0.0111 in Fig. 5, intercept ω0=
570.20；To Raman phonon modes E2(high) for, its Gruneisen parameter γ value is about 1.47 or so, establishes equivalent pass
System：
-3ω0α γ=- 0.0111
It is computed understanding, thermalexpansioncoefficientα=4.41 × 10-6/ K, this value is with GaN thermal coefficient of expansions in following table in a side
To the average value 4.38 × 10 with c directions-6/ K is relatively；
It should be noted that, although to GaN thermal coefficient of expansions, often there be point in a directions and c directions in educational circles, still, for
Gruneisen parameters γ and ω0, but without the differentiation in a directions and c directions, therefore, calculated using the two constants
Overall thermal expansion behavior is relevant in itself for GaN thermal coefficient of expansion has been comprehensive characterization material.
The Main physical property (300K) of III hi-nitride semiconductor material
Claims (4)
1. a kind of Raman scattering methods of GaN thermal coefficient of expansions measurement, it is characterised in that comprise the following steps：
First, GaN epitaxial layer film sample is sampled, and cleans；
With diamond glass cutter to growth, a diameter of 2 inches of GaN film sample carry out scribing, make size be 1cm ×
1cm sample, described GaN epitaxial layer film carry out surface cleaning processing, are that a faces GaN epitaxial layer film is placed on into vacuum
Degree 5.0 × 10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, removes film
The cut and surface attachments on surface；
Second, alternating temperature Raman tests are carried out to GaN epitaxial layer film sample；
Sample is placed on the testboard of Raman scatterometers, test surfaces are bright and clean, mat surface is the back side；Before test
The Ar for being at room temperature 514.5nm with wavelength+Laser is tested,Under polarization mode, measurement GaN epitaxial layer is thin
Phonon vibration pattern E in film2(high) frequency shift value；
First, instrument parameter is calibrated, chooses supporting grating, by the position to standard silicon single crystal main peak come to light
The dead-center position of grid is calibrated, and spectrometry is adopted after the completion of calibration, and measurement carries software by instrument after terminating and carried out at data
Reason, first cuts baseline, then, data is fitted by the mixed function of Lorentz and Gauss, draw peak position and halfwidth
Information, the alternating temperature platform model Linkam-Examina-THMS 600 of Raman scatterometers, extent of alternating temperature from 83K to 503K,
Step-length is 52.5K, and precision controlling connects liquid nitrogen container within 0.1K when doing low temperature test, cooling medium is carried out using liquid nitrogen
Cooling；
3rd, the processing to the alternating temperature Raman data of measurement, extract thermal coefficient of expansion therein；
1) sample is taken out from Raman test systems, the relation tested between obtained phonon peak frequency displacement and temperature is carried out
Linear fit, d ω/dT straight slopes are obtained, is analyzed and is handled using following theory：
According to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；Understand that γ is phonon peak Gruneisen parameters according to definition, the change for characterizing volume causes Raman to scatter phonon
The change of peak frequency displacement, and the behavior related to thermal expansion and information are contained in the change of volume；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is 10-5~
10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out linear by measuring Raman phonons frequency displacement in certain temperature range by above formula
Fitting, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α.
A kind of 2. Raman scattering methods of GaN thermal coefficient of expansions measurement according to claim 1, it is characterised in that including
Following steps：
Step 1, GaN epitaxial layer film sample is sampled, and cleaned；
Carry out scribing with GaN film sample of the diamond glass cutter to growth, a diameter of 2 inches, make size for 1cm ×
1cm sample, described GaN epitaxial layer film carry out surface cleaning processing, are that a faces GaN epitaxial layer film is placed on into vacuum
Degree 5.0 × 10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, removes film
The cut and surface attachments on surface；
Step 2, alternating temperature Raman tests are carried out to GaN samples；
1) the GaN epitaxial layer film sample after cleaning is placed on Raman scattering testboards, adjusts Raman scatterometers, connection becomes
Warm platform and liquid nitrogen container, set Range of measuring temp and step-length；Excitation source uses Ar of the wavelength for 514.5nm+Laser；
2) set polarization mode asAlternating temperature cooling device is slowly opened, 77K is cooled to whole test system, treats temperature
When stable, test is proceeded by；
Step 3, the alternating temperature Raman data of measurement are handled, extract thermal coefficient of expansion therein；
1) sample is taken out from Raman test systems, using Origin8.0 softwares to the phonon peak frequency displacement that test obtains and temperature
Relation between degree carries out linear fit, obtains d ω/dT straight slopes, is then analyzed and is handled using following theory：
According to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；Understand that γ is phonon peak Gruneisen parameters according to definition, the change for characterizing volume causes Raman to scatter phonon
The change of peak frequency displacement, and the behavior related to thermal expansion and information are contained in the change of volume；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is 10-5~
10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out linear by measuring Raman phonons frequency displacement in certain temperature range by above formula
Fitting, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α：
Calculating process is as follows：D ω/dT are as fitted obtained straight slope -0.0110, intercept ω0=573.46；To Raman
For phonon modes E2 (high), its Gruneisen parameter γ value is about 1.47, establishes relation of equal quantity：
-3ω0α γ=- 0.0110
Be computed understanding, thermalexpansioncoefficientα=4.35 × 10-6/K, in this value and following table GaN thermal coefficient of expansions in a directions and
The average value 4.38 × 10 in c directions-6/ K differences are smaller.
A kind of 3. Raman scattering methods of GaN thermal coefficient of expansions measurement according to claim 1, it is characterised in that including
Following steps：
Step 1, GaN epitaxial layer film sample is sampled, and cleaned；
Carry out scribing with GaN film sample of the diamond glass cutter to growth, a diameter of 2 inches, make size for 1cm ×
1cm sample, described GaN epitaxial layer film carry out surface cleaning processing, are that a faces GaN epitaxial layer film is placed on into vacuum
Degree 5.0 × 10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, removes film
The cut and surface attachments on surface；
Step 2, alternating temperature Raman tests are carried out to GaN samples；
1) the GaN epitaxial layer film sample after cleaning is placed on Raman scattering testboards, adjusts Raman scatterometers, connection becomes
Warm platform and liquid nitrogen container, set Range of measuring temp and step-length；Excitation source uses Ar of the wavelength for 514.5nm+Laser；
2) set polarization mode asAlternating temperature cooling device is slowly opened, 77K is cooled to whole test system, treats temperature
When stable, test is proceeded by；
Step 3, the alternating temperature Raman data of measurement are handled, extract thermal coefficient of expansion therein；
1) sample is taken out from Raman test systems, using Origin8.0 softwares to the phonon peak frequency displacement that test obtains and temperature
Relation between degree carries out linear fit, obtains d ω/dT straight slopes, is analyzed and handled using following theory：
According to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；Understand that γ is phonon peak Gruneisen parameters according to definition, the change for characterizing volume causes Raman to scatter phonon
The change of peak frequency displacement, and the behavior related to thermal expansion and information are contained in the change of volume；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is 10-5~
10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out linear by measuring Raman phonons frequency displacement in certain temperature range by above formula
Fitting, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α：
Calculating process is as follows：D ω/dT straight slope -0.0111, intercept ω0=574.40；To Raman phonon modes E2
(high) for, its Gruneisen parameter γ value is about 1.47, establishes relation of equal quantity：
-3ω0α γ=- 0.0111
It is computed understanding, thermalexpansioncoefficientα=4.34 × 10-6/ K, this value is with GaN thermal coefficient of expansions in following table in a directions and c
The average value 4.38 × 10 in direction-6/ K is relatively.
A kind of 4. Raman scattering methods of GaN thermal coefficient of expansions measurement according to claim 1, it is characterised in that including
Following steps：
Step 1, GaN epitaxial layer film sample is sampled, and cleaned；
With diamond glass cutter to growth forms, 2 inches of GaN film samples carry out scribing, the sample that size is 1cm × 1cm is made
Product, described GaN epitaxial layer film carry out surface cleaning processing, be by a faces GaN epitaxial layer film be placed on vacuum 5.0 ×
10-3In mbar CVD furnace chambers, the nitrogen that flow is 60~100 liters/min is passed through at ambient temperature, removes film surface
Cut and surface attachments；
Step 2, alternating temperature Raman tests are carried out to GaN epitaxial layer film sample；
1) the GaN epitaxial layer film sample after cleaning is placed on Raman scattering testboards, adjusts Raman scatterometers, connection becomes
Warm platform and liquid nitrogen container, set Range of measuring temp and step-length；Excitation source uses Ar of the wavelength for 514.5nm+Laser；
2) set polarization mode asAlternating temperature cooling device is slowly opened, 77K is cooled to whole test system, treats temperature
When stable, test is proceeded by；
Step 3, the alternating temperature Raman data of measurement are handled, extract thermal coefficient of expansion therein；
1) sample is taken out from Raman test systems, using Origin8.0 softwares to the phonon peak frequency displacement that test obtains and temperature
Relation between degree carries out linear fit, obtains d ω/dT straight slopes, is then analyzed and is handled using following theory：
According to the definition of Gruneisen parameters：Understand：
In above formula, V is volume, V0For absolute 0K when volume, ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；Understand that γ is phonon peak Gruneisen parameters according to definition, the change for characterizing volume causes Raman to scatter phonon
The change of peak frequency displacement, and the behavior related to thermal expansion and information are contained in the change of volume；
2) according to formula V (T)=V above0(1+3 α Δ T) is understood,
In above formula, T is KShi temperature；Δ T is the change of temperature；ω0Frequency displacement during frequency displacement, i.e. absolute 0K intrinsic for phonon；ω is
Phonon frequency displacement；γ is phonon peak Gruneisen parameters；α is thermal coefficient of expansion, and its value is smaller, and the order of magnitude of representative value is 10-5~
10-6/ K, therefore：
ω=ω0(1+3αT)-γ≈ω0(1-3αγT)
It can be seen that, to the relation of temperature, carried out linear by measuring Raman phonons frequency displacement in certain temperature range by above formula
Fitting, the α γ of straight slope -3 ω0Numerical value in, can extract value on material thermal expansion coefficient α：
Calculating process is as follows：D ω/dT straight slope -0.0111, intercept ω0=570.20；To Raman phonon modes E2
(high) for, its Gruneisen parameter γ value is about 1.47 or so, establishes relation of equal quantity：
-3ω0α γ=- 0.0111
It is computed understanding, thermalexpansioncoefficientα=4.41 × 10-6/ K, this value is with GaN thermal coefficient of expansions in following table in a directions and c
The average value 4.38 × 10 in direction-6/ K is relatively.
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